United States Office of Research EPA/600/R-93/187 

Environmental Protection and Development December 1993 

Agency (8603) 

Wildlife Exposure

Factors Handbook

Volume I of II 
EPA/600/R-93/187 

December 1993 

WILDLIFE EXPOSURE FACTORS 

HANDBOOK 

Volume I of II 

Office of Health and Environmental Assessment

Office of Research and Development

U.S. Environmental Protection Agency

Washington, DC 20460

Additional major funding for this Handbook was provided by the 

Office of Emergency and Remedial Response,

Office of Solid Waste and Emergency Response

and by the

Office of Science and Technology, Office of Water

U.S. Environmental Protection Agency

Washington, DC 20460
DISCLAIMER 

This document has been reviewed in accordance with U.S. Environmental 

Protection Agency policy and approved for publication. Mention of trade names or 

commercial products does not constitute endorsement or recommendation for use. 

ii 
CONTENTS

Foreword ............................................................ xi

Preface .............................................................. xii

Authors, Managers, Contributors, and Reviewers ............................ xiii

1. INTRODUCTION ................................................... 1-1

1.1. PURPOSE AND SCOPE ........................................ 1-1

1.2. ORGANIZATION OF THE HANDBOOK ............................ 1-5

1.3. LIST OF SELECTED SPECIES ................................... 1-6

1.4. LIST OF EXPOSURE FACTORS ................................. 1-11

1.4.1. Normalizing Factors ................................... 1-11

1.4.1.1. Body Weight .................................. 1-13

1.4.1.2. Growth Rate .................................. 1-13

1.4.1.3. Metabolic Rate ................................ 1-14

1.4.2. Contact Rate Factors ................................... 1-14

1.4.2.1. Oral Route .................................... 1-14

1.4.2.2. Inhalation Route ............................... 1-16

1.4.2.3. Dermal Route ................................. 1-16

1.4.3. Population Dynamics .................................. 1-17

1.4.3.1. Social Organization ............................. 1-17

1.4.3.2. Home Range/Territory Size/Foraging Radius ........ 1-17

1.4.3.3. Population Density ............................. 1-19

1.4.3.4. Annual Fecundity .............................. 1-19

1.4.3.5. Annual Mortality and Longevity ................... 1-19

1.4.4. Seasonal Activities .................................... 1-20

1.5. DATA PRESENTATION FORMAT ................................ 1-20

1.5.1. Normalizing and Contact Rate Factors ..................... 1-21

1.5.1.1. All Animals ................................... 1-21

1.5.1.2. Birds ........................................ 1-22

1.5.1.3. Mammals ..................................... 1-23

1.5.1.4. Reptiles and Amphibians ........................ 1-23

iii 
CONTENTS (continued) 

1.5.2. Dietary Composition ................................... 1-24

1.5.2.1. All Animals ................................... 1-24

1.5.3. Population Dynamics .................................. 1-25

1.5.3.1. All Animals ................................... 1-25

1.5.3.2. Birds ........................................ 1-26

1.5.3.3. Mammals ..................................... 1-27

1.5.3.4. Reptiles and Amphibians ........................ 1-27

1.5.4. Seasonal Activities .................................... 1-28

1.5.4.1. Birds ........................................ 1-29

1.5.4.2. Mammals ..................................... 1-29

1.5.4.3. Reptiles and Amphibians ........................ 1-29

1.5.5. Abbreviations Used in Tables ............................ 1-29

1.6. LITERATURE SEARCH STRATEGY .............................. 1-30

1.7. REFERENCES ............................................... 1-32

2. EXPOSURE FACTORS AND DESCRIPTIONS OF SELECTED SPECIES ....... 2-1

2.1. BIRDS .................................................... 2-1

2.1.1. Great Blue Heron ...................................... 2-3

2.1.2. Canada Goose ........................................ 2-19

2.1.3. Mallard ............................................. 2-39

2.1.4. Lesser Scaup ......................................... 2-53

2.1.5. Osprey .............................................. 2-65

2.1.6. Red-Tailed Hawk ...................................... 2-79

2.1.7. Bald Eagle ........................................... 2-91

2.1.8. American Kestrel ...................................... 2-109

2.1.9. Northern Bobwhite .................................... 2-121

2.1.10. American Woodcock ................................... 2-137

2.1.11. Spotted Sandpiper ..................................... 2-149

2.1.12. Herring Gull .......................................... 2-157

2.1.13. Belted Kingfisher ...................................... 2-173

2.1.14. Marsh Wren .......................................... 2-183

2.1.15. American Robin ....................................... 2-193

iv 
CONTENTS (continued) 

2.2. MAMMALS .................................................. 2-207

2.2.1. Short-Tailed Shrew .................................... 2-209

2.2.2. Red Fox ............................................. 2-221

2.2.3. Raccoon ............................................. 2-233

2.2.4. Mink ................................................ 2-247

2.2.5. River Otter ........................................... 2-261

2.2.6. Harbor Seal .......................................... 2-275

2.2.7. Deer Mouse .......................................... 2-291

2.2.8. Prairie Vole .......................................... 2-311

2.2.9. Meadow Vole ......................................... 2-323

2.2.10. Muskrat ............................................. 2-337

2.2.11. Eastern Cottontail ..................................... 2-351

2.3. REPTILES AND AMPHIBIANS ................................... 2-365

2.3.1. Snapping Turtle ....................................... 2-367

2.3.2. Painted Turtle ........................................ 2-381

2.3.3. Eastern Box Turtle .................................... 2-397

2.3.4. Racer ............................................... 2-407

2.3.5. Northern Water Snake .................................. 2-419

2.3.6. Eastern Newt ......................................... 2-429

2.3.7. Green Frog........................................... 2-443

2.3.8. Bullfrog ............................................. 2-453

3. ALLOMETRIC EQUATIONS .......................................... 3-1

3.1. FOOD INGESTION RATES ...................................... 3-3

3.1.1. Birds ............................................... 3-4

3.1.2. Mammals ............................................ 3-5

3.1.3. Reptiles and Amphibians ............................... 3-6

3.2. WATER INTAKE RATES ....................................... 3-7

3.2.1. Birds ............................................... 3-8

3.2.2. Mammals ............................................ 3-10

3.2.3. Reptiles and Amphibians ............................... 3-10

3.3. INHALATION RATES .......................................... 3-11

3.3.1. Birds ............................................... 3-11

3.3.2. Mammals ............................................ 3-12

3.3.3. Reptiles and Amphibians ............................... 3-12

v 
CONTENTS (continued) 

3.4. SURFACE AREAS ............................................ 3-13

3.4.1. Birds ............................................... 3-13

3.4.2. Mammals ............................................ 3-14

3.4.3. Reptiles and Amphibians ............................... 3-14

3.5. ALLOMETRIC EQUATIONS FOR METABOLIC RATE ................ 3-15

3.5.1. Birds ............................................... 3-18

3.5.1.1 Basal Metabolic Rate ........................... 3-19

3.5.1.2. Existence Metabolic Rates ....................... 3-20

3.5.1.3. Free-Living Metabolic Rate ....................... 3-22

3.5.1.4. Temperature and Metabolic Rate .................. 3-24

3.5.2. Mammals ............................................ 3-26

3.5.2.1. Basal Metablic Rate ............................ 3-26

3.5.2.2. Resting Metabolism ............................ 3-27

3.5.2.3. Field Metabolic Rate ............................ 3-27

3.5.2.4. Temperature and Metabolic Rate .................. 3-28

3.5.3. Reptiles and Amphibians ............................... 3-29

3.5.3.1. Basal and Resting Metabolic Rates ................ 3-29

3.5.3.2. Free-Living Metabolic Rates ...................... 3-30

3.6. MATH PRIMER AND UNIT CONVERSIONS ......................... 3-32

3.6.1. Summary of Operations Involving Logarithms .............. 3-32

3.6.2. Summary of Operations Involving Powers .................. 3-32

3.6.3. Unit Conversions ...................................... 3-33

3.6.3.1. Approximate Factors for Metabolic Equations ....... 3-33

3.6.3.2. Exact Conversions ............................. 3-33

3.7. ESTIMATING CONFIDENCE INTERVALS .......................... 3-34

3.8. REFERENCES ............................................... 3-38

4. EXPOSURE ESTIMATES ............................................ 4-1

4.1. GENERAL DOSE EQUATIONS .................................. 4-1

4.1.1. Drinking Water ........................................ 4-3

vi 
CONTENTS (continued) 

4.1.2. Diet ................................................. 4-6

4.1.2.1. Dose Equations ................................ 4-6

4.1.2.2. Energy Content and Assimilation Efficiencies ........ 4-10

4.1.3. Soil and Sediment Ingestion ............................. 4-16

4.1.3.1. Background ................................... 4-18

4.1.3.2. Methods ..................................... 4-18

4.1.3.3. Results ...................................... 4-19

4.1.3.4. Dose Equations ................................ 4-21

4.1.4. Air.................................................. 4-21

4.1.5. Dermal Exposure ...................................... 4-23

4.2. ANALYSIS OF UNCERTAINTY ................................... 4-23

4.2.1. Natural Variation ...................................... 4-24

4.2.2. Sampling Uncertainty .................................. 4-25

4.2.3. Model Uncertainty ..................................... 4-26

4.3. REFERENCES ............................................... 4-26

APPENDIX: LITERATURE REVIEW DATABASE ....................... See Volume II

vii 

2 
LIST OF TABLES

Table 1-1. Characteristics of Selected Birds ............................... 1-8

Table 1-2. Characteristics of Selected Mammals ............................ 1-9

Table 1-3. Characteristics of Selected Reptiles and Amphibians ............... 1-10

Table 1-4. Wildlife Exposure Factors Included in the Handbook ................ 1-12

Table 1-5. Wildlife Contact Rate Exposure Factors .......................... 1-15

Table 1-6. Column Headers for Tables of Normalizing and Contact

Rate Factors ................................................ 1-21

Table 1-7. Column Headers for Tables on Dietary Composition ................ 1-24

Table 1-8. Column Headers for Tables of Factors for Population Dynamics ...... 1-26

Table 1-9. Column Headers for Tables on Seasonal Activities ................. 1-28

Table 2-1. Birds Included in the Handbook ................................ 2-2

Tables for 2.1.1. Great Blue Heron ..................................... 2-8

2.1.2. Canada Goose ....................................... 2-23

2.1.3. Mallard ............................................ 2-43

2.1.4. Lesser Scaup ........................................ 2-56

2.1.5. Osprey ............................................. 2-68

2.1.6. Red-Tailed Hawk ..................................... 2-82

2.1.7. Bald Eagle .......................................... 2-95

2.1.8. American Kestrel ..................................... 2-112

2.1.9. Northern Bobwhite ................................... 2-126

2.1.10. American Woodcock .................................. 2-140

2.1.11. Spotted Sandpiper .................................... 2-152

2.1.12. Herring Gull ......................................... 2-162

2.1.13. Belted Kingfisher ..................................... 2-176

2.1.14. Marsh Wren ......................................... 2-186

2.1.15. American Robin ...................................... 2-197

Table 2-2. Mammals Included in the Handbook ............................. 2-208

Tables for 2.2.1. Short-Tailed Shrew ................................... 2-213

2.2.2. Red Fox ............................................ 2-224

2.2.3. Raccoon ............................................ 2-236

2.2.4. Mink ............................................... 2-251

2.2.5. River Otter .......................................... 2-264

viii 
LIST OF TABLES (continued) 

2.2.6. Harbor Seal ......................................... 2-280

2.2.7. Deer Mouse ......................................... 2-295

2.2.8. Prairie Vole ......................................... 2-314

2.2.9. Meadow Vole ........................................ 2-327

2.2.10. Muskrat ............................................ 2-340

2.2.11. Eastern Cottontail .................................... 2-355

Table 2-3. Reptiles and Amphibians Included in the Handbook ................ 2-366

Tables for 2.3.1. Snapping Turtle ...................................... 2-370

2.3.2. Painted Turtle ....................................... 2-386

2.3.3. Eastern Box Turtle ................................... 2-400

2.3.4. Racer .............................................. 2-411

2.3.5. Northern Water Snake ................................. 2-423

2.3.6. Eastern Newt ........................................ 2-433

2.3.7. Green Frog .......................................... 2-446

2.3.8. Bullfrog ............................................ 2-456

Table 3-1. Metabolizable Energy (ME) of Various Diets for Birds

and Mammals ............................................... 3-5

Table 3-2. Allometric Equations for Basal Metabolic Rate (BMR) in Birds ........ 3-21

Table 3-3. Regression Statistics for Nagy's (1987) Allometric Equations

for Food Ingestion Rates for Free-Living Animals .................. 3-36

Table 3-4. Regression Statistics for Nagy's (1987) Allometric Equations

for Free-Living (Field) Metabolic Rates ........................... 3-37

Table 4-1. Gross Energy and Water Composition of Wildlife Foods:

Animal Prey ................................................ 4-13

Table 4-2. Energy and Water Composition of Wildlife Foods:

Plants ..................................................... 4-14

Table 4-3. General Assimilation Efficiency (AE) Values ....................... 4-15

Table 4-4. Percent Soil or Sediment in Diet Estimated From

Acid-Insoluble Ash of Scat ..................................... 4-20

Table 4-5. Other Estimates of Percentage of Soil or Sediment in Diet ........... 4-21

ix 
LIST OF FIGURES

Figure 3-1. Monthly Variation in Energy Budget Estimated for a

House Sparrow ............................................ 3-25

Figure 4-1. Wildlife Dose Equations for Drinking Water Exposures ............. 4-4

Figure 4-2. Wildlife Dose Equations for Dietary Exposures ................... 4-6

Figure 4-3. Estimating NIRk When Dietary Composition Is Known on a

Wet-Weight Basis .......................................... 4-8

Figure 4-4. Estimating NIRk Based on Different ME Values When

Dietary Composition Is Expressed as Percentage of

Total Prey Captured ........................................ 4-9

Figure 4-5. Utilization of Food Energy by Animals .......................... 4-11

Figure 4-6. Metabolizable Energy (ME) Equation ........................... 4-12

Figure 4-7. Example of Estimating Food Ingestion Rates for

Wildlife Species From Free-Living Metabolic Rate and

Dietary Composition: Male Mink .............................. 4-17

Figure 4-8. Wildlife Oral Dose Equation for Soil or Sediment

Ingestion Exposures ........................................ 4-22

x 
FOREWORD 

The Exposure Assessment Group (EAG) of EPA's Office of Research and 

Development has three main functions: (1) to conduct human health and ecological 

exposure and risk assessments, (2) to review exposure and risk assessments and related 

documents, and (3) to develop guidelines and handbooks for use in these assessments. 

The activities under each of these functions are supported by and respond to the needs of 

the various program offices, regional offices, and the technical community. 

The Wildlife Exposure Factors Handbook was produced in response to the 

increased interest in assessing risks to ecological systems. Its purpose is to improve 

exposure assessments for wildlife and support the quantification of risk estimates. It is a 

companion document to the Exposure Factors Handbook, which contains information 

useful for quantifying exposure to humans. Because information and methods for 

estimating exposure are continually improving, we will revise these handbooks as 

necessary in the future. 

Michael A. Callahan

Director

Exposure Assessment Group

xi 
PREFACE 

The Exposure Assessment Group of the Office of Health and Environmental 

Assessment (OHEA) has prepared the Wildlife Exposure Handbook in support of the Office 

of Solid Waste and Emergency Response and the Office of Water. The Handbook provides 

information on various factors used to assess exposure to wildlife. The goals of the 

project are (1) to promote the application of risk assessment methods to wildlife species, 

(2) to foster a consistent approach to wildlife exposure and risk assessments, and (3) to 

increase the accessibility of the literature applicable to these assessments. 

The bulk of the document summarizes literature values for exposure factors for 34 

species of birds, mammals, amphibians, and reptiles. In addition, we include a chapter on 

allometric equations that can be used to estimate some of the exposure factors when data 

are lacking. Finally, we describe some common equations used to estimate exposure. The 

basic literature search was completed in May 1990 and was supplemented by targeted 

searches conducted in 1992. 

We anticipate updating this Handbook and would appreciate any assistance in 

identifying additional sources of information that fill data gaps or otherwise improve the 

Handbook. Comments can be sent to: 

Exposure Assessment Group 

Wildlife Exposure Factors Handbook Project 

USEPA (8603) 

401 M Street, SW 

Washington, DC 20460 

xii 
AUTHORS, MANAGERS, CONTRIBUTORS, AND REVIEWERS 

The Exposure Assessment Group (EAG) within EPA's Office of Health and 

Environmental Assessment (OHEA) was responsible for preparing this document. 

Additional major contract funding was provided by the Office of Emergency and Remedial 

Response within the Office of Solid Waste and Emergency Response (OSWER) and by the 

Office of Science and Technology within the Office of Water. The document was prepared 

by ICF, Incorporated under contracts 68-C8-0003, 68-W8-0098, 68-DO-0101, and 68-C2-

0107. Susan Braen Norton served as the EAG project manager and provided overall 

direction and coordination of the project. Thanks to Doug Norton for the cover illustration. 

AUTHORS 

Dr. Margaret McVey

Kimberly Hall, Peter Trenham, Alexander Soast, Leslie Frymier, and Ansara Hirst

ICF, Incorporated

PROJECT MANAGER 

Susan Braen Norton

Exposure Assessment Group, Office of Health and Environmental Assessment

Office of Research and Development

U.S. Environmental Protection Agency

TASK MANAGERS 

Cynthia Nolt

Office of Science and Technology

Office of Water

U.S. Environmental Protection Agency

Ron Preston

Office of Emergency and Remedial Response

Office of Solid Waste and Emergency Response

U.S. Environmental Protection Agency

CONTRIBUTORS 

Dr. Sarah Gerould 

Office of Water Quality 

U.S. Geological Survey 

xiii 
Dr. Ronald Kirby

Office of Information Transfer

U.S. Fish and Wildlife Service (USFWS)

Department of the Interior

REVIEWERS 

Dr. Cynthia Annett, USFWS, Arkansas Cooperative Fish and Wildlife Research

Unit, AR

Dr. Richard J. Aulerich, Michigan State University, MI

Dr. Richard Bennett, USEPA, Environmental Research Laboratory (ERL),

Corvallis, OR

Dr. Christine A. Bishop, Canadian Wildlife Service, Ontario, Canada

Dr. Brad Bortner, USFWS, Office of Migratory Bird Management, MD

Dr. Steven Bradbury, USEPA, ERL-Duluth, MN

Dr. Robert Burr, USFWS, VA

Ms. Janet Burris, ABB Environmental Services, Washington, DC

Dr. Joseph Chapman, Utah State University, UT

Dr. Lewis Cowardin, USFWS, Northern Prairie Wildlife Research Center, ND

Ms. Deanna Dawson, USFWS, Patuxent Wildlife Research Center, MD

Dr. Donald L. DeAngelis, Oak Ridge National Laboratory, TN

Dr. Bruce Duncan, USEPA, Region 10, Seattle, WA

Dr. Robert Foley, USFWS, Annapolis Field Office, MD

Dr. Glen Fox, Canadian Wildlife Service, Ontario, Canada

Dr. J.H.B. Garner, USEPA, OHEA, Environmental Criteria and Assessment Office

(ECAO), Research Triangle Park, NC

Dr. J. Whitfield Gibbons, University of Georgia, Savannah River Ecology

Laboratory, GA

Mr. Keith A. Grasman, Virginia Polytechnic Institute and State University, VA

Dr. Fred Guthery, Caesar Kleberg Wildlife Research Institute, Texas A&I

University, TX

Dr. Richard S. Halbrook, Oak Ridge National Laboratory, TN

Dr. Michael J. Hamas, Central Michigan University, MI

Dr. Charles J. Henny, USFWS, Pacific Northwest Research Station, OR

Dr. Paula F. P. Henry, USFWS, Patuxent Wildlife Research Center, MD

Dr. Gary Heinz, USFWS, Patuxent Wildlife Research Center, MD

Dr. Doug James, University of Arkansas, AR

Mr. K. Bruce Jones, USEPA, Environmental Monitoring Systems Laboratory,

EMAP Terrestrial Ecosystems, CA

Dr. Dennis G. Jorde, USFWS, Patuxent Wildlife Research Center, MD

Dr. Norm Kowal, USEPA, OHEA, ECAO, Cincinnati, OH

Dr. Gary L. Krapu, USFWS, Northern Prairie Wildlife Research Center, ND

Dr. David Krementz, USFWS, Patuxent Wildlife Research Center, MD

Dr. James Kushlan, University of Mississippi, MS

Dr. John T. Lokemoen, USFWS, Northern Prairie Wildlife Research Center, ND

Dr. Dave Ludwig, EA Engineering, Inc., MD

Dr. Drew Major, USFWS, Concord, NH

Dr. Karen McBee, Oklahoma State University, OK

xiv 
REVIEWERS (continued) 

Dr. Linda Meyers-Schöne, International Technology Corp., NM

Mr. Jerry Moore, USEPA, OHEA, Washington, DC

Dr. Lewis Oring, University of Nevada at Reno, NV

Dr. Raymond Pierotti, University of Arkansas, AR

Dr. Richard M. Poché, Genesis Laboratories, WI

Dr. Douglas Reagan, Woodward-Clyde Consultants, CO

Dr. Lorenz Rhomberg, USEPA, OHEA, Human Health Assessment Group,

Washington, DC

Dr. Robert Ringer, Mount Dora, FL

Dr. John L. Roseberry, Southern Illinois University at Carbondale, IL

Dr. Alan Sargeant, USFWS, Northern Prairie Wildlife Research Center, ND

Dr. Edward Schafer, USDA, Denver Wildlife Research Center, CO

Dr. Laird Schutt, Canadian Wildlife Service, Quebec, Canada

Ms. Anne Sergeant, USEPA, OHEA, EAG, Washington, DC

Dr. Kim Smith, University of Arkansas, AR

Dr. Mark Sprenger, USEPA, OSWER, Environmental Response Team, Edison, NJ

Dr. George A. Swanson, USFWS, Northern Prairie Wildlife Research Center, ND

Dr. Sylvia Talmage, Oak Ridge National Laboratory, TN

Dr. Bob Trost, USFWS, Office of Migratory Bird Management, MD

Dr. D.V. (Chip) Weseloh, Canadian Wildlife Service, Ontario, Canada

Dr. Nathaniel Wheelwright, Bowdoin College, ME

Dr. Donald H. White, USFWS, Southeast Research Station, GA

Dr. Stanley N. Wiemeyer, USFWS, Patuxent Wildlife Research Center, MD

Dr. Bill Williams, Environmental Planning and Toxicology, Corvallis, OR

Dr. Dean M. Wilkinson, U.S. Department of Commerce, National Oceanic and

Atmospheric Administration, National Marine Fisheries Service

Dr. Jerry O. Wolff, USEPA, ERL, Corvallis, OR

Dr. John P. Wolfin, USFWS, Annapolis Field Station, MD

xv 
1. INTRODUCTION 

The Wildlife Exposure Factors Handbook (hereafter referred to as the Handbook) 

provides data, references, and guidance for conducting exposure assessments for wildlife 

species exposed to toxic chemicals in their environment. It is the product of a joint effort 

by EPA's Office of Research and Development (ORD), Office of Solid Waste and 

Emergency Response (OSWER), and Office of Water (OW). The goals of this Handbook are 

(1) to promote the application of risk assessment methods to wildlife species, (2) to foster 

a consistent approach to wildlife exposure and risk assessments, and (3) to increase the 

accessibility of the literature applicable to these assessments. 

1.1. PURPOSE AND SCOPE 

The purpose of the Handbook is to provide a convenient source of information and 

an analytic framework for screening-level risk assessments for common wildlife species. 

These screening-level risk assessments may be used for several purposes, including: to 

assess potential effects of environmental contamination on wildlife species and to support 

site-specific decisions (e.g., for hazardous waste sites); to support the development of 

water-quality or other media-specific criteria for limiting environmental levels of toxic 

substances to protect wildlife species; or to focus research and monitoring efforts. The 

Handbook provides data (analogous to EPA's Exposure Factors Handbook for humans, 

USEPA, 1989c) and methods for estimating wildlife intakes or doses of environmental 

contaminants. Although the data presented in the Handbook can be used for screening 

analyses, we recommend that anyone establishing a cleanup goal or criterion on the basis 

of values contained herein obtain the original literature on which the values are based to 

confirm that the study quality is sufficient to support the criterion. This Handbook does 

not include data or extrapolation methods required to assess the toxicity of substances to 

wildlife species, nor does it include any chemical-specific data (e.g., bioavailability factors). 

For the Office of Water, data gathered for the Handbook were used to identify 

wildlife species that are likely to be at greater risk from bioaccumulative pollutants in 

surface waters and to estimate likely exposures for these species. Data on diets and on 

1-1
food and water ingestion rates can be used with chemical-specific information, such as 

bioaccumulation potential and wildlife toxicity, to calculate site- or region-specific 

concentrations of a chemical in water (or soil or sediment) that are unlikely to cause 

adverse effects. 

For the Superfund program, this Handbook supplements the existing environmental 

evaluation guidance. EPA's Risk Assessment Guidance for Superfund: Volume II--

Environmental Evaluation Manual (U.S. EPA, 1989a) provides an overview of ecological 

assessment in the Superfund process. It includes a description of the statutory and 

regulatory bases for ecological assessments in Superfund and fundamental concepts for 

understanding ecological effects of environmental contaminants. The Environmental 

Evaluation Manual also reviews elements of planning an ecological assessment and how to 

organize and present the results of the assessment. EPA's Ecological Assessment of 

Hazardous Waste Sites: A Field and Laboratory Reference (U.S. EPA, 1989b) and 

Evaluation of Terrestrial Indicators for Use in Ecological Assessments at Hazardous Waste 

Sites (U.S. EPA, 1992) are companion documents that describe biological assessment 

strategies, field sampling designs, toxicity tests, biomarkers, biological field assessments, 

and data interpretation. The ECO Update intermittent bulletin series (published by EPA's 

Office of Solid Waste and Emergency Response, publication no. 9345.0-05I, available from 

the National Technical Information Service, Springfield, Virginia) provides supplemental 

guidance for Superfund on selected issues. Although these documents have identified 

decreases in wildlife populations as potential endpoints for ecological assessments, they 

do not provide guidance on how to conduct a wildlife exposure assessment that is 

comparable to the guidance provided by the Superfund program for human health 

exposure assessments. This Handbook provides both guidance and data to facilitate 

estimating wildlife exposure to contaminants in the environment. 

Exposure assessments for wildlife and humans differ in several important ways. 

One key distinction is that many different wildlife species may be exposed, as compared 

with a single species of concern for a human health assessment. Exposure varies between 

different species and even between different populations of the same species; behavioral 

attributes and diet and habitat preferences influence this variation. Second, whereas it is 

1-2
�

seldom possible to confirm estimated levels of human exposure without invasive sampling 

of human tissues, confirmatory sampling for many chemicals can be done in wildlife 

species (protected species excepted). However, the tissue sampling required to quantify 

actual exposure levels can be costly, and interpretation of tissue concentrations can be 

complex. 

For both human health and wildlife exposure assessments, the most cost-effective 

approach is often to first screen for potentially significant exposures using measures (or 

estimates) of environmental contamination (e.g., in soils, water, prey species) to estimate 

contaminant intakes or doses by significant routes of exposure. If estimated doses fall far 

below the toxicity values associated with adverse effects, especially from chronic 

exposures, further assessment may be unnecessary. If estimated doses far exceed 

reference toxicity values, it may be possible to determine appropriate actions on the basis 

of these estimates alone. When a screening-level exposure assessment indicates that 

adverse effects are likely, additional confirmatory data may be needed in the decisionmaking process. For humans, it is usually not practicable to obtain additional types of data 

(e.g., tissue concentrations, biomarkers), and human exposure estimates are often refined 

by using more site-specific data for exposure parameters. For wildlife, confirmatory data 

may be obtained from chemical analyses of tissue samples from potentially exposed 

wildlife or their prey and from observed incidence of disease, reproductive failure, or death 

in exposed wildlife. These are reviewed in EPA's field and laboratory reference and 

terrestrial indicators documents described above (EPA, 1989b, 1992). If this more direct 

approach is not possible, the exposure analysis can be refined on the basis of more sitespecific data for the species of concern. 

Wildlife can be exposed to environmental contaminants through inhalation, dermal 

contact with contaminated water or soil, or ingestion of contaminated food, water, or soil. 

Exposure assessment seeks to answer several questions, including: 

� What organisms are actually or potentially exposed to contaminants? 

1-3
�

�

�

�

�

�

�

� Which organisms or life stages might be most vulnerable to environmental 

contaminants (e.g., ingest the largest quantities of contaminated media 

relative to body size)? 

� What are the significant routes of exposure?

� To what amounts of each contaminant are organisms actually or potentially

exposed? 

� How long is each exposure? 

� How often does or will exposure to the environmental contaminants take 

place? 

� What seasonal and climatic variations in conditions are likely to affect 

exposure? 

� What are the site-specific geophysical, physical, and chemical conditions 

affecting exposure? 

The parameters for which data are presented in the Handbook are intended to help a risk 

assessor answer these questions. The population parameter data (e.g., birth and death 

rates) may be useful for placing estimates of risks to wildlife populations in a broader 

ecological context and for planning monitoring activities. 

This Handbook focuses on selected groups of mammals, birds, amphibians, and 

reptiles. Fish and aquatic or terrestrial invertebrates were not included in this effort. The 

profiles on amphibians and reptiles are, in general, less developed than those for birds and 

mammals. We emphasized birds and mammals because methods for assessing their 

exposure are more common and well developed. As more assessments are done for 

amphibians and reptiles, we anticipate that additional methods and supporting factors will 

be necessary. Until then, we hope the information presented here will encourage 

assessors to begin considering and quantifying their exposure. 

For all exposure parameters and species in the Handbook, we try to present data 

indicative of the range of values that different populations of a species may assume across 

North America. For site-specific ecological risk assessments, it is important to note that 

the values for exposure factors presented in this Handbook may not accurately represent 

1-4
specific local populations. The species included in the Handbook have broad geographic 

ranges, and they may exhibit different values for many of the exposure factors in different 

portions of their range. Some species exhibit geographic variation in body size, survival, 

and reproduction. Breeding and migration also influence exposure. Site-specific values 

for these parameters can be determined more accurately using published studies of local 

populations and assistance from the U.S. Fish and Wildlife Service, state departments of 

fish and game, and organizations such as local Audubon Society chapters. In addition, The 

Nature Conservancy develops and maintains wildlife databases (including endangered 

species) in cooperation with all 50 states. Local information increases the certainty of a 

risk assessment. Thus, for site-specific assessments, we strongly recommend contacting 

local wildlife experts to determine the presence and characteristics of species of concern. 

Finally, we do not intend to imply that risk assessments for wildlife should be 

restricted to the species described in this Handbook, or should always be conducted for 

these species. We emphasize that locally important or rare species not included in this 

Handbook may still be very important for site-specific risk assessments. To assist users 

who wish to evaluate other species, we list general references for birds, mammals, 

reptiles, and amphibians in North America. The Handbook also provides allometric 

equations to assist in extrapolating exposure factors (e.g., water ingestion rate, surface 

area) to closely related species on the basis of body size. 

1.2. ORGANIZATION OF THE HANDBOOK 

The Handbook is organized into four chapters. The remainder of this chapter 

provides an overview of the species and exposure factors included in the Handbook and 

discusses the literature search strategy used to identify factors. Chapter 2 presents 

exposure profiles for the selected species (described in greater detail below). Chapter 3 

provides allometric models that may be used to estimate food and water ingestion rates, 

inhalation rates, surface areas, and metabolic rates for wildlife species on the basis of 

body size. Chapter 4 describes common equations used to estimate wildlife exposure to 

environmental contaminants. Included are methods for estimating diet-specific food 

1-5
�

�

ingestion rates on the basis of metabolic rate and for estimating exposure to chemicals in 

soil and sediment. 

Chapter 2 is the core of the Handbook; it presents exposure profiles for selected 

birds (Section 2.1), mammals (Section 2.2), and reptiles and amphibians (Section 2.3), 

along with brief descriptions of their natural history. Each species profile includes an 

introduction to the species' general taxonomic group, qualitative description of the 

species, list of similar species, table of exposure factors, and reference list (which also 

covers that species' section in Volume II, the Appendix). The values included in the 

exposure factors tables are a subset of those we found in the literature and also include 

values that we estimated using the allometric equations presented in Chapter 3. We 

selected values for the tables in Chapter 2 based on a variety of factors including sample 

size, quantification of variability (e.g., standard deviations, standard errors, ranges), 

relevance of the measurement technique for exposure assessment, and coverage of 

habitats, subspecies, and the variability seen in the literature. A complete listing of the 

parameter values identified in our literature survey is provided in the Appendix. The 

Appendix also includes more details concerning sample size, methods, and qualifying 

information than the species profiles. Users are encouraged to consult the Appendix to 

select the most appropriate values for their particular assessment. 

The remainder of this introductory chapter describes the species and exposure 

factors covered in the Handbook in greater detail. The literature search strategy is 

discussed in Section 1.6. 

1.3. LIST OF SELECTED SPECIES 

Wildlife species were selected for the Handbook to provide several types of 

coverage: 

� Major taxonomic groups (major vertebrate groups, orders, and families); 

� A range of diets (e.g., piscivore, probing insectivore) likely to result in 

contact with contaminated environmental media; 

1-6

Table 1-1. Characteristics of Selected Birds 

Diet General Foraging Habitat Body Size Selected 

Insectivorea

probing/soil-dwelling invertebrates

gleaning/insects

Herbivore gleaning/seeds 

grazing/shoots 

Omnivore Carnivoreb 

Carnivore/Piscivore/Scavenger 

small birds & mammals/fish/dead fish 

fish/invertebrates/small birds/garbage 

c Piscivore 

Aquatic Insectivored 

probing/soil-dwelling invertebrates 

diving/aquatic invertebrates 

Aquatic Herbivore/Insectivore 

woodlands, marshes marshes 

woodlands, fields and brush 

open fields 

open woodland, suburbs 

open fields, forest edge 

most open areas 

open water bodies Great Lakes and coastal 

most streams, rivers, small 

lakes most freshwater and saltwater bodies large water bodies 

most rivers and streams 

oceans and coastal areas 

most wetlands, ponds 

medium 

small 

medium 

large 

small 

medium 

medium 

large 

medium 

medium 

large 

large 

small 

medium 

medium 

American marsh w

northern 

Canada g

American 

American 

red-tailed 

bald eagl

herring gbelted kin

great blu

osprey 

spotted s

lesser scmallard 

1-8

aIncludes consumption of insects, other arthropods, worms, and other terrestrial invertebrates.bIncludes consumption of terrestrial vertebrates and large invertebrates. cIncludes consumption of fish, amphibians, crustaceans, and other larger aquatic animals.dIncludes consumption of aquatic invertebrates and amphibian larvae by gleaning or probing. 
Table 1-2. Characteristics of Selected Mammals 

Diet General Foraging Habitat Body Size Mam

S

Insectivorea 

gleaning/surface-dwelling invertebrates most habitat types 

most dry-land habitats 

grassy fields, marshes, bogs 

prairie grass communities 

most habitat types 

woodlands, suburbs 

mixed woodlands and open areas 

most areas near water 

rivers 

coastal, estuaries, lakes 

small 

Herbivore gleaning/seeds small deer mgrazing or browsing/shoots, roots, or small meado

leaves small prairie 

medium eastern 

Omnivore medium raccoo

medium red fox 

Carnivore medium mink b 

Piscivore medium river o

c 

medium harbor 

Aquatic Herbivore most aquatic habitats medium muskra

short-t

1-9

aIncludes consumption of insects, other arthropods, worms, and other terrestrial invertebrates.bIncludes consumption of aquatic and terrestrial vertebrates and large invertebrates. cIncludes consumption of fish, amphibians, crustaceans, molluscs, and other large aquatic animals.
Table 1-3. Characteristics of Selected Reptiles and Amphibians 

Adult Diet for Adults Body Size Amphibi

General Foraging Habitat Selected 

REPTILES 

Terrestrial Carnivorea 

Aquatic Piscivoreb Omnivore 

Aquatic Herbivore AMPHIBIANS Insectivorec 

Aquatic Piscivore/Insectivored 

open woods, fields and brush 

most types of water bodies 

open fields, forest edge, 

marshes most freshwater bodies 

most wetlands, ponds 

shallow freshwater bodies 

lakes, ponds, bogs, streams 

small lakes, ponds, streams 

medium 

medium 

medium 

large medium 

small medium 

small 

racer 

northern wate

eastern box t

snapping turtpainted turtle 

green frog 

bullfrog 

eastern newt 

1-10

aIncludes consumption of terrestrial vertebrates and invertebrates, insects, other arthropods, worms, and other terrestrbIncludes consumption of fish, amphibians, and crustaceans. cIncludes consumption of insects, other arthropods, worms, and other terrestrial invertebrates.dIncludes consumption of fish, amphibians, crustaceans, molluscs, other aquatic animals, and terrestrial insects and o
�

�

Species of societal significance or concern (e.g., game species, familiar 

species); and 

� Species that have been shown to be particularly sensitive to the stressor 

being addressed. 

When species of concern for a risk assessment include species for which data are 

presented in this Handbook, it can serve as a readily available source of data for 

screening-level exposure analyses. 

1.4. LIST OF EXPOSURE FACTORS 

Three routes of exposure may be of concern for wildlife in the vicinity of 

contaminated surface waters and terrestrial habitats: oral, inhalation, and dermal. Oral 

exposures might occur via ingestion of contaminated food (e.g., aquatic prey) or water or 

incidental ingestion of contaminated media (e.g., soils, sediments) during foraging or other 

activities. Inhalation of gases or particulates might be a significant route of exposure for 

some animals. Dermal exposures are likely to be most significant for burrowing mammals 

(i.e., via contact with contaminated soils) and animals that spend considerable amounts of 

time submerged in surface waters. This Handbook tabulates selected data for all three 

routes of exposure (Table 1-4), emphasizing oral exposures. It also provides quantitative 

information on population parameters and qualitative information related to seasonal 

activities, geographic ranges, habitats, and other life-history characteristics. 

The exposure factors presented in the Handbook are conceptually separated into 

four types: normalizing factors (Section 1.4.1), contact rates (Section 1.4.2), population 

dynamics (Section 1.4.3), and seasonal activities (Section 1.4.4). Section 1.5 describes the 

format in which values for these exposure factors are presented in Chapter 2. 

1.4.1. Normalizing Factors 

Normalizing factors include body weight, growth rate, and metabolic rate, which are 

discussed in turn below. 

1-11

1.4.1.1. Body Weight 

Body weights (in units of mass) are reported as fresh weight as might be obtained 

by weighing a live animal in the field. Several of the contact rate parameters are 

normalized to body weight. For example, both food and water ingestion rates are reported 

on a per body weight basis (e.g., gram of fresh food or water per gram of fresh body weight 

per day). Using empirical models, body weight data also were used to estimate contact 

rate parameters for which we could not find measured values. 

Adult body weights are listed for all species. For birds, we also provide egg weight, 

weight at hatching, nestling or chick weights, and weight at fledging, when available, to 

assist risk assessors concerned with estimating exposures of embryos and young birds. 

For mammals, we also provide gestating female weight, birth weight, pup weights at 

various ages, weight at weaning, and weight at sexual maturity, when available, for a 

similar purpose. Finally, for reptiles and amphibians, we also provide egg weight, larval or 

juvenile weights with age, and weight at metamorphosis, if available and applicable. Body 

size for reptiles and amphibians is often reported as body length instead of body weight, 

so we also provide data on body length and the relationship between body length and body 

weight, when available. 

1.4.1.2. Growth Rate 

Young animals generally consume more food (per unit body weight) than adults 

because they grow and develop rapidly. Growth rates change as animals mature, whether 

expressed as absolute (g/day) or relative (percent body weight) terms. Weight gain is rapid 

after birth, but slows over time. Different types of animals exhibit different patterns of 

growth over time. Plots of body weight versus age for some animal groups are sigmoidal 

whereas others may approximate logistic functions or other shapes. As a result, 

investigators often report growth rates as various constants associated with particular 

mathematical models (e.g., Gompertz equation, von Bertalanffy equation; see Peters, 1983) 

that fit the growth pattern for a given species. Instead of presenting a variety of growth 

constants and models, however, we report growth rates for young animals, when available, 

1-13
 in grams per day for specific age groups. Growth rates also can be inferred from a series 

of juvenile body weights with age. These measures are included under body weight (see 

Section 1.4.1.1). 

1.4.1.3. Metabolic Rate 

Metabolic rate is reported on the basis of kilocalories per day normalized to body 

weight (e.g., kcal/kg-day). If metabolic rate was measured and reported on the basis of 

oxygen consumption only, we provide those values as liters O2/kg-day. Normalized 

metabolic rates based on kilocalories can be used to estimate normalized food ingestion 

rates (see Section 4.1.2). Metabolic rates based on oxygen consumption can be used to 

estimate metabolic rates based on kilocalories for subsequent use in estimating food 

ingestion rates (see Section 3.6.3.1). 

1.4.2. Contact Rate Factors 

Table 1-5 summarizes the six contact rate factors included for the oral, inhalation, 

and dermal routes of exposure. 

1.4.2.1. Oral Route 

Three environmental media are the primary contributors to wildlife exposure by the 

oral route: food, water, and soils and sediments. Four contact rate exposure parameters 

related to these three exposure media are discussed below. 

1.4.2.1.1. Food ingestion rates. Food ingestion rates are expressed in this 

Handbook as grams of food (wet weight) per gram of body weight (wet weight) per day 

(g/g-day). Food ingestion rates can vary by age, size, and sex and by seasonal changes in 

ambient temperature, activity levels, reproductive activities, and the type of diet consumed. 

Food ingestion rates have not been measured for many wildlife species. Methods for 

estimating food ingestion rates on the basis of free-living (or field) metabolic rate, energy 

content of the diet, and assimilation efficiency are discussed in Section 4.1.2. 

1-14
Table 1-5. Wildlife Contact Rate Exposure Factors 

Exposure 

Route Medium Factor Expression Units 

ORAL Food ingestion rate fraction body 

weight 

6 g/g-day 

dietary 

composition 

fraction of total 

intake 

represented by 

each food type 

Water ingestion rate fraction body 

weight 

g/g-day 

Soil/Sediment intake rate fraction of total 

food intake 

g/g-day 

INHALATION Vapor or 

Particulates 

inhalation rate daily volume m /day 3 

DERMAL Water or 

Soil/Sediment 

surface area total area 

potentially 

exposeda 

cm2 

a

Total unprotected or permeable surface area that might be exposed under some circumstances (e.g., dust

 bathing), even though it would not be exposed under other conditions (e.g., swimming with a trapped air 

layer between the feathers or fur and skin). 

1.4.2.1.2. Dietary composition. Dietary composition varies seasonally and by age, 

size, reproductive status, and habitat. Dietary composition (e.g., proportion of diet 

consisting of various plant or animal materials), often measured by stomach-content 

analyses, is expressed whenever possible as percentage of total intake on a wet-weight 

basis. This convention facilitates comparison with contaminant concentrations in dietary 

items reported on a wet-weight basis. Methods for converting other measures of dietary 

composition (e.g., percentage of total prey items captured, proportion of intake on a dryweight basis) to estimates of dietary intake on a wet-weight basis are provided in Section 

4.1.2. 

1.4.2.1.3. Water ingestion rates. For drinking-water exposures, ingestion rates are 

expressed in this Handbook as grams of water per gram of wet body weight per day (g/gday). Water consumption rates depend on body weight, physiological adaptations, 

1-15
diet, temperature, and activity levels. It is important to remember that, under some 

conditions, some species can meet their water requirements with only the water contained 

in the diet and metabolic water production (see Section 3.2). 

1.4.2.1.4. Incidental soil and sediment intakes. Wildlife can incidentally ingest 

soils or sediments while foraging or during other activities such as dust bathing and 

preening or grooming. Data quantifying soil and sediment ingestion are limited; we 

present available values for selected species in Section 4.1.3. 

1.4.2.2. Inhalation Route 

Average daily inhalation rates are reported in the Handbook in units of m3/day. 

Inhalation rates vary with size, seasonal activity levels, ambient temperature, and daily 

activities. EPA's current approach to calculating inhalation exposures requires additional 

information on species' respiratory physiology to fully estimate inhalation exposures (see 

Section 4.1.4). 

1.4.2.3. Dermal Route 

Dermal contact with contaminated soil, sediment, or water is likely to be an 

exposure pathway for some wildlife species. An animal's surface area could be used to 

estimate the potential for uptake of contaminants through its skin. For some exposures 

(e.g., dust bathing), the entire surface area of the animal might be important. For other 

types (e.g., swimming), only the uninsulated portions (e.g., no fur or feathers that create a 

trapped air layer) of the animal might contact the contaminated medium. In the Handbook, 

we provide measures or estimates of the entire potentially exposed surface area of an 

animal, when possible. We have not attempted to determine what portions would be 

exposed and protected for swimming animals. 

1-16
1.4.3. Population Dynamics 

Several parameters can be used to describe the spatial distribution and abundance 

of a population of animals in relation to the spatial extent of contamination. Three 

parameters related to spatial distribution are social organization, home-range size, and 

population density. These are important for estimating the number of individuals or 

proportion of a population that might be exposed to a contaminated area. Parameters 

related to population size and persistence include age at sexual maturity and maturation, 

mortality, and annual fecundity rates. These parameters may be useful to assessors 

planning or evaluating field studies or monitoring programs. 

1.4.3.1. Social Organization 

The Handbook includes a qualitative description of each species' social 

organization, which influences how animals of various ages and sizes are distributed in 

space. In some species, individual home ranges do not overlap. In others, all individuals 

use the same home range. In between these extremes, home ranges can be shared with 

mates, offspring, or extended family groups. 

Social organization can vary substantially among species that appear otherwise 

similar; therefore, it is not possible to extrapolate the social organization of similar species 

from the selected species in this Handbook. Consult the general bibliographies for 

information sources to determine the social organization of species not covered in the 

Handbook. 

1.4.3.2. Home Range/Territory Size/Foraging Radius 

Home range size can be used to determine the proportion of time that an individual 

animal is expected to contact contaminated environmental media. Home range is defined 

as the geographic area encompassed by an animal's activities (except migration) over a 

specified time. While home range values often are expressed in units of area, for species 

dependent on riparian or coastal habitats, a more meaningful measure can be foraging 

1-17
radius, or the distances the animals are willing to travel to potential food sources. Although 

home ranges may be roughly circular in homogeneous habitats, it is important to 

remember that depending on habitat needs and conditions, home ranges may be irregular 

in shape. The size and spatial attributes of a home range often are defined by foraging 

activities, but also might depend on the location of specific resources such as dens or nest 

sites in other areas. An animal might not visit all areas of its home range every day or 

even every week, but over longer time periods, it can be expected to visit most of the areas 

within the home range that contain needed resources such as forage, prey, or protected 

resting areas. 

Home range size for individuals within a population can vary with season, latitude, 

or altitude as a consequence of changes in the distribution and abundance of food or other 

resources. It generally varies with animal body size and age because of differences in the 

distribution of preferred forage or prey. It can also depend on habitat quality, increasing as 

habitat quality decreases to a condition beyond which the habitat does not sustain even 

sparse populations. Finally, home ranges can vary by sex and season. For example, if a 

female is responsible for most or all of the feeding of young, her foraging range might be 

restricted to an area close to her nest or den when she has dependent young, whereas the 

foraging range of males would not be so restricted. 

Nonterritorial species may allow significant overlap of activity areas among 

neighboring individuals or groups. For example, several individuals or mated pairs may 

share the same area, although signalling behaviors may ensure temporal segregation. For 

these species, we report a home range size or foraging radius. Other species are strongly 

territorial and defend mutually exclusive areas: individuals, breeding pairs, or family units 

actively advertise identifiable boundaries and exclude neighboring individuals or groups. 

Foraging activities are usually restricted to the defended territories. For these species, we 

report the size of the defended territory and note whether foraging occurs outside of the 

territory. 

1-18
1.4.3.3. Population Density 

Population density (the number of animals per unit area) influences how many 

individuals (or what proportion of a local population) might be exposed within a 

contaminated area. For strongly territorial species, population density can be inferred 

from territory size in many cases. For species with overlapping home ranges, particularly 

colonially breeding animals (e.g., most seabirds), population density cannot be inferred 

from home range size. 

1.4.3.4. Annual Fecundity 

Attributes related to the number of offspring produced each year that reach sexual 

maturity (annual fecundity) are measured in different ways depending on the life history of 

the species. For birds, data are generally available for clutch size, number of clutches per 

year, nest success (generally reflecting predation pressure), number of young fledged per 

successful nest (generally reflecting food availability), and number of young fledged per 

active nest (reflecting all causes of mortality). For mammals, litter size in wild populations 

often is determined by placental scars or embryo counts, and the number of young 

surviving to weaning is seldom known. For reptiles that lay eggs, clutch size and percent 

hatching can be measured in the field. For viviparous reptiles, we report the number born 

in a litter. For amphibians, egg masses may include thousands of eggs, but these are 

seldom counted. 

1.4.3.5. Annual Mortality and Longevity 

Longevity can influence the potential for cumulative deleterious effects and the 

appropriate averaging times for chronic exposures. For birds, annual adult mortality tends 

to be constant. For large mammalian species, however, annual adult mortality tends to be 

constant for several years, and then increases rapidly with age. For reptiles and 

amphibians, annual adult mortality can decrease with age for some time as the animals 

continue to grow larger and become less susceptible to predation. In the Handbook, we 

1-19
�

�

�

�

report annual mortality rates by age category and typical or mean and maximum 

longevities, when possible. 

1.4.4. Seasonal Activities 

Many life-cycle attributes affect an animal's activity and foraging patterns in time 

and space. For example, many species of birds are present in the northern hemisphere 

only during the warmer months or move seasonally between the northern and southern 

parts of North America. Some species of mammals, reptiles, and amphibians hibernate or 

spend a dormant period in a burrow or den during the winter months. The species profiles 

describe these and other seasonal activity patterns that can influence exposure frequency 

and duration. 

For each species, we summarize information on the seasonal occurrence of several 

activities including breeding, molting, migration, dispersal, and occurrence of 

dormancy/denning (if applicable). Deposition and utilization of fat reserves are discussed 

where information is available. Trends in these factors with latitude are identified. 

1.5. DATA PRESENTATION FORMAT 

Species-specific values for the exposure factors are presented in Chapter 2. 

Quantitative data for each species are presented in tables arranged in four main sections: 

� Normalizing and Contact Rate Factors; 

� Dietary Composition; 

� Population Dynamics; and 

� Seasonal Activities. 

The parameter values and units used for each exposure factor are described in the 

remainder of this section. In the species profiles and in the Appendix, all values are 

identified as measured or estimated, and references are provided. 

1-20
1.5.1. Normalizing and Contact Rate Factors 

Normalizing and contact rate factors are presented under the heading "Factors" in 

Chapter 2. Several of them apply to all animals included in the Handbook, whereas some 

apply only to specific groups, as described in Sections 1.5.1.1 through 1.5.1.4. The column 

headers for these factors are explained in Table 1-6. 

Table 1-6. Column Headers for Tables of Normalizing and Contact Rate Factors 

Age/Sex/ Age (e.g., A for adult, J for juvenile) 

Cond./Seas. Sex (e.g., M for male, F for female) 

Condition (e.g., I for incubating, NB for nonbreeding) 

Season (e.g., SP for spring, SU for summer). 

[Note: Only information needed to correctly interpret the value is 

included.] 

Mean Mean value for population sampled ± standard deviation (SD), if 

reported. If SD is not reported, mean value for population sampled ± 

standard error (SE) of the mean, if reported. For some studies, a 

range of typical values may be presented instead of a mean value 

(check the notes). 

Range or Range of values reported for the population sampled, or 

(95% CI of (95th percent confidence interval of the mean value). 

Mean) 

Location State(s) or province(s) in which the study was conducted 

(subspecies) (subspecies studied, if reported). 

Reference Reference for study. 

Note No. Footnote number. 

1.5.1.1. All Animals 

Body weight (grams or Measured values only. Although we use the term 

kilograms) weight, all data are presented in units of mass. The age 

and sex of the animal are specified as appropriate, and 

1-21
Metabolic rate (liters O2/kg-day) 

Metabolic rate (kcal/kg-day) 

Food ingestion rate (g/g-day) 

Water ingestion rate (g/g-day) 

Sediment/soil ingestion rate 

Inhalation rate (m3/day) 

Surface area (cm2) 

1.5.1.2. Birds 

Egg weight (grams) 

Weight at hatching (grams) 

weights may include age-weight series for young 

animals. 

Included only if measured values were available. These 

data can be used to estimate metabolic rate on a kcal 

basis. 

Measured or estimated basal and free-living (or field) 

metabolic rates. Most of the free-living values were 

estimated from body weight using an appropriate 

allometric equation. 

Measured on a wet-weight basis. For birds and 

mammals, values measured in captivity are generally 

lower than for free-ranging animals. For reptiles and 

amphibians, food ingestion rates can be higher in 

captivity than in the field. Food ingestion rates can also 

be different in captivity than in the wild if the diet differs 

substantially from that consumed in the wild (e.g., dry 

laboratory chow has a substantially lower water content 

than most natural diets). 

Most of these values were estimated from body weight 

using an allometric equation. 

These values are not presented in the individual species 

profiles in Chapter 2; instead, the limited data available 

for soil/sediment ingestion rates (as percent soil or 

sediment in diet on a dry weight basis) for selected 

species are presented in Section 4.1.3. 

Note that this value is not normalized to body weight, 

but is the total volume inhaled each day. Most values 

were estimated from body weight using an appropriate 

allometric equation. 

Most values were estimated from body weight using an 

appropriate allometric equation. 

Included only if measured values were available. 

Included only if measured values were available. 

1-22
Chick or nestling growth 

rate (g/day) 

Weight at fledging (grams) 

1.5.1.3. Mammals 

Neonate weight (grams) 

Pup growth rate (g/day) 

Weight at weaning (grams) 

1.5.1.4. Reptiles and Amphibians 

Body length (mm) 

Egg weight (grams) 

Weight at hatching (grams) 

Juvenile growth rate (g/day) 

Tadpole weight (grams) 

Larval or eft weight (grams) 

Included only if measured values were available. The 

ages to which the growth rate applies are indicated. 

Included only if measured values were available. 

Included only if measured values were available. 

Included only if measured values were available. The 

ages to which the growth rate applies are indicated. 

Included only if measured values were available. 

Length is the most common measure of size and growth 

rate reported for reptiles and amphibians. Body lengthweight relationships are reported whenever possible. 

Data for snakes include snout-to-vent lengths (SVL) and 

total lengths; for frogs, SVLs only; and for turtles, 

carapace (dorsal shell) and plastron (ventral shell) 

lengths. 

Included only if measured values were available. 

Included only if measured values were available. 

Included only if measured values were available. The 

ages to which the growth rate applies are indicated. 

For frogs only; included only if measured values were 

available. 

For newts only; included only if measured values were 

available. 

1-23
1.5.2. Dietary Composition 

1.5.2.1. All Animals 

The diet of all animals is separated by season whenever possible. Up to three 

months of data were combined for each of the four seasons, provided the animals were in 

the same location and habitat during the 3-month period (Table 1-7). The diet components 

are listed in the first column shaded in grey. The measure of dietary composition is 

enclosed in parentheses under the "Location (subspecies)/Habitat (measure)" column 

header. 

Table 1-7. Column Headers for Tables on Dietary Composition 

Dietary Composition List of food types. 

Spring Dietary composition during spring (March, April, May). 

Summer Dietary composition during summer (June, July, August). 

Fall Dietary composition during fall (September, October, 

November). 

Winter Dietary composition during winter (December, January, 

February). 

Location State(s) or Canadian province(s) in which study was 

(subspecies)/ conducted (subspecies studied, if reported). 

Habitat Type of habitat associated with the reported values 

(measure) (measure used to quantify dietary composition). 

Reference Reference for study. 

Note No. Footnote number. 

Dietary composition can be expressed in many ways. In the Appendix, we have 

presented all measures of dietary composition encountered in the literature review. In the 

species profiles in Chapter 2, we have emphasized dietary composition measured as the 

percentage of the total food intake of each food type on a wet-weight basis. These data 

1-24
are usually determined by analysis of stomach or other digestive tract contents. For 

entries based on these measures, the total of the values listed under each seasonal 

column should approximate 100 percent. As Chapter 4 indicates, it is relatively simple to 

estimate contaminant intakes when dietary composition is measured on a wet-weight 

basis. Dietary composition may also be measured on a dry-weight basis; information on 

the relative water content of the different dietary items provided in Chapter 4 can be used 

to convert dry-weight composition to wet-weight composition if needed. Dietary 

composition is often reported as frequency of occurrence in digestive tract contents, 

scats, or regurgitated pellets. For these measures, the total of the values in the seasonal 

columns can exceed 100 (e.g., fish occurred in 90 percent of scats, amphibia in 75 percent 

of scats, and molluscs in 15 percent of scats). We do not provide guidance on how to 

estimate contaminant intakes based on these measures; however, studies using these 

measures can indicate seasonal and geographic differences in diet. 

1.5.3. Population Dynamics 

Distribution and mortality parameters can be defined similarly for birds, mammals, 

reptiles, and amphibians (Section 1.5.3.1). Reproductive parameters, however, differ 

among these groups (Sections 1.5.3.2 through 1.5.3.5). The column headers for population 

dynamics are described in Table 1-8. 

1.5.3.1. All Animals 

Home range size (ha)/ Area usually listed in hectares, radius in kilometers. The home 

Territory size (ha)/ range for species such as mink or kingfishers, which spend 

Foraging radius (m) most of their time along shoreline areas, is sometimes 

described as kilometers of shoreline. For some species with 

extremely small breeding territories, we used m2 instead of 

hectares. For colonially nesting birds, foraging radii are listed 

in kilometers. For frogs, we found information only on male 

breeding territory size, which does not include the foraging 

range of either sex. 

Population density Usually listed as number (N) of individuals per hectare, 

(N/ha) although numbers of breeding pairs or nests per hectare are 

used for some species. 

1-25
Table 1-8. Column Headers for Tables of Factors for Population Dynamics 

Age/Sex/ Age (e.g., A for adult, J for juvenile) 

Cond./Seas. Sex (e.g., M for male, F for female) 

Condition (e.g., I for incubating, NB for nonbreeding) 

Season (e.g., SP for spring, SU for summer). 

[Note: Only information needed to correctly interpret the value is 

included.] 

Mean Mean value for population sampled ± standard deviation (SD), if 

reported. If SD is not reported, mean value for population sampled ± 

standard error (SE) of the mean, if reported. For some studies, a 

range of typical values may be presented instead of a mean. 

Range Range of values reported for the population sampled. 

Location State(s) or province(s) in which the study was conducted 

(subspecies)/ (subspecies studied, if reported). 

Habitat Type of habitat associated with the reported values. 

Reference Reference for study. 

Note No. Footnote number. 

Age at sexual maturity Age at which first successful reproduction occurs. In many 

long-lived species, only a portion of the population breeds at 

this age. 

Annual mortality rates Usually listed as percent per year. Can vary with age and sex 

of the animal. 

Longevity Mean longevity of adult members of the population (does not 

include juvenile mortality). When available, an estimate of 

maximum longevity is also provided (usually from studies of 

captive individuals). 

1.5.3.2. Birds 

Clutch size Number of eggs laid per active nest (usually the number laid 

per female, but in some species, more than one female may lay 

in a single nest). 

1-26
Clutches per year Number of successful clutches laid per year. Additional 

clutches may be laid if a clutch is lost early in incubation. 

Days incubation Measured from day incubation starts (often after laying of last 

egg) to hatching. 

Age at fledging Age at which young can maintain sustained flight. Parents 

usually continue to feed or to accompany young for some time 

after fledging. 

Number fledged per Number fledged for each nest for which incubation was 

active nest initiated. 

Percent nests Percent of active nests hatching eggs. 

successful 

Number fledged per Number fledged for each nest for which at least one young 

successful nest hatched. 

1.5.3.3. Mammals 

Litter size Based on embryo counts whenever possible. Use of placental 

scars can result in overestimation of litter size and counts of 

live pups in dens can result in underestimation of litter size. 

Litters per year Number of litters born each year. 

Days gestation Days of active gestation. For species with delayed 

implantation, this period can be substantially shorter than the 

period from mating to birth. 

Pup growth rate Usually reported as grams per day during a specified age 

interval. May be reported instead as a series of weights for 

pups of specified ages. 

Age at weaning Age when the pups begin to leave the nest or den to actively 

feed for most of their food. 

1.5.3.4. Reptiles and Amphibians 

Clutch or litter size Number of eggs laid per female for egg-laying species; number 

of live offspring born for species bearing live young (e.g., water 

snake). Reported by age and size of the female when 

appropriate. 

1-27
Clutches or litters Number of clutches or litters produced each year. Not limited 

per year to successful clutches because there is no parental care in 

most temperate species. 

Days incubation Measured from laying of last egg to hatching. The duration of 

incubation depends on the temperature of the substrate into 

which eggs are laid. 

Juvenile growth rate Usually reported as grams per day during a specified age (or 

size) interval. May be reported instead as a series of weights 

for juveniles of specified sizes if those are the only data 

available. 

Length at sexual maturity Length at which the first successful reproduction usually 

occurs (see above). More commonly reported than weight or 

age at sexual maturity. 

1.5.4. Seasonal Activities 

The meaning of most of the factors included under seasonal activities are selfevident. Those requiring additional explanation are described in Sections 1.5.4.1 through 

1.5.4.3. The column headers for this section of the table are shown in Table 1-9. 

Table 1-9. Column Headers for Tables on Seasonal Activities 

Begin Month that the activity usually begins. 

Peak Month(s) that the activity peaks (most of the population is involved). 

End Month that the activity usually ends. 

Location State(s) or province(s) in which the study was conducted 

(subspecies) (subspecies studied, if reported). 

Reference Reference for study. 

Note No. Footnote number. 

1-28
1.5.4.1. Birds 

Mating/laying These two factors are combined because birds lay eggs within 

a day or two of mating (they begin mating a day or two prior to 

laying the first egg). 

1.5.4.2. Mammals 

Mating Although for most mammals the mating season corresponds to 

conception and is followed immediately by gestation, some 

species exhibit delayed implantation. 

Parturition Birth of the pups (also known as whelping for canids). 

1.5.4.3. Reptiles and Amphibians 

Mating Because fertilization is external for many amphibians (i.e., most 

toads and frogs and some salamanders), mating occurs at the 

same time as egg-laying for these species. For reptiles, 

fertilization is internal, and for some species, sperm may be 

stored for months or years following mating. 

Nesting Because many female reptiles can store sperm, nesting (i.e., 

egg-laying) often occurs weeks or months after mating. 

1.5.5. Abbreviations Used in Tables 

Age (life stage) 

A adult (for all groups)

B both adults and juveniles/yearlings (for all groups)

C chick (for birds)

E eft (for newts)

F fledgling (for birds)

H hatchling (for birds, reptiles, and amphibians)

J juvenile (for all groups)

N nestling (for birds)

or 

neonate (for mammals, water snakes) 

P pup (for mammals) 

T tadpole (for frogs) 

Y yearling (for all groups) 

1-29
�

Sex 

B both sexes 

F female

M male

Units 

time: 

d day 

wk week 

yr year 

mass: 

g gram 

kg kilogram 

length: 

mm millimeter 

cm centimeter 

m meter 

km kilometer 

temperature: 

�C degrees Centigrade 

Other 

NS not stated 

energy: 

cal 

kcal 

area: 

ha 

m 2

volume: 

ml 

l 

calorie 

kilocalorie 

hectare 

square meter 

milliliter 

liter 

1.6. LITERATURE SEARCH STRATEGY 

The profiles in this Handbook are intended to provide a readily available 

compendium of representative data for each selected species to assist in conducting 

screening-level exposure assessments. They are not intended to provide complete 

reviews of all available published and unpublished information or indepth biological 

summaries. Moreover, the Handbook is not intended to replace field guides or natural 

history or animal physiology texts. We have attempted to balance generalities, accuracy, 

and coverage of each species relative to the available literature to meet our stated 

purposes. We describe the process by which we identified literature for the Handbook 

below. 

1-30
The U.S. Fish and Wildlife Service (USFWS) Office of Information Transfer 

conducted the primary literature search for species-specific information using their Wildlife 

Review/Fisheries Review database. The database is compiled by USFWS personnel from a 

review of over 1,130 publication sources (largely journals, but also USFWS publications) 

from the United States and other countries, most dating back to 1971. The search was 

conducted in May 1990 using common and scientific species names, but no further 

restrictions on search terms were applied. All titles identified for each species were 

reviewed to determine potential utility for the Handbook, and promising references were 

reviewed in full. Recent review articles, handbooks, and natural history texts were used to 

identify other relevant literature and literature from before 1971. Commercial databases 

were not searched initially. Following peer review of the Handbook in 1991 and 1992, all 

references submitted or identified by peer reviewers were evaluated, and additional 

relevant citations were obtained for review. Limited (1970 forward) literature searches for 

some species were conducted using commercial databases in 1992. 

For information concerning physiology, allometric equations, energetics, and other 

general topics, literature was identified on the basis of recent review articles or books in 

the field suggested by experts in the field and by peer reviewers. 

Because of resource limitations, we have included some values from secondary 

citations. In these cases, our intent was to carefully record the original source and to 

clearly indicate from which secondary source it was obtained. Users are encouraged to 

obtain the primary sources to verify these values. 

We used certain field guides consistently throughout each taxonomic category to 

provide greater comparability of general species characteristics. The use of a specific field 

guide does not constitute endorsement. 

Because our literature search strategy may not have included all journals of interest 

and did not consistently cover other sources of information (e.g., books, theses, 

dissertations, state wildlife reports, conference proceedings), we would appreciate any 

assistance that users might provide in identifying additional sources of information that 

1-31
would help to fill data gaps or to improve the information in the Handbook. In particular, 

Ph.D. dissertations and master's theses often contain relevant but unpublished 

information. 

1.7. REFERENCES 

Peters, R.H. (1983) The ecological implications of body size. Cambridge, England: 

Cambridge University Press. 

U.S. Environmental Protection Agency. (1989a) Risk assessment guidance for Superfund: 

volume II--environmental evaluation manual, interim final. Washington, DC: Office of 

Solid Waste, Office of Emergency and Remedial Response; EPA report no. 

EPA/540/1-89/001A. 

U.S. Environmental Protection Agency. (1989b) Ecological assessment of hazardous waste 

sites: a field and laboratory reference. Corvallis, OR: Environmental Research 

Laboratory; EPA report no. EPA/600/3-89/013. 

U.S. Environmental Protection Agency. (1989c) Exposure factors handbook. Washington, 

DC: Office of Health and Environmental Assessment; EPA report no. EPA/600/8-

89/043. 

U.S. Environmental Protection Agency. (1992) Evaluation of terrestrial indicators for use in 

ecological assessments at hazardous waste sites. Washington, DC: Office of 

Research and Development; EPA report no. EPA/600/R-92/183. 

1-32
2. EXPOSURE FACTORS AND DESCRIPTIONS 

OF SELECTED SPECIES 

Chapter 2 includes exposure profiles for the selected species in three subsections: 

birds (Section 2.1), mammals (Section 2.2), and reptiles and amphibians (Section 2.3). 

Each species profile follows the same format, beginning with an introduction to the 

taxonomic group to which the species belongs and a qualitative description of relevant 

aspects of the species' natural history. Next, a list of similar species is provided to help 

identify species that might share certain exposure characteristics, although they may have 

different geographic ranges, diets, and habitat preferences. Each species profile then 

presents a series of tables presenting values for normalizing and contact rate factors, 

dietary composition, population dynamics, and seasonal activity patterns that represent 

the range of values that we identified in our literature review. Table format is described in 

Section 1.5. Data on soil and sediment ingestion are limited; we present these data in a 

separate section (4.1.3) for easy comparison among species. Finally, each profile includes 

the references cited in the species profile and in the corresponding Appendix tables. 

2.1. BIRDS 

Table 2-1 lists the bird species described in this section. For range maps, refer to 

the general references identified in individual species profiles. The remainder of this 

section is organized by species in the order presented in Table 2-1. The availability of 

published information varies substantially among species, as is reflected in the profiles. 

Some species include two or more subspecies; these are indicated in the profiles when 

reported by the investigators. For many studies, the subspecies, although not identified, 

can be inferred from the study location and geographic range of the subspecies. Average 

lengths of birds are reported from museum study skins measured from bill tip to tail tip. 

Body weight is reported as fresh wet weight with plumage, unless otherwise noted. 

2-1
 Table 2-1. Birds Included in the Handbook 

Order 

Family Common name Scientific name Section 

Ciconiformes 

Ardeidae great blue heron Ardea herodias 2.1.1 

Anseriformes 

Anatidae Canada goose Branta canadensis 2.1.2 

mallard Anas platyrhynchos 2.1.3 

lesser scaup Aythya affinis 2.1.4 

Falconiformes 

Accipitridae osprey Pandion haliaetus 2.1.5 

red-tailed hawk Buteo jamaicensis 2.1.6 

bald eagle Haliaeetus leucocephalus 2.1.7 

Falconidae American kestrel Falco sparverius 2.1.8 

Galliformes 

Phasianidae northern bobwhite Colinus virginianus 2.1.9 

Charadriiformes 

Scolopacidae American woodcock Scolopax minor 2.1.10 

spotted sandpiper Actitis macularia 2.1.11 

Laridae herring gull Larus argentatus 2.1.12 

Coraciiformes 

Alcedinidae belted kingfisher Ceryle alcyon 2.1.13 

Passeriformes 

Troglodytidae marsh wren Cistothorus palustris 2.1.14 

Muscicapidae American robin Turdus migratorius 2.1.15 

2-2
2.1.1. Great Blue Heron (herons) 

Order Ciconiiformes, Family Ardeidae. Herons, egrets, and bitterns are medium to 

large wading birds with long necks and spear-like bills. Nearly all species feed primarily on 

aquatic animal life (e.g., fish, frogs, crayfish, insects) and are common along the margins 

of most freshwater and saltwater bodies and wetlands (Kushlan, 1978). Their long legs, 

necks, and bills are adapted for wading in shallow water and stabbing prey. Most species 

build their nests in trees near their foraging habitat, and many nest colonially. Members of 

this group range in size from the least bittern (28 to 36 cm bill tip to tail tip) to the great 

blue heron (106 to 132 cm tall). The sexes are similar in size and appearance. 

Selected species 

The great blue heron (Ardea herodias) is the largest member of the group in North 

America and feeds primarily on aquatic animals. It is widely distributed in both saltwater 

and freshwater environments. There are four subspecies in the United States and Canada: 

A. h. wardi (Kansas and Oklahoma across the Mississippi River to Florida), A. h. herodias 

(remainder of the North and Central American range), A. h. fannini (Pacific coast of North 

America from Alaska to Washington), and A. h. occidentalis (extreme south of Florida) 

(Bancroft, 1969, cited in Hancock and Kushlan, 1984). A. h. occidentalis (the great white 

heron) is an all white color morph that was formerly considered a separate species 

(National Geographic Society, 1987). 

Body size. Males average slightly heavier in weight than females (Hartman, 1961; 

Palmer, 1962). Northern continental herons are somewhat smaller than those found in the 

south (Palmer, 1962). Quinney (1982) determined a relationship between age and body 

weight for nestling great blue herons (r = 0.996, N = 16 nestlings, and 274 measurements): 

BW = 55.6 × A - 47.4 

where BW equals body weight in grams and A equals age in days. 

Habitat. Great blue herons inhabit a variety of freshwater and marine areas, 

including freshwater lakes and rivers, brackish marshes, lagoons, mangroves, and coastal 

wetlands, particularly where small fish are plentiful in shallow areas (Spendelow and 

Patton, 1988; Short and Cooper, 1985). They are often seen on tidal flats and sandbars and 

occasionally forage in wet meadows, pastures, and other terrestrial habitats (Palmer, 

1962). Great blue herons tend to nest in dense colonies, or heronries. The location of the 

heronry is generally close to foraging grounds, and tall trees are preferred over shorter 

trees or bushes for nest sites (Bent, 1926; Palmer, 1962; Gibbs et al., 1987). They also may 

nest on the ground, on rock ledges, or on sea cliffs (Palmer, 1962). 

Food habits. Fish are the preferred prey, but great blues also eat amphibians, 

reptiles, crustaceans, insects, birds, and mammals (Alexander, 1977; Bent, 1926; Hoffman, 

1978; Kirkpatrick, 1940; Peifer, 1979). When fishing, they mainly use two foraging 

techniques: standing still and waiting for fish to swim within striking distance or 

2-3 Great Blue Heron 
slow wading to catch more sedentary prey (such as flounder and sculpin) (Bent, 1926; 

Willard, 1977). To fish, they require shallow waters (up to 0.5 m) with a firm substrate 

(Short and Cooper, 1985). Fish up to about 20 cm in length were dominant in the diet of 

herons foraging in southwestern Lake Erie (Hoffman, 1978), and 95 percent of fish 

consumed by great blues in a Wisconsin population were less than 25 cm in length 

(Kirkpatrick, 1940). Great blues sometimes forage in wet meadows and pastures in pursuit 

of lizards, small mammals, and large insects (Palmer, 1962; Peifer, 1979). In northern 

areas, small mammals such as meadow voles may be an important part of the diet early in 

the breeding season, possibly because some aquatic foraging areas may still be partially 

frozen when the herons arrive (Collazo, 1985). Consumption of larger prey (fish, frogs, 

rodents) is often followed by drinks of water (Hedeen, 1967); terrestrial prey such as voles 

are usually dunked in water before they are swallowed (Peifer, 1979). Adult herons tend to 

deliver the same type and size of food to their nestlings that they consume themselves, but 

they deliver it well digested for young nestlings and less well digested as the nestlings 

grow (Kushlan, 1978). Adults tend to feed solitarily, although they may feed in single or 

mixed species flocks where there are large concentrations of prey (Bayer, 1978; Krebs, 

1974; Kushlan, 1978; Willard, 1977); fledglings are frequently seen foraging together (Dowd 

and Flake, 1985). Kushlan (1978) developed a regression equation relating the amount of 

food ingested per day to body weight for wading birds (N = seven species): 

log(FI) = 0.966 log(BW) - 0.640 

where FI equals food ingestion in grams per day and BW equals body weight in grams. 

Molt. Adults undergo a complete molt in the late summer and fall and a partial molt 

of the contour feathers in the late winter and early spring (Bent, 1926). Young herons 

attain full adult plumage in the summer/fall molt at the end of their second year (Bent, 

1926). 

Migration. In the northern part of its range, most great blues are migratory, some 

moving to the southern Atlantic and Gulf States to overwinter with the resident populations 

of herons (Bent, 1926; Palmer, 1962), others continuing on to Cuba and Central and South 

America (Hancock and Kushlan, 1984). Most migrating herons leave their breeding 

grounds by October or November and return between February and April (Bent, 1926). 

Breeding activities and social organization. The male great blue heron selects the 

site for the breeding territory, and nests generally consist of a stick platform over 1 m in 

diameter (Palmer, 1962). Great blues often use a nest for more than 1 year, expanding it 

with each use (Palmer, 1962). Mean clutch sizes range from three to five (see table); in 

general, clutch size tends to increase with latitude (Pratt, 1972). Only one brood is raised 

per year; however, if a clutch is destroyed, great blues may lay a replacement clutch, 

usually with fewer eggs than the initial clutch (Palmer, 1962; Pratt and Winkler, 1985). Both 

parents incubate and feed the young (Palmer, 1962; Hancock and Kushlan, 1984). During 

the breeding season, great blues are monogamous and colonial, with from a few to 

hundreds of pairs nesting in the same area or heronry (Gibbs et al., 1987). Colonies may 

2-4 Great Blue Heron 
�

include other species, such as great egrets or double-crested cormorants (Pratt and 

Winkler, 1985; Mock et al., 1987). 

Home range and resources. Breeding colonies are generally close to foraging 

grounds (Bent, 1926; Palmer, 1962; Gibbs et al., 1987). Mathisen and Richards (1978) 

found the distance between heronries and possible feeding areas in Minnesota lakes to 

range from 0 to 4.2 km, averaging 1.8 km. Another study found that most heronries along 

the North Carolina coast were located near inlets with large concentrations of fish, an 

average of 7 to 8 km away (Parnell and Soots, 1978, cited in Short and Cooper, 1985). 

Fifteen to 20 km is the farthest great blue herons regularly travel between foraging areas 

and colonies (Gibbs et al., 1987; Gibbs, 1991; Peifer, 1979). In the northern portion of their 

range, great blue herons often build nests in tall trees over dry land, whereas in the 

southern part of their range, they usually nest in swamp trees, including mangroves 

(Palmer, 1962). Each breeding pair defends a small territory around the nest, the size of 

which depends on local habitat and the birds' stage of reproduction (Hancock and Kushlan, 

1984). Herons in some areas also defend feeding territories (Peifer, 1979). In other areas, 

great blues appear to be opportunistic foragers, lacking strict fidelity to particular feeding 

sites (Dowd and Flake, 1985). A study in North Dakota found that herons often returned to 

the same general areas, but different individuals often used the same areas at different 

times (Dowd and Flake, 1985). 

Population density. Because great blues nest colonially, local population density 

(i.e., colony density, colony size, and number of colonies) varies with the availability of 

suitable nesting habitat as well as foraging habitat. On islands in coastal Maine, Gibbs and 

others (1987) found a significant correlation between colony size and the area of tidal and 

intertidal wetlands within 20 km of the colonies, which was the longest distance herons in 

the study colonies traveled on foraging trips. In western Oregon, the size of heronries was 

found to range from 32 to 161 active nests; the area enclosed by peripheral nest trees 

within the colonies ranged from 0.08 to 1.21 ha (Werschkul et al., 1977). 

Population dynamics. Most nestling loss is a result of starvation, although some 

losses to predation do occur (Collazo, 1981; Hancock and Kushlan, 1984). In a study of 243 

nests in a coastal California colony, 65 percent of the chicks fledged, 20 percent starved, 7 

percent were taken by predators, and 7 percent were lost to other causes (Pratt and 

Winkler, 1985). Estimates of the number of young fledged each year by breeding pairs 

range from 0.85 to 3.1 (Pratt, 1970; Pratt, 1972; McAloney, 1973; Pratt and Winkler, 1985; 

Quinney, 1982). Based on banding studies, about two-thirds of the fledglings do not 

survive more than 1 year, although they may survive better in protected wildlife refuges 

(Bayer, 1981a). Values for later years indicate that about one-third to one-fifth of the 2-

year-old and older birds are lost each year (Bayer, 1981a; Henny, 1972; Owen, 1959). 

Similar species (from general references) 

� The great egret (Casmerodius albus) is almost the same size (96 cm length) 

as the great blue heron and is found over a limited range in the breeding 

season, including areas in the central and eastern United States and the east 

and west coasts. It winters in coastal areas of the United States and in 

2-5 Great Blue Heron 
�

�

�

�

�

�

�

�

Mexico and farther south. The great egret's habitat preferences are similar 

to those of the great blue heron. 

� The snowy egret (Egretta thula), one of the medium-sized herons (51 to 69 

cm), shuffles its feet to stir up benthic aquatic prey. It is found mostly in 

freshwater and saltwater marshes but also sometimes follows cattle and 

other livestock as does the cattle egret. It breeds in parts of the western, 

southeastern, and east coasts of the United States and winters along both 

coasts of the southern United States and farther south. 

� The cattle egret (Bubulcus ibis) is seen in agricultural pastures and fields, 

where it follows livestock to pick up insects disturbed by grazing. An Old 

World species, it was introduced into South America and reached Florida in 

the 1950's. It reached California by the 1960's and has been continuing to 

expand its range. 

� The green-backed heron (Butorides striatus), one of the smaller herons (41 

to 56 cm), breeds over most of the United States except for the northwest 

and southern midwest. It has a winter range similar to that of the snowy 

egret and seems to prefer water bodies with woodland cover. 

� The tricolored heron (Egretta tricolor) (formerly known as the Louisiana 

heron) is common in salt marshes and mangrove swamps of the east and 

gulf coasts, but it is rare inland. 

� The little blue heron (Egretta caerulea) is common in freshwater ponds, 

lakes, and marshes and coastal saltwater wetlands of the Gulf Coast States. 

Juveniles are easily confused with juvenile snowy egrets. This species 

hunts by walking slowly in shallow waters, and its diet typically includes fish, 

amphibians, crayfish, and insects. 

� The black-crowned night heron (Nycticorax nycticorax), characterized by a 

heavy body, short thick neck, and short legs (64 cm), is a common heron of 

freshwater swamps and tidal marshes, roosting by day in trees. It typically 

feeds by night, predominantly on aquatic species, fish, amphibians, and 

insects. This heron is extremely widespread, occurring in North and South 

America, Eurasia, and Africa. It breeds over much of the United States and 

parts of central Canada and winters along both coasts of the United States 

and farther south. 

� The yellow-crowned night heron (Nyctanassa violacea) (61 cm) is similar to 

the black-crowned but is more restricted in its range to the southeastern 

United States. It roosts in trees in wet woods, swamps, and low coastal 

shrubs. 

� The American bittern (Botaurus lentiginosus), another of the medium-sized 

herons (58 to 70 cm), is a relatively common but elusive inhabitant of 

freshwater and brackish marshes and reedy lakes. It is a solitary feeder, 

2-6 Great Blue Heron 
�

consuming fish, crayfish, reptiles, amphibians, insects, and even small 

mammals. Its breeding range includes most of Canada and the United 

States, although much of the southern United States is inhabited only during 

the winter. 

� The least bittern (Ixobrychus exilis), the smallest of the North American 

herons (33 cm), also is an elusive inhabitant of reedy areas. Its breeding 

range is restricted largely to the eastern half of the United States. 

General references 

Hancock and Kushlan (1984); Robbins et al. (1983); National Geographic Society 

(1987); Palmer (1962); Short and Cooper (1985). 

2-7 Great Blue Heron 
Great Blue Heron (Ardea herodias) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referenc

Body Weight A B 2,229 ± 762 SD eastern North America Quinney

(g) 

A F 2,204 ± 337 SD NS Hartman

A M 2,576 ± 299 SD yearlings 2,340 ± 490 SD 1,940 - 2,970 central Oregon Bayer, 19

juveniles 1,990 ± 550 SD 1,370 - 2,750 

nestlings: Nova Scotia, Canada McAlone

day 1 86 day 5 170 day 10 567 day 15 983 day 20 1,115 day 25 1,441 

day 30 1,593 

day 35 1,786 

day 40 2,055 

Metabolic Rate A B basal 62 estimate

(kcal/kg-day) 

A B free-living 165 (78 - 353) estimate

Food Ingestion A B 0.18 NS Kushlan

Rate (g/g-day) 

Water A B 0.045 estimate

Ingestion Rate 

(g/g-day) Inhalation Rate A B 0.76 estimate

(m /day) 3 

Surface Area A B 1,711 estimate(cm )2 

2-8 Great Blue Heron 
2-9 Great Blue He

ron 

Dietary Composition Spring 

trout 

non-trout fish 

crustaceans/amphibian 

s trout 

non-trout fish crustaceans amphibians birds and mammals Atlantic silverside mummichog 

American eel 

Gaspereaux pollack yellow perch 

staghorn sculpin 

small 

medium large 

starry flounder 

small medium 

large 

other 

small medium 

Great Blue Heron (Ardea herodias) 

Summer Fall Winter (measure) 

Location/Habitat 

59 lower Michigan/lake 

39 

2 (% wet weight; stomach 

contents) 

89 lower Michigan/river 

5 

1 (% wet weight; stomach 

4 contents) 

1 3.6 Nova Scotia/Boot Island 

2.4 

52.6 (% wet weight; items 

29.9 regurgitated by nestlings) 

8.9 2.6 

Vancouver, BC/coastal 

27.8 island 

7.6 

2.2 (% of fish observed caught; 

small = less than 1/3 beak 

15.0 length; medium = about 1/2 

8.1 beak length; large = longer 

5.2 than beak; other includes 

shiner sea perch and 

30.6 penpoint gunnels) 

3.5 

Referen

Alexand

Alexand

Quinney

Krebs, 1
Great Blue Heron (Ardea herodias) 

Population 

Dynamics 

Age/Sex Cond./Seas. Mean Range ion/Habitat Referen

Size Feeding A B fall 0.6 ± 0.1 SD ha Oregon/freshwater marsh Bayer, 

Territory A B winter 8.4 ± 5.4 SD ha Oregon/estuary 

Foraging A B summer 3.1 km up to 24.4 km South Dakota/river & Dowd & 

Distance from streams 

Colony A B summer 7 to 8 km North Carolina/coastal Parnell 

Population summer North Dakota/rivers & Dowd & 

Density along stream 2.3 birds/km streams 

along river 3.6 birds/km 

summer 149 ± 53 SD Maine/coastal islands Gibbs e

summer 461 nests/ha 447 - 475 Oregon/coastal island Wersch

nests/ha 

Clutch Size 3.16 ± 0.04 SE 1 - 5 California/coastal canyon Pratt & 

4.17 ± 0.85 SD 3 - 6 Nova Scotia/island McAlon

4.37 3 - 6 Pennsylvania/NS Miller, 1

Clutches/Year 1 lvania; Oregon/NS Miller, 1

Days 27.1 25 - 30 Nova Scotia/island McAlon

Incubation 

28 United States/NS Bent, 1

Age at Fledging 45 Nova Scotia/island McAlon

(days) 60 NS/NS Hancoc

49 to 56 Nova Scotia/island Quinne

Number Fledge 1.7 central California/coastal Pratt, 1

per Pair 1.96 northwest Oregon/river English

2.8 Nova Scotia/island Quinne

Locat

Pennsy

2-10 Great Blue Heron 
1

23456

Population 

Dynamics 

Age/Sex Cond./Seas. Mean Range ion/Habitat Referen

Number 2.19 ± 0.25 SD 2 - 3 central California/coastal Pratt & 

Fledge per 2.43 northwest Oregon/river English

Successful 3.09 Nova Scotia/island McAlon

Nest Age at Sexual B 2 years NS Bent, 1

Maturity Annual during 1st yr 64 United States and Henny, 

Mortality Rates during 2nd yr 36 Canada/NS 

(percent) during 3rd yr 22 

Seasonal 

Activity Begin Peak End Location Referen

Mating/Laying Nov. to Dec. April Florida Howell, 

mid-February mid-March June central California Pratt & 

mid-March northwest Oregon English

late March early April Pennsylvania Miller, 1

mid-April early May late May Nova Scotia McAlon

Hatching early May northwest Oregon English

mid-April Idaho Collazo

mid-May mid-July Ohio Hoffma

Migration (fall) mid-Sept. late October northern US Palmer

(spring arrival) mid-February mid-March western Oregon Wersch

mid-March Wisconsin; Minnesota Bent, 1

late March Nova Scotia Bent, 1

Locat

Estimated using equation 3-28 (Lasiewski and Dawson, 1967) and body weights from Quinney (1982).

Estimated using equation 3-37 (Nagy, 1987) and body weights from Quinney (1982).

Estimated from Kushlan's (1978) allometric equation for wading birds, assuming a body weight of 2,230 g.

Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Quinney (1982).

Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Quinney (1982).

2-11 Great Blue Heron 

As cited in Dunning, 1984. 

Great Blue Heron (Ardea herodias) 
7 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

(1982). 

8 Cited in Short and Cooper (1985). 

9 Cited in Palmer (1962). 

10 May replace clutch if eggs are lost, but only rear one brood (Henny, 1972). 

11 Young fed around colony for 10 days after leaving nest at 45 days of age. 

2-12 Great Blue Heron 

Great Blue Heron (Ardea herodias) 
References (including Appendix) 

Alexander, G. (1977) Food of vertebrate predators on trout waters in north central lower 

Michigan. Michigan Academician 10: 181-195. 

Altman, P. L.; Dittmer, D. S., eds. (1968) Biology data book. 2nd ed., 3v. Bethesda, MD: 

Federation of American Societies for Experimental Biology. 

Baird, S. F.; Brewer, T. M.; Ridgeway, R. (1884) Water birds of North America. Boston, MA: 

Little, Brown & Co. 

Bancroft, G. (1969) (as cited in Hancock and Kushlan, 1984). Auk 86: 141-142. 

Bayer, R. D. (1978) Aspects of an Oregon estuarine great blue heron population. In: Sprunt, 

A.; Ogden, J.; Winckler, S., eds. Wading birds. Natl. Audubon Soc. Res. Rep. 7; pp. 

213-217. 

Bayer, R. D. (1981a) Regional variation of great blue heron Ardea herodias longevity. J. 

Field Ornithol. 52: 210-213. 

Bayer, R. D. (1981b) Weights of great blue herons (Ardea herodias) at the Yaquina Estuary, 

Oregon. Murrelet 62: 18-19. 

Benedict, F. G.; Fox, E. L. (1927) (cited in Altman and Dittmer, 1968). Proc. Am. Phil. Soc. 

66: 411. 

Bent, A. C. (1926) Life histories of North American marsh birds. Washington, DC: U.S. 

Government Printing Office; Smithsonian Inst. U.S. Nat. Mus., Bull. 135. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Collazo, J. A. (1981) Some aspects of the breeding ecology of the great blue heron at 

Heyburn State Park. Northwest Sci. 55: 293-297. 

Collazo, J. A. (1985) Food habits of nestling great blue herons (Ardea herodias) at Heyburn 

State Park, Idaho. Northwest Sci. 59: 144-146. 

Cottam, C. A.; Uhler, F. M. (1945) Birds in relation to fishes. U.S. Fish Wildl. Serv. Leaflet 

272. 

Cottam, C. A.; Williams, J. (1939) (as cited in Palmer, 1962). Wilson Bull. 51: 150-155. 

Dowd, E.; Flake, L. D. (1985) Foraging habitats and movements of nesting great blue 

herons in a prairie river ecosystem, South Dakota. J. Field Ornithol. 56: 379-387. 

2-13 Great Blue Heron 
Dunning, J. B., Jr. (1984) Body weights of 686 species of North American birds. Western 

Bird Banding Association, Monograph No. 1. Cave Creek, AZ: Eldon Publishing. 

English, S. M. (1978) Distribution and ecology of great blue heron colonies on the 

Willamette River, Oregon. In: Sprunt, A.; Ogden, J.; Winckler, S., eds. Wading birds. 

Natl. Audubon Soc. Res. Rep. 7; pp. 235-244. 

Forbes, L. S.; Simpson, K.; Kelsall, J. P., et al. (1985) Reproductive success of great blue 

herons in British Columbia. Can. J. Zool. 63: 1110-1113. 

Gibbs, J. P. (1991) Spatial relationships between nesting colonies and foraging areas of 

great blue herons. Auk 108: 764-770. 

Gibbs, J. P.; Woodward, S.; Hunter, M. L., et al. (1987) Determinants of great blue heron 

colony distribution in coastal Maine. Auk 104: 38-47. 

Hancock, J.; Kushlan, J. (1984) The herons handbook. New York, NY: Harper & Row. 

Hartman, F. A. (1961) Locomotor mechanisms in birds. Washington, DC: Smithsonian Misc. 

Coll. 143. 

Hedeen, S. (1967) Feeding behavior of the great blue heron in Itasca State Park, Minnesota. 

Loon 39: 116-120. 

Henny, C. J. (1972) An analysis of the population dynamics of selected avian species with 

special reference to changes during the modern pesticide era. Washington, DC: Bur. 

Sport. Fish. Wildl.; Wildl. Res. Rep. 1. 

Henny, C. J.; Bethers, M. R. (1971) Ecology of the great blue heron with special reference 

to western Oregon. Can. Field-Nat. 85: 205-209. 

Hoffman, R. D. (1978) The diets of herons and egrets in southwestern Lake Erie. In: Sprunt, 

A.; Ogden, J.; Winckler, S., eds. Wading birds. Natl. Audubon Soc. Res. Rep. 7: 

365-369. 

Hoffman, R. D.; Curnow, R. D. (1979) Mercury in herons, egrets, and their foods. J. Wildl. 

Manage 43: 85-93. 

Howell, A. H. (1932) Florida bird life. Florida Dept. Game and Freshwater Fish and Bur. Biol. 

Survey, USDA. 

Kelsall, J. P.; Simpson, K. (1979) A three year study of the great blue heron in 

southwestern British Columbia. Proc. Col. Waterbird Group 3: 69-74. 

Kirkpatrick, C. M. (1940) Some foods of young great blue herons. Am. Midl. Nat. 24: 

594-601. 

2-14 Great Blue Heron 
Krebs, J. R. (1974) Colonial nesting and social feeding as strategies for exploiting food 

resources in the great blue heron (Ardea herodias). Behaviour 51: 93-134. 

Kushlan, J. A. (1978) Feeding ecology of wading birds. In: Sprunt, A.; Ogden, J.; Winckler, 

S., eds. Wading birds. Natl. Audubon Soc. Res. Rep. 7; pp. 249-296. 

Lasiewski, R. C.; Calder, W. A. (1971) A preliminary allometric analysis of respiratory 

variables in resting birds. Resp. Phys. 11: 152-166. 

Lasiewski, R. C.; Dawson, W. R. (1967). A reexamination of the relation between standard 

metabolic rate and body weight in birds. Condor 69: 12-23. 

Mathisen, J.; Richards, A. (1978) Status of great blue herons on the Chippewa National 

Forest. Loon 50: 104-106. 

McAloney, K. (1973) The breeding biology of the great blue heron on Tobacco Island, Nova 

Scotia. Can. Field-Nat. 87: 137-140. 

Meeh, K. (1879) Oberflachenmessungen des mensclichen Korpers. Z. Biol. 15: 426-458. 

Miller, R. F. (1943) The great blue herons: the breeding birds of the Philadelphia region 

(Part II). Cassinia 33: 1-23. 

Mitchell, C. A. (1981) Reproductive success of great blue herons at Nueces Bay, Corpus 

Christi, Texas. Bull. Texas Ornithol. Soc. 14: 18-21. 

Mock, D. W.; Lamey, T. C.; Williams, C. F.; et al. (1987) Flexibility in the development of 

heron sibling aggression: an interspecific test of the prey-size hypothesis. Anim. 

Behav. 35: 1386-1393. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

National Geographic Society. (1987) Field guide to the birds of North America. Washington, 

DC: National Geographic Society. 

Owen, D. F. (1959) Mortality of the great blue heron as shown by banding recoveries. Auk 

76: 464-470. 

Page, P. J. (1970) Appendix. San Joaquin River rookery study 1970. Sacramento, CA: Calif. 

Dept. Fish and Game; statewide heron rookery survey progress report. 

Palmer, R. S. (1949) Marine birds. Bull. Mus. Comp. Zool. Harvard 102. 

Palmer, R. S. (1962) Handbook of North American birds: v. 1. New Haven, CT: Yale 

University Press. 

2-15 Great Blue Heron 
Parnell, J. F.; Soots, R. F. (1978) The use of dredge islands by wading birds. Wading birds. 

Nat. Audubon Soc. Res. Rep. 7: 105-111. 

Peifer, R. W. (1979) Great blue herons foraging for small mammals. Wilson Bull. 91: 

630-631. 

Poole, E. L. (1938) Weights and wing areas in North American birds. Auk 55: 511-517. 

Powell, G. V.; Powell, A. H. (1986) Reproduction by great white herons Ardea herodias in 

Florida Bay as an indicator of habitat quality. Biol. Conserv. 36: 101-113. 

Pratt, H. M. (1970) Breeding biology of great blue herons and common egrets in central 

California. Condor 72: 407-416. 

Pratt, H. M. (1972) Nesting success of common egrets and great blue herons in the San 

Francisco Bay region. Condor 74: 447-453. 

Pratt, H. M.; Winkler, D. W. (1985) Clutch size timing of laying and reproductive success in 

a colony of great blue herons (Ardea herodias) and great egrets (Casmerodius 

albus). Auk 102: 49-63. 

Quinney, T. E. (1982) Growth, diet, and mortality of nestling great blue herons. Wilson Bull. 

94: 571-577. 

Robbins, C. S.; Bruun, B.; Zim, H. S. (1983) A guide to field identification: birds of North 

America. New York, NY: Golden Press. 

Rubner, M. (1883) Uber den Einfluss der Korpergrosse auf Stoff- und Kraftweschsel. Z. 

Biol. 19: 535-562. 

Short, H. L.; Cooper, R. J. (1985) Habitat suitability index models: great blue heron. U.S. 

Fish Wildl. Serv. Biol. Rep. No. 82(10.99); 23 pp. 

Spendelow, J. A.; Patton, S. R. (1988) National atlas of coastal waterbird colonies: 

1976-1982. U.S. Fish Wildl. Serv. Biol. Rep. No. 88(5). 

Thompson, D. H. (1978) Feeding areas of great blue herons and great egrets nesting within 

the floodplain of the upper Mississippi River. Colonial Waterbirds 2: 202-213. 

Vermeer, K. (1969) Great blue heron colonies in Alberta. Can. Field-Nat. 83: 237-242. 

Walsberg, G. E.; King, J. R. (1978) The relationship of the external surface area of birds to 

skin surface area and body mass. J. Exp. Biol. 76: 185-189. 

Werschkul, D. F.; McMahon, E.; Leitschuh, M.; et al. (1977) Observations on the 

reproductive ecology of the great blue heron (Ardea herodias) in western Oregon. 

Murrelet 58: 7-12. 

2-16 Great Blue Heron 
Willard, D. E. (1977) The feeding ecology and behavior of five species of herons in 

southeastern New Jersey. Condor 79: 462-470. 

Wood (1951) (cited in Palmer, 1962). Univ. Mich. Mus. Misc. Publ. No. 75. 

2-17 Great Blue Heron 
2.1.2. Canada Goose (geese) 

Order Anseriformes, Family Anatidae. Geese are large herbivorous waterfowl that 

feed on grains, grass sprouts, and some aquatic vegetation. Although adapted for life on 

the water, they forage primarily in open fields. They breed in open forested areas near lake 

shores and coastal marshes from the arctic tundra through temperate climates. These 

birds migrate in noisy flocks in the familiar V-formation, stopping in cultivated fields, 

wetlands, and grasslands to feed. Geese show a wide variation in size even within a 

species; the sexes look alike. 

Selected species 

The Canada goose (Branta canadensis) is the most widespread and abundant goose 

in North America. It is a popular game species and is commonly encountered on cultivated 

fields, golf courses, other parklands, and wetland refuge areas. Depending on subspecies, 

these geese can range in size from 64 to 114 cm (bill tip to tail tip), the larger geese 

breeding in more southerly locations than the smaller subspecies. The reverse is true in 

winter, with the larger subspecies wintering in the more northerly parts of the range 

(Palmer, 1962). The number of existing recognized subspecies varies, but most 

ornithologists agree that there are 11: canadensis (Atlantic Canada goose), fulva 

(Vancouver Canada goose), hutchinsii (Richardson's Canada goose), interior (interior 

Canada goose), leucopareia (Aleutian Canada goose), maxima (giant Canada goose), 

minima (cackling Canada goose), moffitti (Great Basin or western Canada goose), 

occidentalis (dusky Canada goose), parvipes (lesser Canada goose), and taverneri 

(Taverner's Canada goose) (Bellrose, 1976; Johnson et al., 1979; Palmer, 1962). Several 

subspecies usually mingle during migration and in wintering areas, but they breed in 

geographically distinct ranges. Six of the subspecies breed in Alaska (fulva, leucopareia, 

minima, occidentalis, parvipes, and taverni) (Johnson et al., 1979). The leucopareia 

subspecies, found in Oregon, Washington, California, and Alaska, currently is a United 

States federally designated threatened species (50 CFR 17.11, 1992). It is only known to 

breed on one of the western Aleutian islands off Alaska (Byrd and Woolington, 1983). See 

Bellrose (1976) for ranges, migration corridors, and wintering areas of specific subspecies 

and populations. 

Body size. Canada geese subspecies vary greatly in size, but males are on average 

larger than females (see table). Body weight reaches its maximum just prior to or during 

the spring migration and then declines during egg-laying and incubation, sometimes by as 

much as 20 percent (Mainguy and Thomas, 1985; McLandress and Raveling, 1981). Most of 

the weight lost during incubation reflects loss of fat, which can provide over 80 percent of 

the energy requirements for the incubating females (Mainguy and Thomas, 1985; Murphy 

and Boag, 1989). Young are similar to parents in size by 2 months of age (Palmer, 1962). 

Habitat. Breeding habitat includes tundra, forest muskeg in the far north, tall- and 

shortgrass prairie, marshes, ponds, and lakes. Most nesting sites are close to open water 

with high visibility in all directions (Palmer, 1962; Steel et al., 1957). In many areas, Canada 

geese nest predominantly on islands in ponds or lakes (Geis, 1956). Former 

2-19 Canada Goose 
muskrat houses often serve as nest sites in marshes (Steel et al., 1957). Brood-rearing 

habitats, on the other hand, require adequate cover, and riparian areas are used more 

frequently than open water (Eberhardt et al., 1989a). During the fall and winter in Maryland, 

Harvey et al. (1988) found Canada geese to spend 57 percent of their time in farmlands 

(mostly corn, soybeans, and winter wheat fields) and 24 percent in forested areas. 

Food habits. Canada geese are almost exclusively vegetarian, and feeding activity 

is concentrated in areas where food is plentiful (e.g., standing crops, scattered whole 

grain) (Palmer, 1962). They are primarily grazers, but must consume grit at some point to 

assure proper digestion (Palmer, 1962). They prefer certain foods, but will change their 

diet depending on the availability of a food type (Coleman and Boag, 1987). For example, 

when water levels are low in the south Yukon (Canada) river delta, Canada geese forage on 

rhizomes of Potamogeton richardsonii even though other forage is available; at higher 

water levels when the Potamogeton is unreachable, the geese will feed on other plants 

(Coleman and Boag, 1987). During fall, geese often consume green crops (e.g., winter 

wheat). During winter, however, they consume more energy-rich foods such as corn 

(Harvey et al., 1988; McLandress and Raveling, 1981). In late winter and early spring, green 

crops that are high in nitrogen and other important nutrients again constitute an important 

part of the diet (McLandress and Raveling, 1981). Canada geese often feed preferentially 

on the blade tips of many plants, which are higher in nitrogen than other parts of the plant 

(Buchsbaum et al., 1981). In Minnesota, Canada geese begin consuming green grasses as 

soon as they are exposed by the melting snow (McLandress and Raveling, 1981). In 

Maryland, on the other hand, Harvey et al. (1988) found that Canada geese did not begin 

consuming green crops before migration to the breeding grounds, indicating that this 

population may rely on green forage available at staging areas to obtain the protein and 

lipids required for reproduction. In the spring in Falmouth Harbor, Massachusetts, Canada 

geese initially consume predominantly the marsh grasses Spartina spp. and rushes 

Juncus gerardi, which are high in protein (Buchsbaum and Valiela, 1987). As the summer 

progresses, however, they feed increasingly on submerged eelgrass, Zostera marina, 

which provides more carbohydrates (Buchsbaum and Valiela, 1987). 

Molt. Nonbreeders and yearlings migrate to a separate molting ground soon after 

arrival at the breeding grounds, while breeding birds molt on the brood-rearing grounds 

(Bellrose, 1976). Molting occurs earlier in nonbreeders, at least a month earlier in the 

larger subspecies (Palmer, 1962). Molting parents do not regain flight feathers until just 

prior to the time when their young first attain flight (Palmer, 1962). The flightless period of 

B. c. interior is estimated to be 32 days. For B. c. maxima and B. c. moffitti, the flightless 

period lasts from 39 to 40 days (Balham, 1954; Hanson, 1965, as cited in Palmer, 1962). 

Migration. Migratory Canada geese leave their breeding grounds during late 

summer and early autumn; they return in the spring around the time the first water is 

opening (i.e., ice melting) but well before snow cover has disappeared (Bellrose, 1976). 

Spring migration begins later for northerly populations, with geese that winter in mild 

climates departing as early as mid-January, while those wintering in the coldest areas do 

not move northward until the beginning of March (Bellrose, 1976). The bulk of the migrants 

typically arrive on the summer breeding grounds 3 weeks after the first birds 

2-20 Canada Goose 
(Bellrose, 1976). Some populations have become resident year-round, for example, 

B. c. maxima in Missouri (Brakhage, 1965) and in southeast Georgia and southwest 

Alabama (Combs et al., 1984). During both the spring and fall migrations, geese tend to 

gather in large flocks and feed for several weeks in "staging" areas along major waterfowl 

flyways (Bellrose, 1976). 

Breeding activities and social organization. Canada geese arrive on the breeding 

grounds in flocks, and soon after, the male becomes territorial and aggressive toward 

other birds (Palmer, 1962). Lifelong monogamy following their first breeding is the general 

rule with these geese (Palmer, 1962). Nests are built on the ground in a position with good 

visibility (Palmer, 1962). During incubation the male stands guard, while the female 

incubates the eggs, which she normally leaves two or three times daily to feed, bath, drink, 

and preen (Murphy and Boag, 1989). Both parents accompany the young through the 

brood period (Bellrose, 1976; Brakhage, 1965). Canada geese return to the breeding 

grounds as family units, but the yearlings leave their parents soon after arrival (Bellrose, 

1976). 

Home range and resources. The foraging home range of Canada geese varies with 

season, latitude, and breeding condition. Soon after hatching, goose families move away 

from the nesting sites to other areas with adequate cover and forage to rear their broods 

(Byrd and Woolington, 1983). Newly hatched families may have to travel 10 to 20 km from 

the nest site to reach areas with adequate aquatic vegetation or pasture grasses (Geis, 

1956). Although the families stay predominantly on land, often in riparian areas, they 

usually are close to water. Eberhardt et al. (1989a) found goslings within 5 m of water 

most of the time; only 7 percent of sightings were farther than 50 m away. During the 

spring and fall migrations and in winter, Canada geese can be found on open water or 

refuges near grain fields or coastal estuaries (Leopold et al., 1981). 

Population density. Breeding population densities of Canada geese vary widely. 

Low nesting densities (i.e., less than 0.005 per hectare) are common in the Northwest 

Territories of Canada (Smith and Sutton, 1953, 1954) and intermediate densities (i.e., 0.02 

to 0.7 per hectare) have been reported for Alaska (Cornley et al., 1985). In some more 

southerly locations (e.g., California), colonial nesting situations have been reported, with 

as many as 32 nests located on half an acre (Naylor, 1953, as cited in Palmer, 1962). 

Population dynamics. The earliest Canada geese begin breeding is around 2 to 3 

years of age (MacInnes and Dunn, 1988; Brakhage, 1965). In the larger subspecies, only a 

small proportion of the birds under 4 years may attempt to breed. For example, in 

Manitoba, Moser and Rusch (1989) found that only 7 percent of 2-year-old and 15 percent 

of 3-year-old B. c. interior laid eggs. Canada geese only attempt to rear one brood per 

year. In the more southerly latitudes, Canada geese will renest if a clutch is lost prior to 

incubation (Brakhage, 1965; Geis, 1956). In general, both clutch size and success at 

rearing goslings increase with the age of the breeder (Brakhage, 1965). Raveling (1981) 

found that older B. c. maxima (4 plus years) raised more than twice as many goslings to 

fledging as did younger (2 to 3 years) birds. Population age structure and annual mortality 

vary with hunting pressure as well as natural factors. 

2-21 Canada Goose 
�

�

�

�

Similar species (from general references) 

� The Brant goose (Branta bernicla) is approximately the size of the smaller 

Canada geese subspecies (length 25 cm). It is primarily a sea goose and is 

rare inland. It winters along both the east and west coasts of the United 

States, where it feeds on aquatic plants in shallow bays and estuaries. It 

breeds in the high arctic. 

� The greater white-fronted goose (Anser albifrons) is limited to certain areas 

west of the Mississippi River and averages 71 cm in length. Its habits are 

similar to those of other geese. 

� The snow goose (Chen caerulescens) breeds in the Arctic and winters in 

selected coastal areas across the United States. However, this averagesized goose (71 cm) is a migratory visitor to much of the central United 

States. 

� The Ross' goose (Chen rosii) breeds in the high arctic tundra and winters in 

some areas of the southwest United States. This relatively small (58 cm) 

goose is a rare visitor to the mid-Atlantic States and is always seen with 

snow geese. 

General references 

Bellrose (1976); Kortright (1955); National Geographic Society (1987); Palmer (1962). 

2-22 Canada Goose 
Canada Goose (Branta canadensis) 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean Location (subspecies) Referen

Range or 

Body Weight (g) A M late sum. 1,443 ± 32 SE 1,260 - 1,605 Alaska (minima) Ravelin

A F late sum. 1,362 ± 54 SE 1,195 - 1,590 

A M winter 2,769 ± 30 SE Colorado (parvipes) Grieb, 1

A F winter 2,472 ± 23 SE 

A M not spec. 3,992 NS (canadensis) Webste

A F not spec. 3,447 Bellrose

A M fall 4,212 ± 35 SE 3,799 - 4,727 Illinois (interior) Ravelin

A F fall 3,550 ± 31 SE 3,147 - 3,856 

A M late sum. 4,960 Missouri (maxima) Brakha

A F late sum. 4,160 

M at hatching 108.7 Alberta (moffitti) LeBlanc

F at hatching 109.5 

B day 10 150 Alaska (minima) Sedinge

B day 20 450 

B day 30 755 

B day 40 950 

B day 47 1,050 

B day 0 110 NS (moffitti) William

B day 9 240 Palmer, 

B day 16 440 B day 30 1,400 B day 44 2,400 B day 51 2,600 M at fledging 87% adult wt Alaska (minima) Sedinge

F at fledging 89% adult wt 

2-23 Canada Goose 
Canada Goose (Branta canadensis) 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean Location (subspecies) Referen

Range or 

Body Fat F fall migr. 182 ± 24 SE 117 - 264 Alaska in winter (minima) Ravelin

(g lipid) F winter 57 ± 6 SE 34 - 71 California in summer 

F spring migr. 172 ± 25 SE 68 - 362 

F prelaying 171 (no SE; N=2) 136 - 205 

F end incub. 33 ± 5 SE 14 - 51 

F early molt 108 ± 13 SE 62 - 179 

F prelaying 751 ± 45 SE Ontario, Canada (maxima) Thomas 

F incubating 611 ± 40 SE 

F late incub. 166 ± 18 SE 

F molting 485 ± 37 SE 

Egg Weight 96 NS (minima) Owen, 1

(g) 127 NS (leucopa) Owen, 1

163 Alberta, Canada (moffitti) LeBlanc

Metabolic Rate free-living: 

(kcal/kg-day) A M winter 105 - 209 Illinois in winter (interior) William

A M spring 105 - 203 Ontario, Canada in A M summer 115 - 253 summer A M fall 100 - 209 A F spring 130 - 220 William

A F summer 143 - 274 (interior) 

free-living: 

A M 185 (87 - 391) estimat

A F 187 (88 - 397) (minima) 

A M 141 (65 - 304) estimat

A F 147 (69 - 316) (interior) 

A M 135 (63 - 292) estimat

A F 142 (66 - 305) (maxima) 

2-24 Canada Goose 
Canada Goose (Branta canadensis) 

2-25 Canada Goose 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean Location (subspecies) Referen

Range or 

Food Ingestion A M winter 0.030 (interior) captive Joyner 

Rate (g/g-day) A F winter 0.033 

A M spring 0.030 (interior) captive Joyner 

A F spring 0.031 

Water Ingestion A M 0.052 (minima) estimat

Rate A F 0.053 

(g/g-day) 

A M 0.035 (maxima) estimat

A F 0.037 

Inhalation Rate A M 0.54 (minima) estimat

(m /day) A F 0.52 3 

A M 1.40 (maxima) estimat

A F 1.22 

Surface Area A M 1,280 (minima) estimat

(cm ) A F 1,230 2 

A M 2,920 (maxima) estimat

A F 2,590 

Dietary Composition Spring Summer Fall Winter (measure) Referen

Location/Habitat 

sedges 63 North Carolina/lake Yelvert

native grasses 11 

corn kernels 22 (% volume; crop and gizzard 

animal 0.01 contents) other 4 
Canada Goose (Branta canadensis) 

Dietary Composition Spring Summer Fall Winter (measure) Referen

Location/Habitat 

Equisetum sp. Ontario, Canada/bay Prevett 

(shoot) 9.2 

Triglochin palustris (% dry weight; esophagus 

(root) 3.4 and proventriculus 

grasses (root) 23.4 contents) 

(shoot) 2.1 

sedges (shoot) 25.3 

(root) 5.3 

(reed) 17.9 

Plantago maritima 

(root) 6.5 

unidentified plants 6.1 

invertebrates 0.7 

corn 23 Wisconsin/marsh Craven unidentified plants 8.6 

alfalfa 10.4 (% dry volume; gizzard 

Gramineae 12.6 and proventriculus 

oats 25.1 contents) 

Setaria lutescens 8.4 Trifolium repens 10.9 

Population 

Dynamics 

Age/Sex/ Location (subspecies)/ 

Cond./Seas. Mean Range habitat Refere

a 

Home Range A F & brood 983 ± 822 SD ha 290 - 2,830 Washington (moffitti)/river Eberh

Size 

A F & brood 8.8 ± 4.4 SD km 2.8 - 18.1 Washington (moffitti)/river Eberh

2-26 Canada Goose 
Canada Goose (Branta canadensis) 

Population 

Dynamics 

Age/Sex/ Location (subspecies)/ 

Cond./Seas. Mean Range habitat Refere

a 

Population summer 0.02-12.4 nests/ha various locations Coope

Density 

fall 22 birds/ha Missouri/wildlife refuge Humb

winter 4 birds/ha Missouri/wildlife refuge Humb

16.6 nests/ha Montana (moffitti)/ Geis, 

1.3 nests/ha Montana (moffitti)/ 

0.35 nests/ha Alaska (leucopus)/ Byrd & 

on 0.2-0.8 ha island on 8-121 ha island 

island preferred habitat 

Clutch Size 4.7 Alaska (minima) Spenc

5.6 ± 0.1 SE 2 - 8 Alaska (leucopa) Byrd & 

4.6 Ontario, Canada (interior) Ravel

5.6 Alabama, Georgia (maxima) Comb

Clutches/Year 1 issouri Brakh

Days 25 NS (minima) Laidle

Incubation 28 Missouri (maxima) Brakh

Age at 40-46 Alaska (minima) Micke

Fledging 55 NS (leucopa) Lee (p

(days) & W

63 Ontario, Canada (interior) Hanso

71-73 Michigan (maxima) Sherw

Percent Nests 91 89 - 93 Alaska/island (leucopa) Byrd & 

Successful 44 27 - 64 Alabama, Georgia (maxima) Comb

Number 2.19 ± 2.42 SD 0 - 7 Washington (moffitti) Eberh

Fledge per Active Nest 

M

2-27 Canada Goose 
Canada Goose (Branta canadensis) 

Population 

Dynamics 

Age/Sex/ Location (subspecies)/ 

Cond./Seas. Mean Range habitat Refere

a 

Number 4.0 ± 0.008 SE 1 - 7 Alaska (leucopa) Byrd & 

Fledge per 2.2 IL, WI (interior) Hardy 

Successful 3.9 ± 1.9 SD 1 - 7 Washington (moffitti) Eberh

Nest Age at Sexual B 2 - 3 Northwest Territories MacIn

Maturity (smaller subspecies) 

F 4 - 5 > 2 Manitoba, Canada (interior) Moser 

M 2 - 3 > 1 Missouri (maxima) Brakh

F 2 - 3 > 2 

Annual A B 35.9 Alaska (minima) Nelso

Mortality Rates J B 46.0 

(percent) 

A B 28 ± 0.8 SD California, Nevada (moffitti) Riene

J B 49 ± 3.7 SD 

A B 22.9 Ohio (maxima) Cumm

J B 37.0 

Seasonal 

Activity Begin Peak End Location (subspecies) Referenc

Mating/Laying late February March - April mid-May Georgia, Alabama (maxima) Combs e

early March late March OR, WA, CA (moffitti) McCabe, 

mid-March late March - April May Montana (moffitti) Geis, 195

early April mid-April early May Idaho (moffitti) Steel et a

early April mid-April Ontario, Canada (maxima) Mainguy 

late May late May early June Alaska (leucopa) Byrd & W

1976 

Hatching March April - May early June Georgia, Alabama (maxima) Combs e

mid-April late April - May late May Montana (moffitti) Geis, 195

early May mid-May late June Idaho (moffitti) Steel et a

early July Alaska (leucopa) Byrd & W

2-28 Canada Goose 
�

Canada Goose (Branta canadensis) 

Seasonal 

Activity Begin Peak End Location (subspecies) Referenc

Molt (fall) mid-June Idaho (moffitti) Steel et a

mid-July mid-August late August Alaska (leucopa) Byrd & W

late June late October Illinois (interior) Williams 

Migration fall mid-Sept. November arrive south Illinois (interior) Bell & Kl

spring February early March leave Illinois (interior) Bell & Kl

October early November mid-December arrive CO, TX (parvipes) Grieb, 19

late March early April leave Minnesota (maxima) Raveling

1 Weights estimated from graph. 

2 Cited in Dunn and MacInnes (1987). 

2-29 Canada Goose 

3 Estimated range of existence to maximum free-living metabolism at typical breeding ground (Ontario, Canada in spr

typical wintering ground (south Illinois in fall and winter). Estimated using regression equations developed by the a

metabolic rates at temperatures from -40 to 41�C, and temperatures typical for the season and location. 

4 Estimated using equation 3-37 (Nagy, 1987) and body weights from (a) Raveling (1979); (b) Raveling (1968); and (c) B

5 Reported as grams dry weight of feed; corrected to grams wet weight of feed using the measured moisture content 

the feed items (i.e., corn, sunflower seeds, wheat, and milo). 

6 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from (a) Raveling (1979) and (b) Brakhage 

7 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from (a) Raveling (1979) and (b) Brak

8 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

and (b) Brakhage (1965). 

9 Summarizing several studies, cited in Byrd & Woolington (1983). 

10 Cited in Palmer (1976). 

11 Cited in Bellrose (1976). 

12 For parents older than 5 years of age. 
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2-30 Canada Goose 
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2-31 Canada Goose 
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2-32 Canada Goose 
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2-33 Canada Goose 
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2-34 Canada Goose 
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2-35 Canada Goose 
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2-36 Canada Goose 
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2-37 Canada Goose 
2.1.3. Mallard (surface-feeding ducks) 

Order Anseriformes, Family Anatidae. Surface-feeding ducks are the most familiar 

ducks of freshwater and saltwater wetlands. They feed by dabbling and tipping up in 

shallow water, often filtering through soft mud for food. They feed primarily on seeds of 

aquatic plants and cultivated grains, although they also consume aquatic invertebrates, 

particularly during the breeding season (Jorde et al., 1983; Swanson et al., 1985). All 

species have a bright colored patch of feathers on the trailing edge of each wing, and the 

overall plumage of the males is more colorful than that of the females. Dabbling ducks 

range in size from the green-winged teal (average 37 cm bill tip to tail tip) to the northern 

pintail (average 66 cm). 

Selected species 

The mallard (Anas platyrhynchos) feeds mostly on aquatic plants, seeds, and 

aquatic invertebrates, depending on the season, and forages in ponds and wetlands by 

dabbling and filtering through sediments. It is widespread throughout most of the United 

States and is the most abundant of the United States ducks (USFWS, 1991). In the past 

decade, however, its numbers have declined markedly across its principal range in the 

mid-continental region because of habitat degradation and drought (USFWS, 1991). 

Mallards interbreed with domestic ducks and black ducks (Anas rubripes). 

Body size. Mallards average 58 cm from bill tip to tail tip. Male mallards are 

generally heavier than females (Delnicki and Reinecke, 1986; Whyte and Bolen, 1984; see 

table). Female mallards lose weight during the laying and incubation periods; males lose 

weight from their spring arrival through the peak of the breeding season and then gain 

weight while the females are incubating (Lokemoen et al., 1990a). 

Habitat. Wintering mallards prefer natural bottomland wetlands and rivers to 

reservoirs and farm ponds (Heitmeyer and Vohs, 1984); water depths of 20 to 40 cm are 

optimum for foraging (Heitmeyer, 1985, cited in Allen, 1987). The primary habitat 

requirement for nesting appears to be dense grassy vegetation at least a half meter high 

(Bellrose, 1976). Mallards prefer areas that provide concealment from predators such as 

seeded cover (fields established on former croplands) (Klett et al., 1988; Lokemoen et al., 

1990b), cool-season introduced legumes and grasses (Duebbert and Lokemoen, 1976), and 

idle grassland with tall, dense, rank cover in the area (Duebbert and Kantrud, 1974). Nests 

usually are located within a few kilometers of water, but if choice nesting habitat is not 

available nearby, females may nest further away (Bellrose, 1976; Duebbert and Lokemoen, 

1976). 

Food habits. In winter, mallards feed primarily on seeds but also on invertebrates 

associated with leaf litter and wetlands, mast, agricultural grains, and to a limited extent, 

leaves, buds, stems, rootlets, and tubers (Goodman and Fisher, 1962; Heitmeyer, 1985, 

cited in Allen, 1987). In spring, females shift from a largely herbivorous diet to a diet of 

mainly invertebrates to obtain protein for their prebasic molt and then for egg production 

(Swanson and Meyer, 1973; Swanson et al., 1979; Swanson et al., 1985; Heitmeyer, 1988b). 

Laying females consume a higher proportion of animal foods on the breeding 

2-39 Mallard 
grounds than do males or nonlaying females (Swanson et al., 1985). The animal diet 

continues throughout the summer, as many females lay clutches to replace destroyed 

nests (Swanson et al., 1979; Swanson et al., 1985). Ducklings also consume aquatic 

invertebrates almost exclusively, particularly during the period of rapid growth (Chura, 

1961). Mallards concentrate in wetlands at night, apparently feeding on emerging insects 

(Swanson and Meyer, 1973). Flocks may feed in unharvested grain fields and stubble fields 

during fall and winter (Dillon, 1959). During periods of food shortage, fat reserves are used 

as an energy source. During breeding, females continue to feed but also use fat to meet 

the demands of egg production; females may lose 25 percent of their body mass (in fat) 

during laying and early incubation (Krapu, 1981). 

Molt. Female mallards molt into basic plumage in late winter or early spring, except 

for the wing molt, which is delayed until about the time broods are fledged. In males, headbody-tail molt commences in early summer and overlaps or is followed by the wing molt. 

Mallards generally are flightless for about 25 days during the wing molt (Palmer, 1976). 

Migration. Although the mallard winters in all four waterfowl flyways of North 

America (i.e., Pacific, Central, Mississippi, and Atlantic), the Mississippi flyway (alluvial 

valley from Missouri to the Gulf of Mexico) contains the highest numbers (Bellrose, 1976). 

Human creation and alteration of water bodies and plant communities have changed the 

migration and wintering patterns of mallards; in North America the ducks winter farther 

north than in the past (Jorde et al., 1983). Mallards tend to arrive at their wintering grounds 

in the Mississippi Valley in mid-September through early November and depart for their 

northerly breeding grounds again in March (Fredrickson and Heitmeyer, 1988). Adult 

females that reproduce successfully are likely to return to the same nesting ground the 

following year (Lokemoen et al., 1990a, 1990b). 

Breeding activities and social organization. Older females arrive at breeding 

grounds earlier than yearling birds, which probably increases their chances of 

reproductive success because they can select the best nest sites (Lokemoen et al., 1990b). 

First clutches are generally finished by mid-April in the southern part of the breeding range 

and late April to May in the northern United States (Palmer, 1976). High rates of nest failure 

require females to renest persistently to reproduce successfully (Swanson et al., 1985). 

Average clutch size decreases as the season progresses because the clutch size of 

renesting females is smaller than initial clutches (Eldridge and Krapu, 1988; Lokemoen et 

al., 1990b). Older females produce larger clutches than do yearlings (Lokemoen et al., 

1990a). Mallards mate for one breeding season, and males typically leave the females at 

the onset of incubation (Palmer, 1976). Females remain with the brood until fledging. 

Mallards are serially monogamous and thus remate annually (Palmer, 1976). 

Home range and resources. Each pair of mallards uses a home range, and the 

drake commonly establishes a territory that he defends against other mallards (Bellrose, 

1976). Home-range size depends on habitat, in particular the type and distribution of water 

habitats (e.g., prairie potholes, rivers), and population density (Bellrose, 1976; Dwyer et al., 

1979; Kirby et al., 1985). 

2-40 Mallard 
�

�

�

�

Population density. Mallard densities during the breeding season are positively 

correlated with availability of terrestrial cover for nesting and with availability of wetlands 

and ponds that provide the aquatic diet of mallards (Pospahala et al., 1974). Availability of 

suitable wetland habitat for breeding and wintering depends on environmental conditions 

(e.g., rainfall) (Heitmeyer and Vohs, 1984; Lokemoen et al., 1990a). Average densities of 

breeding mallards in the prairie pothole region range from 0.006 to 0.67 pairs per hectare 

(Duebbert and Kantrud, 1974; Duebbert and Lokemoen, 1976; Kantrud and Stewart, 1977; 

Lokemoen et al., 1990b). Mallards attain their highest densities in prairie and parkland of 

the southern prairie provinces and in the Cooper River and Athabasca River deltas of 

Canada (Johnson and Grier, 1988). 

Population dynamics. Nest success or failure is an important factor affecting 

mallard populations. Mammalian predation is the main cause of nest failure, followed by 

human disturbance (e.g., farming operations) and adverse weather conditions (Klett et al., 

1988; Lokemoen et al., 1988). Mammalian predators include fox, badger, and skunk; crows 

also prey on mallard nests (Johnson et al., 1988). Mallards usually renest if the first nest 

fails (Palmer, 1976). Juvenile survival depends on food and preferred habitat availability, 

factors that in turn are affected by environmental conditions. For example, high rainfall is 

related to increased wetland area, which is positively correlated with duckling growth 

(Lokemoen et al., 1990a). Annual adult mortality rates vary with year, location, hunting 

pressure, age, and sex. Females suffer greater natural mortality rates (e.g., typical values 

of 40 to 50 percent) than do males (e.g., typical values of 30 to 40 percent) (Chu and 

Hestbeck, 1989). By fall, there is a higher proportion of males than females in most 

populations (Bellrose, 1976). Immature mortality rates of 70 percent have been recorded in 

many areas, although lower immature mortality rates are more common (Bellrose, 1976; 

Chu and Hestbeck, 1989). Annual mortality rates also are greater in areas with higher 

hunting pressure (Bellrose, 1976). 

Similar species (from general references) 

� The American black duck (Anas rubripes) is only present in the wooded 

parts of northeastern and north central United States. It nests near 

woodland lakes and streams or in freshwater and tidal marshes. It is similar 

in size (58 cm) to mallards using the same habitats. 

� The northern pintail (Anas acuta) is widespread, occurring in most parts of 

North America and breeding throughout Canada and the north central United 

States. Although formerly farily abundant, North American pintail 

populations have declined dramatically during the past decade (USFWS, 

1991). It prefers marshes and open areas with ponds and lakes. Pintails 

average slightly longer (66 cm) than mallards. 

� The gadwall (Anas strepera) (51 cm) occurs throughout most of the United 

States. In Canada, its breeding range is limited to the south central potholes 

region. It is more common in the west than in the east. 

� The American wigeon (Anas americana) (48 cm) breeds throughout most of 

Canada and in the prairie pothole regions of the United States. It winters 

2-41 Mallard 
�

�

�

�

along both the east and west coasts of the United States as well as farther 

south into Mexico. 

� Northern shovelers (Anas clypeata) (48 cm), inhabitants of marshes, ponds, 

and bays, breed throughout mid to western Canada and the prairie pothole 

regions of the United States. They winter along the gulf coast, southern 

Atlantic coast, in Texas, and a few other southwestern states as well as 

throughout Mexico. 

� Blue-winged teal (Anas discors) (39 cm) are fairly common in open country 

in marshes and on ponds and lakes. Breeding populations occur throughout 

the central United States and Canada, but wintering populations are 

restricted to Atlantic and Pacific coastal areas. 

� The green-winged teal (Anas crecca) (37 cm) is the smallest of the dabbling 

ducks. A. c. carolinensis is the most common subspecies in the United 

States. It breeds throughout most of Canada and the prairie pothole region 

of the United States. It overwinters in the southern half of the United States 

and in Mexico. 

� Cinnamon teal (Anas cyanoptera) (41 cm) breeding populations are restricted 

to the western United States and Mexico, with few reaching southern 

Canada. Some populations in California and Mexico are year-round 

residents. 

General references 

Allen (1987); National Geographic Society (1987); Pospahala et al. (1974); Palmer 

(1976); Bellrose (1976). 

2-42 Mallard 
Mallard Duck (Anas platyrhynchos) 

Factors 

Age/Sex/ Range or 

Cond./Seas. Mean (95% CI of mean) Location Referen

Body Weight A M 1,225 up to 1,814 throughout North America Nelson 

(g) A F 1,043 up to 1,633 

A M winter 1,246 ± 108 SD western Mississippi Delnick

A F winter 1,095 ± 106 SD (alluvial valley) 

A M winter 1,237 ± 118 SD Texas Whyte & 

A F winter 1,088 ± 105 SD A F spring 1,197 ± 105 SD North Dakota Krapu & 

egg 52.2 32.2 - 66.7 North Dakota Eldridg

at hatching 32.4 ± 2.4 SD central North Dakota Lokemo

B at 3.5 days 32.4 ± 2.4 SD central North Dakota Lokemo

F at 9.5 days 115 ± 37 central North Dakota Lokemo

F at 15.5 days 265 ± 92 

F at 30.5 days 401 ± 92 

F fledging at 

56.0 days 740 ± 115 SD 

M at 9.5 days 92 ± 12 SD central North Dakota Lokemo

M at 15.5 days 215 ± 5 

M at 30.5 days 460 ± 93 

M fledging at 

56.0 days 817 ± 91 

Body Fat A M winter 174 ± 66 SD Texas Whyte & 

(g lipid) A F winter 171 ± 56 SD 

A F April 106 ± 34 SD North Dakota Krapu & 

Y F April 82 ± 37 SD A F June 22 ± 22 SD Y F June 9.6 ± 8.3 SD 

SD 

SD SD 

SD 

SD SD 

2-43 Mallard 
Mallard Duck (Anas platyrhynchos) 

2-44 Mallard 

Factors 

Age/Sex/ Range or 

Cond./Seas. Mean (95% CI of mean) Location Referen

Metabolic Rate A F basal 77 estimat

(kcal/kg-day) A M basal 73 

A F winter 280 Texas Whyte & 

A M winter 220 A F free-living 200 (94 - 424) estimat

A M free-living 192 (91 - 408) 

Food Ingestion Rate (g/g-day) 

Water A F 0.058 estimat

Ingestion A M 0.055 

Rate (g/g-day) 

Inhalation A F 0.42 estimat

Rate (m /day) A M 0.48 3 

Surface Area A F 1,030 estimat(cm ) A M 1,148 2 Dietary Composition 

Location/Habitat 

(measure) Referenc

adults: Winter Louisiana/coastal marsh Dillon, 19

rice 24 and prairie 

jungle rice 21 

brownseed paspalum 19 (% volume; gullet contents) barnyard grass 8.0 

red rice 8.0 

knot grass 6.5 signal grass 2.5 

coast cockspur 1.9 

Mamaica sawgrass 1.3 snails 1.0 other 6.8 
Mallard Duck (Anas platyrhynchos) 

Dietary Composition 

Location/Habitat 

(measure) Referenc

breeding female: April May June south central North Swanson 

(total animal) (67.8) (66.8) (89.4) Dakota/prairie potholes 

gastropods trace 24.9 16.5 

insects 13.1 25.6 48.1 (% wet volume; esophagus 

crustacea 7.9 15.1 13.9 contents) 

annelids 38.3 0.2 10.9 

misc. animal 8.5 1.0 -

(total plant) (32.2) (33.2) (10.6) 

seeds 28.7 28.7 10.6 

tubers 2.4 4.3 -

stems 1.1 0.2 -

Population 

Dynamics 

Age/Sex Cond./Seas. Mean Range Location/Habitat Referenc

Home Range spring: 

Size (ha) A F total 468 ± 159 SD 307 - 719 North Dakota/prairie Dwyer et 

A F laying 111 ± 76 SD 38 - 240 potholes 

spring: 

A F 540 40 - 1,440 Minnesota/wetlands, river Kirby et a

A M 620 70 - 1,140 

Population A B spring 0.036 0.006 - 0.076 central North Dakota/range Lokemoe

Density (area 1) of 6 years of data from 

(pairs/ha) A B spring 0.047 0.031 - 0.087 two different pothole 

(area 2) areas 

Clutch yearling 9.3 ± 1.7 SE North Dakota/prairie Krapu & 

Size A 10.3 ± 1.1 SE potholes 

9 1 - 18 NS/NS Bellrose

Clutches if lost up to 4.5 North Dakota/experimental Swanson

/Year ponds (nests purposely Swanson 

if successful 1 North America/NS Bellrose

destroyed) 

Days 26 23 - 29 NS/NS Bent, 192

Incubation 25 North Dakota/wetlands Klett & J

2-45 Mallard 
Mallard Duck (Anas platyrhynchos) 

Population 

Dynamics 

Age/Sex Cond./Seas. Mean Range Location/Habitat Referenc

Age at 52 - 60 NS/NS Bellrose

Fledging (days) 56 central North Dakota/ Lokemoe

potholes 

Percent Nests 51 - 61 South Dakota/prairie Duebber

Successful potholes and fields 

9 - 10 eastern South Dakota/ Klett et a

potholes 

Number 4.9 NS/NS Cowardi

Fledge per 8.4 United States/NS Bellrose

Successful Nest Age at 1 yr United States/NS Krapu & 

Sexual Maturity Annual A M 27.2 eastern-central flyway/NS Bellrose

Mortality A F 38.2 

Rates (percent) A M fall 40.1 ± 3.1 SE 22 - 51 western mid-Atlantic/NS Chu & He

J M fall 41.1 ± 7.2 SE 31 - 59 1971 to 1985 

A F all 49.9 ± 3.3 SE 20 - 72 

J F all 48.8 ± 6.0 SE 15 - 68 

A M fall 39.0 ± 2.3 SE 9 - 60 northeastern United Chu & He

J M fall 48.1 ± 5.3 SE 7 - 69 States/NS 

A F all 51.5 ± 1.9 SE 33 - 64 1971 to 1985 

J F all 56.8 ± 3.2 SE 38 - 68 

Seasonal 

Activity Begin Peak End Location Referenc

Mating May CA, UT, MT, SD, NY, VT Bellrose

early April early May mid-July south central N Dakota Krapu & 

Hatching June NW Territory, Canada Toft et al

f

f

f

f

2-46 Mallard 
�

Mallard Duck (Anas platyrhynchos) 

Seasonal 

Activity Begin Peak End Location Referenc

Molt 

spring December March Mississippi Valley Fredricks

fall mid-Sept. November 

Migration 

spring mid-March mid-May arrive north central US Johnson 

fall mid-October November leave northern US Palmer, 1

1 Estimated using equation 3-28 (Lasiewski and Dawson, 1967) and body weights from Nelson and Martin (1953).

2 Estimated daily existence energy at 0�C.

3 Estimated using equation 3-37 (Nagy, 1987) and body weights from Nelson and Martin (1953).

4 See Chapters 3 and 4 for methods of estimating food ingestion rates from free-living metabolic rate and dietary com

5 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Nelson and Martin (1953).

6 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Nelson and Martin (1953).

7 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

(1953). 

8 Cited in Palmer (1976). 9 Cited in Johnson et al. (1987). 

2-47 Mallard 
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recovery rates for the mallard, 1950 through 1985. Washington, DC: U.S. Fish Wildl. 

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Chura, N. J. (1961) Food availability and preference of juvenile mallards. Trans. N. Am. 

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Coulter, M. W.; Miller, W. R. (1968) Nesting biology of black ducks and mallards in northern 

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Delnicki, D.; Reinecke, K. J. (1986) Mid-winter food use and body weights of mallards and 

wood ducks in Mississippi. J. Wildl. Manage. 50: 43-51. 

Dillon, O. W. (1959) Food habits of wild mallard ducks in three Louisiana parishes. Trans. 

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Doty, H. A. (1975) Renesting and second broods of wild mallards. Wilson Bull. 87: 115. 

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2-48 Mallard 
Duebbert, H. F.; Lokemoen, J. T. (1976) Duck nesting in fields of undisturbed grass-legume 

cover. J. Wildl. Manage. 40: 39-49. 

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2-49 Mallard 
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2-50 Mallard 
Lokemoen, J. T.; Duebbert, H. F.; Sharp, D. E. (1990a) Homing and reproductive habits of 

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2-51 Mallard 
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2-52 Mallard 
2.1.4. Lesser Scaup (bay ducks) 

Order Anseriformes, Family Anatidae. Bay ducks are adapted for diving and 

characteristically need a running start to become airborne because their legs are located 

further back on their body than on other ducks. They breed at mid to high latitudes and 

winter in flocks on large water bodies and in protected coastal bays and river mouths. Bay 

ducks dive for their food, and their diet is omnivorous (i.e., both plant and animal matter) 

and depends on the seasonal and regional abundance of food resources. Because of their 

food habits, bay ducks prefer deeper, more permanent ponds than dabbling ducks 

(Bellrose, 1976). The sexes vary in coloration, and different bay duck species range in 

length from 42 to 53 cm (bill tip to tail tip). 

Selected species 

The lesser scaup (Aythya affinis) is one of the most abundant North American 

ducks (Allen, 1986). They breed principally throughout western Canada and Alaska, 

although their breeding range extends into the western United States as far south as 

Colorado and Ohio. Lesser scaup winter in the United States in the Mississippi flyway and 

the Atlantic flyway (Bellrose, 1976). They also winter along all coastal areas in the 

southern states and into Mexico (National Geographic Society, 1987). 

Body size. The lesser scaup averages 42 cm from bill tip to tail tip. Males are 

larger and more colorful than the brown females (Bellrose, 1976; see table). Following their 

postbreeding molt, scaups increase their fat reserves in preparation for migration (Austin 

and Fredrickson, 1987; see table). 

Habitat. Lesser scaup are found on large lakes and bays during the fall and winter 

and are common on smaller bodies of water (e.g., ponds) during the spring. They breed in 

the prairie potholes region, most often on permanent or semipermanent wetlands of 0.85 to 

2.0 ha with trees and shrubs bordering at least half of the shorelines (Bellrose, 1976; 

Smith, 1971, cited in Allen, 1986). Primary brood habitat is characterized by permanent 

wetlands dominated by emergent vegetation (Smith, 1971, cited in Allen, 1986). In a study 

of ducks wintering in South Carolina, Bergan and Smith (1989) found lesser scaup would 

forage primarily in areas with submergent vegetation but also in areas of emergent 

vegetation, shallow open water, and floating-leaved vegetation. They found some 

differences in foraging habitat use by season and between males and females. In 

particular, females tended to use more shallow habitats than males, and males preferred 

open water in late fall (Bergan and Smith, 1989). 

Food habits. Most populations of lesser scaup consume primarily aquatic 

invertebrates, both from the water column and from the surfaces of aquatic vegetation and 

other substrates (Tome and Wrubleski, 1988; Bartonek and Hickey, 1969). Common prey 

include snails, clams, scuds (amphipods), midges, chironomids, and leeches (see table). 

Scaup are omnivorous, however, and the percentage of plant materials (almost exclusively 

seeds) in the diet varies seasonally as the availability of different foods changes (Afton et 

al., 1991; Dirschl, 1969; Rogers and Korschgen, 1966). When seeds are locally abundant, 

they may be consumed in large quantities (Dirschl, 1969). Breeding females and ducklings 

2-53 Lesser Scaup 
eat mostly aquatic invertebrates (Sugden, 1973). Young ducklings feed primarily on watercolumn invertebrates (e.g., phantom midges, clam shrimps, water mites), whereas older 

ducklings forage mainly on bottom-dwelling invertebrates (e.g., scuds or amphipods, 

dragonflies, caddisflies) (Bartonek and Murdy, 1970). During the winter, there are no 

significant differences in diet between juveniles and adults or between males and females 

(Afton et al., 1991). 

Molt. Nonbreeding and postbreeding males and nonbreeding females generally 

leave the breeding grounds in June to molt on lakes. However, some males complete their 

molt on the breeding grounds (Trauger, 1971, cited in Bellrose, 1976). Large flocks of 

molting birds become flightless during the wing molt phase, which begins in July and is 

usually complete by late August (McKnight and Buss, 1962). 

Migration. The axis of the main migration corridor extends from the breeding 

grounds on the Yukon Flats, Alaska, to wintering areas in Florida (Bellrose, 1976). Most 

scaup winter in the United States, with the greatest numbers in the Mississippi flyway and 

the Atlantic flyway. They start to arrive at their wintering areas in mid-October (Bellrose, 

1976). The timing of northward migration in the spring varies from February to May 

(Bellrose, 1976). Before migration, scaup gain weight by increasing their body fat content 

(Austin and Fredrickson, 1987). 

Breeding activities and social organization. Scaup build nests on the ground 

among tall grasses, shrubs, or forbs where plant heights range from 20 to 60 cm (Hines, 

1977). Nests can be located along the edge of shorelines to upland areas (Bellrose, 1976). 

Courtship and pair bonds start to form on the wintering grounds, and pairs typically remain 

together for only one season. Males do not remain long after incubation commences 

(Trauger, 1971, cited in Bellrose, 1976). The female and her brood leave the vicinity of the 

nest shortly after the ducklings have hatched. Most broods are on their own by 4 to 5 

weeks of age (Gehrman, 1951, cited in Bellrose, 1976) and fledge between 7 and 9 weeks of 

age (Bellrose, 1976; Lightbody and Ankney, 1984). Females of this species often lay eggs 

in other lesser scaup nests (nest parasitism), which can result in large compound clutches 

of lesser scaup eggs in a single nest (Hines, 1977). Hines (1977) also found that mixing of 

broods was common in Saskatchewan; by August, groups of 15 to 40 ducklings led by two 

to three hens would be common. Female lesser scaup also occasionally lay eggs in the 

nests of other ducks (e.g., gadwall; Hines, 1977). 

Home range and resources. Relatively small nesting territories and large highly 

overlapping foraging ranges are characteristic of lesser scaup (Hammel, 1973, cited in 

Allen, 1986). Several pairs can nest in close proximity without aggression, each defending 

only a small area immediately surrounding the nest (Bellrose, 1976; Vermeer, 1970). In 

Manitoba, Hammel (1973) estimated the mean minimum foraging home range to be 89 ± 6.5 

ha. Initial areas occupied by pairs usually contain stumps, logs, boulders, or beaches as 

loafing sites, but later lesser scaup rely solely on open water (Gehrman, 1951, cited in 

Bellrose, 1976). 

Population density. In winter, local densities of scaup can be very high, as large 

flocks float on favored feeding areas (Bellrose, 1976). In summer, the density of breeding 

2-54 Lesser Scaup 
�

�

�

�

pairs increases with the permanence and size of the ponds (Kantrud and Stewart, 1977; 

see table). 

Population dynamics. In some populations, many yearling and some 2-year-olds do 

not breed; the proportion breeding tends to increase with improving water and habitat 

conditions (Afton, 1984; McKnight and Buss, 1962). In a 4-year study in Manitoba, Afton 

(1984) found that, on average, 30 percent of 1-year-olds and 10 percent of 2-year-olds, did 

not breed. Clutch size and reproductive performance of adult females generally increase 

with age (Afton, 1984). Most nest failures are due to predation (e.g., by mink, raccoons, red 

fox), and scaup often attempt to renest if the initial nest fails (Afton, 1984; Bellrose, 1976). 

Annual mortality for juveniles is higher than that for adults, and adult female mortality 

exceeds adult male mortality (Smith, 1963; see table). 

Similar species (from general references) 

� The redhead (Aythya americana), a larger bay duck (48 cm), breeds on lakes 

and ponds in the northwestern United States and in midwestern Canada. 

They winter in coastal areas and the southern United States and Mexico. In 

summer, adult female and juvenile redheads consume predominantly animal 

matter (e.g., caddis flies, midges, water fleas, snails), while males include 

more plant materials in their diet. 

� The canvasback (Aythya valisineria) is the largest bay duck (53 cm). They 

are common on lakes and ponds in the northern United States and southern 

Canada during the breeding season and along coastal areas of the United 

States during winter. Studies during the winter in North and South Carolina 

have found varying diets for canvasbacks, consuming mostly animal matter 

(e.g., clams); others eat only vegetation. In summer, adult female and 

juvenile canvasbacks eat predominantly animal material (e.g., caddis flies, 

snails, mayflies, midges), whereas adult males may eat predominantly 

vegetable material, particularly tubers of Potamogeton. 

� The ring-necked duck (Aythya collaris) is similar in size (43 cm) to the lesser 

scaup and prefers freshwater wetlands. They are commonly seen on 

woodland lakes and ponds, but in winter also use southern coastal marshes. 

During the winter, ring-necked ducks eat mostly plant materials (81 percent) 

and a variety of animal matter (19 percent). 

� The greater scaup (Aythya marila) (46 cm) is common in coastal areas and 

the Great Lakes during winter. They are omnivorous, eating 50 to 99 percent 

animal matter and the remainder plant foods during the winter. 

General references 

Allen (1986); Bartonek and Hickey (1969); Bellrose (1976); National Geographic 

Society (1987); Perry and Uhler (1982). 

2-55 Lesser Scaup 
Lesser Scaup (Aythya affinis) 

Factors 

Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referen

Body Weight F preflightless 688 Manitoba, Canada Austin 

(g) F flightless 647 

F postflightless 693 

F migratory 842 

F 770 up to 950 United States Nelson 

M 860 up to 1,100 

Adult Body Fat F preflightless 50.7 7.4%) Manitoba, Canada Austin 

(grams lipid: F flightless 37.2 (5.7%) 

% of total body F postflightless 46.5 6.7%) 

weight) F migratory 188.1 (22.3%) 

Duckling age in weeks growth in g/day (final body weight) Utah or Canada Sugden 

Growth Rate 0-3 6.9 (190 g) 

3-6 (485 g) 

6-9 5 (516 g) 9-12 2 (542 g) 

Metabolic Rate A F basal 83 estimat

(kcal/kg-day) A M basal 81 

A B resting Canada McEwa

20 to 30�C 

A F free-living 211 (102 - 457) estimat

A M free-living (99 - 445) 

90 216 

Food Ingestion juveniles, dry matter intake/ Saskatchewan/captive: Sugden 

Rate (g/g-day) both sexes: wet body weight reared in large brooder 

1 - 5 weeks 0.162 and in outdoor pens 

6 - 12 weeks 0.077 

Water A F 0.064 estimat

Ingestion A M 0.062 

Rate (g/g-day) 

Inhalation A F 0.34 estimat

Rate (m /day) A M 0.36 3 

(

(

14 1.1.

2-56 Lesser Scaup 
Lesser Scaup (Aythya affinis) 

Factors 

Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referen

Surface Area A F 842 estimat

(cm ) A M 906 2 

Dietary Composition Spring Summer Fall Winter (measure) Referen

Location/Habitat 

(animal) (60.9) Louisiana/lakes, marshes Afton e

midges 45.9 snails 7.7 (% dry weight; 

grass shrimp 7.3 esophageal & proventricular 

(plant - seeds) (36.1) contents) 

bulrush 36.0 

(plant - vegetative) (3.0) 

green algae 2.3 

juveniles only: Northwest Territories/lake Bartone

(animal) (100) (100) 

scuds 1 ± 1 57 ± 9 (% wet volume ± SE; phantom midges 54 ± 8 1 ± 1 esophageal contents) 

clam shrimps 30 ± 8 2 ± 2 

dragon/damselflies - 17 ± 8 

water bugs 4 ± 3 11 ± 7 

water mites 8 ± 3 -

caddis flies - 6 ± 5 

water beetles 1 ± 1 4 ± 3 

mayflies 2 ± 1 -

(plants) (trace) (trace) 

2-57 Lesser Scaup 
Lesser Scaup (Aythya affinis) 

Dietary Composition Spring Summer Fall Winter (measure) Referen

Location/Habitat 

adults only: nw Minnesota: spring and fall Afton e

(animal) (91.8) (90.5) migrations/lakes, marshes, 

scuds (amphipods) 33.2 54.9 pools 

dragonflies - 2.4 

caddis flies 8.8 7.6 (% dry weight; 

midges 2.3 - esophageal & proventricular 

other insects 4.9 - contents) snails 31.9 10.2 

fingernail clams 6.0 5.1 

brook stickleback - 4.1 

fathead minnow - 5.0 

other fish 3.5 

(plants - seeds) (6.0) (9.4) 

(plants - vegetative) (2.2) (0.1) 

(animal) (90.9) (75.1) (49.6) Saskatchewan, Dirschl

scuds 66.0 9.8 42.5 Canada/shallow lakes 

diptera - 1.3 0.1 

leeches 12.0 23.7 1.6 (% dry weight; esophagus 

fingernail clams 12.7 25.7 - and proventriculus contents) 

cyprinid fish - 2.9 -caddis flies 0.2 1.6 1.9 

clam shrimps - 3.1 0.5 

(plant - seeds) (9.1) (24.9) (50.4) 

Nuphar variegatum - 13.2 42.8 

other seeds 9.1 11.7 7.6 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Location/Habitat Refe

Home Range breeding 89 ± 6.5 SE Manitoba, Canada Ham

Size (ha) 

Range 

2-58 Lesser Scaup 
Lesser Scaup (Aythya affinis) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Location/Habitat Refe

Population A B seasonal North Dakota/ Kant

Density wetland 0.029 prairie potholes 

(pairs/ha) A B permanent 

wetland 0.061 

A B island in 28.9 13.1 - 58.5 Alberta, Canada/islands in Verm

lake lakes of parklands and 

boreal forest 

Clutch 9.47 ± 0.18 SE 7 - 12 Saskatchewan/marsh island Hine

Size 

2nd yr female 10.0 ± 0.2 SE 8 - 12 Manitoba/lake Afto

4th yr female 12.1 ± 0.2 SE 11 - 14 

Clutches 1, but often NS/NS Afto

/Year renest if lost 

Days 24.8 21 - 27 NS/NS Verm

Incubation Age at B 65 ± 0.91 SE Manitoba/captive Ligh

Fledging (days) Percent Nests 1st yr female 26.3 Manitoba/lake Afto

Hatching 2nd yr female 22.2 

3rd yr female 45.5 

76 Saskatchewan/marsh islands Hine

Percent up to 20 days 67.5 ± 4.9 SE Manitoba/lake Afto

Broods of age 

Surviving 

Age at First M most in 2nd yr NS/NS Palm

Breeding F 1 - 2 years Manitoba/lake Palm

Annual juveniles 68 - 71 NS/NS Smit

Mortality Rates A males 38 - 52 

(percent) A females 49 - 60 

Range 

2-59 Lesser Scaup 
�

Lesser Scaup (Aythya affinis) 

Seasonal 

Activity Begin Peak End Location Referenc

Mating/Laying early June Manitoba, Canada Afton, 19

early May early June early July Montana Ellig, 195

Hatching early July mid-July early August NW Territory and Toft et al

Saskatchewan, Canada 

Molt (fall) July September Manitoba, Canada Austin & 

Migration 

spring early February March - April May departing United States Bellrose

mid-April arriving Manitoba, Canada Afton, 19

fall September mid-November Pacific flyway (s OR, n CA) Gammon

mid-October mid- December arriving United States 

November 

Bellrose

1 Four stages of feather molt evaluated. 

2-60 Lesser Scaup 

2 Ducklings stopped growing at rate typical of wild birds around 6 weeks of age. By 12 weeks, they weighed approxim

of wild scaup. 

3 Estimated using equation 3-28 (Lasiewski and Dawson, 1967) and body weights from Nelson and Martin (1953). 4 Estimated using equation 3-37 (Nagy, 1987) and body weights from Nelson and Martin (1953). 5 Young ducklings maintained in 18 to 27�C brooder, then in outdoor pens with same temperature range. Metabolizab

(estimated to be 3.11 kcal/g dry wt), a typical scaup food, is similar to the commercial diet used in the experiment (3.

stopped growing as rapidly as would wild ducklings at about 6 weeks of age. For methods of estimating food inges

Chapters 3 and 4. 

6 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Nelson and Martin (1953).

7 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Nelson and Martin (1953).

8 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, cited in Walsberg and King, 1978) and body weights f

9 Relatively small, highly overlapping, home ranges. Cited in Allen (1986).

10 Cited in Bellrose (1976).
References (including Appendix) 

Afton, A. D. (1984) Influence of age and time on reproductive performance of female lesser 

scaup. Auk 101: 255-265. 

Afton, A. D.; Hier, R. H.; Paulus, S. L. (1991) Lesser scaup diets during migration and winter 

in the Mississippi flyway. Can. J. Zool. 69: 328-333. 

Allen, A. W. (1986) Habitat suitability index models: lesser scaup. U.S. Fish Wildl. Serv. 

Biol. Rep. 82(10.117). 

Austin, J. E.; Fredrickson, L. H. (1987) Body and organ mass and body composition of 

postbreeding female lesser scaup. Auk 104: 694-699. 

Bartonek, J. C.; Hickey, J. J. (1969) Food habits of canvasbacks, redheads, and lesser 

scaup in Manitoba. Condor 71: 280-290. 

Bartonek, J. C.; Murdy, H. W. (1970) Summer foods of lesser scaup in subarctic taiga. 

Arctic 23: 35-44. 

Bellrose, F. C. (1976) Ducks, geese, and swans of North America. Harrisburg, PA: The 

Stackpole Co. 

Bergan, J. F.; Smith, L. M. (1989) Differential habitat use by diving ducks wintering in South 

Carolina. J. Wildl. Manage. 53: 1117-1126. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Chabreck, R. H.; Takagi, T. (1985) Foods of lesser scaup in crayfish impoundments in 

Louisiana. Proc. Annu. Conf. Southeast. Assoc. Fish Wildl. Agencies 39: 465-470. 

Chappel, W. A.; Titman, R. D. (1983) Estimating reserve lipids in greater scaup (Aythya 

marila) and lesser scaup (A. affinis). Can. J. Zool. 61: 35-38. 

Dirschl, H. J. (1969) Foods of lesser scaup and blue-winged teal in the Saskatchewan River 

Delta. J. Wildl. Manage. 33: 77-87. 

Dunning, J. B., Jr. (1984) Body weights of 686 species of North American birds. Western 

Bird Banding Association, Monograph No. 1. Cave Creek, AZ: Eldon Publishing. 

Ellig, L. J. (1955) Waterfowl relationships to Greenfields Lake, Teton County, Montana. 

Mont. Fish. and Game Comm. Tech. Bull. 1. 

Gammonley, J. H.; Heitmeyer, M. E. (1990) Behavior, body condition, and foods of 

buffleheads and lesser scaups during spring migration through the Klamath Basin, 

California. Wilson Bull. 102: 672-683. 

2-61 Lesser Scaup 
Gehrman, K. H. (1951) An ecological study of the lesser scaup duck (Athaya affinis Eyton) 

at West Medical Lake, Spokane County, Washington [master's thesis]. Pullman, WA: 

Washington State College. 

Gollop, J. B.; Marshall, W. H. (1954) A guide for aging duck broods in the field (mimeo). MS: 

Mississippi Flyway Council Tech. Sect. 

Hammel, G. S. (1973) The ecology of the lesser scaup (Athaya affinis Eyton) in 

southwestern Manitoba [master's thesis]. Guelph, Ontario: University of Guelph. 

Hines, J. E. (1977) Nesting and brood ecology of lesser scaup at Waterhen Marsh, 

Saskatchewan. Can. Field-Nat. 91: 248-255. 

Hoppe, R. T.; Smith, L. M.; Wester, D. B. (1986) Foods of wintering diving ducks in South 

Carolina. J. Field Ornithol. 57: 126-134. 

Hunt, E. G.; Anderson, W. (1966) Renesting of ducks at Mountain Meadows, Lassen 

County, California. Calif. Fish and Game 52: 17-27. 

Kantrud, H. A.; Stewart, R. E. (1977) Use of natural basin wetlands by breeding waterfowl in 

North Dakota. J. Wildl. Manage. 41: 243-253. 

Lasiewski, R. C.; Calder, W. A. (1971) A preliminary allometric analysis of respiratory 

variables in resting birds. Resp. Phys. 11: 152-166. 

Lasiewski, R. C.; Dawson, W. R. (1967). A reexamination of the relation between standard 

metabolic rate and body weight in birds. Condor 69: 12-23. 

Lightbody, J. P.; Ankney, C. D. (1984) Seasonal influence on the strategies of growth and 

development of canvasback and lesser scaup ducklings. Auk 101: 121-133. 

McEwan, E. H.; Koelink, A. F. (1973) The heat production of oiled mallards and scaup. Can. 

J. Zool. 51: 27-31. 

McKnight, D. E.; Buss, I. O. (1962) Evidence of breeding in yearling female lesser scaup. J. 

Wildl. Manage. 26: 328-329. 

Meeh, K. (1879) Oberflachenmessungen des mensclichen Korpers. Z. Biol. 15: 426-458. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

Nasser, J. R. (1982) Management of impoundments for crayfish and waterfowl [master's 

thesis]. Baton Rouge, LA: Louisiana State University. 

National Geographic Society. (1987) Field guide to the birds of North America. Washington, 

DC: National Geographic Society. 

2-62 Lesser Scaup 
Nelson, A. L.; Martin, A. C. (1953) Gamebird weights. J. Wildl. Manage. 17: 36-42. 

Palmer, R. S. (1976) Handbook of North American birds: v. 2, 3. New Haven, CT: Yale 

University Press. 

Perry, M. C.; Uhler, F. M. (1982) Food habits of diving ducks in the Carolinas. Proc. Annu. 

Conf. Southeast. Assoc. Fish Wildl. Agencies 36: 492-504. 

Poole, E. L. (1938) Weights and wing areas in North American birds. Auk 55: 511-517. 

Rienecker, W. C.; Anderson, W. (1960) A waterfowl nesting study on Tule Lake and Lower 

Klamath National Wildlife Refuges, 1957. Calif. Fish and Game 46: 481-506. 

Ringelman, J. K.; Eddleman, W. R.; Miller, H. W. (1989) High plains reservoirs and sloughs. 

In: Smith, L. M.; Pederson, R. L.; Kaminski, R. M., eds. Habitat management for 

wintering waterfowl in North America. Lubbock, TX: Texas Tech University Press; 

pp. 311-340. 

Rogers, J. P. (1962) The ecological effects of drought on reproduction of the lesser scaup, 

Aythya affinis (Eyton) [Ph.D. dissertation]. Columbia, MO: University of Missouri. 

Rogers, J. P.; Korschgen, L. J. (1966) Foods of lesser scaups on breeding, migration, and 

wintering areas. J. Wildl. Manage. 30: 258-264. 

Rowinski, L. J. (1958) A review of waterfowl investigations and a comparison of aerial and 

ground censusing of waterfowl at Minto Flats, Alaska. Mimeogr. Rep. 

Rubner, M. (1883) Uber den Einfluss der Korpergrosse auf Stoff- und Kraftweschsel. Z. 

Biol. 19: 535-562. 

Rutherford, W. H. (1966) Chronology of waterfowl migration in Colorado. Colo. Div. Wildl.; 

Game Inf. Leafl. No. 42. 

Siegfried, W. R. (1974) Time budget of behavior among lesser scaups on Delta Marsh. J. 

Wildl. Manage. 38: 708-713. 

Smith, A. G. (1971) Ecological factors affecting waterfowl production in Alberta parklands. 

U.S. Fish Wildl. Serv. Resour. Publ. 92. 

Smith, R. I. (1963) Lesser scaup and ring-necked duck shooting pressure and mortality 

rates. Bur. Sport Fish & Wildl. Adm. Rep. 20. 

Sugden, L. G. (1973) Feeding ecology of pintail, gadwall, American widgeon and lesser 

scaup ducklings in Southern Alberta. Can. Wildl. Serv. Rep. Ser. No. 24. 

Sugden, L. G.; Harris, L. E. (1972) Energy requirements and growth of captive lesser scaup. 

Poultry Sci. 51: 625-633. 

2-63 Lesser Scaup 
Swanson, G. A.; Krapu, G. L.; Bartonek, J. C.; et al. (1974) Advantages in mathematically 

weighting waterfowl food habits data. J. Wildl. Manage. 38: 302-307. 

Toft, C. A.; Trauger, D. L.; Murdy, H. W. (1984) Seasonal decline in brood sizes of sympatric 

waterfowl (Anas and Athya, Anatidae) and a proposed evolutionary explanation. J. 

Anim. Ecol. 53: 75-92. 

Tome, M. W.; Wrubleski, D. A. (1988) Underwater foraging behavior of canvasbacks, lesser 

scaups, and ruddy ducks. Condor 90: 168-172. 

Townsend, G. H. (1966) A study of waterfowl nesting on the Saskatchewan River delta. 

Can. Field. Nat. 80: 74-88. 

Trauger, D. L. (1971) Population ecology of lesser scaup (Athaya affinis) in subarctic taiga 

[Ph.D. dissertation]. Ames, IA: Iowa State University. 

Vermeer, K. (1968) Ecological aspects of ducks nesting in high densities among larids. 

Wilson Bull. 80: 78-83. 

Vermeer, K. (1970) Some aspects of the nesting of ducks on islands in Lake Newell, 

Alberta. J. Wildl. Manage. 34: 126-129. 

Walsberg, G. E.; King, J. R. (1978) The relationship of the external surface area of birds to 

skin surface area and body mass. J. Exp. Biol. 76: 185-189. 

2-64 Lesser Scaup 
2.1.5. Osprey (Pandion haliaetus) 

Order Falconiformes, Family Accipitridae. The only North American member of the 

subfamily Pandioninae, these large birds of prey have long narrow wings, a sharp hooked 

bill, and powerful talons. Osprey are found near freshwater or saltwater, and their diet is 

almost completely restricted to fish. They are adapted for hovering over the water and 

dive feet-first, seizing fish with their talons (Robbins et al., 1983). Once very rare owing to 

DDT accumulation in their food (1950's to early 1970's), osprey now are increasing in 

numbers. In the United States, there are five regional populations of osprey (in order of 

abundance): Atlantic coast, Florida and gulf coast, Pacific Northwest, western interior, and 

Great Lakes (Henny, 1983). In North America, osprey breed primarily in a wide band from 

coast to coast across Canada and the southern half of Alaska, where they are not 

restricted to coastal and Great Lake areas as they are in the United States. However, 

osprey are reported from all States during the fall and spring migrations (Henny, 1986). 

Body size. The various subspecies of osprey around the world differ in size, and in 

general females are heavier than males (Poole, 1989a; see table). Osprey found in the 

United States are considered to be of the subspecies carolinenesis and average 56 cm 

from bill tip to tail tip (Robbins et al., 1983) and weigh between 1.2 and 1.9 kg (see table). 

Habitat. In the United States, the majority of osprey populations are associated with 

marine environments, but large inland rivers, lakes, and reservoirs also may support 

osprey (Henny, 1986, 1988b). Good nesting sites in proximity to open, shallow water and a 

plentiful supply of fish are the primary resources required for osprey success (Poole, 

1989a). The tops of isolated and often dead trees and man-made structures are preferred 

nesting sites. Osprey often nest in colonies (Poole, 1989a). 

Food habits. Osprey are almost completely piscivorous, although they have been 

observed on occasion taking other prey including birds, frogs, and crustaceans (Brown 

and Amadon, 1968). Their prey preferences change seasonally with the abundance of the 

local fish (Edwards, 1988; Greene et al., 1983). Osprey occasionally will pick up dead fish 

but only if fresh (Bent, 1937). Osprey are most successful catching species of slowmoving fish that eat benthic organisms in shallow waters and fish that remain near the 

water's surface (Poole, 1989a). Osprey consume all parts of a fish except the larger bones; 

later, bones and other undigestible parts are ejected in fecal pellets (Bent, 1937). 

Molt. Juvenile plumage is fully developed by fledging at about 60 days of age 

(Henny, 1988b). Juveniles undergo a gradual molt to adult plumage at approximately 18 

months of age (Brown and Amadon, 1968). For adults, the basic molt takes place in two 

phases; the first phase occurs primarily on the wintering grounds prior to spring migration. 

Completion of the molt occurs in the summer range prior to fall migration (Henny, 1988b). 

Migration. Osprey are year-round residents in the most southern parts of their 

range (e.g., south Florida, Mexico) but are migratory over the rest of their range in the 

United States and Canada (Poole, 1989a). Studies of banded osprey have shown that the 

fall migration begins in late August in the north temperate zone, with adults and juveniles 

2-65 Osprey 
from the eastern and central United States comprising a broad front flying south and then 

directly across open ocean to their wintering grounds in Central and South America (Poole, 

1989a). Spring migration appears to follow the same routes with birds reaching, for 

example, the Chesapeake Bay area in mid-March (Reese, 1977) and Minnesota by the first 

half of April (Dunstan, 1973; Henny and Van Velzen, 1972). The majority of migrating 

osprey appear to follow the coastline, perhaps because they come from coastal colonies or 

because the coast offers abundant food (Poole, 1989a). After their first migration south, 

juveniles remain in their wintering grounds for about a year and a half, returning north to 

the breeding grounds as 2-year-olds (Henny and Van Velzen, 1972). 

Breeding activities and social organization. Nonmigratory (i.e., year-round resident) 

populations breed during the winter; whereas migratory populations breed during the 

summer (Poole, 1989a). Monogamy is the general rule for osprey; breeding pairs remain 

together and return to the same nest site year after year (Fernandez and Fernandez, 1977; 

Henny, 1988b). Colonies of osprey occur in areas such as islands, reservoirs, or lakes that 

offer secure nesting sites and abundant food (Henny, 1986), but most osprey are solitary 

nesters, often separated from other nests by tens to hundreds of kilometers (Poole, 1989a). 

The female performs most of the incubation and relies completely on the male for food 

from just after mating until the young have fledged (Poole, 1989a). Van Daele and Van 

Daele (1982) found that ospreys at successful nests incubated 99.5 to 100 percent of the 

daylight hours; disturbance of the nest during this time can kill the eggs if the adults are 

kept from returning to the nest for some time. After hatching, the female is in constant 

attendance at the nest for the first 35 days but may perch nearby at intervals after that 

(Henny, 1988b). The female distributes the food delivered by the male by biting off pieces 

to feed to the young (Poole, 1989a). By 30 days, the nestlings have reached 70 to 80 

percent of their adult weight and begin to be active in the nest (Poole, 1989a). The young 

fledge by age 60 to 65 days in nonmigratory populations and by about 50 to 55 days in 

migratory populations (Henny et al., 1991). After fledging, the young remain dependent on 

both parents for food usually for an additional 2 to 3 weeks (Poole, 1989a), but dependency 

can continue up to 6 weeks in the more southern populations (Henny, 1986). 

Home range and resources. Osprey build large stick nests in the tops of tall trees 

or artificial structures such as buoys and radio towers (Poole, 1989a). In the Chesapeake 

Bay area, less than one third of the 1,450 breeding pairs built their nests in trees, while 

over half nested on channel markers and duck blinds, and the remainder on miscellaneous 

man-made structures (Henny et al., 1974). Osprey build their nest at the top of the chosen 

site, which can make it vulnerable to destruction from high winds (Henny, 1986). If not lost, 

the same nest often is used year after year, and it can become quite large (e.g., over 2 m 

tall and 1.5 m across) (Dunstan, 1973; Henny, 1988a). On islands where no predators are 

present, osprey will nest on the ground (Poole, 1989b). The distance osprey travel from 

their nests to forage (i.e., foraging radius) depends on the availability of appropriate nest 

sites near areas with sufficient fish; osprey will travel up to 10 to 15 km to obtain food (Van 

Daele and Van Daele, 1982). 

Population density. Population density depends on the availability and distribution 

of resources and can be highly variable. Henny (1988a) reported as many as 1.9 nests per 

hectare in one of the largest osprey colonies in the western United States in 1899, with an 

2-66 Osprey 
estimated 1.0 to 1.2 nests per hectare occupied that year. Lower densities on the order of 

0.005 to 0.1 nests per hectare are more common (see table). 

Population dynamics. Breeding data from many locations in the United States and 

Canada during the years 1950 to 1976 show low productivity (fewer than one chick fledged 

per active nest on average). Evidence indicates the cause to be egg-shell thinning that 

resulted from the ospreys' exposure to DDT that had bioaccumulated in fish (Henny and 

Anthony, 1989; Henny et al., 1977; Poole, 1989a). Thus, data from reproductive studies 

conducted during this time can only be used with this in mind (Spitzer et al., 1978).a 

Because of their terminal position in the aquatic food chain, osprey can be a sensitive 

indicator of toxic contaminants that bioaccumulate (Henny et al., 1978; Henny, 1988b). 

Osprey are only known to start a second clutch if the first one is destroyed (Poole, 

1989a). Juveniles do not return to their place of birth until 2 years of age, and they do not 

breed until their third season (Henny and Van Velzen, 1972). Often, breeding is delayed 

until 4 to 7 years of age in areas such as the Chesapeake Bay, where good nesting sites 

are scarce (Poole, 1989b). 

General references 

Poole (1989a); Brown and Amadon (1968); Henny (1986); Henny (1988b). 

a

In the table beginning on the next page, data on the number fledged per active nest and the

 number fledged per successful nest are provided only for studies of populations that appeared 

to be unaffected by DDT. 

2-67 Osprey 
Osprey (Pandion haliaetus) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location (subspecies) Referenc

Body Weight A F 1,568 1,250 - 1,900 NS Brown & 

(g) A M 1,403 1,220 - 1,600 

A F courtship 1,880 ± 20 SE se Massachusetts Poole, 19

A F incubation 1,925 ± 25 SE A F late nestl. 1,725 ± 25 SE A M courtship 1,480 ± 15 SE A M late nestl. 1,420 ± 15 SE F at fledging 1,510 Maryland, Virginia McLean, 

M at fledging 1,210 

Egg Weight (g) 72.2 ± 5.35 SD 66.0 - 81.3 North Carolina Whittemo

(carolinensis) 

Metabolic Rate A F basal 69 estimate

(kcal/kg-day) A M basal 71 

A F free-living 181 (85 - 384) estimate

A M free-living 186 (87 - 395) 

Food Ingestion A F courtship 0.21 se Massachusetts Poole, 19

Rate (g/g-day) period 

Water Ingest. A F 0.051 estimate

Rate (g/g-day) A M 0.053 Inhalation A F 0.578 estimateRate (m /day) A M 0.531 3 

Surface Area A F 1,353 estimate(cm )2 

2-68 Osprey 
Osprey (Pandion haliaetus) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

alewife 32 Nova Scotia, Canada/ Greene e

smelt 5 harbor, bay 

pollock 53 

winter flounder 10 (% wet weight; observed 

captures) 

starry flounder 95 se Alaska/NS Hughes, 

cutthroat trout 5 

(% wet weight; observed 

captures, noting fish length) 

carp 67 w Oregon/NS Hughes, 

crappie 33 

(% wet weight; observed 

captures, noting fish length) 

gizzard shad 63 Florida/lake Collopy, 

sunfish 29 

largemouth bass 5 (% of prey caught; identified 

golden shiner 3 at nests) 

brown bullhead 37.7 Idaho/reservoir Van Dae

salmonids 20.8 

northern squawfish 19.3 (% of fish caught; observed 

yellow perch 11.6 captures) 

largescale sucker 10.6 Size of fish caught: Idaho/reservoir Van Dae

< 10 cm 3.3 11 - 20 cm 42.1 (% of fish in each size class; 

21 - 30 cm 46.7 determined from remains at 

31 - 40 cm 6.6 nest) 

41 + cm 1.3 

2-69 Osprey 
Osprey (Pandion haliaetus) 

Population 

Dynamics 

Age/Sex Cond/Seas Mean Range Location/Habitat Referenc

Foraging A M 1.7 0.7 - 2.7 Minnesota/lakes Dunstan

Radius (km) A B spring 10 Nova Scotia/coastal Greene e

A B 3 to 8 > 1 nw California/coastal, bay Koplin, 1

Population A B summer 1.9 Oregon/lake in 1899 only Henny, 1

Density A B spring 0.028 Florida/wetland Eichholz

(nests/ha) A B spring 0.10 North Carolina/reservoir Henny & 

A B spring 0.005 North Carolina/lake Henny & 

Clutch 3.23 ± 0.03 SE Atlantic Seaboard/NS Judge, 1

Size 2.84 ± 0.07 SE Georgia, Florida/NS Judge, 1

2.67 ± 0.07 SE s California, n Mexico/NS Judge, 1

3.23 ± 0.09 SE ne United States/NS Spitzer, 1

2.82 1 - 4 Idaho/river, lakes Henny et 

Clutches/Year 1 NS/NS Poole, 19

Days 38.1 ± 3.2 SD 32 - 42 Baja California, Judge, 1

Incubation Mexico/coastal islands 

35 - 43 Massachusetts/NS Poole, 19

Age at non-migr. 62.5 ± 4.9 SD 52 - 76 Baja California, Judge, 1

Fledging pop. Mexico/coastal islands 

(days) 

migratory 

pop. 

54 3.0 SD 48 - 59 Maryland/Cheasapeake Bay Stotts & 

Number 1.16 0.79 - 1.47 (10 yrs) N. Carolina/lake Whittemo

Fledge per 1.34 S. Carolina/lake Henny & 

Active Nest 1.58 1.17 - 1.89 (3 yrs) Idaho/reservoir Van Dae

1.92 e United States/coastal Poole, 19

±

2-70 Osprey 
Osprey (Pandion haliaetus) 

Population 

Dynamics 

Age/Sex Cond/Seas Mean Range Location/Habitat Referenc

Number 1.7 Baja California, Judge, 1

Fledge per Mexico/coastal islands 

Successful Nest 2.14 Idaho/river Henny et 

1.83 orida/lake Collopy, 

1.79 Delaware/coastal bay Henny et 

2.05 Montana/lake Henny et 

Age at B 3 - 5 yrs New York, Spitzer, 1

Sexual B 3 yrs Massachusetts/NS Henny & 

Maturity North America/NS 

Annual 1st year 57.3 New York, New Jersey/NS Henny & 

Mortality years 2 - 18 18.5 ± 1.8 Rates (percent) J B 41 NS/NS Spitzer, 1

A B 15 

Average if reach sex. 4.8 NS/NS Brown & 

Longevity maturity 

Seasonal 

Activity Begin Peak End Location Referenc

Mating late April May mid-June Delaware, New Jersey Bent, 193

early Dec. late February Florida (nonmigratory) Poole, 19

early January early March Baja California, Mexico Judge, 1

May Minnesota Dunstan

(nonmigratory) 

Hatching mid-March early May late May Maryland, Virginia Bent, 193

late April mid-May mid-June New York/New England Bent, 193

February late April Baja California, Mexico Judge, 1

(nonmigratory) 

Migration fall late August September November most of United States Henny, 1

spring early April Minnesota Dunstan

early March North Carolina Parnell & 

Fl

2-71 Osprey 
1

23456

Osprey (Pandion haliaetus) 

Late nestl. indicates late nestling stage of the breeding season. Cited in Poole (1989a).

Estimated using equation 3-28 (Lasiewski and Dawson, 1967) and body weights from Brown and Amadon (1968).

Estimated using equation 3-37 (Nagy, 1987) and body weights from Brown and Amadon (1968).

Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Brown and Amadon (1968).

Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Brown and Amadon (1968).

Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, cited in Walsberg and King, 1978) and body weights f

(1968).

7 Percent wet weight of food ingested by free-flying osprey estimated by identifying species of fish captured (using b

length of each fish captured by comparison with osprey, and using laboratory measures of weights and lengths of s

8 Second clutch produced only if first is lost. 

9 Nestlings in migratory populations fledge at an earlier age than nestlings in nonmigratory populations, such as thos

Florida. 

10 Cited in Henny (1988b). 

11 Cited in Henny (1986). 

2-72 Osprey 
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Brown, L.; Amadon, D. (1968) Eagles, hawks, and falcons of the world, v. 1. New York, NY: 

McGraw-Hill. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Collopy, M. W. (1984) Parental care, productivity, and predator-prey relationships of 

ospreys in three North Florida Lakes: preliminary report. In: Westall, M. A., ed. Proc. 

southeastern U.S. and Caribbean osprey symposium; pp. 85-98. 

Cramp, S., chief ed. (1980) Handbook of the birds of Europe, the Middle East and North 

Africa: v. 2. Oxford, UK: Oxford University Press. 

Dunstan, T. C. (1968) Breeding success of osprey in Minnesota from 1963-1968. Loon 40: 

109-112. 

Dunstan, T. C. (1973) The biology of ospreys in Minnesota. Loon 45: 108-113. 

Edwards, T. C., Jr. (1988) Temporal variation in prey preference patterns of adult ospreys. 

Auk 105: 244-251. 

Eichholz, N. F. (1980) Osprey nest concentrations in northwest Florida. Fla. Field Nat. 8: 

18-19. 

Fernandez, G.; Fernandez, J. (1977) Some instant benefits and long range hopes of color 

banding ospreys. Transactions of the North American osprey research conference. 

U.S. Natl. Park Serv. Trans. Proc. Ser. 2. 

French, J. M. (1972) Distribution, abundance, and breeding status of ospreys in 

northwestern California [master's thesis]. Arcata, CA: Humboldt State University. 

French, J. M.; Koplin, J. R. (1977) Distribution, abundance, and breeding status of ospreys 

in northwestern California. Transactions of the North American osprey research 

conference. U.S. Natl. Park Serv. Trans. Proc. Ser. 2: 223-240. 

Garber, D. P. (1972) Osprey nesting ecology in Lassen and Plumas Counties, California 

[master's thesis]. Arcata, CA: Humboldt State University. 

2-73 Osprey 
Greene, E. P.; Greene, A. E.; Freedman, B. (1983) Foraging behavior and prey selection by 

ospreys in coastal habitats in Nova Scotia, Canada. In: Bird, D. M.; Seymour, N. R.; 

Gerrard, J. M., eds. Biology and management of bald eagles and ospreys. St. Anne 

de Bellvue, Quebec: Harpell Press; pp. 257-267. 

Grubb, T. C., Jr. (1977) Weather dependent foraging in ospreys. Auk 94: 146-149. 

Hagan, J. M. (1984) North Carolina osprey population: social group or breeding 

aggregation? In: Westall, M. A., ed. Proc. southeastern U.S. and Caribbean osprey 

symposium. 

Henny, C. J. (1977) Research, management and status of the osprey in North America. In: 

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Vienna, Austria; pp. 199-222. 

Henny, C. J. (1983) Distribution and abundance of nesting ospreys in the United States. In: 

Bird, D. M.; Seymour, N. R.; Gerrard, J. M., eds. Biology and management of bald 

eagles and ospreys. St. Anne de Bellvue, Quebec: Harpell Press; pp. 175-186. 

Henny, C. J. (1986) Osprey (Pandion haliaetus), Section 4.3.1, US Army Corps of Engineers 

Wildlife Resources Management Manual. Prepared by U.S. Fish Wildl. Serv., 

Patuxent Wildl. Res. Center, Corvallis, OR for US Army Engineer Waterways 

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Henny, C. J. (1988a) Large osprey colony discovered in Oregon. Murrelet 69: 33-36. 

Henny, C. J. (1988b) Osprey [sections]. In: Palmer, R. S., ed. Handbook of North American 

birds: v. 4. New Haven, CT: Yale University Press. 

Henny, C. J.; Anthony, R. G. (1989) Bald eagle and osprey. Natl. Wildl. Fed. Sci. Tech. Ser. 

No. 12: 66-82. 

Henny, C. J.; Noltemeier, A. P. (1975) Osprey nesting populations in the coastal Carolinas. 

Amer. Birds 29: 1073-1079. 

Henny, C. J.; Van Velzen, W. T. (1972) Migration patterns and wintering localities of 

American ospreys. J. Wildl. Manage. 36: 1133-1141. 

Henny, C. J.; Wight, H. M. (1969) An endangered osprey population: estimates of mortality 

and production. Auk 86: 288-198. 

Henny, C. J.; Smith, M. M.; Stotts, V. D. (1974) The 1973 distribution and abundance of 

breeding ospreys in the Chesapeake Bay. Chesapeake Sci. 15: 125-133. 

Henny, C. J.; Byrd, M. A.; Jacobs, J. A.; et al. (1977) Mid-Atlantic coast osprey population: 

present numbers, productivity, pollutant contamination, and status. J. Wildl. 

Manage. 41: 254-265. 

2-74 Osprey 
Henny, C. J.; Collins, J. A.; Deibert, W. J. (1978) Osprey distribution, abundance, and status 

in western North America. Murrlet 59: 14-25. 

Henny, C. J.; Blus, L. J.; Hoffman, D. J.; et al. (1991) Lead accumulation and osprey 

production near a mining site on the Coeur d'Alene River, Idaho. Arch. Environ. 

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Seymour, N. R.; Gerrard, J. M., eds. Biology and management of bald eagles and 

ospreys. St. Anne de Bellvue, Quebec: Harpell Press; pp. 269-273. 

Judge, D. S. (1983) Productivity of ospreys in the gulf of California. Wilson Bull. 95: 

243-255. 

Kennedy, R. S. (1973) Notes on the migration of juvenile ospreys from Maryland and 

Virginia. Bird-Banding 44: 180-186. 

Koplin, J. R. (1981) Reproductive performance of ospreys (Pandion haliaetus) in 

northwestern California. Natl. Geogr. Soc. Res. Rep. 13: 337-344. 

Lasiewski, R. C.; Calder, W. A. (1971) A preliminary allometric analysis of respiratory 

variables in resting birds. Resp. Phys. 11: 152-166. 

Lasiewski, R. C.; Dawson, W. R. (1967) A re-examination of the relation between standard 

metabolic rate and body weight in birds. Condor 69: 12-23. 

Lind, G. S. (1976) Production, nest site selection, and food habits of ospreys in Deschutes 

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Arcata, CA: Humboldt State University. 

MacNamara, M. (1977) Sexing the American osprey using secondary sexual characteristics. 

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2-75 Osprey 
Nesbitt, S. (1974) Foods of the osprey at Newnans Lake. Fla. Field Nat. 2: 45. 

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2-76 Osprey 
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2-77 Osprey 
2.1.6. Red-Tailed Hawk (buteo hawks) 

Order Falconiformes, Family Accipitridae. The family Accipitridae includes most 

birds of prey except falcons, owls, and American vultures. Buteo hawks are covered in 

this section.b Buteo hawks are moderately large soaring hawks that inhabit open or semiopen areas. They are the most common daytime avian predators on ground-dwelling 

vertebrates, particularly rodents and other small mammals. They range in size from the 

broad winged hawk (41 cm bill tip to tail tip) to the ferruginous hawk (58 cm). Hawks egest 

pellets that contain undigestible parts of their prey, such as hair and feathers, that can be 

useful in identifying the types of prey eaten (bones usually are digested completely; Duke 

et al., 1987). 

Selected species 

The red-tailed hawk (Buteo jamaicensis) is the most common Buteo species in the 

United States (National Geographic Society, 1987). Breeding populations are distributed 

throughout most wooded and semiwooded regions of the United States and Canada south 

of the tundra (Adamcik et al., 1979), although some populations are found in deserts and 

prairie habitats. Six subspecies are recognized (Brown and Amadon, 1968). Nesting 

primarily in woodlands, red-tails feed in open country on a wide variety of small- to 

medium-sized prey. 

Body size. Males of this medium-sized buteo (46 cm) weigh about 1 kg, and females 

are approximately 20 percent heavier than the males (see table). Otherwise, the sexes look 

alike (Brown and Amadon, 1968). 

Habitat. Red-tails are found in habitats ranging from woodlands, wetlands, 

pastures, and prairies to deserts (Bohm 1978b; Gates, 1972; MacLaren et al., 1988; Mader, 

1978). They appear to prefer a mixed landscape containing old fields, wetlands, and 

pastures for foraging interspersed with groves of woodlands and bluffs and streamside 

trees for perching and nesting (Brown and Amadon, 1968; Preston, 1990). Red-tails build 

their nests close to the tops of trees in low-density forests and often in trees that are on a 

slope (Bednarz and Dinsmore, 1982). In areas where trees are scarce, nests are built on 

other structures, occasionally in cactus (Mader, 1978), on rock pinnacles or ledges, or 

man-made structures (Brown and Amadon, 1968; MacLaren et al., 1988). In winter, night 

roosts usually are in thick conifers if available and in other types of trees otherwise (Brown 

and Amadon, 1968). 

Food habits. Red-tails hunt primarily from an elevated perch, often near woodland 

edges (Bohm, 1978a; Janes, 1984; Preston, 1990). Small mammals, including mice, 

shrews, voles, rabbits, and squirrels, are important prey, particularly during winter. Redtails also eat a wide variety of foods depending on availability, including birds, lizards, 

snakes, and large insects (Bent, 1937; Craighead and Craighead, 1956; Fitch et al., 1946). 

In general, red-tails are opportunistic and will feed on whatever species are most abundant 

b

Other members of the family Accipitridae, eagles and the osprey, are covered in Sections 2.1.7 

and 2.1.5, respectively. 

2-79 Red-Tailed Hawk 
(Brown and Amadon, 1968). Winter food choices vary with snow cover; when small 

mammals such as voles become unavailable (under the snow), red-tails may concentrate 

on larger prey, such as pheasants (Gates, 1972). 

Molt. Juveniles molt into adult plumage in a gradual process from the spring (age 

about 14 months) to summer or early fall (Bent, 1937). 

Migration. The more northerly red-tailed hawk populations are migratory while the 

more southerly are year-round residents (Bent, 1937). 

Breeding activities and social organization. Red-tails lay one clutch per year 

consisting of one to three eggs, although a replacement clutch is possible if the initial 

clutch is lost early in the breeding season (Bent, 1937). Their nests are large and built of 

twigs (Bohm, 1978b). Both sexes incubate, but the male provides food for the female 

during incubation and the entire family following hatching (Brown and Amadon, 1968). The 

parents continue to feed their young after fledging while they are learning to hunt (Brown 

and Amadon, 1968). 

Home range and resources. Red-tailed hawks are territorial throughout the year, 

including winter (Brown and Amadon, 1968). Trees or other sites for nesting and perching 

are important requirements for breeding territories and can determine which habitats are 

used in a particular area (Preston, 1990; Rothfels and Lein, 1983). Home range size can 

vary from a few hundred hectares to over 1,500 hectares, depending on the habitat 

(Andersen and Rongstad, 1989; Petersen, 1979). In a 10-year study in Oregon, Janes 

(1984) found that the size of red-tail territories and the location of boundaries between 

territories varied little from year to year, even though individual birds or pairs died and 

were replaced. 

Population density. Population densities generally do not exceed 0.03 pairs per 

hectare, and usually are lower than 0.005 pairs per hectare (see Appendix). Populations in 

southern areas such as Florida can increase substantially in the winter with the influx of 

migrants from the more northerly populations (Bohall and Collopy, 1984). 

Population dynamics. Beginning at 2 years of age, most red-tailed hawks attempt to 

breed, although the proportion breeding can vary by population and environmental 

conditions (Henny and Wight, 1970, 1972). Average clutch size varies regionally, tending to 

increase from east to west and from south to north (Henny and Wight, 1970, 1972). In a 10-

year study of red-tails in Alberta, Canada, Adamcik et al. (1979) found that the breeding 

population of adults remained stable despite strong cyclical fluctuations in the density of 

their main prey, the snowshoe hare, over the years. The mean clutch size for the red-tail 

population, however, appeared to vary with prey density, from 1.7 to 2.6 eggs/nest 

(Adamcik et al., 1979). Over the course of the study, about 50 percent of observed nestling 

losses occurred within 3 to 4 weeks after hatching due to starvation. Most of the variance 

in yearly mortality of nestlings could be attributed to the amount of food supplied and the 

frequency of rain. Large raptors such as horned owls also can be important sources of 

mortality for red-tail nestlings in some areas (Adamcik et al., 1979). 

2-80 Red-Tailed Hawk 
�

�

�

�

�

�

�

�

Similar species (from general references) 

� The ferruginous hawk (Buteo regalis), one of the larger buteos (58 cm), 

inhabits the dry open country of the western United States. 

� The red-shouldered hawk (Buteo lineatus) is slightly smaller (53 cm) and 

feeds on snakes, frogs, crayfish, mice, and some small birds. Its range is 

east of the Rocky Mountains and in California, with moist mixed woodlands 

preferred. 

� Swainson's hawk (Buteo swainsoni) is restricted to the open plains of the 

western United States. Although it is as large (53 cm) as the red-tail, it preys 

mostly on insects. 

� The broad-winged hawk (Buteo platypterus) is one of the smaller buteos (41 

cm) and preys on mice, frogs, snakes, and insects. It prefers woodlands and 

is found almost exclusively east of the Mississippi River. 

� Harris' hawk (Parabuteo unicinctus) is similar in size (53 cm) to the red-tailed 

hawk but is restricted to the semiarid wood and brushlands of the southwest. 

This bird nests in saguaro, mesquite, and yucca and preys on rodents, 

lizards, and small birds. 

� The rough-legged hawk (Buteo lagopus) is one of the larger buteos 

(56 cm). It winters throughout most of the United States in open 

country but breeds only in the high arctic of North America. 

� The zone-tailed hawk (Buteo albonotatus) is slightly smaller (51 cm) 

than most buteos and feeds on rodents, lizards, fish, frogs, and small 

birds. It can be found in mesa and mountain country within its limited 

range between the southwest United States and Mexico. 

� The short-tailed hawk (Buteo brachyurus) is the smallest buteo (39 

cm) and can only be found in the southern tip of Florida in mixed 

woodland and grassland habitats. 

General references 

Brown and Amadon (1968); Craighead and Craighead (1956); Fitch et al. (1946); 

National Geographic Society (1987). 

2-81 Red-Tailed Hawk 
 Red-Tailed Hawk (Buteo jamaicensis) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referenc

Body Weight A F 1,224 Michigan, Pennsylvania Craighea

(g) A M 1,028 

A F 1,154 sw Idaho Steenhof

A M 957 A F 1,235 Ohio Springer 

A M 1,204 hatchling F 58 

hatchling M 57 juvenile F 1,149 

juvenile M 962 

Metabolic Rate A B standard 17.7 ± 5.9 SD Michigan/metabolism Pakpaha

(lO /kg-day) MR /spring chamber 2 

Metabolic Rate A F basal 73 estimate

(kcal/kg-day) A M basal 77 

A M breeding 109 California/mountains Soltz, 19

A F breeding 102 

A F free-living 192 (91 - 408) estimate

A M free-living 201 (95 - 426) 

Food Ingestion A F winter 0.11 Michigan/captive outdoors Craighea

Rate (g/g-day) A M winter 0.10 

A M summer 0.086 

Water A F 0.055 estimate

Ingestion A M 0.059 

Rate (g/g-day) 

Inhalation A F 0.48 estimate

Rate (m /day) A M 0.42 3 

Surface Area A F 1,147 estimate(cm ) A M 1,021 2 

2-82 Red-Tailed Hawk 
 Red-Tailed Hawk (Buteo jamaicensis) 

2-83 Red-Tailed Hawk 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

summary of 10 years: mean ± SD Alberta, Canada/ Adamcik 

snowshoe hare 25.6 ± 19 farm & woodlands 

Richard's ground 

squirrel 30.4 ± 10 (% wet weight of prey 

Franklin's ground brought to chicks) 

squirrel 5.1 ± 2 

voles & mice 4.8 ± 2 

other mammals 7.8 ± 6 

waterfowl 16.2 ± 10 

ruffed grouse 2.0 ± 2 

sharp-tailed grouse 1.2 ± 1 

other grouse 0.9 ± 1 

other birds 6.3 ± 3 

(mammals) (78.5) nc Oregon/ Janes, 1

Belding's ground pasture and wheat fields 

squirrel 52.8 

mtn cottontail 13.1 (% wet weight of prey 

pocket gopher 7.3 brought to nests; March to 

Townsend's ground June) 

squirrel 2.9 

(birds) (8.5) 

Alectoris graeca 3.5 

western meadowlark 1.8 

(snakes) (13.1) 

gopher snake 6.1 

ground squirrel 60.8 c California/foothills Fitch et a

rabbit 26.5 

pocket gopher 4.3 (% wet weight of prey 

other mammals 2.6 brought to nests) 

gopher snake 3.8 

whiptail lizard 0.3 

birds 1.3 
 Red-Tailed Hawk (Buteo jamaicensis) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Range Location/Habitat Referenc

Territory A B spring 60 - 160 c California/foothills Fitch et a

Size (ha) 

A B winter 697 ± 316 SD 381 - 989 s Michigan/fields, woodlots Craighea

A B fall 1,770 957 - 2,465 Colorado/upland prairie, Anderse

pinyon-juniper woodlands 

Population mer: pairs/ha: 

Density A B 0.0017 - Colorado/open aspen McGove

A B area a 0.0004 0.0002 - 0.0005 s Michigan/fields, woodlots Craighea

A B area b 0.0012 0.0010 - 0.0013 

A B 0.0012 0.0010 - 0.0015 Alberta, Canada/farm, Adamcik 

winter: N/ha: 

B B 0.014 Toronto, Canada/mixed old Baker & 

B B 0.0015 ± 0.0012 - 0.0018 s Michigan/fields, woodlots Craighea

0.0050 0.0003 SD 

woodlands fields 

Clutch 2.0 ± 0.77 SD 1 - 3 c California/foothills Fitch et a

Size 2.32 Arizona/desert Mader, 1

2.2 1.9 - 2.6 /10 yrs Alberta, Canada/farm, Adamcik 

2.11 woodlands Henny & 

2.96 Florida/NS Henny & 

Oregon, Washington/NS 

Clutches/Year 1 Bent, 193Days 32 Alberta, Canada Adamcik 

Incubation 

sum

2-84 Red-Tailed Hawk 
 Red-Tailed Hawk (Buteo jamaicensis) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Range Location/Habitat Referenc

Growth Rate to 1 week 20 g/day Ohio/free-living, habitat NS Springer 

1 to 2 weeks 34 g/day 2 to 3 weeks 39 g/day 

3 to 4 weeks 26 g/day 4 to 5 weeks 10 g/day 

Age at 45 to 46 days California/foothills Fitch et a

Fledging Number 1.47 ± 0.25 SE Oregon/pasture Janes, 1

Fledge 1.15 0.28 - 1.90/ Alberta, Canada/farm, Adamcik 

per Active Nest 10 yrs woodlands 

high prey 1.9 Idaho/canyon, shrub steppe Steenho

low prey 1.2 

Number 2.12 north of 42�N latitude/ Henny & 

Fledge per North America 

Successful 1.85 south of 42�N latitude/ Henny & 

Nest North America 

Age at B 2 years throughout range Henny & 

Sexual Maturity Annual J B 1st year 62.4 north of 42�N latitude/ Henny & 

Mortality A B 20.6 ± 1.3 SE North America 

Rates (percent) 

J B 1st year 66.0 south of 42�N latitude/ Henny & 

A B 23.9 ± 2.2 SE North America 

Longevity maximum 18 yrs North America/NS Henny & 

Seasonal 

Activity Begin Peak End Location Referenc

Mating mid-February early April Arizona Mader, 1

mid-April early May mid-May Alberta Canada Luttich e

late March early April south Michigan Craighea

2-85 Red-Tailed Hawk 
� �

 Red-Tailed Hawk (Buteo jamaicensis) 

Seasonal 

Activity Begin Peak End Location Referenc

Hatching late March early May Arizona Mader, 1

mid-May early June mid-June Alberta, Canada Luttich e

late April early May south Michigan Craighea

Fall Migration mid-October Montana, Alberta, Canada Bent, 193

late October North Dakota Bent, 193

late November Minnesota Bent, 193

1971 

Spring late February early March south Michigan Craighea

Migration mid-March Maine, Montana Bent, 193

early April Alberta, Canada Luttich e

1 Estimated from data provided by authors. 

2-86 Red-Tailed Hawk 

2 Estimated using equation 3-28 (Lasiewski and Dawson, 1967) and body weights from Craighead and Craighead (195

3 Estimated from time and energy budgets for breeding season only.

4 Estimated using equation 3-37 (Nagy, 1987) and body weights from Craighead and Craighead (1956).

5 Hawks maintained outdoors using falconer's techniques; fed lean raw beef supplemented with natural prey. Overal

Winter temperatures averaged 3 to 5�C and summer temperatures averaged 15�C during trials. Females weighed 1,

weighed 1,147 g; males in summer weighed 855 g. 

6 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Craighead and Craighead (1956).

7 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Craighead and Craighead (1956

8 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

Craighead (1956). 

9 Percent biomass (wet weight) estimated from observations of prey brought to the nest (identified to species) and re

nests, using standard wet weights for each species of prey from other studies or measured in the lab. 

10 Home range determined by 95 percent ellipse method; radio-tagged hawks, two of each sex. 

11 Estimated from figure. 

12 Summarizing data from several studies. 

13 Summarizing banding recoveries prior to 1951. 

14 Late departure dates. 

15 Early arrival dates. 
References (including Appendix) 

Adamcik, R. S.; Tood, A. W.; Keith, L. B. (1979) Demographic and dietary responses of 

red-tailed hawks during a snowshoe hare fluctuation. Can. Field-Nat. 93: 16-27. 

Andersen, D. E.; Rongstad, O. J. (1989) Home-range estimates of red-tailed hawks based 

on random and systematic relocations. J. Wildl. Manage. 53: 802-807. 

Baker, J. A.; Brooks, R. J. (1981) Distribution patterns of raptors in relation to density of 

meadow voles. Condor 83: 42-47. 

Bednarz, J. C.; Dinsmore, J. J. (1982) Nest-sites and habitat of red-shouldered and 

red-tailed hawks in Iowa. Wilson Bull. 94: 31-45. 

Bent, A. C. (1937) Life histories of North American birds of prey. Part 1: Order 

falconiformes. Washington, DC: U.S. Government Printing Office; Smithsonian Inst. 

U.S. Nat. Mus., Bull. 167. 

Bohall, P. G.; Collopy, M. W. (1984) Seasonal abundance, habitat use, and perch sites of 

four raptor species in north-central Florida. J. Field Ornithol. 55: 181-189. 

Bohm, R. T. (1978a) Observation of nest decoration and food habits of red-tailed hawks. 

Loon 50: 6-8. 

Bohm, R. T. (1978b) A study of nesting red-tailed hawks in central Minnesota. Loon 50: 

129-137. 

Bosakowski, T.; Smith, D. G. (1992) Comparative diets of sympatric nesting raptors in the 

eastern deciduous forest biome. Can. J. Zool 70: 984-992. 

Brown, L.; Amadon, D. (1968) Eagles, hawks, and falcons of the world: v. 1. New York, NY: 

McGraw-Hill. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Craighead, J. J.; Craighead, F. C. (1956) Hawks, owls and wildlife. Harrisburg, PA: The 

Stackpole Co. and Washington, DC: Wildl. Manage. Inst. 

Duke, G. E.; Evanson, O. A.; Jegers, A. A. (1976) Meal to pellet intervals in 14 species of 

captive raptors. Comp. Biochem. Physiol. 53A: 1-6. 

Duke, G. E.; Mauro, L.; Bird, D. M. (1987) Physiology. In: Pendleton, B. A.; Millsap, B. A.; 

Cline, K. W.; et al., eds. Raptor management techniques manual. Washington, DC: 

Institute for Wildlife Research, National Wildlife Federation; Sci. Tech. Ser. No. 10; 

pp. 262-267. 

2-87 Red-Tailed Hawk 
Fitch, H. S.; Swenson, F.; Tillotson, D. F. (1946) Behavior and food habits of the red-tailed 

hawk. Condor 48: 205-237. 

Gates, J. M. (1972) Red-tailed hawk populations and ecology in east-central Wisconsin. 

Wilson Bull. 84: 421-433. 

Gatz, T. A.; Hegdal, P. L. (1987) Local winter movements of four raptor species in central 

Colorado. West. Birds 17: 107-114. 

Hagar, D. C., Jr. (1957) Nesting populations of red-tailed hawks and horned owls in central 

New York state. Wilson Bull. 69: 263-272. 

Hardy, R. (1939) Nesting habits of the western red-tailed hawk. Condor 41: 79-80. 

Henny, C. J.; Wight, H. M. (1970) Population ecology and environmental pollution: red-tailed 

and Cooper's hawks. Symposium: Population ecology of migratory birds; Patuxent 

Wildlife Research Center; pp. 229-249. 

Henny, C. J.; Wight, H. M. (1972) Population ecology and environmental pollution: red-tailed 

and Cooper's hawks. U.S. Bur. Sport Fish. Wildl., Wildl. Res. Rep. 2: 229-250. 

Janes, S. W. (1984) Influences of territory composition and interspecific competition on 

red-tailed hawk reproductive success. Ecology 65: 862-870. 

Johnson, S. J. (1975) Productivity of the red-tailed hawk in southwestern Montana. Auk 92: 

732-736. 

Lasiewski, R. C.; Calder, W. A. (1971) A preliminary allometric analysis of respiratory 

variables in resting birds. Resp. Phys. 11: 152-166. 

Lasiewski, R. C.; Dawson, W. R. (1967). A reexamination of the relation between standard 

metabolic rate and body weight in birds. Condor 69: 12-23. 

Luttich, S. N.; Keith, L. B.; Stephenson, J. D. (1971) Population dynamics of the red-tailed 

hawk (Buteo jamaicensis) at Rochester, Alberta. Auk 88: 75-87. 

MacLaren, P. A.; Anderson, S. H.; Runde, D. E. (1988) Food habits and nest characteristics 

of breeding raptors in southwestern Wyoming. Great Basin Nat. 48: 548-553. 

Mader, W. J. (1978) A comparative nesting study of red-tailed hawks and Harris' hawks in 

southern Arizona. Auk 95: 327-337. 

McGovern, M.; McNurney, J. M. (1986) Densities of red-tailed hawk nests in aspen stands in 

the Piceance Basin, Colorado. Raptor Res. 20: 43-45. 

Meeh, K. (1879) Oberflachenmessungen des mensclichen Korpers. Z. Biol. 15: 426-458. 

2-88 Red-Tailed Hawk 
Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

National Geographic Society. (1987) Field guide to the birds of North America. Washington, 

DC: National Geographic Society. 

Nice, M. M. (1954) Problems of incubation periods in North American birds. Condor 56: 

173-197. 

Orians, G.; Kuhlman, J. (1956) The red-tailed hawk and great horned owl populations in 

Wisconsin. Condor 58: 371-385. 

Pakpahan, A. M.; Haufler, J. B.; Prince, H. H. (1989) Metabolic rates of red-tailed hawks and 

great horned owls. Condor 91: 1000-1002. 

Petersen, L. (1979) Ecology of great horned owls and red-tailed hawks in southeastern 

Wisconsin. Wisc. Dept. Nat. Resour. Tech. Bull. No. 111. 

Poole, E. L. (1938) Weights and wing areas in North American birds. Auk 55: 511-517. 

Preston, C. R. (1990) Distribution of raptor foraging in relation to prey biomass and habitat 

structure. Condor 92: 107-112. 

Rothfels, M.; Lein, M. R. (1983) Territoriality in sympatric populations of red-tailed and 

Swainson's hawks. Can. J. Zool. 61: 60-64. 

Rubner, M. (1883) Uber den Einfluss der Korpergrosse auf Stoff- und Kraftweschsel. Z. 

Biol. 19: 535-562. 

Smith, D. G.; Murphy, J. R. (1973) Breeding ecology of raptors in the eastern Great Basin of 

Utah. Brigham Young Univ. Sci. Bull., Biol. Ser. 18: 1-76. 

Soltz, R. L. (1984) Time and energy budgets of the red-tailed hawk (Buteo jamaicensis) in 

southern California. Southwest Nat. 29: 149-156. 

Springer, M. A.; Kirkley, J. S. (1978) Inter- and intraspecific interactions between red-tailed 

hawks and great horned owls in central Ohio. Ohio J. Sci. 78: 323-328. 

Springer, M. A.; Osborne, D. R. (1983) Analysis of growth of the red-tailed hawk (Buteo 

jamaicensis). Ohio J. Sci 83: 13-19. 

Steenhof, K. (1983) Prey weights for computing percent biomass in raptor diets. Raptor 

Res. 17: 15-27. 

Steenhof, K. (1987) Assessing raptor reproductive success and productivity. In: Giron 

Pendleton, B. A.; Millsap, B. A.; Cline, K. W., et al., eds. Raptor management 

techniques manual. Washington, DC: National Wildlife Federation; pp. 157-170. 

2-89 Red-Tailed Hawk 
Steenhof, K.; Kochert, M. N. (1985) Dietary shifts of sympatric buteos during a prey decline. 

Oecologia 66: 6-16. 

U. S. Department of Interior. (1979) Snake River birds of prey special research report. 

Boise, ID: Bureau of Land Management. 

Walsberg, G. E.; King, J. R. (1978) The relationship of the external surface area of birds to 

skin surface area and body mass. J. Exp. Biol. 76: 185-189. 

2-90 Red-Tailed Hawk 
2.1.7. Bald Eagle (eagles) 

Order Falconiformes, Family Accipitridae. Eagles have long rounded wings, large 

hooked bills, sharp talons, and are the largest birds of prey in the United States. They 

swoop down on their prey at high speeds, and their diet varies by species and 

considerably by habitat. In most species, the male is smaller than the female, but 

otherwise the sexes are similar in appearance. This family also includes kites and hawks. 

Selected species 

The bald eagle (Haliaeetus leucocephalus), our national symbol, is a federally 

designated endangered species. Relatively common in Alaska, populations in the lower 48 

States have been seriously diminished, although they are recovering in some areas. Bald 

eagles are most commonly sighted in coastal areas or near rivers or lakes. Bald eagles are 

primarily carrion feeders. 

Body size. Females are significantly larger than males, but otherwise the sexes 

look alike (Brown and Amadon, 1968). Body size increases with latitude and is the sole 

basis by which the northern and southern subspecies are divided (Snow, 1973). Length 

from bill tip to tail tip averages 81 cm in the more northerly populations. 

Habitat. Bald eagles generally are restricted to coastal areas, lakes, and rivers 

(Brown and Amadon, 1968), although some may winter in areas not associated with water 

(Platt, 1976). Preferred breeding sites include proximity to large bodies of open water and 

large nest trees with sturdy branches (often conifers) and areas of old-growth timber with 

an open and discontinuous canopy (Andrew and Mosher, 1982; Anthony et al., 1982; 

Grubb, 1980; Peterson, 1986). In an analysis of more than 200 nests, Grubb (1980) found 

55 percent within 46 m of a shoreline and 92 percent within 183 m of shore. During 

migration and in winter, conifers often are used for communal roosting both during the day 

and at night, perhaps to minimize heat loss (Anthony et al., 1982; Stalmaster, 1980). 

Mature trees with large open crowns and stout, horizontal perching limbs are preferred for 

roosting in general (Anthony et al., 1982; Chester et al., 1990). Bald eagles reach maximum 

densities in areas of minimal human activity and are almost never found in areas of heavy 

human use (Peterson, 1986). 

Food habits. Primarily carrion feeders, bald eagles eat dead or dying fish when 

available but also will catch live fish swimming near the surface or fish in shallow waters 

(Brown and Amadon, 1968). In general, bald eagles can be described as opportunistic 

feeders, taking advantage of whatever food source is most plentiful and easy to scavenge 

or to capture, including birds and mammals (Brown and Amadon, 1968; Green, 1985; 

Watson et al., 1991). In many areas, especially in winter, waterfowl, killed or injured by 

hunters, and shore birds are an important food source (Todd et al., 1982). Eagles forage in 

upland areas in the winter when surface waters are frozen over, consuming carrion 

including rabbits, squirrels, and dead domestic livestock such as pigs and chickens 

(Brown and Amadon, 1968; Harper et al., 1988). Bald eagles also have been known to steal 

food from other members of their own species as well as from hawks, osprey, gulls, and 

mergansers (Grubb, 1971; Jorde and Lingle, 1988; Sobkowiak and Titman, 1989). This 

2-91 Bald Eagle 
may occur when there is a shortage of a primary food source, such as fish, and an 

abundance of other prey such as waterfowl being used by other predatory birds (Jorde and 

Lingle, 1988). Some prey are important to a few populations; for example, in the 

Chesapeake Bay region, turtles are consumed during the breeding season (Clark, 1982), 

and at Amchitka Island in Alaska, sea otter pups are found regularly in bald eagle nests 

(Sherrod et al., 1975). In the Pacific Northwest during the breeding season, Watson et al. 

(1991) found that bald eagles hunted live prey 57 percent of the time, scavenged for 24 

percent of their prey, and pirated 19 percent (mostly from gulls or other eagles). Because 

bald eagles scavenge dead or dying prey, they are particularly vulnerable to environmental 

contaminants and pesticides (e.g., from feeding on birds that died from pesticides, 

consuming lead shot from waterfowl killed or disabled by hunters) (Henny and Anthony, 

1989; Harper et al., 1988; Lingle and Krapu, 1988). Bald eagles also are vulnerable to 

biomagnification of contaminants in food chains. For example, near Lake Superior (WI), 

herring gulls, which were consumed by over 20 percent of nesting bald eagle pairs, were 

found to be a significant source of DDE and PCB intake by the eagles (Kozie and Anderson, 

1991). The gulls contained higher contaminant levels than the local fish because of their 

higher trophic level. 

Molt. Adult eagles molt yearly. In northern populations, molting occurs from late 

spring to early fall; in southern populations, molting may be initiated earlier (McCollough, 

1989). It is likely that the molt is not complete, and that some feathers are retained for 2 

years. Young bald eagles generally molt into their adult plumage by their fifth year 

(McCollough, 1989). 

Migration. Bald eagles migrate out of areas where lakes are completely frozen over 

in winter, but will remain as far north as the availability of open water and a reliable food 

supply allow (Brown and Amadon, 1968). Areas with ice-free waterways, such as the 

Columbia River estuary in Washington and Oregon, may support both resident and 

migratory populations in the winter (Watson et al., 1991). The far northern breeding 

populations migrate south for the winter and often congregate in areas with abundant food, 

particularly the Mississippi Valley and the northwestern States (Snow, 1973). Some 

populations of eagles that breed in southern latitudes (e.g., Arizona, Florida) show a 

reverse migration and migrate north in midsummer (following breeding), returning south in 

early autumn or winter (Brown and Amadon, 1968; Grubb et al., 1983). 

Breeding activities and social organization. Bald eagles have been observed to 

nest successfully at 4 years of age, but most do not breed until at least their fifth year (Nye, 

1983). Breeding pairs remain together as long as both are alive (Brown and Amadon, 

1968). Large stick nests (approximately 1.5 m across and 0.6 m deep) are built near water 

and most often in a large tree, but sometimes on rocky outcrops or even on the ground on 

some islands (Brown and Amadon, 1968; Grubb, 1980). In the absence of disturbance, the 

same nest site may be used for many years (Nash et al., 1980). In Florida, eggs are laid in 

late autumn or winter, while over the rest of the eagle's range, mating and egg laying occur 

in spring (Brown and Amadon, 1968). Clutch sizes are larger in the north, and both sexes 

take responsibility for feeding the young (Brown and Amadon, 1968). Young fledge at 

about 10 to 12 weeks of age; after leaving the nest, they are still dependent on their parents 

for several weeks and often return to the nest for food (Sprunt et al., 1973). After nesting, 

large groups will often gather at sites with plentiful food 

2-92 Bald Eagle 
�

resources, such as along rivers following a salmon spawn (Fitzner and Hanson, 1979; 

Keister et al., 1987; McClelland, 1973). 

Home range and resources. During the breeding season, eagles require large areas 

in the vicinity of open water, with an adequate supply of nesting trees (Brown and Amadon, 

1968). Distance from human disturbance is an important factor in nest site selection, and 

nests have been reported to fail as a result of disturbance (Andrew and Mosher, 1982). 

During incubation and brooding, eagles show territorial defense of an area around the nest 

site. Following fledging, there is little need for nest defense, and eagles are opportunistic 

in their search for abundant sources of prey (Mahaffy and Frenzel, 1987). During winter, 

eagles roost communally in large aggregations and share a foraging home range. For 

example, Opp (1980) described a population of 150 eagles that fed on meadow voles in a 

250-ha flooded field for a 4-week period. This group also established a communal night 

roost in the vicinity. 

Population density. Because population density depends strongly on the 

configuration of the surface water bodies used for foraging, few investigators have 

published explicit density estimates on an area basis; most report breeding densities along 

a shoreline on a linear basis. During the breeding season, 0.03 to 0.4 pairs have been 

recorded per km shore (see table). Eagles migrating south from their summer territories in 

Canada have aggregated in communal roosts of up to 400 eagles in a 40-ha area 

(Crenshaw and McClelland, 1989). In the winter, communal roost sites may also contain 

large numbers of eagles. Opp (1980) described a group of 150 eagles that roosted and 

foraged together in the Klamath Basin (OR/CA), and communal night roosts of up to 300 

eagles in Oregon in late winter. 

Population dynamics. Not all adults in an area are part of the breeding population. 

Some pairs may establish territories and not breed, while others may not even pair. The 

percentage of adults breeding and the breeding success of those that do vary with local 

food abundance, weather, and habitat conditions (Hansen, 1987; Hansen and Hodges, 

1985; McAllister et al., 1986). In past years, bioaccumulation of organochlorine pollutants 

reduced the reproductive success of bald eagles. Now, in many areas, these raptors are 

reproducing at rates similar to those prior to the widespread use of these pesticides 

(Green, 1985). Eagles lay one clutch per year, although replacement clutches may be laid 

upon loss of the initial one (Sherrod et al., 1987). Very little is known about mortality rates 

of bald eagles; Grier (1980) concluded from population models that adult survival is more 

important than reproductive rate to the continued success of bald eagle populations. In 

captivity, bald eagles have lived for up to 50 years (Snow, 1973), and one wild eagle, 

banded and recaptured in Alaska, was estimated to be almost 22 years old (Cain, 1986). 

Upon loss of an initial clutch, bald eagles may lay replacement clutches if sufficient time 

remains (Sherrod et al., 1987). 

Similar species (from general references) 

� The golden eagle (Aquila chrysaetos) is similar in size (81 cm) to the bald 

eagle, and its range encompasses all but the southeastern United States. 

Small mammals, snakes, birds, and carrion are primary prey items, and 

golden eagles prefer mountainous or hilly terrain. 

2-93 Bald Eagle 
General references 

Brown and Amadon (1968); Green (1985); Peterson (1986); Stalmaster and 

Gessaman (1982, 1984). 

2-94 Bald Eagle 
Bald Eagle (Haliaeetus leucocephalus) 

Factors 

Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referen

Body Weight (g) J F summer 5,089 4,359 - 5,756 Alaska Imler & 

J M summer 4,014 3,524 - 4,568 

A F 4,500 Florida Wiemey

A M 3,000 egg 120.6 ± 8.2 SD 108 - 134 Wisconsin Krantz 

egg 102.5 ± 17.9 SD 71 - 125 Florida 

at hatching 91.5 ± 5.2 SD Saskatchewan, Canada 

nestlings: Bortolo

M 10 days 500 (est.) Saskatchewan, Canada 

M 30 days 2,700 (est.) M 50 days 3,600 (est.) M 60 days 4,066 ± 35.1 SE 3,575 - 4,500 

F 10 days 500 (est.) Saskatchewan, Canada 

F 30 days 3,000 (est.) 

F 50 days 4,600 (est.) 

F 60 days 5,172 ± 46.5 SE 4,800 - 5,600 

Krantz Bortolo

Bortolo

Metabolic Rate free-living Connecticut Craig e

(kcal/kg-day) A winter 99 

J winter 111 

A F free-living 135 (62 - 290) estimat

A M free-living 143 (66 - 307) 

2-95 Bald Eagle 
Bald Eagle (Haliaeetus leucocephalus) 

Factors 

Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referen

Food Ingestion winter: 

Rate (g/g-day) B B salmon 0.092 ± 0.026 SD Utah (captive) Stalma

B B rabbit 0.075 ± 0.013 SD 

B B duck 0.065 ± 0.012 SD 

A B 0.12 Washington (free-flying) Stalmas

subadult B 0.10 

juvenile B 0.091 

A B 0.12 Connecticut (free-flying) Craig e

juvenile B 0.14 

Water Ingestion A F 0.035 estimat

Rate (g/g-day) A M 0.037 

Inhalation A F 1.43 estimat

Rate (m /day) A M 1.19 3 

Surface Area A F 2,970 estimat

(cm ) A M 2,530 2 

Dietary Composition Spring Summer Fall Winter (measure) Refere

Location/Habitat 

mallard 32 Washington/river Fitzne

American widgeon 9 

American coot 9 (% biomass; prey remains 

other birds 3 found below communal 

Chinook salmon 21 roost) 

sucker 4 

European carp 1 

other fish 1 

unaccounted 20 

2-96 Bald Eagle 
Bald Eagle (Haliaeetus leucocephalus) 

Dietary Composition Spring Summer Fall Winter (measure) Refere

Location/Habitat 

brown bullhead 24.8 Maine/inland river Todd 

white sucker 19.5 

chain pickerel 20.1 (% occurrence in pellets) 

smallmouth bass 3.8 

white perch 3.6 samples from all seasons 

other fish 4.9 except winter 

black duck 3.0 

other birds 13.5 

mammals 6.8 

(fish) (57.6) central Arizona/desert Haywo

channel catfish 21.8 scrub, riparian 

Sonora sucker 8.6 

carp 17.3 (% biomass; prey observed 

other fish 8.5 brought to nest or found at 

(birds) (14.1) nests) 

American coot 8.1 

great blue heron 4.4 

(mammals) (28.1) 

desert cottontail 8.1 

jackrabbit 14.9 

rock squirrel 1.1 

(reptiles) (0.2) 

pink salmon 15.5 Alaska/coastal Ofelt, 

herring 32.0 

trout 4.5 (% frequency of occurrence; 

other fish 24.0 prey observed brought to 

other animals 24.0 the nest) 

2-97 Bald Eagle 
Bald Eagle (Haliaeetus leucocephalus) 

Population 

Dynamics 

Age/Sex Cond./Seas. Mean Range Location/Habitat Referen

Territory Area pair spring 3,494 ± 2,520 SD 1,821 - 6,392 Arizona/desert, riparian river Haywoo

(ha) Territory pair 3.5 1.4 - 7.2 Washington/SJ Islands; Grubb, 

Length (km) pair 15.8 11.1 - 26.6 Grays Harbor 

Territory pair incubat. 0.56 ± 0.18 SE Minnesota/lake, woods Mahaffy 

Radius (km) pair brooding 0.72 ± 0.21 SE 

Winter Home J B winter 1,830 ± 1,460 SD Missouri/lake Griffin & 

Range (ha) A B winter 1,880 ± 900 SD 

Foraging B B winter 3 to 7 Connecticut/river Craig e

Distance (km) 

Population summer 0.38 se Alaska/riverine Hansen

Density (pair/km summer WY, ID, MT/: Swenso

shore) 0.035 Yellowstone 

0.026 Continental 

0.045 Snake 

Clutch 2 1 - 3 NS/NS Brown 

Size 2.3 1 - 4 PA, DE, MD, NJ Schmid

Clutches/Yea 1 NS/NS Sherrod 

r Days 35 34 - 38 Maryland (captive) Maestre

Incubation 

Age at M 79.9 ± 1.08 SE Saskatchewan/lake Bortolo

Fledging F 83.0 ± 0.94 SE 

(days) Number 1.01 0.58 - 1.22/10 yr California/NS Henny 

Fledge per 1.28 1.07 - 1.58/9 yr Montana/NS Henny 

Active Nest 0.90 0.76 - 1.14/7 yr Washington/NS Henny 

1.14 Florida/NS McEwa

1.00 ± 0.06 SE 0 - 3 Alaska/NS Sprunt 

2-98 Bald Eagle 
Bald Eagle (Haliaeetus leucocephalus) 

2-99 Bald Eagle 

Population 

Dynamics 

Age/Sex Cond./Seas. Mean Range Location/Habitat Referen

Number 1.65 ± 0.26 SD Arizona/desert scrub, river Grubb e

Fledge per 1.35 ± 0.11 SD 1.22 - 1.48/6 yr Washington/San Juan Island Grubb 

Successful 2.2 1 - 3 PA, DE, MD, NJ/NS Schmid

Nest 1.64 ID, MT, WY/river, lake Swenso

Age at B 4 3 - 5 United States/NS Nye, 19

Sexual Maturity Annual A B 5.4 Alaska/Amchitka Island Sherrod 

Mortality fledging to 1 yr 89.3 

(percent) 

Longevity A B up to 50 yrs captivity Snow, 1

Seasonal 

Activity Begin Peak End Location Referen

Mating/Layin late September November Florida, Texas Mager, 

g December late December late January Arizona Grubb 

late October March se United States USFWS

February late March late April MD, VA, DE LeFran

early March early April WY, MT, ID Swenso

late March Vancouver BC Brown 

Fledging April May s Louisiana Harris e

early July late July mid-August WY, MT, ID Swens

late August se Alaska Hansen

Fall Migration June Arizona Grubb 

early October November mid-December Montana Crensh

late October 1989 November December January se Alaska Hodges 

December/January sc Oregon, n California Keister 

Spring December Arizona Grubb 

Migration April sc Oregon, n California Keister 

late March early April WY, MT, ID Swenso

early March Illinois Sabine
Bald Eagle (Haliaeetus leucocephalus) 

1 Cited in Maestrelli and Wiemeyer (1975) and Bortolotti (1984a); juveniles up to 3 years of age.

2 Estimated from Figure 4.

3 Daily energy budget for free-living eagles based on time-activity budgets and metabolic models; assuming 4.5 kg ea

4 Estimated using equation 3-37 (Nagy, 1987) and body weights from Imler and Kalmbach (1955).

5 Estimated from observed captures of preweighed salmon provided at feeding stations. Eagle body weight assumed 

may have occurred elsewhere. 

6 Estimate of food consumed based on observed feeding behaviors and an eagle body weight of 4.5 kg. 

7 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Imler and Kalmbach (1955). 

8 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Imler and Kalmbach (1955). 

9 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

(1955). 

10 Cited in Green, 1985. 

2-100 Bald Eagle 
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2-102 Bald Eagle 
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2-103 Bald Eagle 
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2-106 Bald Eagle 
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2-107 Bald Eagle 
2.1.8. American Kestrel (falcons) 

Order Falconiformes, Family Falconidae. Falcons are the more streamlined of the 

raptor species, with long pointed wings bent back at the wrists and large tails that taper at 

the tips. They consume many kinds of animals including insects, reptiles, small mammals, 

and birds. Falcons are found in a variety of habitats, from cities to the most remote areas. 

Strong fliers that achieve high speeds, falcons range in size from the American kestrel (27 

cm bill tip to tail tip) to the peregrine falcon (41 to 51 cm). 

Selected species 

The American kestrel (Falco sparverius), or sparrow hawk, is the most common 

falcon in open and semi-open areas throughout North America. There are three recognized 

subspecies: F. s. paulus (year-round resident from South Carolina to Florida and southern 

Alabama), F. s. peninsularis (year-round resident of southern Baja California), and F. s. 

sparverius (widespread and migratory) (Bohall-Wood and Collopy, 1986). Predators of the 

kestrel include large raptors such as great horned owls, golden eagles, and red-tailed 

hawks (Meyer and Balgooyen, 1987). 

Body size. Weighing slightly over one tenth of a kilogram, the kestrel is the 

smallest falcon native to the United States (Brown and Amadon, 1968). As for most 

raptors, females are 10 to 20 percent larger than males (Bloom, 1973; Craighead and 

Craighead, 1956). Kestrel body weights vary seasonally, with maximum weight (and fat 

deposits) being achieved in winter and minimum weights in summer (Bloom, 1973; 

Gessaman and Haggas, 1987). 

Habitat. Kestrels inhabit open deserts, semi-open areas, the edges of groves 

(Brown and Amadon, 1968), and even cities (National Geographic Society, 1987). In several 

areas, investigators have found that male kestrels tend to use woodland openings and 

edges, while females tend to utilize more open areas characterized by short or sparse 

ground vegetation, particularly during the winter (Koplin, 1973, cited in Mills, 1976; Meyer 

and Balgooyen, 1987; Mills, 1975, 1976; Smallwood, 1987). In other areas, however, 

investigators have found no such differentiation (Toland, 1987; Sferra, 1984). In Florida, 

kestrels appear to prefer sandhill communities (particularly pine/oak woodlands); these 

areas provide high-quality foraging habitat and the majority of available nest sites (BohallWood and Collopy, 1986). Kestrels are more likely to use habitats close to centers of 

human activities than are most other raptors (Fischer et al., 1984). 

Food habits. Kestrels prey on a variety of small animals including invertebrates 

such as worms, spiders, scorpions, beetles, other large insects, amphibians and reptiles 

such as frogs, lizards, and snakes, and a wide variety of small- to medium-sized birds and 

mammals (Brown and Amadon, 1968; Mueller, 1987). Large insects, such as grasshoppers, 

are the kestrels' primary summer prey, although in their absence kestrels will switch to 

small mammals (Collopy, 1973) and birds (Brown and Amadon, 1968). In winter, small 

mammals and birds comprise most of the diet (Collopy and Koplin, 1983; Koplin et al., 

1980). Kestrels usually cache their vertebrate prey, often in clumps of grass or in tree 

limbs and holes, to be retrieved later (Collopy, 1977; Mueller, 1987; Rudolph, 1982; Toland, 

2-109 American Kestrel 
1984). Invertebrate prey usually are eaten immediately (Rudolph, 1982). In Florida, where 

small mammals are scarce and reptiles are abundant, lizards are an important component 

of the diet (Bohall-Wood and Collopy, 1987). Kestrels forage by three different techniques: 

using open perches from which to spot and attack ground prey, hovering in the air to spot 

ground prey, and catching insects on the wing (Rudolph, 1982, 1983). 

Molt. Females begin their molt during incubation and complete it by the end of the 

breeding season. Males, who are responsible for capturing most of the prey for the family, 

do not begin their molt until near the end of the breeding season (Smallwood, 1988). 

Migration. The American kestrel is a year-round resident over most of the United 

States, but is migratory over the northern-most portions of its range (National Geographic 

Society, 1987). Because of their late molt, males migrate and arrive at the wintering 

grounds later than females or immatures (Smallwood, 1988). 

Breeding activities and social organization. Adult kestrels are solitary, except 

during the breeding season, and maintain territories even in winter (Brown and Amadon, 

1968). Kestrels typically build their nests in tree cavities, but have used holes in telephone 

poles, buildings, or stream banks when tree cavities are not available (Brown and Amadon, 

1968). Both parents participate in incubation, but the female performs most of the 

incubation, while the male provides her with food (Brown and Amadon, 1968). Following 

hatching, the male brings the majority of the prey to the nestlings (Brown and Amadon, 

1968). After fledging, young kestrels remain dependent on their parents for food for at 

least 2 to 4 additional weeks (Lett and Bird, 1987). Fledglings often perch and socialize 

with their siblings prior to dispersal (Lett and Bird, 1987). In Florida, resident kestrels 

(paulus subspecies) maintain year-round pair bonds and joint territories. The resident 

pairs have a competitive advantage over winter migrants (sparverius subspecies) in their 

territories (Bohall-Wood and Collopy, 1986). 

Home range and resources. Although some investigators have not noted territorial 

defense (e.g., Craighead and Craighead, 1956), Mills (1975) demonstrated that kestrels 

defend territories by introducing captured birds into other birds' territories. Winter 

foraging territories range from a few hectares in productive areas (e.g., in California) 

(Meyer and Balgooyen, 1987) to hundreds of hectares in less productive areas (e.g., Illinois, 

Michigan) (Craighead and Craighead, 1956; Mills, 1975). Summer breeding territories 

probably follow the same pattern (Craighead and Craighead, 1956). 

Population density. Although much smaller than red-tailed hawks and bald eagles, 

reported kestrel breeding population densities can be similarly low (e.g., 0.0003 to 0.004 

nests per hectare; see table). 

Population dynamics. Kestrels are sexually mature in the first breeding season 

after their birth (Carpenter et al., 1987). Scarcity of suitable nesting cavities probably limits 

the size of kestrel populations in parts of the United States (Cade, 1982). Three to four 

young may fledge per nest per year, but mortality of juveniles in the first year is high (60 to 

90 percent) (Craighead and Craighead, 1956; Henny, 1972). Adult mortality can be low 

(e.g., 12 percent per year) (Craighead and Craighead, 1956). 

2-110 American Kestrel 
�

�

�

Similar species (from general references) 

� The peregrine falcon (Falco peregrinus), a rare resident of woods, 

mountains, and coasts, preys almost exclusively on birds. Though 

uncommon, they can be found wintering in most states, but rarely breeding. 

These large falcons (38 cm) have been reintroduced in some areas in the 

United States and have nested in urban environments. 

� The merlin (Falco columbarius), larger (30 cm) than the kestrel, can be found 

in a variety of habitats but nests in open woods or wooded prairies. 

Wintering along coasts and near cities of the Great Plains, it primarily eats 

birds. 

� The prairie falcon (Falco mexicanus) also is larger (39 to 50 cm) than the 

kestrel and inhabits dry, open country and prairies. A year-round resident of 

the western United States, prairie falcons prey chiefly on birds and small 

mammals. 

General references 

Cade (1982); Craighead and Craighead (1956); National Geographic Society (1987); 

Brown and Amadon (1968). 

2-111 American Kestrel 
American Kestrel (Falco sparverius) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Refere

Body Weight F fall 115 ± 8.6 SD California, Imperial Valley Bloom

(g) F winter 132 ± 13 SD 

M fall 103 ± 6.7 SD California, Imperial Valley Bloom

M winter 114 ± 7.8 SD 

F laying/inc. 124 Utah Gessa

F fall 127 

F winter 138 

M incubate 108 Utah Gessa

M fall 111 

M winter 119 

Metabolic F laying/inc. 414.4 ± 9.84 SE Utah (free-living) Gessa

Rate F fall 368.7 ± 17.0 SE 

(kcal/kg-day) F winter 327.2 ± 5.72 SE 

M incubate 337.6 ± 16.8 SE Utah (free-living) Gessa

M fall 364.9 ± 26.9 SE 

M winter 386.4 ± 9.41 SE 

A F basal 134 estima

A M basal 140 

A F free-living 333 (157 - 706) estima

A M free-living 345 (162 - 733) 

Food A B winter 0.29 nw California (free-living) Koplin 

Ingestion Rate (vert. prey) (0.18) 

(g/g-day) (invert. prey) (0.11) 

A M summer 0.31 Ohio (seminatural Barret

enclosure) 

Water A F 0.11 estima

Ingestion A M 0.12 Rate (g/g-day) 

2-112 American Kestrel 
American Kestrel (Falco sparverius) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Refere

Inhalation A F 0.089 estima

Rate (m /day) A M 0.079 3 

Surface Area A F 267 estima(cm ) A M 242 2 

Dietary Composition Spring Summer Fall Winter (measure) Refere

Location/Habitat 

invertebrates 32.6 California/open areas, woods Meyer 

mammals 31.7 

birds 30.3 (% wet weight of prey 

reptiles 1.9 observed captured) 

other 3.5 

vertebrates 49 Florida/dry pine-oak Bohal

(primarily lizards) woodlands (sandhill) 1987 

invertebrates 

(% wet weight of prey observed 

captured) 

Coleoptera 10.8 California/hayfields, pasture Collop

other invertebrates 14.2 

frogs (Rana aurora) 8.0 (% wet weight of prey 

other herpetofauna 12.2 observed captured) 

Microtus californicus 

Sorex vagrans 

other mammals 

30.2 

9.4 

11.5 

51 

2-113 American Kestrel 
American Kestrel (Falco sparverius) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Location/Habitat Re

Territory A F winter 31.6 ± 10.7 SD 18.7 - 42.0 California/open areas, Me

Size (ha) A M winter 13.1 ± 2.0 SD 9.7 - 14.8 woods 19

A B winter 154 < 452 

A B summer 202 ± 131 SD 41 - 500 Wyoming/grasslands, Cr

A B summer 131 ± 100 SD 21 - 215 Michigan/woodlots, fields Cr

Illinois/agricultural area Mi

forests 

19

Population pairs 0.0026 nests/ha 0.0023 - 0.0031 Missouri/urban To

Density summer 0.0004 nests/ha 0.0003 - 0.0006 Missouri/rural To

pairs 

summer 0.0035 pairs/ha Wyoming/grasslands, forest Cr

pairs birds/ha: 

summer 0.0007 ± 0.00004 SD 0.0005 - 0.0012 s Michigan/fields, woodlots Cr

B B fall A B winter A B spring 

0.0005 ± 0.0001 0.0005 - 0.0006 19

0.0010 ± 0.0002 0.0008 - 0.0011 

19

Clutch 4.3 California/juniper, Blo

Size sagebrush 

4 to 5 3 - 7 NS/NS Br

Clutches/Year 1 Quebec, Canada/captive Ca

Days 33.7 ± 0.33 SE 33 - 35 Maryland/captive Po

Incubation Br

29 to 30 NS/NS 

Age at 27.4 days 26 - 30 days Maryland/captive Po

Fledging 

Range 

19

SD SD 

2-114 American Kestrel 
American Kestrel (Falco sparverius) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Location/Habitat Re

Number 3.1 California/juniper, Blo

Fledge per sagebrush Active Nest 3.8 Wyoming/grasslands, forest Cr

19

Number 3.7 California/juniper, Blo

Fledge per sagebrush 

Successful Nest Age at Sexual B 1 yr Quebec, Canada/captive Ca

Maturity Annual A B 12 s Michigan, Wyoming/ Cr

Mortality J B 88 open areas, woods 19

(percent) 

A B 46.0 ± 4.6 SE North America/NS He

J B 60.7 

Longevity up to 9 yrs Quebec, Canada/captive Ca

Seasonal 

Activity Begin Peak End Location Ref

Mating/ early May late May late June California Blo

Laying mid-April early June central US Bro

early April mid-May northern Utah Ges

mid-March early June Florida Bro

198

Hatching early June late June late July California Blo

early May mid-June northern Utah Ges

early May central Missouri Tola

198

Molt mid-May mid-September northern Utah Ges

198

Range 

2-115 American Kestrel 
American Kestrel (Falco sparverius) 

Seasonal 

Activity Begin Peak End Location Ref

Migration fall early early November northern Utah Ges

spring early March south Michigan Cra

September 198

mid-April Wyoming Cra

195195

1 Investigators estimated values from time-activity budget studies of kestrels in the field and rates of energy expendit

measured in the laboratory. 

2 Estimated using equation 3-28 (Lasiewski and Dawson, 1967) and body weights from winter measurements by Gess

3 Estimated using equation 3-37 (Nagy, 1987) and body weights from winter measurements by Gessaman and Haggas 

4 Authors observed prey captured daily, and estimated total wet-weight prey intake using measured or reported weigh

estimated weights for unidentifiable invertebrate prey (also, assumed kestrel weighed 119 g). Also, see Chapters 3 estimating food ingestion rates. 

5 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from winter measurements by Gessaman 

6 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from winter measurements by Gessa

7 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, cited in Walsberg and King, 1978) and body weights f

Gessaman and Haggas (1987). 

2-116 American Kestrel 
References (including Appendix) 

Barrett, G. W.; Mackey, C. V. (1975) Prey selection and caloric ingestion rate of captive 

American kestrels. Wilson Bull. 87: 514-519. 

Bird, D. M.; Clark, R. G. (1983) Growth of body components in parent- and hand-reared 

captive kestrels. Raptor Res. 17: 77-84. 

Bloom, P. H. (1973) Seasonal variation in body weight of sparrow hawks in California. 

Western Bird Bander 48: 17-19. 

Bloom, P. H.; Hawks, S. J. (1983) Nest box use and reproductive biology of the American 

kestrel in Lassen County, California. Raptor Res. 17: 9-14. 

Bohall-Wood, P.; Collopy, M. W. (1986) Abundance and habitat selection of two American 

kestrel subspecies in north-central Florida. Auk 103: 557-563. 

Bohall-Wood, P. G.; Collopy, M. W. (1987) Foraging behavior of southeastern American 

kestrels in relation to habitat use. Raptor Res. 6: 58-65. 

Brown, L.; Amadon, D. (1968) Eagles, hawks, and falcons of the world. New York, NY: 

McGraw Hill Book Co. 

Cade, T. J. (1982) The falcons of the world. Ithaca, NY: Cornell University Press. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Carpenter, J. W.; Gabel, R. R.; Wiemeyer, S. N.; et al. (1987) Captive breeding. In: 

Pendleton, B. A.; Millsap, B. A.; Cline, K. W.; et al., eds. Raptor management 

techniques manual. Washington, DC: National Wildlife Federation; pp. 350-355. 

Collopy, M. W. (1973) Predatory efficiency of American kestrels wintering in northwestern 

Califonia. Raptor Res. 7: 25-31. 

Collopy, M. W. (1977) Food caching by female American kestrels in winter. Condor 79: 

63-68. 

Collopy, M. W.; Koplin, J. R. (1983) Diet, capture success, and mode of hunting by female 

American kestrels in winter. Condor 85: 369-371. 

Craighead, J. J.; Craighead, F. C. (1956) Hawks, owls and wildlife. Harrisburg, PA: The 

Stackpole Co. and Washington, DC: Wildlife Management Institute. 

Duke, G. E.; Evanson, O. A.; Jegers, A. A. (1976) Meal to pellet intervals in 14 species of 

captive raptors. Comp. Biochem. Physiol. 53A: 1-6. 

2-117 American Kestrel 
Duke, G. E.; Mauro, L.; Bird, D. M. (1987) Physiology. In: Pendleton, B. A.; Millsap, B. A.; 

Cline, K. W.; et al., eds. Raptor management techniques manual. Washington, DC: 

Institute for Wildlife Research, National Wildlife Federation; Sci. Tech. Ser. No. 10; 

pp. 262-267. 

Enderson, J. H. (1960) A population study of the sparrow hawk in east-central Illinois. 

Wilson Bull. 72: 222-231. 

Fischer, D. L.; Ellis, K. L.; Meese, R. J. (1984) Winter habitat selection of diurnal raptors in 

central Utah. Raptor Res. 18: 98-102. 

Gessaman, J. A. (1979) Premigratory fat in the American kestrel. Wilson Bull. 91: 625-262. 

Gessaman, J. A.; Haggas, L. (1987) Energetics of the American kestrel in northern Utah. 

Raptor Res. 6: 137-144. 

Henny, C. J. (1972) An analysis of the population dynamics of selected avian species with 

special reference to changes during the modern pesticide era. Washington, DC: Bur. 

Sport. Fish. Wildl.; Wildl. Res. Rep. 1. 

King, J. R. (1974) Seasonal allocation of time and energy resources in birds. In: Paynter, R. 

A., Jr., ed. Avian energetics. Cambridge, MA: Nuttall Ornithol. Club; pp. 4-70. 

Koplin, J. R. (1973) Differential habitat use by sexes of American kestrels wintering in 

northern California. Raptor Res. 7: 39-42. 

Koplin, J. R.; Collopy, M. W.; Bammann, A. R.; et al. (1980) Energetics of two wintering 

raptors. Auk 97: 795-806. 

Lasiewski, R. C.; Calder, W. A. (1971) A preliminary allometric analysis of respiratory 

variables in resting birds. Resp. Phys. 11: 152-166. 

Lasiewski, R. C.; Dawson, W. R. (1967). A reexamination of the relation between standard 

metabolic rate and body weight in birds. Condor 69: 12-23. 

Lett, D. W.; Bird, D. M. (1987) Postfledging behavior of American kestrels in southwestern 

Quebec. Wilson Bull. 99: 77-82. 

Meeh, K. (1879) Oberflachenmessungen des mensclichen Korpers. Z. Biol. 15: 426-458. 

Meyer, R. L.; Balgooyen, T. G. (1987) A study and implications of habitat separation by sex 

of wintering American kestrels (Falco sparverius L.). Raptor Res. 6: 107-123. 

Mills, G. S. (1975) A winter population study of the American kestrel in central Ohio. Wilson 

Bull. 87: 241-247. 

Mills, G. S. (1976) American kestrel sex ratios and habitat separation. Auk 93: 740-748. 

2-118 American Kestrel 
Mueller, H. C. (1987) Prey selection by kestrels: a review. Raptor Res. 6: 83-106. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

National Geographic Society. (1987) Field guide to the birds of North America. Washington, 

DC: National Geographic Society. 

Porter, R. D.; Wiemeyer, S. N. (1972) Reproductive patterns in captive American kestrels 

(sparrow hawks). Condor 74: 46-53. 

Rubner, M. (1883) Uber den Einfluss der Korpergrosse auf Stoff- und Kraftweschsel. Z. 

Biol. 19: 535-562. 

Rudolph, S. G. (1982) Foraging strategies of American kestrels during breeding. Ecology 

63: 1268-1276. 

Rudolph, S. G. (1983) Aerial insect-catching by American kestrels. Condor 85: 368-369. 

Sferra, N. J. (1984) Habitat selection by the American kestrel (Falco sparverius) and 

red-tailed hawk (Buteo jamaicensis) wintering in Madison County, Kentucky. Raptor 

Res. 18: 148-150. 

Smallwood, J. A. (1987) Sexual segregation by habitat in American kestrels wintering in 

southcentral Florida: vegetative structure and responses to differential prey 

availability. Condor 89: 842-849. 

Smallwood, J. A. (1988) A mechanism of sexual segregation by habitat by American 

kestrels (Falco sparverius) wintering in south-central Florida. Auk 105: 36-46. 

Sparrowe, R. D. (1972) Prey-catching behavior in the sparrow hawk. J. Wildl. Manage. 36: 

279-308. 

Toland, B. R. (1984) Unusual predatory and caching behavior of American kestrels in 

central Missouri. Raptor Res. 18: 107-110. 

Toland, B. R. (1987) The effect of vegetative cover on foraging strategies, hunting success 

and nesting distribution of American kestrels in central Missouri. Raptor Res. 21: 

14-20. 

Toland, B. R.; Elder, W. H. (1987) Influence of nest-box placement and density on 

abundance and productivity of American kestrels in central Missouri. Wilson Bull. 

99: 712-717. 

Walsberg, G. E.; King, J. R. (1978) The relationship of the external surface area of birds to 

skin surface area and body mass. J. Exp. Biol. 76: 185-189. 

Wing, L.; Wing, A. H. (1939) Food consumption of a sparrow hawk. Condor 41: 168-170. 

2-119 American Kestrel 
Zar, J. H. (1968) Standard metabolism comparisons between orders of birds. Condor 70: 

278. 

Zar, J. H. (1969) The use of the allometric model for avian standard metabolism - body 

weight relationships. Comp. Biochem. Physiol. 29: 227-234. 

2-120 American Kestrel 
2.1.9. Northern Bobwhite (quail) 

Order Galliformes, Family Phasiadinae. Quail are ground-dwelling birds with short, 

heavy bills adapted for foraging on the ground for seeds and insects. Most species inhabit 

brush, abandoned fields, and open woodlands; some inhabit parklands. Quail and most 

other gallinaceous birds are poor flyers that seldom leave the ground and do not migrate. 

All species of this family gather in coveys (i.e., flocks of varying size) during some part of 

the year. Quail range in size from Montezuma's quail (22 cm bill tip to tail tip) to the 

mountain and Gambel's quail (28 cm); sexes are similar in size but differ in appearance. 

Selected species 

The northern bobwhite (Colinus virginianus) feeds mainly on seeds by gleaning on 

the ground and low vegetation. It ranges from southeastern Wyoming, east to southern 

Minnesota and across to southern Maine, south through the central and eastern United 

States to eastern New Mexico in the west and to Florida in the east (American 

Ornithologists' Union, 1983). It is the most widespread of the North American quail and 

used to be very common, particularly east of the Rocky Mountains. Over the past three 

decades, however, populations have been declining throughout its range (Brennan, 1991). 

Body size. Northern bobwhite are average-sized quail (25 cm). Wild bobwhites 

typically weigh between 150 and 200 g depending on location and season (see table), while 

commercially bred stock usually exceed 200 g and may reach 300 g or more (Brenner and 

Reeder, 1985; Koerth and Guthery, 1991). Males and females are similar in size, and 

weights tend to increase with latitude and toward the west coast of the United States 

(Hamilton, 1957; Rosene, 1969; Roseberry and Klimstra, 1971). Females are heaviest in the 

spring and summer when they are laying eggs; males are lightest at this time of year 

(Hamilton, 1957; Roseberry and Klimstra, 1971). Juveniles tend to weigh slightly less than 

adults through winter (Hamilton, 1957; Roseberry and Klimstra, 1971). Koerth and Guthery 

(1987) found both males and females to maintain between 9 and 11 percent body fat (as a 

percentage of dry body weight) throughout the year in southern Texas; more northern 

populations may maintain higher body fat ratios, particularly just prior to breeding (McRae 

and Dimmick, 1982). 

Habitat. During the breeding season, grasslands, idle fields, and pastures are the 

preferred nesting habitat, and bobwhite often nest in large clumps of grasses (Roseberry 

and Klimstra, 1984). Shade, open herbaceous cover, and green and growing vegetation are 

required for suitable nest sites (Lehmann, 1984). Bobwhites forage in areas with open 

vegetation, some bare ground, and light litter (Stoddard, 1931). Nearby dry powdery soils 

are important for dust bathing (Johnsgard, 1988). Shrubby thickets up to 2 m high are 

used for cover during midday (Schroeder, 1985). Although their range is extensive, 

northern bobwhite reproduce poorly in the arid western portions of their range and during 

droughts elsewhere (Schroeder, 1985). During the winter, they require wooded cover with 

understory for daytime cover, preferably adjacent to open fields for foraging (Yoho and 

Dimmick, 1972). They tend to roost at night in more open habitats with short and sparse 

vegetation (Schroeder, 1985). In the more northern latitudes, cover and food can be limited 

during the winter (Rosene, 1969). Changes in land use, primarily 

2-121 Northern Bobwhite 
the distribution of farms and farming methods, have eliminated large areas of bobwhite 

habitat in the last three decades (Brennan, 1991). 

Food habits. Bobwhites forage during the day, primarily on the ground or in a light 

litter layer less than 5 cm deep (Rosene, 1969). Seeds from weeds, woody plants, and 

grasses comprise the majority of the adult bobwhite's diet throughout the year (Handley, 

1931; Bent, 1932; Lehmann, 1984), although in winter in the south, green vegetation has 

been found to dominate the plant materials in their diet (Campbell-Kissock et al., 1985). 

Insects and other invertebrates can comprise up to 10 to 25 percent of the adults' diet 

during the spring and summer in more northerly areas and year-round in the south 

(Campbell-Kissock et al., 1985; Handley, 1931; Lehmann, 1984). Insects comprise the bulk 

of the chicks' diet; up to 2 or 3 weeks of age chicks may consume almost 85 percent 

insects, the remainder of the diet consisting of berries and seeds (Handley, 1931). Most 

insects consumed by bobwhite chicks are very small, less than 8 mm in length and 0.005 g 

(Hurst, 1972). Juvenile bobwhite, on the other hand, may consume only 25 percent insects, 

the remainder of their diet being fruit and seeds (Handley, 1931). Quail consume little grit. 

Korschgen (1948) found grit in only 3.4 percent of over 5,000 crops examined, and agreed 

with Nestler (1946) that hard seeds can replace grit as the grinding agent for northern 

bobwhite. 

In some areas, bobwhites apparently can acquire their daily water needs from dew, 

succulent plants, and insects (Stoddard, 1931); in more arid areas or in times of drought, 

however, northern bobwhite need surface water for drinking (Johnsgard, 1988; Lehmann, 

1984; Prasad and Guthery, 1986). Females need more water than males during the 

breeding season, and both sexes may require more water in the winter than in the summer 

when their diet is more restricted to seeds with low water content (Koerth and Guthery, 

1990). Measurements on captive quail have indicated a daily water requirement of up to 13 

percent of their body mass (see table); however, water intake requirements for free-ranging 

birds may be higher, perhaps 14 to 21 percent of body mass per day (Koerth and Guthery, 

1990). In the absence of adequate water, females may fail to reproduce (Koerth and 

Guthery, 1991). 

Dustbathing. Quail frequently dustbathe, although the reason for the behavior is c debated. They scratch in dry dirt or dust, toss the dust up into their feathers, rub their

head and sides in the dust, and then shake the dust from their plumage (Borchelt and 

Duncan, 1974). Experiments by Driver et al. (1991) indicate that ingestion of materials 

preened from feathers and direct dermal uptake can be significant exposure pathways for 

quail exposed to aerial application of pesticides. Dust bathing might, therefore, provide a 

significant exposure route for bobwhites using contaminated soils. 

Molt. Juveniles attain adult plumage during their first fall molt at about 3 to 5 

months of age (Hamilton, 1957; Stoddard, 1931). Adults undergo a complete prebasic 

c

Stoddard (1931) and others have suggested that dust bathing helps to control ectoparasites;

Borchelt and Duncan (1974) suggest that dust bathing helps control the amount of oil on the 

quails' feathers. 

2-122 Northern Bobwhite 
molt in the late summer and fall into winter plumage; in spring, a limited renewal of 

feathers around the head and throat provides the breeding plumage (Bent, 1932). 

Migration. The northern bobwhite is a year-round resident over its entire range but 

may disperse locally to a different cover type or altitude with the changing season 

(Lehmann, 1984). Most winter in wooded or brushy areas, returning to more open habitats 

in spring for the breeding season (Lehmann, 1984; Rosene, 1969). Populations nesting at 

higher elevations tend to move to lower ground where the winters are less severe 

(Stoddard, 1931). The more southerly populations may be more sedentary; in a study in 

Florida, northern bobwhite were found no further than 1 km from where they were banded, 

and 86 percent were found within 400 m from their banding site over a 1- to 5-year period 

(Smith et al., 1982). 

Breeding activities and social organization. Northern bobwhite build nests on the 

ground in open woodlands or in or around fields used for foraging. Most nests are 

constructed in grassy growth near open ground, often in areas with scattered shrubs and 

herbaceous growth (Klimstra and Roseberry, 1975; Stoddard, 1931). Both the male and 

female scrape out a saucer-shaped depression in the ground 2 to 6 cm deep and 10 to 12 

cm across, lining it with dead grasses from the previous year's growth (Bent, 1932; 

Rosene, 1969). They lay large clutches, 12 to 30 eggs, which one or both parents incubate 

for approximately 23 days (Lehmann, 1984; Simpson, 1976). As a general rule, clutch size 

and nest success both decrease as the season progresses (Roseberry and Klimstra, 1984). 

Family units, consisting of both the male and female as well as the offspring, sometimes 

remain intact through the summer, but more often, one or both parents are lost to 

predation (some females leave their brood to the male and begin another), and other pairs 

or individual adults may adopt chicks from other broods (Lehmann, 1984). By fall, northern 

bobwhites of all ages gather in larger coveys for the fall and winter. The quail remain in 

coveys until the next spring, when they disperse as mating season begins (Lehmann, 1984; 

Roseberry and Klimstra, 1984). Coveys of northern bobwhite tend to average 10 to 12 or 

15 birds (up to 30) (Johnsgard, 1988; Lehmann, 1984; Rosene, 1969). When roosting in 

winter, the birds in a covey form a small circle on the ground under a tree or in thick brush, 

with heads facing outward and their bodies closely packed to conserve heat. 

Home range and resources. In the breeding season, the bobwhite's home range 

includes foraging areas, cover, and the nest site and may encompass several hectares. 

Mated males and incubating females have the smallest spring and summer home ranges; 

bachelor males and post-nesting males and females have much larger foraging ranges (see 

table). Bobwhite tend to use a portion of their home range more intensively than the 

remainder of the range (Urban, 1972). In the fall and winter, the range of each bobwhite 

covey must include adequate open foraging areas and cover, typically shrubby or woody 

thickets (Rosene, 1969). Each covey may utilize an area of several hectares, although as in 

summer, there tend to be activity centers where the quail spend most of their time (Yoho 

and Dimmick, 1972). 

Population density. Bobwhite density depends on food and cover availability and 

varies from year to year as well as from one location to another (Roseberry and Klimstra, 

1984). Densities are highest at the end of the breeding season in the fall. In the 

2-123 Northern Bobwhite 
�

�

�

�

�

southeast, densities may reach values as high as 7.5 birds (adults and juveniles) per 

hectare, although average values of 2 to 3 may be more common in these areas (Guthery, 

1988; Lehmann, 1984; Smith et al., 1982). Winter and spring densities between 0.1 and 0.8 

birds per hectare have been recorded in the spring further north (Roseberry et al., 1979). 

Population dynamics. Bobwhites attempt to rear one or two broods per year (up to 

three in the south) (Bent, 1932; CKWRI, 1991; Stanford, 1972b). Bobwhite clutch sizes are 

generally smaller in more southerly populations (Roseberry and Klimstra, 1984) and 

smaller as the breeding season progresses in any given locale (Lehmann, 1984; Simpson, 

1976). Predation is a major cause of nest loss; once hatched, chicks leave the nest 

immediately to follow both or one parent (Lehmann, 1984; Roseberry and Klimstra, 1984). 

Juveniles can survive without parental care after about 6 weeks of age (Lehmann, 1984). 

They reach maturity by 16 weeks of age in the laboratory although they continue to gain 

weight through about 20 weeks (Moore and Cain, 1975), and they may require 8 to 9 

months to mature in the wild (Johnsgard, 1988; Jones and Hughes, 1978). Adult mortality 

as well as juvenile mortality is high, with 70 to 85 percent of birds surviving less than 1 

year (Brownie et al., 1985; Lehmann, 1984); thus, the bulk of the population turns over each 

year. 

Similar species (from general references) 

� California quail (Callipepla californica), also known as valley quail, are 

similar in size (25 cm) to the bobwhite and also gather in coveys during 

autumn and winter. They are common in open woodlands, brushy foothills, 

stream valleys, and suburbs, usually near permanent surface waters; 

however, their range is restricted largely to the western coastal States and 

Baja California. 

� Gambel's quail (Callipepla gambelii) is larger (28 cm) than the bobwhite, and 

is a resident of the southwestern desert scrublands, usually near permanent 

surface waters. It also gathers in coveys in winter. 

� The scaled quail (Callipepla squamata), similar in size (25 cm) to the 

bobwhite, is restricted to the mesas, plateaus, semidesert scrublands, and 

grasslands mixed with scrub, primarily of western Texas, New Mexico, and 

Mexico. 

� Mountain quail (Oreortyx pictus) are found in the chapparal, brushy ravines, 

and mountain slopes of the west up to 3,000 m. These also are large quail 

(28 cm). During the fall, they gather in coveys and descend to lower altitudes 

for the winter. 

� The Montezuma quail (Cyrtonyx montezumae), formerly known as the 

harlequin quail, is a small (22 cm), secretive resident of the southwest. This 

species is usually found in grassy undergrowth of juniper or oak-pine 

woodlands. 

2-124 Northern Bobwhite 
General references 

Johnsgard (1988); Lehmann (1984); National Geographic Society (1987); Rosene 

(1969); Roseberry and Klimstra (1984); Stoddard (1931). 

2-125 Northern Bobwhite 
Northern Bobwhite (Colinus virginianus) 

Factors Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referenc

Body Weight A B fall 189.9 ± 3.28 SE Kansas Robel, 19

(g) A B winter 193.9 ± 4.56 SE 

A B spring 190.0 ± 4.98 SE 

A M winter 181 Illinois Roseber

A M summer 163 

A F winter 183 

A F summer 180 

A M winter 161 west Rio Grande, Texas Guthery 

A M summer 154 

A F winter 157 

A F summer 157 

at hatching 6.3 southwest Georgia/both Stoddard

day 6 9 - 10 (0.5 - 0.75 g/day) captive and wild birds 

day 10 10 - 13 living in farms, woods, 

day 19 20 - 25 (1.5 g/day) and thickets 

day 32 35 - 45 day 43 55 - 65 (1.75 g/day) 

day 55 75 - 85 day 71 110 - 120 (1.75 - 2.0 g/day) 

day 88 125 - 150 day 106 140 - 160 J B fall 174.0 ± 3.49 SE Kansas Robel, 19

(weight gain:) 

Body Fat A M winter 15.5 ± 2.8 SD Tennessee McRae & 

(% dry weight) A M spring 8.8 ± 3.2 SD 

A F winter 13.8 ± 2.7 SD 

A F spring 12.7 ± 2.4 SD 

Body Fat A M winter 10.2 ± 0.6 SE 9.0 - 11.9 southern Texas/captive Koerth & 

(% dry weight) A M spring 7.9 ± 0.2 SE 6.5 - 10.0 

(continued) A F winter 10.6 ± 0.8 SE 8.3 - 19.9 

A F spring 9.7 ± 0.3 SE 7.7 - 11.2 

2-126 Northern Bobwhite 
Northern Bobwhite (Colinus virginianus) 

2-127 Northern Bobwhite 

Factors Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referenc

Egg Weight 9.3 ± 0.3 SE Texas Koerth & 

(grams) 8.6 8.0 - 10.2 southwest Georgia Stoddard

Metabolic Rate A F nonbreed 183.3 Nebraska/captive Case, 19

(kcal/kg-day) A F laying 243.9 

A M basal 129 estimate

A F basal 125 A M free-living 320 (151 - 677) estimate

A F free-living 311 (147 - 659) 

Food Ingestion A B winter 0.093 ± 0.0032 SE southern Texas/captive Koerth & 

Rate (g/g-day) A B spring 0.067 ± 0.0021 SE 

(kcal/kg-day) A B winter 587 Kansas Robel, 19

A B summer 0.079 ± 0.0061 SE 

A B fall 0.072 ± 0.0017 SE 

A B fall 657 

A B spring 519 

Water A M summer 0.10 ± 0.023 SD southern Texas/captive Koerth & 

Ingestion Rate A F summer 0.13 ± 0.037 SD 

(g/g-day) 

A M summer 0.11 estimateA F summer 0.10 

Inhalation Rate A M summer 0.10 estimate

(m /day) A F summer 0.11 3 

Surface Area A M summer 298 estimate

(cm ) A F summer 320 2 
Northern Bobwhite (Colinus virginianus) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

adults: (total plant foods) (87.2) (78.7) (79.7) (96.8) southeastern United Handley, 

misc. seeds 21.1 6.0 11.1 2.6 States/NS 

other seeds: 

legumes 15.2 3.9 10.1 31.5 (% volume; crop and gizzard 

senna 7.2 0.4 0.2 12.8 contents) 

cultivated plants 2.1 2.1 5.3 2.6 

grasses 3.1 11.3 26.0 2.3 

sedges 1.1 1.2 2.4 1.1 

mast 14.1 0.2 0.5 28.0 

spurges 0.1 1.2 5.5 0.4 

fruits 11.1 45.8 11.3 9.5 

forage plants 12 0.3 0.3 5.2 

(total animal foods) (12.8) (19.6) (20.3) (3.2) 

grasshoppers 3.2 7.5 16.6 2.4 

bugs 2.8 4.4 0.6 0.1 

beetles 4.6 6.3 0.8 0.2 

adults: 

seeds of weeds 43.64 33.7 30.0 34.3 south Texas/semi-prairie, Lehmann

seeds of woody 4.03 20.5 39.7 9.5 brushland 

plants 13.2 24.8 0.7 7.2 

seeds of grasses 3.7 1.9 8.3 15.4 (% dry volume; crop 

cultivated grains, etc. 27.4 4.9 3.4 10.3 contents) 

greens 8.03 14.2 17.9 23.3 insects 

adults: 

seeds of forbs 3.5 19.0 12.0 southwest Campbe

seeds of grasses 51.7 42.9 4.9 Texas/grasslands 

seeds/fruits of drought conditions 

woody plants 9.7 - 1.4 

unidentified seeds 4.6 - 2.3 (% wet volume; crop 

green vegetation 4.8 1.8 72.4 contents) 

invertebrates 25.8 36.2 6.5 

2-128 Northern Bobwhite 
Northern Bobwhite (Colinus virginianus) 

Population 

Dynamics 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location/Habitat Referen

Home Range summer: 

Size (ha/bird) A B 3.6 Iowa/State game area Crim & 

(ha/covey) winter: 

A M mated 7.6 ± 5.0 SD south Illinois/idle farms Urban, 

A M unmated 16.7 ± 9.5 SD woods, brush, cornfields 

A F nesting 6.4 ± 4.0 SD 

A F post-nest 15.6 ± 9.1 SD 

B B 6.8 ± 2.9 SD 4.0 - 11.7 Tennessee/woods, old fields Yoho & 

B B 15.4 12.1 - 18.6 south Illinois/NS Barthol

cultivated fields 

Population B B fall 0.21 ± 0.0031 SE south Texas/upland Guthery

Density rangeland (N/ha) B B spring 0.10 ± 0.0003 SE 

B B fall 0.63 ± 0.24 SD 0.28 - 0.92 south Illinois/agricultural Rosebe

B B spring 0.24 ± 0.05 SD 0.18 - 0.33 

B B fall 5.0 ± 0.30 SE south Texas/mixed brush Guthery

B B spring 2.2 ± 0.21 SE rangeland 

B B winter 0.63 ± 0.18 SD 0.37 - 0.88 South Carolina/farms, Rosene

B B winter 2.25 ± 1.16 SD 0.6 - 3.9 Smith e

B B winter 3.65 ± 2.22 SD 1.7 - 7.6 Florida/pine woods 

woods 

Clutch Size 12.9 4 - 33 south Texas/prairie, brush Lehman

March 25.0 southwest Georgia/pine Simpso

August 9.4 woods, farms 

13.7 ± 3.28 SD 6 - 28 Illinois/agricultural Rosebe

Clutches/Year 1 0 - 3 NS/NS CKWRI

Days 23 21 - 25 south Texas/prairie, brush Lehman

Incubation 

2-129 Northern Bobwhite 
Northern Bobwhite (Colinus virginianus) 

Population 

Dynamics 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location/Habitat Referen

Percent Nests 17.5 15.4 - 19.0 southwest Georgia/pine Simpso

Successful woods, farms 

32.6 ± 8.1 SD 21.0 - 52.8 south Illinois/agricultural Rosebe

Number Hatch spring/ 12.2 south Texas/semiprairie, Lehman

per summer brush Successful March 20.0 southwest Georgia/pine Simpso

Nest August 8.4 woods, farms 

Age at Sexual B 8 - 9 months NS/NS (wild) Johnsg

Maturity B 16 weeks South Carolina/lab Jones & 

Annual A M 78.8 ± 2.47 SE 64.7 - 94.8 Florida/open woods Browni

Mortality Rates A F 85.3 ± 2.72 SE 68.4 - 98.6 

(percent) J M 81.8 ± 2.46 SE 73.0 - 93.7 

J F 87.2 ± 1.68 SE 67.9 - 95.8 

B B 81 Illinois/agricultural Rosebe

no hunting 

B M 52 Florida/pine woods Pollock 

B F 56 

Longevity starting: 

(months) B November 10.6 Texas/semiprairie, brush Lehma

B October 8.5 central Missouri/NS Marsde

Seasonal 

Activity Begin Peak End Location Referenc

Mating/ Laying March May - June August Florida Bent, 193

mid-April mid-August south Texas Lehmann

April mid-May - July September south Illinois Roseber

Hatching mid-March May - June mid-September south Texas Lehmann

late April May - August October sw Georgia, northern Florida Stoddard

early May mid-June October Missouri Stanford

mid-May June - August early October south Illinois Roseber

2-130 Northern Bobwhite 
Northern Bobwhite (Colinus virginianus) 

Seasonal 

Activity Begin Peak End Location Referenc

Molt fall August September October NS Bent, 193

spring early February March - April early June sw Georgia, northern Florida Stoddard

1 Metabolized energy requirements of farm-raised birds in captivity: (1) 7 weeks prior to laying (mean weight of hens = 

(mean weight of hens = 215 g). 

2 Estimated using equation 3-28 (Lasiewski and Dawson, 1967) and summer body weights from Roseberry and Klimst3 Estimated using equation 3-37 (Nagy, 1987) and summer body weights from Roseberry and Klimstra (1971). 4 Diet of commercial game food with only 5 to 10 percent water content; maintained at temperature, humidity, and ligh5 Gross energy intake calculated from the average volume of crop contents in shot birds, assuming a 1.5-hour retenti

the contents, and constant foraging throughout the daylight hours, which is likely to overestimate food intake. 

6 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Roseberry and Klimstra (1971). 

7 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Roseberry and Klimstra (1971). 

8 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

Klimstra (1971). 

9 Expected remaining longevity for those juvenile quail that survived to the month indicated. 

2-131 Northern Bobwhite 
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2-132 Northern Bobwhite 
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2-133 Northern Bobwhite 
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2-134 Northern Bobwhite 
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2-135 Northern Bobwhite 
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Natl. Bobwhite Quail Symp. 1: 90-99. 

2-136 Northern Bobwhite 
2.1.10. American Woodcock (woodcock and snipe) 

Order Charadriformes, Family Scolopacidae. These inland members of the 

sandpiper family have a stocky build, long bill, and short legs. However, their habitats and 

diet are distinct. Woodcock inhabit primarily woodlands and abandoned fields, whereas 

snipe are found in association with bogs and freshwater wetlands. Both species use their 

long bills to probe the substrate for invertebrates. The woodcock and snipe are similar in 

length, although the female woodcock weighs almost twice as much as the female snipe. 

Selected species 

The American woodcock (Scolopax minor) breeds from southern Canada to 

Louisiana throughout forested regions of the eastern half of North America. The highest 

breeding densities are found in the northern portion of this range, especially in the Great 

Lakes area of the United States, northern New England, and southern Canada (Gregg, 

1984; Owen et al., 1977). Woodcock winter primarily in the southeastern United States and 

are year-round residents in some of these areas. Woodcock are important game animals 

over much of their range (Owen et al., 1977). 

Body size. Woodcock are large for sandpipers (28 cm bill tip to tail tip), and females 

weigh more than males (Keppie and Redmond, 1988). Most young are full grown by 5 to 6 

weeks after hatching (Gregg, 1984). 

Habitat. Woodcock inhabit both woodlands and abandoned fields, particularly those 

with rich and moderately to poorly drained loamy soils, which tend to support abundant 

earthworm populations (Cade, 1985; Owen and Galbraith, 1989; Rabe et al., 1983a). In the 

spring, males use early successional open areas and woods openings, interspersed with 

low brush and grassy vegetation, for singing displays at dawn and dusk (Cade, 1985; 

Keppie and Redmond, 1985). Females nest in brushy areas of secondary growth 

woodlands near their feeding areas, often near the edge of the woodland or near a break in 

the forest canopy (Gregg, 1984). During the summer, both sexes use second growth 

hardwood or early successional mixed hardwood and conifer woodlands for diurnal cover 

(Cade, 1985). At night, they move into open pastures and early successional abandoned 

agricultural fields, including former male singing grounds, to roost (Cade, 1985; Dunford 

and Owen, 1973; Krohn, 1970). During the winter, woodcock use bottomland hardwood 

forests, hardwood thickets, and upland mixed hardwood and conifer forests during the 

day. At night, they use open areas to some degree, but also forested habitats (Cade, 1985). 

Diurnal habitat and nocturnal roosting fields need to be in close proximity to be useful for 

woodcock (Owen et al., 1977). 

Food habits. Woodcocks feed primarily on invertebrates found in moist upland 

soils by probing the soil with their long prehensile-tipped bill (Owen et al., 1977; Sperry, 

1940). Earthworms are the preferred diet, but when earthworms are not available, other 

soil invertebrates are consumed (Miller and Causey, 1985; Sperry, 1940; Stribling and 

Doerr, 1985). Some seeds and other plant matter may also be consumed (Sperry, 1940). 

Krohn (1970) found that during summer most feeding was done in wooded areas prior to 

entering fields at night, but other studies have indicated that a significant amount of food 

2-137 American Woodcock 
is acquired during nocturnal activities (Britt, 1971, as cited in Dunford and Owen, 1973). 

Dyer and Hamilton (1974) found that during the winter in southern Louisiana, woodcock 

exhibited three feeding periods: early morning (0100 to 0500 hours) in the nocturnal 

habitat, midday (1000 to 1300 hours) in the diurnal habitat, and at dusk (1700 to 2100 

hours) again in the nocturnal fields; earthworms and millipedes were consumed in both 

habitat types. Most of the woodcocks' metabolic water needs are met by their food 

(Mendall and Aldous, 1943, as cited in Cade, 1985), but captive birds have been observed 

to drink (Sheldon, 1967). The chicks leave the nest soon after hatching, but are dependent 

on the female for food for the first week after hatching (Gregg, 1984). 

Molt. Woodcock molt twice annually. The prenuptial molt involves body plumage, 

some wing coverts, scapulars, and tertials and occurs in late winter or early spring; the 

complete postnuptial molt takes place in July or August (Bent, 1927). 

Migration. Fall migration begins in late September and continues through 

December, often following the first heavy frost (Sheldon, 1967). The migration may take 4 

to 6 weeks (Sheldon, 1967). Some woodcock winter in the south Atlantic region, while 

those that breed west of the Appalachian Mountains winter in Louisiana and other Gulf 

States (Martin et al., 1969, as cited in Owen et al., 1977). Woodcock are early spring 

migrants, leaving their wintering grounds in February and arriving on their northern 

breeding grounds in late March to early April (Gregg, 1984; Sheldon, 1967; Owen et al., 

1977). Dates of woodcock arrival at their breeding grounds vary from year to year 

depending on the timing of snowmelt (Gregg, 1984). Sheldon (1967) summarizes spring 

and fall migration dates by States from numerous studies. 

Breeding activities and social organization. From their arrival in the spring, male 

woodcock perform daily courtship flights at dawn and at dusk, defending a site on the 

singing grounds in order to attract females for mating (Owen et al., 1977; Gregg, 1984). 

Often several males display on a single singing ground, with each defending his own 

section of the area. Females construct their nests on the ground, usually at the base of a 

tree or shrub located in a brushy area adjacent to an opening or male singing ground 

(Gregg and Hale, 1977; McAuley et al., 1990; Owen et al., 1977). Females are responsible 

for all of the incubation and care of their brood (Trippensee, 1948). The young leave the 

nest soon after hatching and can sustain flight by approximately 18 days of age (Gregg, 

1984). 

Home range and resources. The home range of woodcocks encompasses both 

diurnal cover areas and nocturnal roosting areas and varies in size depending on season 

and the distribution of feeding sites and suitable cover. During the day, movements are 

usually limited until dusk, when woodcock fly to nocturnal roost sites. Hudgins et al. 

(1985) and Gregg (1984) found spring and summer diurnal ranges to be only 1 to 10 

percent of the total home range. Movement on the nocturnal roost sites also is limited; 

however, during winter, woodcock are more likely to feed and move around at night 

(Bortner, pers. comm.). Singing males generally restrict their movements more than nonsinging males, juveniles, and females (Owen et al., 1977). 

Population density. The annual singing-ground survey conducted by the United 

States and Canada provides information on the population trends of woodcock in the 

2-138 American Woodcock 
�

northern states and Canada during the breeding season (note from B. Bortner, U.S. Fish 

and Wildlife Service, Office of Migrating Bird Management, to Susan Norton, January 9, 

1992). Gregg (1984) summarized results of several published singing-ground surveys and 

found estimates to vary from 1.7 male singing grounds per 100 ha in Minnesota (Godfrey, 

1974, cited in Gregg, 1984) to 10.4 male singing grounds per 100 ha in Maine (Mendall and 

Aldous, 1943, cited in Gregg, 1984). Although this method is appropriate for assessing 

population trends, flushing surveys, telemetry, and mark-recapture are better methods for 

estimating woodcock densities because there are variable numbers of females and 

nonsinging males associated with active singing grounds (Dilworth, Krohn, Riffenberger, 

and Whitcomb pers. comm., cited by Owen et al., 1977). For example, Dwyer et al. (1988) 

found 2.2 singing males per 100 ha in a wildlife refuge in Maine, but with mark-recapture 

techniques, they found yearly summer densities of 19 to 25 birds per 100 ha in the same 

area. 

Population dynamics. Woodcocks attempt to raise only a single brood in a given 

year but may renest if the initial clutch is destroyed (McAuley et al., 1990; Sheldon, 1967). 

In 12 years of study in Wisconsin, Gregg (1984) found 42 percent of all nests to be lost to 

predators and another 11 percent lost to other causes. Survival of juveniles in their first 

year ranges from 20 to 40 percent, and survival of adults ranges from 35 to 40 percent for 

males to approximately 40 to 50 percent for females (Dwyer and Nichols, 1982; Krohn et al., 

1974). Derleth and Sepik (1990) found high adult survival rates (0.88 to 0.90 for both sexes) 

between June and October in Maine, indicating that adult mortality may occur primarily in 

the winter and early spring. They found lower summer survival rates for young woodcock 

between fledging and migration than for adults during the same months, with most losses 

of young attributed to predation. 

Similar species (from general references) 

� The common snipe (Gallinago gallinago) is similar in length (27 cm) to the 

woodcock, although lighter in weight. Snipe are primarily found in 

association with bogs and freshwater wetlands and feed on the various 

invertebrates associated with wetland soils. Snipe breed primarily in boreal 

forest regions and thus are found slightly north of the woodcock breeding 

range, with some areas of overlap in the eastern half of the continent. The 

breeding range of the snipe, however, extends westward to the Pacific coast 

and throughout most of Alaska, thus occupying a more extensive east-west 

range than the woodcock. 

General references 

Cade (1985); Dwyer et al. (1979); Dwyer and Storm (1982); Gregg (1984); National 

Geographic Society (1987); Owen et al. (1977); Sheldon (1967); Trippensee (1948). 

2-139 American Woodcock 
American Woodcock (Scolopax minor) 

Factors 

Age/Sex/ (95% CI of 

Cond./Seas. Mean mean) Location erenc

Range or 

Body Weight A M 176 throughout range Nelson & 

(g) A F 218 

A M April 134.6 ± 2.9 SE Maine Dwyer et 

A M May 133.8 ± 5.8 SE 

A M June 151.2 ± 9.5 SE 

A M summer 145.9 127 - 165 central Massachusetts Sheldon

J M summer 140.4 117 - 152 

A F summer 182.9 162 - 216 

J F summer 168.8 151 - 192 

A M fall 169 Minnesota Marshall 

J M fall 164 

A F fall 213 

J F fall 212 

at hatching 13.0 Wisconsin Gregg, 1

9 - 16 

Egg Weight (g) at laying 18 - 19 Wisconsin Gregg, 1

near hatching 14 - 16 

Chick Growth M 5.1 Maine Dwyer et 

Rate (g/day) F 6.2 Metabolic Rate A F basal 115 s Michigan Rabe et a

(kcal/kg-day) 

A M basal 126 estimate

A F basal 118 A F free-living 315 s Michigan Rabe et a

A F nesting 553 

A M free-living 313 (148 - 662) estimate

A F free-living 296 (140 - 627) 

Ref

2-140 American Woodcock 
American Woodcock (Scolopax minor) 

2-141 American Woodcock 

Factors 

Age/Sex/ (95% CI of 

Cond./Seas. Mean mean) Location erenc

Range or 

Food Ingestion A B winter 0.77 0.11 - 1.43 Louisiana (captive) Stickel e

Rate (g/g-day) (earthworm 

diet) 

Water A M 0.10 estimate

Ingestion A F 0.10 

Rate (g/g-day) 

Inhalation A M 0.11 estimate

Rate (m /day) A F 0.13 3 

Surface Area A M 314 estimate(cm ) A F 362 2 Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

earthworms 67.8 North America/NS Sperry, 1

Diptera 6.9 

Coleoptera 6.2 (% volume; stomach 

Lepidoptera 3.3 contents) 

other animals 5.3 

plants 10.5 

earthworms 58 Maine/fields Krohn, 1

beetle larvae 10 

grit (inorganic) 31 (% wet weight; mouth 

other organic 1 esophagus, stomach, & 

proventriculus contents) 

earthworms 99+ N Carolina/soybean fields Stribling 

other invertebrates <1 (% wet weight; digestive 

tract) 

earthworms 87 Alabama/NS Miller & C

Coleoptera 11 Hymenoptera 2 (% volume; esophagus 

contents) 

Ref
American Woodcock (Scolopax minor) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Location/Habitat Referenc

Home Range A M inactive 3.1 (median) 0.3 - 6.0 Pennsylvania/mixed forests Hudgins 

Size (ha) A M active 73.6 (median) 38.2 - 171.2 with shrubs and fields 

A M singing 10.5 (median) 4.6 - 24.1 

B B summer 32.4 ± 27.6 SD 7 - 98 Wisconsin/woods, open Gregg, 1

A F with 4.5 areas, brush 

brood 

Population North Carolina/agricultural: Connors 

Density B B winter 3.38 untilled soy stubble 

(birds/ha) B B winter 0.20 untilled corn stubble 

B B winter 0.034 rebedded corn fields 

nests in 0.21 (nests/ha) Pennsylvania/mixed pine Coon et 

spring and 

A M summer 0.056 0.037 - 0.074 Maine/second growth forest, 

A F summer 0.125 0.108 - 0.143 meadows, and ponds 

J B summer 0.223 0.190 - 0.250 

B B summer 

0.035 0.026 - 0.046 hardwoods, open fields Dwyer et 

Clutch 4 3 - 5 throughout range and Bent, 192

Size habitats 

1st clutch 3.8 ± 0.42 SD Maine/mixed forests, McAuley 

2nd clutch 3.0 ± 0.67 SD agricultural fields 

Clutches/ 1 but renest if 1st throughout range and McAuley 

Year lost habitats 

Percent Nests about 50 Maine/mixed forests, fields McAuley 

Hatching Days 19 - 21 NS/NS Mendall 

Incubation Pettingil

Age at 18 - 19 days Wisconsin/woods, open Gregg, 1

Fledging areas, brush 

Range 

2-142 American Woodcock 
American Woodcock (Scolopax minor) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Location/Habitat Referenc

Age at M < 1 year throughout range and Sheldon

Sexual F year habitats 

Maturity Annual A M east 65 ± 5.2 SD eastern and central United Dwyer & 

Mortality A M central 60 ± 15 SD States/NS 

Rates J M east 80 ± 4.8 SD 

J M central 64 ± 12 SD 

A F east 51 ± 7.3 SD 

A F central 47 ± 9.6 SD J F east 64 ± 7.7 SD J F central 69 ± 9.4 SD 

Seasonal 

Activity Begin Peak End Location Referenc

Mating/Laying early February mid-March Texas Whiting & 

early April Maine Dwyer et 

Hatching early February Louisiana Pettingill

late February Virginia Pettingill

late March Connecticut Pettingill

mid-April early May early June Massachusetts Sheldon

mid-May Maine Dwyer et 

Molt August to NS/NS Owen & 

early September 

Migration 

spring mid-February early March leaving North Carolina Connors 

fall October December arriving North Carolina Sheldon

March April arriving in northern range Gregg, 1

late mid-December leaving Canada Owen et September 

Range 

1 

2-143 American Woodcock 
1

2345678

American Woodcock (Scolopax minor) 

As cited in Sheldon (1967).

Metabolic rate estimated by authors from equation of Aschoff and Pohl (1970).

Estimated using equation 3-28 (Lasiewski and Dawson, 1967) and summer body weights from Nelson and Martin (19

Estimate of free-living metabolism based on energy budget model. Metabolism during nesting estimated for peak n

Estimated using equation 3-37 (Nagy, 1987) and summer body weights from Nelson and Martin (1953).

Estimated using equation 3-15 (Calder and Braun, 1983) and summer body weights from Nelson and Martin (1953).

Estimated using equation 3-19 (Lasiewski and Calder, 1971) and summer body weights from Nelson and Martin (195

Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and summer bod

Martin (1953).

9 Grit comprised only 14 percent of total digestive tract contents volume. 

10 Should provide a more accurate estimate of proportion of soft-bodied earthworms consumed than would including 

tract. 

11 Cited in Trippensee (1948). 

12 Cited in Owen et al. (1977). 

2-144 American Woodcock 
References (including Appendix) 

Aldous, C. M. (1938) Woodcock management studies in Maine 1937. Trans. North Am. 

Wildl. Nat. Resour. Conf. 3: 839-846. 

Aschoff, J.; Pohl, H. (1970) Rhythmic variations in energy metabolism. Fed. Proc. 29: 

1541-1552. 

Bent, A. C. (1927) Life histories of North American shore birds. Part 1. Washington, DC: 

U.S. Government Printing Office; Smithsonian Inst. U.S. Nat. Mus., Bull. 142. 

Britt, T. L. (1971) Studies of woodcock on the Louisiana wintering ground [master's thesis]. 

Shreveport, LA: Louisiana State University. 

Cade, B. S. (1985) Habitat suitability index models: American woodcock (wintering). U.S. 

Fish Wildl. Serv. Biol. Rep. 82(10.105). 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Connors, J. I.; Doerr, P. D. (1982) Woodcock use of agricultural fields in coastal North 

Carolina. In: Dwyer, T. J.; Storm, G. W., tech. coords. Woodcock ecology and 

management. U.S. Fish Wildl. Serv., Wildl. Res. Rep. 14; pp. 139-147. 

Coon, R. A.; Williams, B. K.; Lindzey, J. S.; et al. (1982) Examination of woodcock nest sites 

in central Pennsylvania. U.S. Fish Wildl. Serv., Wildl. Res. Rep. 14; pp. 55-62. 

Derleth, E. L.; Sepik, G. F. (1990) Summer-fall survival of the American woodcock in Maine. 

J. Wildl. Manage. 54: 97-106. 

Dunford, R. D.; Owen, R. B. (1973) Summer behavior of immature radio-equipped woodcock 

in central Maine. J. Wildl. Manage. 37: 462-469. 

Dwyer, T. J.; Nichols, J. D. (1982) Regional population inferences for the American 

woodcock. In: Dwyer, T. J.; Storm, G. L., tech. coords. Woodcock ecology and 

management. U.S. Fish Wildl. Serv., Wildl. Res. Rep. 14; pp. 12-21. 

Dwyer, T. J.; Storm, G. L., eds. (1982) Woodcock ecology and management. U.S. Fish Wildl. 

Serv., Wildl. Res. Rep. 14. 

Dwyer, T. J.; Coon, R. A.; Geissler, P. H. (1979) The technical literature on the American 

woodcock 1927-1978. Laurel, MD: U.S. Fish Wildl. Serv., Migratory Bird and Habitat 

Research Laboratory. 

Dwyer, T. J.; Derleth, E. L.; McAuley, D. G. (1982) Woodcock brood ecology in Maine. U.S. 

Fish Wildl. Serv., Wildl. Res. Rep. 14; pp. 63-70. 

2-145 American Woodcock 
Dwyer, T. J.; Sepik, G. F.; Derleth, E. L.; et al. (1988) Demographic characteristics of Maine 

woodcock population and effects of habitat management. Washington, DC: U.S. Fish 

Wildl. Serv. Res. Rep. 4. 

Dyer, J. M.; Hamilton, R. B. (1974) An analysis of feeding habits of the American woodcock 

(Philohela minor) in southern Louisiana. In: Fifth American woodcock workshop 

proceedings; December 3-5, 1974; Athens, GA. Athens, GA: University of Georgia. 

Godfrey, G. A. (1974) Behavior and ecology of American woodcock on the breeding range 

in Minnesota [Ph.D. dissertation]. Minneapolis, MN: University of Minnesota. 

Greeley, F. (1953) Sex and age studies in fall-shot woodcock (Philohela minor) from 

southern Wisconsin. J. Wildl. Manage. 17: 29-32. 

Gregg, L. (1984) Population ecology of woodcock in Wisconsin. Wis. Dept. Nat. Resour. 

Tech. Bull. No. 144; 51 pp. 

Gregg, L. E.; Hale, J. B. (1977) Woodcock nesting habitat in northern Wisconsin. Auk 94: 

489-493. 

Hudgins, J. E.; Storm, G. L.; Wakeley, J. S. (1985) Local movements and diurnal-habitat 

selection by male woodcock in Pennsylvania. J. Wildl. Manage. 49: 614-619. 

Johnson, R.C.; Causey, M. K. (1982) Use of longleaf pine stands by woodcock in southern 

Alabama following prescribed burning. In: Dwyer, T. J.; Storm, G. W., tech. coords. 

Woodcock ecology and management. U.S. Fish Wildl. Serv., Wildl. Res. Rep. 14; pp. 

120-125. 

Keppie, D. M.; Redmond, G. W. (1985) Body weight and the possession of territory for male 

American woodcock. Condor 87: 287-290. 

Keppie, D. M.; Redmond, G. W. (1988) A review of possible explanations for reverse size 

dimorphism of American woodcock. Can. J. Zool. 66: 2390-2397. 

Krohn, W. B. (1970) Woodcock feeding habits as related to summer field usage in central 

Maine. J. Wildl. Manage. 34: 769-775. 

Krohn, W. B.; Martin, F. W.; Burnham, K. P. (1974) Band-recovery distribtution and survival 

estimates of Maine woodcock. Proc. Am. Woodcock Workshop 5: 1-8. 

Lasiewski, R. C.; Calder, W. A. (1971) A preliminary allometric analysis of respiratory 

variables in resting birds. Resp. Phys. 11: 152-166. 

Lasiewski, R. C.; Dawson, W. R. (1967). A reexamination of the relation between standard 

metabolic rate and body weight in birds. Condor 69: 12-23. 

2-146 American Woodcock 
Martin, F. W.; Williams, S. O.; Newsom, J. D.; et al. (1969) Analysis of records of 

Louisiana-banded woodcock. Proc. Ann. Conf. Southeast. Assoc. Game and Fish 

Comm. 23: 85-96. 

McAuley, D. G.; Longcore, J. R.; Sepik, G. F. (1990) Renesting by American woodcock 

(Scolopax minor) in Maine. Auk 107: 407-410. 

Meeh, K. (1879) Oberflachenmessungen des mensclichen Korpers. Z. Biol. 15: 426-458. 

Mendall, H. L.; Aldous, C. M. (1943) The ecology and management of the American 

woodcock. Orono, ME: Maine Coop. Res. Unit, University of Maine; 201 pp. 

Miller, D. L.; Causey, M. K. (1985) Food preferences of American woodcock wintering in 

Alabama. J. Wildl. Manage. 49: 492-496. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

National Geographic Society. (1987) Field guide to the birds of North America. Washington, 

DC: National Geographic Society. 

Nelson, A. L.; Martin, A. C. (1953) Gamebird weights. J. Wildl. Manage. 17: 36-42. 

Norris, R. T.; Buele, J. D.; Studholme, A. T. (1940) Banding woodcocks on Pennsylvania 

singing grounds. J. Wildl. Manage. 4: 8-14. 

Owen, R. B.; Galbraith, W. J. (1989) Earthworm biomass in relation to forest types, soil, and 

land use: implications for woodcock management. Wildl. Soc. Bull. 17: 130-136. 

Owen, R. B.; Krohn, W. B. (1973) Molt patterns and weight changes of the American 

woodcock. Wilson Bull. 85: 31-41. 

Owen, R. B.; Morgan, J. W. (1975) Summer behavior of adult radio-equipped woodcock in 

central Maine. J. Wildl. Manage. 39: 179-182. 

Owen, R. B.; Anderson, J. M.; Artmann, J. W.; et al. (1977) American woodcock. In: 

Sanderson, G. C., ed. Management of migratory shore and upland game birds in 

North America. Washington, DC: Int. Assoc. Fish Wildl. Agencies; pp. 147-175. 

Pettingill, O. S., Jr. (1936) The American woodcock. Boston Soc. Nat. Hist. Mem. 9(2). 

Rabe, D. L.; Prince, H. H.; Beaver, D. L. (1983a) Feeding-site selection and foraging 

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Rabe, D. L.; Prince, H. H.; Goodman, E. D. (1983b) The effect of weather on bioenergetics of 

breeding American woodcock. J. Wildl. Manage. 47: 762-771. 

2-147 American Woodcock 
Rubner, M. (1883) Uber den Einfluss der Korpergrosse auf Stoff- und Kraftweschsel. Z. 

Biol. 19: 535-562. 

Sheldon, W. G. (1967) The book of the American woodcock. Amherst, MA: University of 

Massachusetts Press. 

Sperry, C. (1940) Food habits of a group of shore birds; woodcock, snipe, knot, and 

dowitcher. U.S. Dept. Int., Bur. Biol. Survey, Wildl. Res. Bull. 1; 37 pp. 

Stickel, W. H.; Hayne, D. W.; Stickel, L. F. (1965) Effects of heptachlor-contaminated 

earthworms on woodcocks. J. Wildl. Manage. 29: 132-146. 

Stribling, H. L.; Doerr, P. D. (1985) Nocturnal use of fields by American woodcock. J. Wildl. 

Manage. 49: 485-491. 

Trippensee, R. E. (1948) American woodcock. Wildlife management. New York, NY: 

McGraw-Hill; pp. 323-332. 

Tufts, R. W. (1940) Some studies in bill measurements and body weights of American 

woodcock (Philohela minor). Can. Field-Nat. 54: 132-134. 

Walsberg, G. E.; King, J. R. (1978) The relationship of the external surface area of birds to 

skin surface area and body mass. J. Exp. Biol. 76: 185-189. 

Wetherbee, D. K.; Wetherbee, N. S. (1961) Artificial incubation of eggs of various bird 

species and some attributes of neonates. Bird Banding 32: 141-159. 

Whiting, R. M.; Boggus, T. G. (1982) Breeding biology of American woodcock in east Texas. 

In: Dwyer, T. J.; Storm, G. W., tech. coords. Woodcock ecology and management. 

U.S. Fish Wildl. Serv., Wildl. Res. Rep. 14; pp. 132-138. 

2-148 American Woodcock 
2.1.11. Spotted Sandpiper (sandpipers) 

Order Charadriiformes, Family Scolopacidae. The family Scolopacidae includes 

numerous species of shorebirds, e.g., sandpipers, tattlers, knots, godwits, curlews, 

yellowlegs, willets, and dowitchers. Those known as sandpipers tend to be small with 

moderately long legs and bills. Most sandpipers forage on sandy beaches and mudflats; a 

few utilize upland areas. They feed almost exclusively on small invertebrates, either by 

probing into or gleaning from the substrate. Most species are highly migratory, breeding in 

arctic and subarctic regions and either wintering along the coasts or in southern latitudes 

and the southern hemisphere; therefore, many are only passage migrants throughout most 

of the United States. Scolapids range in size from the least sandpiper (11.5 cm bill tip to 

tail tip) to the long-billed curlew (48 cm). 

Selected species 

The spotted sandpiper (Actitis macularia) (19 cm) is a very common summer 

resident of freshwater and saltwater bodies throughout most of the United States. These 

sandpipers are most often encountered singly but may form small flocks. Most winter in 

the neotropics. 

Body size. Females (approximately 50 g) are significantly larger than males 

(approximately 40 g) (Oring and Lank, 1986). 

Habitat. Spotted sandpipers breed along the edges of bodies of water, usually in 

open habitats, from the northern border of the boreal forest across North America, south to 

the central United States (Oring and Lank, 1986). They require open water for bathing and 

drinking, semi-open habitat for nesting, and dense vegetation for breeding (Bent, 1929; 

Oring et al., 1983). 

Food habits. In coastal areas, spotted sandpipers search the beach and muddy 

edges of inlets and creeks, wading less frequently than most sandpipers; inland they feed 

along the shores of sandy ponds and all types of streams, sometimes straying into 

meadows, fields, and gardens in agricultural areas (Bent, 1929). Their diet is composed 

primarily of terrestrial and marine insects (Bent, 1929). While adult flying insects comprise 

the bulk of the diet, crustaceans, leeches, molluscs, small fish, and carrion also are eaten 

(Oring et al., 1983). Young feed themselves immediately after hatching, concentrating on 

small invertebrates (Oring and Lank, 1986). During insect outbreaks, sandpipers will 

forage in wooded areas near water, and they have been observed eating eggs and fish on 

occasion (Oring, pers. obs.). 

Molt. Partial prenuptial molt of body plumage occurs in March and April, while the 

postnuptial molt begins by August with the body feathers and ends anywhere from October 

to April with the loss of the primary flight feathers (Bent, 1929). 

Migration. Spotted sandpipers generally migrate in small flocks or solitarily 

(National Geographic Society, 1987). They winter from southern United States to northern 

Chile, Argentina, and Uraguay (Oring and Lank, 1986), and breed across North 

2-149 Spotted Sandpiper 
�

�

America, north from Virginia and southern California (National Geographic Society, 1987). 

In the spring, females arrive at the breeding grounds earlier than males (in one study, by 

about 2 weeks; Oring and Lank, 1982). 

Breeding activities and social organization. The primary consideration for nesting 

sites is proximity to water, and spotted sandpipers have been known to build their ground 

nests in such diverse conditions as depressions in volcanic rock and strawberry patches 

(Bent, 1929). Spotted sandpipers are polyandrous (i.e., a single female lays eggs for 

multiple males), with males supplying most of the incubation and parental care (Oring, 

1982). Thus reproduction is limited by the number of males present (Lank et al., 1985). 

Spotted sandpipers lay a determinate clutch of four eggs. Females may lay several 

clutches in a year, often a dozen eggs per season (Maxson and Oring, 1980). Egg laying 

begins between late May and early June in Minnesota (Lank et al., 1985), and males 

incubate after the third egg is laid (Oring et al., 1986). Females sometimes incubate and 

brood when another male is not available (Maxson and Oring, 1980). Parents brood small 

chicks and protect them with warning calls or by distracting or attacking predators (Oring 

and Lank, 1986). 

Home range and resources. Although a variety of vegetation types are used, nests 

usually are placed in semi-open vegetation near the edge of a lake, river, or ocean (Oring et 

al., unpubl., as cited in Oring et al., 1983; McVey, pers. obs.). The suitability of nesting 

habitat varies from year to year in some locations due to levels of precipitation and 

predators (Oring et al., 1983). 

Population density. Spotted sandpiper nesting densities have been studied well at 

only one location, on Little Pelican Island, Leech Lake, Minnesota. At this location, 

densities ranged from 4 to 13 females per hectare and 7 to 20 males per hectare over a 10-

year period, depending on weather and other conditions (Oring et al., 1983). 

Population dynamics. Females may lay one to six clutches for different males over 

one season (Oring et al., 1984), averaging 1.3 to 2.7 mates per year (Oring et al., 1991b). 

Female mating and reproductive success increase with age, but male success does not 

(Oring et al., 1991b). Lifetime reproductive success is most affected by fledging success 

and longevity for both males and females (Oring et al., 1991a). 

Similar species (from general references) 

� The solitary sandpiper (Tringa solitaria) is usually seen singly in freshwater 

swamps or rivers. Present over much of the United States during annual 

migrations, this average-sized sandpiper (18 cm) winters along the southeast 

and Gulf coasts. 

� The western sandpiper (Calidris mauri) is a small sandpiper (13 cm), 

common on mudflats and sandbars, that winters on both the Atlantic and 

Pacific shores of the United States. 

2-150 Spotted Sandpiper 
�

�

�

The least sandpiper (Calidris minutilla), the smallest of this group (11 cm), is 

common in winter on salt marshes and muddy shores of rivers and estuaries 

in coastal areas across the United States. 

� The semipalmated sandpipers (Calidris pusilla) are small birds (13 cm) seen 

in the United States primarily during migration and rarely wintering on 

Florida coasts. 

� Most other members of the family Scolopacidae forage by gleaning. 

General references 

Oring and Lank (1986); Lank et al. (1985); National Geographic Society (1987); Oring 

et al. (1991a, 1991b). 

2-151 Spotted Sandpiper 
Spotted Sandpiper (Actitis macularia) 

2-152 Spotted Sandpiper 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referenc

Body Weight A F spring 47.1 43 - 50 Minnesota island Maxson 

(g) A M spring 37.9 34 - 41 Metabolic Rate A F pre-breed 404 - 787 Minnesota Maxson 

(kcal/kg-day) A F laying 383 - 745 

A F 368 incubating 440 

A M pre-breed 303 

A M incubating 425 

A M brooding 

A F free-living 460 (213 - 994) A M free-living 

436 (202 - 937) estimate

Food Ingestion 

Rate (g/g-day) Water A F 0.16 estimate

Ingestion A M 0.17 

Rate (g/g-day) 

Inhalation A F 0.039 estimate

Rate (m /day) A M 0.033 3 

Surface Area A F 131 estimate(cm ) A M 113 2 Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

mayflies � Minnesota/island in lake Maxson 

midges �

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Location/Habitat Reference 

Territory approx. 0.25 NS/NS Maxson & 

Size (ha) 

Range 
Spotted Sandpiper (Actitis macularia) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Location/Habitat Reference 

Population A F summer 10 3.8 - 12.5 Minnesota/island in lake Oring et a

Density (N/ha) A M summer 13.9 7.5 - 20.0 

Clutch Size 4 3 - 5 NS/NS Bent, 1929

Clutches/Year 1 - 6 Minnesota/NS Oring et a

Days 18 to 24 NS/NS Oring, unp

Incubation Age at approximately NS/NS Oring et a

Fledging 18 days Number 1.83 0.58 - 2.76 Minnesota/island in lake Oring et a

Fledge per Nest That Hatches Number 2.58 1.67 - 2.91 Minnesota/island in lake Oring et a

Fledge per Successful Nest Age at F 1 year Minnesota/island in lake Oring et a

Sexual M 1 year 

Maturity Annual F approx. 31 Minnesota/island in lake Oring et a

Mortality M approx. 30 Lank, 1982

Rates (percent) unpublish

Longevity A F 3.7 years Minnesota/island in lake Oring et a

Seasonal 

Activity Begin Peak End Location Referenc

Mating early May late May - early Minnesota Lank et a

June 

Hatching early June late June Minnesota Lank et a

Range 

2-153 Spotted Sandpiper 
Spotted Sandpiper (Actitis macularia) 

Seasonal 

Activity Begin Peak End Location Referenc

Molt fall August October NS Bent, 192

spring March - April Bent, 192

Migration Minnesota Lank et a

females late June early - mid-July 

males early July mid-July 

1 Estimated by authors; allometric model not specified.

2 Estimated using equation 3-37 (Nagy, 1987) and body weights from Maxson and Oring (1980).

3 See Chapters 3 and 4 for methods of estimating food ingestion rates; also see Section 4.1.3 and Table 4-4 for sedim

sandpipers. 

4 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Maxson and Oring (1980). 

5 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Maxson and Oring (1980). 

6 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

(1980). 

7 Spotted sandpipers are determinate layers, with a clutch size of four eggs. Clutches with fewer eggs are not comple

clutches are the result of more than one female laying in a nest. 

2-154 Spotted Sandpiper 
References (including Appendix) 

Bent, A. C. (1929) Life histories of North American shore birds. Part 2. Washington, DC: 

U.S. Government Printing Office; Smithsonian Inst. U.S. Nat. Mus., Bull. 146. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Dunning, J. B., Jr. (1984) Body weights of 686 species of North American birds. Western 

Bird Banding Association, Monograph No. 1. Cave Creek, AZ: Eldon Publishing. 

Kuenzel, W. J.; Wiegert, R. G. (1973) Energetics of a spotted sandpiper feeding on brine fly 

larvae (Paracoenia; Diptera: Ephydridae) in a thermal spring community. Wilson 

Bull. 85: 473-476. 

Lank, D. B.; Oring, L. W.; Maxson, S. J. (1985) Mate and nutrient limitation of egg-laying in a 

polyandrous shorebird. Ecology 66: 1513-1524. 

Lasiewski, R. C.; Calder, W. A. (1971) A preliminary allometric analysis of respiratory 

variables in resting birds. Resp. Phys. 11: 152-166. 

Maxson, S. J.; Oring, L. W. (1980) Breeding season time and energy budgets of the 

polyandrous spotted sandpiper. Behaviour 74: 200-263. 

Meeh, K. (1879) Oberflachenmessungen des mensclichen Korpers. Z. Biol. 15: 426-458. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

National Geographic Society. (1987) Field guide to the birds of North America. Washington, 

DC: National Geographic Society. 

Oring, L. W. (1982) Avian mating systems. In: Farner, D. S.; King, J. R., eds. Avian biology, 

v. 6. New York, NY: Academic Press; pp. 1-92. 

Oring, L. W.; Lank, D. B. (1982) Sexual selection, arrival times, philopatry and site fidelity in 

the polyandrous spotted sandpiper. Behav. Ecol. Sociobiol. 10: 185-191. 

Oring, L. W.; Lank, D. B. (1986) Polyandry in spotted sandpipers: the impact of environment 

and experience. In: Rubenstein, D. I.; Wrangham, R. W., eds. Ecological aspects of 

social evolution - birds and mammals; pp. 21-42. 

Oring, L. W.; Lank, D. B.; Maxson, S. J. (1983) Population studies of the polyandrous 

spotted sandpiper. Auk 100: 272-285. 

Oring, L. W.; Lank, D. B.; Maxson, S. J. (1984) Mate and nutrient limitation of breeding in 

the polyandrous spotted sandpiper (abstract only). Am. Zool. 24: 60A. 

2-155 Spotted Sandpiper 
Oring, L. W.; Fivizzani, A. J.; Halawani, M. E. (1986) Changes in plasma prolactin associated 

with laying and hatch in the spotted sandpiper. Auk 103: 820-822. 

Oring, L.W.; Colwell, M.A.; Reed, J.M. (1991a) Lifetime reproductive success in the spotted 

sandpiper (Actitis macularia): sex differences and variance components. Behav. 

Ecol. Sociobiol. 28: 425-432. 

Oring, L.W.; Reed, J.M.; Colwell, M.A.; et al. (1991b) Factors regulating annual mating 

success and reproductive success in spotted sandpipers (Actitis macularia). Behav. 

Ecol. Sociobiol. 28: 433-442. 

Palmer, R. S. (1949) Maine birds. Bull. Mus. Comp. Zool. Harvard No. 102. 

Poole, E. L. (1938) Weights and wing areas in North American birds. Auk 55: 511-517. 

Rubner, M. (1883) Uber den Einfluss der Korpergrosse auf Stoff- und Kraftweschsel. Z. 

Biol. 19: 535-562. 

Walsberg, G. E.; King, J.R. (1978) The relationship of the external surface area of birds to 

skin surface area and body mass. J. Exp. Biol. 76: 185-189. 

Zar, J. H. (1968) Standard metabolism comparisons between orders of birds. Condor 10: 

278. 

2-156 Spotted Sandpiper 
2.1.12. Herring Gull (gulls) 

Order Charadriiformes, Family Laridae. Gulls are medium- to large-sized sea birds 

with long pointed wings, a stout, slightly hooked bill, and webbed feet. They are abundant 

in temperate coastal areas and throughout the Great Lakes. Although gulls may feed from 

garbage dumps and landfills, most take natural prey. Gulls nest primarily in colonies, 

although some of the larger species also nest solitarily. Many populations migrate 

annually between breeding and wintering areas. North American gull species range in size 

from Bonaparte's gull (33 cm bill tip to tail tip) to the great black-backed gull (76 cm). 

Selected species 

The herring gull (Larus argentatus) (64 cm) has the largest range of any North 

American gull, from Newfoundland south to the Chesapeake Bay along the north Atlantic 

and west throughout the Great Lakes into Alaska. Along the Pacific coast, the similar-sized 

western gull (L. occidentalis) is the ecological equivalent of the herring gull. Both species 

take primarily natural foods, especially fish, although some individuals of both species 

forage around fishing operations and landfills (Pierotti, 1981, 1987; Pierotti and Annett, 

1987). The increase in number of herring gulls in this century has been attributed to the 

increasing abundance of year-round food supplies found in landfills (Drury, 1965; Harris, 

1970); however, birds specializing on garbage have such low reproductive success that 

they cannot replace themselves in the population (Pierotti and Annett, 1987, 1991). An 

alternative explanation of the species' expansion is that cessation of taking of gulls by the 

feather industry in the late 1800's has allowed gull numbers to return to pre-exploitation 

levels (Graham, 1975). 

Body size. Adult females (800 to 1,000 g) are significantly smaller than males (1,000 

to 1,300 g) in both the herring gull (Greig et al., 1985) and the western gull (Pierotti, 1981). 

Chicks grow from their hatching weight of about 60 to 70 g to 800 to 900 g within 30 to 40 

days, after which time their weight stabilizes (Dunn and Brisbin, 1980; Norstrom et al., 

1986; Pierotti, 1982). Norstrom et al. (1986) fitted chick growth rates to the Gompertz 

equation as follows: 

BW = 997 e-e(-0.088(t - 14.8)) for females, and 

BW = 1193 e-e(-0.075(t - 16.3)) for males, 

where BW equals body weight in grams and t equals days after hatching. Adults show 

seasonal variation in body weight (Coulson et al., 1983; Norstrom et al., 1986). 

Habitat. Nesting colonies of herring gulls along the northeastern coast of the United 

States are found primarily on sandy or rocky offshore or barrier beach islands (Kadlec and 

Drury, 1968). In the Great Lakes, they are found on the more remote, secluded, and 

protected islands and shorelines of the lakes and their connecting rivers (Weseloh, 1989). 

Smaller colonies or isolated pairs also can be found in coastal marshes (Burger, 1980a), 

peninsulas, or cliffs along seacoasts, lakes, and rivers (Weseloh, 1989), and occasionally in 

inland areas or on buildings or piers (Harris, 1964). Gulls are the most abundant seabirds 

2-157 Herring Gull 
offshore from fall through spring, and are only found predominantly inshore during the 

breeding season in late spring and summer (Powers, 1983; Pierotti, 1988). Gulls forage 

predominantly offshore, within 1 to 5 km of the coast (Pierotti, 1988). In all seasons the 

number of birds feeding at sea outnumber those feeding inshore (data from Powers, 1983; 

Pierotti, pers. comm.). Inshore, herring gulls forage primarily in intertidal zones but also 

search for food in wet fields, around lakes, bays, and rock jetties, and at landfills in some 

areas (Burger, 1988). In Florida, herring gull presence at landfills is restricted to the winter 

months (December through April) and may consist primarily of first-year birds that 

migrated from more northerly populations (e.g., from the Great Lakes) (Patton, 1988). 

Food habits. Gulls feed on a variety of foods depending on availability, including 

fish, squid, crustacea, molluscs, worms, insects, small mammals and birds, duck and gull 

eggs and chicks, and garbage (Bourget, 1973; Burger, 1979a; Fox et al., 1990; Pierotti and 

Annett, 1987). Gulls forage on open water by aerial dipping and shallow diving around 

concentrations of prey. At sea, such concentrations often are associated with whales or 

dolphins, other seabirds, or fishing boats (McCleery and Sibly, 1986; Pierotti, 1988). In the 

Great Lakes, concentrations of species such as alewife occur seasonally (e.g., when 

spawning) (Fox et al., 1990). Gulls also forage by stealing food from other birds and by 

scavenging around human refuse sites (e.g., garbage dumps, fish plants, docks, and 

seaside parks) (Burger and Gochfeld, 1981; 1983; Chapman and Parker, 1985). Individual 

pairs of gulls may specialize predominantly on a single type of food; for example, three 

quarters of a population of herring gulls in Newfoundland were found to specialize either 

on blue mussels, garbage, or adults of Leach's storm-petrel, with 60 percent of the 

specialists concentrating on mussels between 0.5 and 3 cm in length (Pierotti and Annett, 

1987; 1991). Diet choices may change with the age and experience of adult birds as well as 

with availability of prey (Pierotti and Annett, 1987; 1991). Females take smaller prey and 

feed less on garbage than do males (Pierotti, 1981; Greig et al., 1985). For example, Fox et 

al. (1990) found females to feed more on smelt (100 to 250 mm) and males more on alewife 

(250 to 300 mm) in the Great Lakes region. Adult gulls sometimes attack and eat chicks of 

neighboring gulls or other species of seabird (Brown, 1967; Schoen and Morris, 1984). 

Juveniles up to 3 years of age forage less efficiently than adults (Greig et al., 1983; 

MacLean, 1986; Verbeek, 1977). In the Great Lakes, herring gulls' high consumption of 

alewife during their spawn may result in high exposures of the gulls to lipophilic 

contaminants that biomagnify (Fox et al., 1990). 

Metabolism. Norstrom et al. (1986) have estimated an annual energy budget for 

free-living female herring gulls that breed in the Great Lakes and an annual energy budget 

for free-living juvenile herring gulls in the Great Lakes in their first year. Between 

September and March, the nonbreeding season, they estimate that adult females require 

250 to 260 kcal/day. Following a dip in energy requirements to 210 kcal/day when the male 

feeds the female during courtship, the female's needs increase to peak at 280 kcal/day for 

egg production, then fall to approximately 210 kcal/day during incubation. The energy 

required to forage for food for the chicks is substantial, rising through July to peak in 

August at 310 to 320 kcal/day, then declining again until September when feeding chicks 

has ceased. These estimates compare well with those derived from Nagy's (1987) equation 

to estimate free-living metabolic rates for seabirds, except that the energy peaks required 

to produce eggs and to feed chicks are not included in Nagy's model. Readers interested 

in the metabolic rates of first-year herring gulls are referred to Norstrom et al. (1986). Ellis 

2-158 Herring Gull 
(1984) provides an overview of seabird energetics and additional discussion of approaches 

and models for estimating metabolic rates of free-ranging seabirds. 

Molt. Gull chicks are downy gray with dark brown spotting and molt into a darkgray or brown mottled juvenile plumage. At the end of the first year, portions of the 

plumage have paled, and by the second year, gray plumage develops along the back and 

top of wings. By their third year, young gulls resemble dirty adults, and they acquire their 

full adult plumage by 4 years (Harrison, 1983; Kadlec and Drury, 1968). Adult gulls, at least 

in some populations, begin their primary feather molt during incubation and complete the 

molt by mid- to late fall (Coulson et al., 1983). They molt and replace the large body 

feathers from mid-summer to early fall (Coulson et al., 1983). 

Migration. Herring gull populations along the northeast coast of North America tend 

to be migratory, while adult herring gulls of the Great Lakes are year-round residents. 

Along the western North Atlantic, most herring gulls arrive on their breeding grounds 

between late February and late April. They remain until late August or early September 

when they leave for their wintering grounds along the Atlantic and Gulf coasts or well 

offshore (Burger, 1982; Pierotti, 1988). Adult and older subadult herring gulls in the Great 

Lakes area are essentially nonmigratory (Mineau et al., 1984; Weseloh et al., 1990). Thus, 

in contrast to other fish-eating birds in the Great Lakes system that migrate south in the 

winter, herring gulls are exposed to any contaminants that may be in Great Lakes' fish 

throughout the year (Mineau et al., 1984). Postbreeding dispersal away from breeding 

colonies begins in late July and ends in August, with all ages traveling short distances. 

Great Lakes herring gulls less than a year old usually migrate to the Gulf or Atlantic coast 

(Smith, 1959; Mineau et al., 1984), traveling along river systems and the coast (Moore, 

1976). 

Breeding activities and social organization. Gulls nest primarily in colonies on 

offshore islands, and nest density is strongly affected by population size (Pierotti, 1981; 

1982; 1987). Typically, males arrive at the breeding grounds first and establish territories. 

Both sexes build the nest of vegetation on the ground in areas that are sheltered from wind 

but may be exposed to the sun (Pierotti, 1981; 1982). Males feed females for 10 to 15 days 

prior to the start of egg laying (Pierotti, 1981). From the laying of the first egg until the 

chicks are 3 to 4 weeks old, one or both parents will be present at all times (Tinbergen, 

1960). Males perform most territorial defense, females perform most incubation, and both 

parents feed the chicks until they are at least 6 to 7 weeks old (Burger, 1981; Pierotti, 1981; 

Tinbergen, 1960). All gulls are strongly monogamous; pair bonds can persist for 10 or 

more years and usually only are terminated by the death of a mate or failure to reproduce 

successfully (Tinbergen, 1960). Males may be promiscuous in populations with more 

females than males (Pierotti, 1981). Herring gull colonies often are found in association 

with colonies of other species, including other gulls (Bourget, 1973; Brown, 1967). In some 

nesting colonies, gulls attack chicks of neighboring gulls and other species (Brown, 1967; 

Schoen and Morris, 1984). 

Home range and resources. During the breeding season, herring gulls defend a 

territory of several tens of square meters around the immediate vicinity of the nest (Burger, 

1980b). Their daily foraging range depends on the availability of prey and on the foraging 

strategy, age, and sex of the gull. Using radiotelemetry on gulls in the Great Lakes, Morris 

2-159 Herring Gull 
�

�

�

and Black (1980) demonstrated that some parents with chicks forage at specific locations 

within 1 km of the colony whereas other parents make extended flights to destinations 

across a lake more than 30 km away. Similarly, gulls that feed at sea may range tens of 

kilometers from their nest whereas gulls from the same colony feeding in the intertidal 

zone may travel less than 1 km (Pierotti and Annett, 1987; 1991). Males typically range 

farther than females and take larger prey items (Pierotti and Annett, 1987; 1991). At sea 

during the nonbreeding season, gulls may range hundreds of kilometers during a day 

(Pierotti, pers. comm.). 

Population density. As described above, population density is determined by 

available nesting space, size of the breeding population, and quality of habitat. Small 

islands with good feeding areas nearby can have several hundred nests per hectare 

(Kadlec, 1971; Parsons, 1976b; Pierotti, 1982). In poor quality habitat, some pairs nest 

solitarily without another nest for several kilometers (Weseloh, 1989). 

Population dynamics. Herring gulls and western gulls usually do not begin 

breeding until at least 4 years of age for males and 5 years of age for females (Burger, 

1988; Pierotti, 1981; Pierotti, pers. comm.). Kadlec and Drury (1968) suggest that in a given 

year, 15 to 30 percent of adults of breeding age do not breed. Most breeding females 

produce three-egg clutches, but individuals in poor condition may lay only one or two eggs 

(Parsons, 1976a; Pierotti, 1982; Pierotti and Annett, 1987; 1991). Herring gulls will lay 

replacement eggs if all or a portion of their original clutch is destroyed (Parsons, 1976a). 

Hatching success appears to be influenced by female diet, with garbage specialists 

hatching a smaller percentage of eggs than fish or intertidal (mussel) specialists (Pierotti 

and Annett, 1987, 1990, 1991). Predation, often by gulls of the same or other species, also 

contributes to egg losses (Paynter, 1949; Harris, 1964; Davis, 1975). Many herring gull 

chicks that hatch die before fledging, most within the first 5 days after hatching (Harris, 

1964; Kadlec et al., 1969; Brown, 1967). Adult mortality is low (around 10 percent per year), 

and some birds may live up to 20 years (Brown, 1967; Kadlec and Drury, 1968). Subadult 

birds exhibit higher mortality (20 to 30 percent per year) (Kadlec and Drury, 1968; Chabrzyk 

and Coulson, 1976). 

Similar species (from general references) 

� The western gull (Larus occidentalis) (64 cm), found on the Pacific coast of 

the United States, is the ecological equivalent of the herring gull and is 

similar in size (53 cm); males range from 1,000 to 1,300 g and females from 

800 to 1,000 g (Pierotti, 1981). 

� The glaucous gull (Larus hyperboreus) is larger (69 cm) than the herring gull 

and is the predominant gull breeding in the high arctic. Birds from Alaska 

are slightly smaller than birds from eastern Canada. 

� The glaucous-winged gull (Larus glaucescens) is similar in size to the 

herring gull (66 cm) and is the primary breeding species north of the 

Columbia River. This species hybridizes extensively with the herring gull in 

Alaska. 

2-160 Herring Gull 
�

�

�

�

The California gull (Larus californicus) is smaller (53 cm) than the herring 

gull. This species breeds primarily in the Great Basin Desert and winters 

along the Pacific coast. 

� The great black-backed gull (Larus marinus) is the largest species of gull (76 

cm) in North America and breeds from Labrador to Long Island. 

� The ring-billed gull (Larus delawarensis) is of average size (45 cm) and is the 

most common breeding gull in the Great Lakes and northern prairies. 

� Franklin's gull (Larus pipixcan) is a small (37 cm), summer resident of the 

Great Plains. 

General references 

For general information: Harrison (1983); National Geographic Society (1987); 

Tinbergen (1960); Graham (1975). For discussion of diet: Burger (1988); Fox et al. (1990); 

Pierotti (1981); Pierotti and Annett (1987). 

2-161 Herring Gull 
Herring Gull (Larus argentatus) 

2-162 Herring Gull 

Factors 

Age/Sex Range or 

Cond./Seas. Mean (95% CI of mean) Location Referenc

Body Weight A F spring 951 ± 88 SD Lake Huron Norstrom 

(g) A M spring 1,184 ± 116 SD 

A F summer 999 ± 90 SD 832 - 1,274 Newfoundland Threlfall & 

A M summer 1,232 ± 107 SD 1,014 - 1,618 

at hatching 65 50 - 80 Maine Dunn & B

10 days old 230 120 - 380 

20 days old 590 420 - 800 

30 days old 810 610 - 1,000 

30 days old 964 ± 77 SD Newfoundland/rocky island Pierotti, 1

30 days old 818 ± 99 SD Newfoundland/grassy island 

Chick Growth < 5 days 8.8 - 13.1 Newfoundland/island Pierotti, 1

Rate (g/day) 5-30 days 26.3 ± 6.5 SD Newfoundland/island Pierotti, 1

5-30 days 33.4 ± 4.7 SD Newfoundland/rocky island Pierotti, 1

5-25 days 30.2 ± 1.75 SD 26.7 - 31.4 Maine/coastal island Hunt, 197

meadow 

Egg Weight (g) 3 egg clutch 87.2 New Brunswick Herbert & 

2 egg clutch 85.7 in 1983 92.0 ± 5.9 SD Lake Superior, Canada Meathrel 

in 1984 98.0 ± 8.0 SD 

Metabolic Rate A M basal 86 estimated 

(kcal/kg-day) A F basal 91 

A standard 99 laboratory Lustick e

A M free- 233 (84 - 646) living A F free- 248 (92 - 669) estimated 

living Also see text for a discussion of annual variation in free-living metabolic rate in herring gulls. 
2-163 

Herring Gull 

Herring Gull (Larus argentatus) 

Factors 

Age/Sex Range or 

Cond./Seas. Mean (95% CI of mean) 

Food Ingestion A M breeding 0.20 

Rate (g/g-day) A F breeding 0.21 

A M breeding 0.19 A F breeding 0.18 

Water A M 0.055 Ingestion Rate A F 0.059 (g/g-day) Inhalation Rate A M 0.48 

(m /day) A F 0.41 3

Surface Area A M 1,150 

(cm ) A F 1,001 2

Location Referenc

Newfoundland - Pierotti & 

diet of mussels 

Newfoundland - Pierotti & 

diet of garbage 

estimated estimated 

estimated 

Dietary Composition Summer Summer Summer Summer (measure) Referenc

Location/Habitat 

months: Mid-May/ Mid-June/ Mid-July/ Newfoundland/island Haycock 

Mytilus edulis 30.9 0.9 9.1 (% occurrence in 

sea urchin 5.8 0.0 4.5 regurgitations and 

fish 11.4 71.1 18.9 pellets) 

Oceanodroma 22.4 7.0 15.9 

leuchorhoa 

Fratercula arctica 5.8 0.0 1.5 

adults 

Fratercula, Uria 0.0 3.5 9.1 

chicks 

Larus sp. eggs 3.1 0.9 0.8 

Vaccinum - - 9.9 

angustifolium 

Gadus morhua 12.4 1.7 14.4 

offal 

assorted refuse 5.8 0.9 6.8 

Mid-June Mid-July Mid-Aug. 
Herring Gull (Larus argentatus) 

Dietary Composition Summer Summer Summer Summer (measure) Referenc

Location/Habitat 

year: 1978 1979 1980 1981 Lake Ontario Fox et al.

American smelt 46.1 18.4 61.2 57.8 

alewife 23.1 73.7 16.7 23.4 (% occurrence in 

other fish 20.5 0 3.4 3.1 regurgitations from and 

birds 2.6 2.6 13.8 6.2 stomach contents of 

voles 2.6 2.6 3.4 9.4 incubating adults) 

insects & refuse 12.8 0 3.4 0 

lake: Ontario Erie Huron Superior Great Lakes Fox et al.

fish 91.8 94.1 75.8 38.6 

insects 5.5 5.9 5.6 42.1 (% occurrence in boli 

offal, garbage 0.5 2.9 13.6 21.0 regurgitated by chicks) 

gull chicks 2.2 0 1.0 0 

adult birds 1.6 0 1.0 3.5 

amphibians 0.5 0 0 0 

earthworms 2.2 0 11.6 1.7 

crayfish 0 0 0.5 0 

snails 3 CA,FL,NY,NJ,TX/ Burger, 1

crabs 14 coastal 

garbage 27 

offal 5 (% of gulls feeding on items) 

worms 23 

other inverts. 28 offshore feeding on fish was 

fish unknown not included in observations 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Foraging A M 10 to 15 3 - 50 NS/coastal Pierotti, p

Radius (km) A F 5 to 10 3 - 25 Population summer 227 138 - 350 Massachusetts/coastal Kadlec, 1

Density islands 

(nests/ha) 

summer 217 Newfoundland/island - rocky Pierotti, 1

75 Newfoundland/island - Pierotti, 1

grassy slope 

2-164 Herring Gull 
Herring Gull (Larus argentatus) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Clutch 2.78 2.51 - 2.90 New Jersey/salt marsh Burger, 1

Size (over 8 sites) islands 

2.54 1 - 6 NE United States/coastal Nisbet & 

2.38 2.3 - 2.8 Maine/coastal islands Hunt, 197

2.84 ± 0.44 SD Lake Superior, Canada/ Meathrel 

(per nest) 

(over 11 years) 

islands 

Clutches/Year 1 1 - 2* (* if first eggs lost) Burger, 1

Days 30.5 28 - 33 Holland/NS Tinberge

Incubation 29 Newfoundland/island Pierotti, 1

Age at 51 35 - 44 to 56 - 61 Massachusetts/coastal Kadlec et 

Fledging 43 31 to 52 island Paynter, 

(days) New Brunswick/island 

Number 3 colonies 1.42 1.40 - 1.44 New Jersey/coastal Burger & 

Fledge per 6 colony-yrs 1.65 1.40 - 2.13 Lake Ontario/lakeshore Mineau e

Active Nest 3 colony-yrs 1.78 1.62 - 2.10 Lake Erie/lakeshore (minimu

6 colony-yrs 2.19 2.16 - 2.25 Lake Huron/lakeshore yearly m

Number 3 colonies 1.80 1.79 - 1.80 New Jersey/coastal Burger & 

Fledge per Successful Nest Age at F 5 years throughout range/NS Greig et a

Sexual M 4 - 5 years pers. coMaturity 

B 4.3 to 5.8 3 - 8 Scotland/coastal Coulson 

Annual A B 8 New England/coastal Kadlec & 

Mortality Rates J B 22 17 - 33 

(percent) A B 7.3 Scotland/coastal Chabryzk 

2-165 Herring Gull 
Herring Gull (Larus argentatus) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Longevity A B 10 up to 30 years NS/NS Pierotti, p

Seasonal 

Activity Begin Peak End Location Referenc

Mating/ late April early May early June ne shore Lake Superior Morris & 

Laying early May mid-May early June Maine Bourget, 

early May mid-May mid-June New Jersey Burger, 1

early May late May end May Newfoundland Pierotti, 1

Hatching mid - late May Great Lakes Fox et al.

May June July Massachusetts Kadlec, 1

early June mid-June end June Newfoundland Pierotti, 1

late June late June mid-July New Brunswick Paynter, 

Migration 

spring February late April northwestern Atlantic Burger, 1

fall August September 

populations 

Molt June July August Newfoundland Pierotti, p

2-166 Herring Gull 

1 Weight of chicks from first egg laid in 1978 for the rocky island and in 1977 for the grassy area. In some years and s

the first egg were heavier than the rest, and at other times and locations, the first chick was lighter. 

2 Estimated using equation 3-29 (Lasiewski and Dawson, 1967) and body weights from Threlfall and Jewer (1978). 3 Estimated using equation 3-38 (Nagy, 1987) and body weights from Threlfall and Jewer (1978). 4 Estimated using 11.2 meals of mussel consumed per day per pair, weight of 80 g per mussel meal of which half is sh

ingestion rate, assuming that the female accounts for 46 percent of pair's energy requirement and the male account

the body weights of Threlfall and Jewer (1978). 

5 Estimated using 4.2 meals of garbage consumed per day per pair, weight of 100 g per garbage meal, assuming that 

percent of pair's energy requirement and the male accounts for 54 percent, and using the body weights of Threlfall a

6 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Threlfall and Jewer (1978). 7 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Threlfall and Jewer (1978). 8 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

(1978). 

9 Beginning with first egg. 
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2-167 Herring Gull 
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2-168 Herring Gull 
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Holley, A. J. (1982) Post-fledging interactions on the territory between parents and young 

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Kadlec, J. A. (1971) Effects of introducing foxes and raccoons on herring gull colonies. J. 

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Kadlec, J. A.; Drury, W. H. (1968) Structure of the New England herring gull population. 

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2-169 Herring Gull 
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Lustick, S.; Battersby, B.; Kelty, M. (1978) Behavioral thermoregulation: orientation toward 

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2-170 Herring Gull 
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2-171 Herring Gull 
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2-172 Herring Gull 
2.1.13. Belted Kingfisher (kingfishers) 

Order Coraciiformes, Family Alcedinidae. Kingfishers are stocky, short-legged 

birds with large heads and bills. They exist on a diet mostly of fish, which they catch by 

diving, from a perch or the air, head first into the water. They nest in burrows in earthen 

banks that they dig using their bills and feet. 

Selected species 

The belted kingfisher (Ceryle alcyon, formerly Megaceryle alcyon) is a mediumsized bird (33 cm bill tip to tail tip) that eats primarily fish. It is one of the few species of 

fish-eating birds found throughout inland areas as well as coastal areas. The belted 

kingfisher's range includes most of the North American continent; it breeds from northern 

Alaska and central Labrador southward to the southern border of the United States (Bent, 

1940). Two subspecies sometimes are recognized: the eastern belted kingfisher (Ceryle 

alcyon alcyon), which occupies the range east of the Rocky Mountains and north to 

Quebec, and the western belted kingfisher (Cercyle alcyon caurina), which occupies the 

remaining range to the west (Bent, 1940). 

Body size. The sexes are similar in size and appearance, although the female tends 

to be slightly larger (Salyer and Lagler, 1946). Bent (1940) reported that western 

populations are somewhat larger than eastern ones. Nestlings reach adult body weight by 

about 16 days after hatching, but then may lose some weight before fledging (Hamas, 

1981). 

Habitat. Belted kingfishers are typically found along rivers and streams and along 

lake and pond edges (Hamas, 1974). They are also common on seacoasts and estuaries 

(Bent, 1940). They prefer waters that are free of thick vegetation that obscures the view of 

the water and water that is not completely overshadowed by trees (Bent, 1940; White, 

1953). Kingfishers also require relatively clear water in order to see their prey and are 

noticeably absent in areas when waters become turbid (Bent, 1940; Davis, 1982; Salyer and 

Lagler, 1946). White (1953) suggested that water less than 60 cm deep is preferred. They 

prefer stream riffles for foraging sites even when pools are more plentiful because of the 

concentration of fish at riffle edges (Davis, 1982). Belted kingfishers nest in burrows within 

steep earthen banks devoid of vegetation beside rivers, streams, ponds, and lakes; they 

also have been found to nest in slopes created by human excavations such as roadcuts 

and landfills (Hamas, 1974). Sandy soil banks, which are easy to excavate and provide 

good drainage, are preferred (Brooks and Davis, 1987; Cornwell, 1963; White, 1953). In 

general, kingfishers nest near suitable fishing areas when possible but will nest away from 

water and feed in bodies of water other than the one closest to home (Cornwell, 1963). 

Food habits. Belted kingfishers generally feed on fish that swim near the surface or 

in shallow water (Salyer and Lagler, 1946; White, 1953; Cornwell, 1963). Davis (pers. 

comm. in Prose, 1985) believes that these kingfishers generally catch fish only in the upper 

12 to 15 cm of the water column. Belted kingfishers capture fish by diving either from a 

perch overhanging the water or after hovering above the water (Bent, 1940). Fish 

2-173 Belted Kingfisher 
are swallowed whole, head first, after being beaten on a perch (Bent, 1940). The average 

length of fish caught in a Michigan study was less than 7.6 cm but ranged from 2.5 to 17.8 

cm (Salyer and Lagler, 1946); Davis (1982) found fish caught in Ohio streams to range from 

4 to 14 cm in length. Several studies indicate that belted kingfishers usually catch the prey 

that are most available (White, 1937, 1953; Salyer and Lagler, 1946; Davis, 1982). Diet 

therefore varies considerably among different water bodies and with season (see examples 

in Appendix). Although kingfishers feed predominantly on fish, they also sometimes 

consume large numbers of crayfish (Davis, 1982; Sayler and Lagler, 1946), and in 

shortages of their preferred foods, have been known to consume crabs, mussels, lizards, 

frogs, toads, small snakes, turtles, insects, salamanders, newts, young birds, mice, and 

berries (Bent, 1940). Parents bring surprisingly large fish to their young. White (1953) 

found that nestlings only 7 to 10 days old were provided fish up to 10 cm long, and 

nestlings only 2 weeks old were provided with fish up to 13 cm in length. After fledging, 

young belted kingfishers fed on flying insects for their first 4 days after leaving the nest, 

crayfish for the next week, and by the 18th day post-fledging, could catch fish (Salyer and 

Lagler, 1946). 

Molt. The juvenile plumage is maintained through the winter, and young birds 

undergo their first prenuptial molt in the spring (between February and April) involving 

most of the body plumage (Bent, 1940). Adults have a complete postnuptial molt in the fall 

(August to October) (Bent, 1940). 

Migration. This kingfisher breeds over most of the area of North America and 

winters in most regions of the continental United States (National Geographic Society, 

1987). Although most northern kingfishers migrate to southern regions during the coldest 

months, some may stay in areas that remain ice-free where fishing is possible (Bent, 1940). 

Breeding activities and social organization. During the breeding season, pairs 

establish territories for nesting and fishing (Davis, 1982); otherwise, belted kingfishers are 

solitary. They are not colonial nesters and will defend an unused bank if it lies within their 

territory (Davis, 1982). In migrating populations, the males arrive before the females to find 

suitable nesting territories (Davis, 1982). Kingfishers excavate their burrows in earthen 

banks, forming a tunnel that averages 1 to 2 m in length, although some burrows may be 

as long as 3 to 4 m (Hamas, 1981; Prose, 1985). The burrow entrance is usually 30 to 90 

cm from the top of the bank (Bent, 1940; White, 1953) and at least 1.5 m from the base 

(Cornwell, 1963). Burrows closer to the top may collapse, and burrows too low may flood 

(Brooks and Davis, 1987). Burrows may be used for more than one season (Bent, 1940). 

Five to seven eggs are laid on bare substrate or on fish bones within the burrow (Hamas, 

1981; White, 1953). Only one adult, usually the female, spends the night in the nest cavity; 

males usually roost in nearby forested areas or heavy cover (Cornwell, 1963). Both 

parents incubate eggs and feed the young (Bent, 1940). After fledging, the young remain 

with their parents for 10 to 15 days (Sayler and Lagler, 1946). 

Home range and resources. During the breeding season, belted kingfishers require 

suitable nesting sites with adequate nearby fishing. During spring and early summer, both 

male and female belted kingfishers defend a territory that includes both their nest site and 

their foraging area (Davis, 1982). By autumn, each bird (including the young of the year) 

2-174 Belted Kingfisher 
�

�

defends an individual feeding territory only (Davis, 1982). The breeding territories (length 

of waterline protected) can be more than twice as long as the fall and winter feeding 

territories, and stream territories tend to be longer than those on lakes (Davis, 1982; Salyer 

and Lagler, 1946). Foraging territory size is inversely related to prey abundance (Davis, 

1982). 

Population density. Breeding densities of between two and six pairs per 10 km of 

river shoreline have been recorded, with density increasing with food availability (Brooks 

and Davis, 1987; White, 1936). 

Population dynamics. Kingfishers are sensitive to disturbance and usually do not 

nest in areas near human activity (White, 1953; Cornwell, 1963). Kingfishers typically 

breed in the first season after they are born (Bent, 1940). Fledging success depends on 

food availability, storms, floods, predation, and the integrity of the nest burrow but can be 

as high as 97 percent (M. J. Hamas, pers. comm.). Dispersal of young occurs within a 

month of fledging (White, 1953). No data concerning annual survivorship rates were found. 

Similar species (from general references) 

� The green kingfisher (Chloroceryle americana) is smaller (22 cm) than the 

belted kingfisher and is only common in the lower Rio Grande Valley. It also 

is found in southeastern Arizona and along the Texas coast, usually during 

fall and winter. 

� The ringed kingfisher (Ceryle torquata) is larger (41 cm) and resides in the 

lower Rio Grande Valley in Texas and Mexico. 

General references 

Bent (1940); Fry (1980); National Geographic Society (1987); Prose (1985); White 

(1953). 

2-175 Belted Kingfisher 
Belted Kingfisher (Ceryle alcyon) 

Factors 

Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referenc

Body Weight A B 148 ± 20.8 SD 125 - 215 Pennsylvania Powderm

(g) (unpub

A B 136 ± 15.6 SE Pennsylvania Brooks & 

A B 158 ± 11.5 SE Ohio Brooks & 

at hatching 10 - 12 Minnesota Hamas, 1at fledging 148 ± 13.3 SE Pennsylvania Brooks & 

at fledging 169 ± 11.9 SE Ohio Brooks & 

Nestling 5 to 6 Pennsylvania, Ohio/streams Brooks & 

Growth Rate 

(g/day) 

Metabolic Rate A B basal 132 estimate

(kcal/kg-day) 

A B free-living 327 (154 - 693) estimate

Food Ingestion A B 0.50 northcentral lower Michigan Alexande

Rate (g/g-day) 

nestlings 1.0 - 1.75 Nova Scotia White, 19

Water A B 0.11 estimate

Ingestion Rate 

(g/g-day) Inhalation A B 0.094 estimate

Rate (m /day) 3 

Surface Area A B 280 estimate(cm )2 

2-176 Belted Kingfisher 
Belted Kingfisher (Ceryle alcyon) 

Dietary Composition Spring Summer Fall Winter Location/Habitat (measure) Referenc

trout 17* lower Michigan/lake Alexande

non-trout fish 29 

crustacea 5 (% wet weight; stomach 

insects 19 contents) 

amphibians 27 birds and mammals 1 *data from spring and fall 

unidentified 2 also 

trout 30 Michigan/trout streams Salyer & 

other game & pan fish 13 

(e.g., perch, (% wet volume; stomach 

centrarchids) contents) 

forage fish (e.g., 15 

minnow, stickleback, sculpins) 

unidentified fish 1 

crayfish 41 

insects < 1 

salmon fry 11 Nova Scotia/riparian - White, 19

salmon (1-yr-old) 42 streams 

salmon (2-yr-old) 1 (% of total number of prey; 

trout 15 fecal pellets) 

sticklebacks 30 killifish < 1 

suckers < 1 

crayfish 13 southwest Ohio/creek Davis, 19

cyprinids 76 

(minnows) (13) (% of total number of prey (stonerollers) (38) brought to nestlings) (unidentified) (26) 

other fish 10 

2-177 Belted Kingfisher 
Belted Kingfisher (Ceryle alcyon) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Territory Size early summer ­

(km shoreline) breeding pairs: 2.19 ± 0.56 SE Pennsylvania/streams Brooks & 

late summer - 1.03 ± 0.22 SE southwest Ohio/streams Davis, 19

nonbreeding individuals: 

1.03 ± 0.28 SE Ohio/streams Brooks & 

0.39 ± 0.093 SE southwest Ohio/streams Davis, 19

Population A B summer 0.11 - 0.19 Pennsylvania/streams Brooks & 

Density (pair/km shore) A B summer 0.6 Nova Scotia/streams White, 19

Clutch Size 5.8 ± 0.7 SE Pennsylvania/streams Brooks & 

6.8 ± 0.4 SE Ohio/streams Brooks & 

Clutches/Year 1 Pennsylvania, Ohio/streams Brooks & 

1 Minnesota/lake Hamas, 1

Days 22 Minnesota/lake Hamas, 1

Incubation Age at 28 days NS/NS Bent, 194

Fledging Number 4.5 ± 1.9 SE Pennsylvania/streams Brooks & 

Fledge per Active Nest 5.3 ± 2.2 SE Ohio/streams Brooks & 

Age at Sexual 1 year throughout range Bent, 194

Maturity 

2-178 Belted Kingfisher 
Belted Kingfisher (Ceryle alcyon) 

Seasonal 

Activity Begin Peak End Location Referenc

Mating April April to May early July Minnesota Hamas, 1

Hatching May June late July Minnesota Hamas, 1

early June Nova Scotia White, 19

Molt fall August October NS Bent, 194

spring February April NS Bent, 194

Migration mid-October Maine Bent, 194

fall departures mid-November NY, SD, WI, NE Bent, 194

spring arrivals late February PA, RI, MO Bent, 194

mid-March NY, CT, IL, WI Bent, 194

early April Maine, Nova Scotia Bent, 194

mid-December Massachusetts, New Jersey Bent, 194

1 Cited in Dunning (1984). 

2-179 Belted Kingfisher 

2 Brooks and Davis (1987) reported fledging weights of 149 and 169 g for two populations. Given a hatching weight o

required to fledge, on average, chicks must gain 5 to 6 g per day. Hamas (1981) found gains of approximately 8.5 g 

loss of approximately 4.5 g per day until fledging. 

3 Estimated using equation 3-28 (Lasiewski and Dawson, 1967) and body weights from Powdermill Nature Center (unp

4 Estimated using equation 3-37 (Nagy, 1987) and body weights from Powdermill Nature Center (unpubl.).

5 Estimated by author.

6 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Powdermill Nature Center (unpubl.).

7 Estimated using equation 3-19 (Lasiewski and Calder, 1971) and body weights from Powdermill Nature Center (unpu

8 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

Center (unpubl.). 

9 They are known to renest up to three times if clutches are lost early (Bent, 1940). 
References (including Appendix) 

Alexander, G. R. (1974) The consumption of trout by bird and mammal predators on the 

North Branch Au Sable River. Michigan Dept. Nat. Resources, Dingell - Johnson 

Proj.; F-30-R, Final Report. 

Alexander, G. R. (1977) Food of vertebrate predators on trout waters in north central lower 

Michigan. Michigan Academician 10: 181-195. 

Bent, A. C. (1940) Life histories of North American cuckoos, goat suckers, hummingbirds, 

and their allies. Washington, DC: U.S. Government Printing Office; Smithsonian Inst. 

US Nat. Mus., Bull. 176. 

Brooks, R. P.; Davis, W. J. (1987) Habitat selection by breeding belted kingfishers (Ceryle 

alcyon). Am. Midl. Nat. 117: 63-70. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Cornwell, G. W. (1963) Observations on the breeding biology and behavior of a nesting 

population of belted kingfishers. Condor 65: 426-431. 

Davis, W. J. (1980) The belted kingfisher, Megaceryle alcyon: its ecology and territoriality 

[master's thesis]. Cincinnati, OH: University of Cincinnati. 

Davis, W. J. (1982) Territory size in Megaceryle alcyon along a stream habitat. Auk 99: 

353-362. 

Dunning, J. B., Jr. (1984) Body weights of 686 species of North American birds. Western 

Bird Banding Association, Monograph No. 1. Cave Creek, AZ: Eldon Publishing. 

Fry, C. (1980) The evolutionary biology of kingfishers (Alcedinidae). In: The living bird, 

1979-80. Ithaca, NY: The Laboratory of Ornithology, Cornell University; pp. 113-160. 

Hamas, M. J. (1974) Human incursion and nesting sites of the belted kingfisher. Auk 91: 

835-836. 

Hamas, M. J. (1975) Ecological and physiological adaptations for breeding in the belted 

kingfisher (Megaceryle alcyon) [Ph.D. dissertation]. Duluth, MN: University of 

Minnesota. 

Hamas, M. J. (1981) Thermoregulatory development in the belted kingfisher. Comp. 

Biochem. Physiol. A: Comp. Physiol. 69: 149-152. 

Lasiewski, R. C.; Calder, W. A. (1971) A preliminary allometric analysis of respiratory 

variables in resting birds. Resp. Phys. 11: 152-166. 

2-180 Belted Kingfisher 
Lasiewski, R. C.; Dawson, W. R. (1967). A reexamination of the relation between standard 

metabolic rate and body weight in birds. Condor 69: 12-23. 

Meeh, K. (1879) Oberflachenmessungen des mensclichen Korpers. Z. Biol. 15: 426-458. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

National Geographic Society. (1987) Field guide to the birds of North America. Washington, 

DC: National Geographic Society. 

Poole, E. L. (1938) Weights and wing areas in North American birds. Auk 55: 511-517. 

Prose, B. L. (1985) Habitat suitability index models: belted kingfisher. U.S. Fish Wildl. Serv. 

Biol. Rep. 82(10.87). 

Rubner, M. (1883) Uber den Einfluss der Korpergrosse auf Stoff- und Kraftweschsel. Z. 

Biol. 19: 535-562. 

Salyer, J. C.; Lagler, K. F. (1946) The eastern belted kingfisher, Megaceryle alcyon alcyon 

(Linnaeus), in relation to fish management. Trans. Am. Fish. Soc. 76: 97-117. 

Walsberg, G. E.; King, J. R. (1978) The relationship of the external surface area of birds to 

skin surface area and body mass. J. Exp. Biol. 76: 185-189. 

White, H. C. (1936) The food of kingfishers and mergansers on the Margaree River, Nova 

Scotia. J. Biol. Board Can. 2: 299-309. 

White, H. C. (1937) Local feeding of kingfishers and mergansers. J. Biol. Board Can. 3: 

323-338. 

White, H. C. (1938) The feeding of kingfishers: food of nestlings and effect of water height. 

J. Biol. Board 4: 48-52. 

White, H. C. (1953) The eastern belted kingfisher in the maritime provinces. Fish. Res. 

Board Can. Bull. 97. 

2-181 Belted Kingfisher 
2.1.14. Marsh Wren (wrens) 

Order Passeriformes, Family Troglodytidae. Wrens are small insectivorous birds 

that live in a variety of habitats throughout the United States. They have long, slender bills 

adapted for gleaning insects from the ground and vegetation. Most species are migratory, 

although some populations are year-round residents. 

Selected species 

The marsh wren (Cistothorus palustris) is a common bird inhabiting freshwater 

cattail marshes and salt marshes. Marsh wrens breed throughout most of the northern half 

of the United States and in coastal areas as far south as Florida; they winter in the 

southern United States and into Mexico, particularly in coastal areas. Marsh wrens eat 

mostly insects, and occasionally snails, which they glean from the surface of vegetation. 

This species was formerly known as the long-billed marsh wren (Telmatodytes palustris). 

Body size. Although wrens are small (13 cm bill tip to tail tip; about 10 g body 

weight), males tend to be about 10 percent heavier than females (see table). Body weight 

varies seasonally; in Georgia, where marsh wrens are resident throughout the year, they 

tend to be heavier in the spring and summer than in the fall and winter (Kale, 1965). 

Habitat. Marsh wrens inhabit freshwater and saltwater marshes, usually nesting in 

association with bulrushes, cattails, and sedges or on occasion in mangroves (Welter, 

1935; Bent, 1948; Kale, 1965; Verner, 1965). Standing water from several centimeters to 

nearly a meter is typical of the areas selected (Bent, 1948). Permanent water is necessary 

to provide a food supply of insects necessary to maintain the birds and as a defense 

against predation (Verner and Engelsen, 1970). Deeper water and denser vegetation are 

associated with reduced predation rates (Leonard and Picman, 1987). 

Food habits. Marsh wrens consume aquatic invertebrates, other insects, and 

spiders, which they glean from the water surface, on stems and leaves of emergent 

vegetation, and the marsh floor (Kale, 1965; Welter, 1935). They sometimes also feed by 

flycatching (Welter, 1935). The insect orders most commonly taken include Coleoptera 

(both adults and larvae), Diptera (adults and larvae), Hemiptera (juveniles and adults), 

Lepidoptera (larvae most commonly fed to nestlings); and Odonata (newly emerged) (Bent, 

1948; Kale, 1964). When feeding the young, at first the parents bring mosquito adults and 

larvae, midges, larval tipulids, and other small insects (Welter, 1935). As the young 

mature, the parents bring larger insects such as ground beetles, diving beetles, longhorned beetles, caterpillars, dragonflies, and sawflies to the nestlings (Welter, 1935). In a 

population in Georgia, spiders (usually 1 to 3 mm in size, sometimes 12 to 15 mm), small 

crabs (5 to 7 mm), small snails (1 to 3 mm), and insect eggs also were consumed and fed 

to nestlings (Kale, 1965). Thus, organisms that are aquatic for all or part of their lives are 

an important component of the diet of marsh wren adults and nestlings. 

Migration. Marsh wrens are year-round residents in some southern and coastal 

maritime regions where marshes do not freeze. Most migratory wrens breed throughout 

the northern half of the United States through southern Canada and winter in Mexico and 

2-183 Marsh Wren 
the southern half of the United States (Bent, 1948; Verner, 1965; American Ornthologists' 

Union, 1983; National Geographic Society, 1987). 

Breeding activities and social organization. Many populations of marsh wren are 

polygynous, with some males mating with two, occasionally three, females in a season, 

while the remaining males have one mate or remain bachelors. For example, Leonard and 

Picman (1987) found 5 to 11 percent bachelor males, 41 to 48 percent monogamous males, 

37 to 43 percent bigamous males, and 5 to 12 percent trigamous males in two marshes in 

Manitoba, Canada. Similarly, Verner and Engelsen (1970) found 16 percent bachelors, 57 

percent monogamous, and 25 percent bigamous males in eastern Washington state. In 

contrast, Kale (1965) found most males to be monogamous through 4 years of study in 

Georgia. 

Males arrive at the breeding marshes before the females to establish territories that 

include both nest sites and foraging areas (Kale, 1965; Verner, 1965; Welter, 1935). Males 

build several nests in their territories throughout the breeding season (Kale, 1965; Verner, 

1965). The female usually only adds lining material to a nest of her choice, although some 

may help construct the breeding nest (Kale, 1965). Breeding nests are oblong in shape, 

with a side opening, and are woven of cattails, reeds, and grasses and lashed to standing 

vegetation, generally 30 cm to 1 m above standing water or high tide (Bent, 1948; Verner, 

1965). Incubation lasts approximately 2 weeks, as does the nestling period (Kale, 1965; 

Verner, 1965). After fledging, one or both parents continue to feed the young for about 12 

days (Verner, 1965). Many populations typically rear two broods per year, although some 

may rear three (Kale, 1965; Verner, 1965). In the more monogamous populations, both 

parents regularly feed young, but in the more polygynous ones, the females may provide 

most of the food, with males assisting only toward the end of the nestling period (Leonard 

and Picman, 1988; Verner, 1965). 

Home range and resources. Marshes smaller than 0.40 ha usually are not used by 

breeding marsh wrens (Bent, 1948). Average male territory size for a given year and 

location can range from 0.006 to 0.17 ha, depending on the habitat and conditions of the 

year (see table). Also, there is a trend in polygynous populations for polygynous males to 

defend larger territories than monogamous males or males that end up as bachelors 

(Verner and Engelson, 1970; Verner, 1964; Kale, 1965). 

Population density. Because the species is polygynous, there may be more females 

than males inhabiting breeding marshes. Population density varies with the suitability and 

patchiness of the habitat. Densities as high as 120 adult birds per hectare have been 

recorded (Kale, 1965). 

Population dynamics. Clutch size and number of clutches per year vary with 

latitude and climate (see table). In some populations, marsh wrens commonly destroy 

eggs and kill the nestlings of other pairs of their own species and other marsh-nesting 

passerines (Orians and Wilson, 1964; Picman, 1977; Welter, 1935). Fledging success 

depends strongly on nest location; nests over deeper water are less vulnerable to 

predation (Leonard and Picman, 1987). Of nests lost to all causes, Leonard and Picman 

(1987) found 44 percent due to mammalian predators, 27 percent due to other wrens, 11 

percent due to weather, 8 percent due to nest abandonment, and 13 percent unknown. The 

2-184 Marsh Wren 
�

�

�

�

�

annual mortality of adults is lower than that of first-year birds. Both sexes of this species 

usually commence breeding in the first year following hatching (Kale, 1965). 

Similar species 

� The sedge wren (Cistothorus platensis, formerly known as the short-billed 

marsh wren) nests locally in wet meadows or shallow sedge marshes and 

hayfields in the northeastern United States, wintering primarily in the 

southeastern United States. It is slightly smaller (11 cm) than the marsh 

wren. 

Note: None of the other wren species inhabit marshes, although all forage 

by gleaning insects from vegetation and other surfaces. Wrens that inhabit 

moist woodlands and open areas are listed below. 

� The house wren (Troglodytes aedon) (12 cm) breeds throughout most of the 

United States, into southern Canada. It inhabits open habitats with brush 

and shrubs and is found in orchards, farmyards, and urban gardens and 

parks. 

� The winter wren (Troglodytes troglodytes) (10 cm) breeds in southern 

Canada, where it nests in dense brush, especially along moist coniferous 

woodlands. It winters primarily in the southeastern United States, where it 

inhabits many types of woodlands. 

� The Carolina wren (Thryothorus ludovicianus) (14 cm) is nonmigratory and 

can be found in both summer and winter in the eastern United States as far 

north as northern Delaware and as far west as Oklahoma. It inhabits moist 

woodlands and swamps and wooded suburban areas. 

� Bewick's wren (Thryomanes bewickii) (13 cm) is more common in western 

States than the house wren and is declining east of the Mississippi. It is 

found in brushland, stream edges, and open woods. 

General references 

Kale (1965); Gutzwiller and Anderson (1987); Leonard and Picman (1987); Verner 

(1965), National Geographic Society (1987). 

2-185 Marsh Wren 
Marsh Wren (Cistothorus palustris) 

2-186 Marsh Wren 

Factors 

Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referen

Body Weight F breeding 10.6 ± 0.99 SD 9.0 - 13.5 New York Tintle (

(g) M breeding 11.9 ± 0.72 SD 10.5 - 13.5 

A F 9.4 ± 1.1 SD Georgia Kale, 19

A M 10.6 ± 0.7 SD 

J B 9.4 ± 1.6 SD 

nestling: New York, Minnesota/fresh Welter, 

day 1 1.1 marshes 

day 3 2.1 

day 5 4.7 

day 7 6.8 

day 9 10.0 day 11 10.6 day 13 11.3 

at fledging 8.84 ± 0.70 SD Georgia Kale, 19

Egg Weight (g) 1.14 ± 0.10 SD Georgia Kale, 19

Metabolic Rate A B basal 91.2 Georgia (captive) Kale, 19

(lO 2 /kg-day) A B near 113 

basal A B light 169 

activity 

Metabolic Rate A B basal 444 Georgia (captive) Kale, 19

(kcal/kg-day) A B near 557 ± 115 SD Kale, 19

basal A B light 788 ± 115 SD Kale, 19

activity 880 ± 90 SD Kale, 19

A B free-living A F free-living 1,174 (554 - 2,486) 

A M freeliving 

1,209 (571 - 2,563) estimat
Marsh Wren (Cistothorus palustris) 

2-187 Marsh Wren 

Factors 

Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referen

Food Ingestion A B free-living 1,155 ± 130 SD Georgia (captive) Kale, 19

Rate kcal/kg-day 

A B free-living 0.67 g/g-day Georgia (captive) estimat

A F free-living 0.99 g/g-day estimat

A M free- 0.96 g/g-day 

living 

Water A F 0.28 estimat

Ingestion Rate A M 0.26 

(g/g-day) Surface Area A F 45 estimat

(cm ) A M 48 2 

Dietary Composition Spring Summer Fall Winter Location/Habitat (measure) Referenc

Hymenoptera 17.3 12.4 Georgia/salt marsh Kale, 196

Homoptera 13.0 40.1 

Coleoptera 11.6 12.6 (% wet volume; 

Lepidoptera 14.6 2.9 stomach contents) 

Diptera 8.9 7.7 

Hemiptera 5.4 10.0 

Orthoptera 5.6 0.8 

spiders 15.1 6.2 

other arthropods 

(crabs, amphipods) 1.8 0.9 

molluscs (snails) 3.5 4.0 

other (insect eggs, 

undetermined, etc.) 4.5 3.3 
Marsh Wren (Cistothorus palustris) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range ion/Habitat Refere

Territory A M spring 0.0060 ± 0.0014 SD Georgia/salt marsh 1, 1958 Kale, 

Size (ha) 0.0156 ± 0.0050 SD Georgia/salt marsh 2, 1958 

A M spring 0.17 ± 0.021 SE 0.0242 - 0.360 west Washington/fresh Verne

A M spring 0.07 ± 0.06 SD Manitoba/fresh cattail marsh Leona

0.0085 ± 0.0042 SD Georgia/salt marsh 2, 1959 

mixed-species marsh 

Population spring: 

Density pairs/ha 48.3 ± 5.3 SD 45.1 - 56.2 Georgia/salt marsh (4 years) Kale, 1

males/ha 8.5 west Washington/fresh Verne

males/ha 3.7 ± 0.5 SD 3.4 - 4.3 Manitoba/fresh mixed- Leona

16.9 mixed-species marsh 

(2 areas) species marsh (3 years) 

Clutch Size 4.5 3 - 5 Georgia/salt marsh Kale, 

6.0 ± 0.19 SD 4 - 8 east Washington/fresh Verne

5.8 ± 0.8 SD Manitoba/fresh cattail marsh Leona

pond-margin marsh 

Clutches/Year 1 - 2 0 - 3 Georgia/salt marsh Kale, 

2 0 - 2 east Washington/fresh Verne

2 - 3 0 - 3 west Washington/fresh Verne

pond- margin marsh 

mixed-species marsh 

Days 13.1 12 - 14 Georgia/salt marsh Kale, 1

Incubation 

15.1 13 - 16 west Washington/fresh Verne

marsh 

Locat

2-188 Marsh Wren 
Marsh Wren (Cistothorus palustris) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range ion/Habitat Refere

Age at B 12 - 13 10 - 15 Georgia/salt marsh Kale, 1

Fledging B 14 11 - 16 Washington/fresh marshes Verne

Number 3.4 ± 3.4 SD Manitoba/fresh mixed marsh Leona

Fledge per Active Nest Number 4.5 ± 1.3 SD Manitoba/fresh mixed- Leona

Fledge per species marsh Successful 5.1 ± 1.2 SD Manitoba/fresh cattail marsh Leona

Nest Age at Sexual B 1 year Manitoba/fresh marsh Leona

Maturity B 1 year Washington/fresh marsh Verne

Annual A B 32 Georgia/salt marsh Kale, 1

Mortality J B 70 

Rates (percent) 

Seasonal 

Activity Begin Peak End Location Referen

Mating/Laying April mid-August Georgia Kale, 19

mid-April May - June early July eastern Washington Verner, 

late March April - May mid-July (Turnbull) Verner, 

late May early August western Washington (Seattle) Welter, 

New York 

Hatching early May mid-July eastern Washington Verner, 

mid-April early August (Turnbull) Verner, 

western Washington (Seattle) 

Migration fall September late October New York, Minnesota Welter, 

spring April May June New York, Minnesota Welter, 

mid-March eastern Washington Verner, 

(nonmigratory) (Turnbull) Verner, 

western Washington (Seattle) 

Locat

2-189 Marsh Wren 
Marsh Wren (Cistothorus palustris) 

1 As cited in Dunning (1984).2 Collection dates not specified. Resident population; presumably averaged from birds captured throughout the year

3 Estimated from Welter's (1935) growth curve based on 50 nestlings.

4 Measured by oxygen respirometry; lowest value of metabolism of postabsorptive wrens resting in the dark (but not 

within the thermoneutral zone. 

5 Measured by oxygen respirometry; birds not postabsorptive, but resting in a dark box at temperatures within the the

6 Measured by oxygen respirometry; birds somewhat active in their cage. 

7 Estimated from oxygen consumption, for conditions, see note 3. 

8 Estimated from oxygen consumption, for conditions, see note 4. 

9 Estimated from oxygen consumption, for conditions, see note 5. 

10 Estimated from measured daily food intake, excretory losses, assimilation, and respiration for active birds in small c

determinations total). Because of the birds' high activity levels, Kale (1965) considered the measure representative 

11 Estimated using allometric equation 3-36 (Nagy, 1987) and body weights from Kale (1965). 

12 Measured daily food intake of birds in cages and measured caloric content of diet provided. Because of the birds' h

considered the measure representative of free-living birds. 

13 Estimated from Kale's (1965) measured daily food intake (see note 11) assuming 5.62 kcal/gram (dry weight) insects

efficiency, and a 67 percent water content for insects. 

14 Estimated from free-living metabolic rate estimated from Nagy's (1987) equation 3-36 (see note 10) assuming the sam

note 12. These predicted food ingestion rates (>0.95 g/g-day) for free-living birds exceed the value estimated for Ka

g/g-day); however, the latter does not include metabolic requirements of searching for food, reproduction, or unusu

15 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Kale (1965).

16 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

17 Summer column represents combination of spring and summer data; winter column represents combination of fall a

2-190 Marsh Wren 
References (including Appendix) 

American Ornithologists' Union. (1983) Check-list of North American birds. Lawrence, KS: 

Allen Press, Inc. 

Bent, A. C. (1948) Life histories of North American nuthatches, wrens, thrashers, and their 

allies. Washington, DC: U.S. Government Printing Office; Smithsonian Inst. U.S. Nat. 

Mus., Bull. 195. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Dunning, J. B., Jr. (1984) Body weights of 686 species of North American birds. Western 

Bird Banding Association, Monograph No. 1. Cave Creek, AZ: Eldon Publishing. 

Gutzwiller, K. J.; Anderson, S. H. (1987) Habitat suitability index models: marsh wren. U.S. 

Fish Wildl. Serv. Biol. Rep. 82(10.139). 

Kale, H. W., II (1964) Food of the long-billed marsh wren, Telmatodytes palustris griseus, in 

the salt marshes of Sapelo Island, Georgia. Oriole 29: 47-61. 

Kale, H. W., II. (1965) Ecology and bioenergetics of the long-billed marsh wren 

Telmatoidytes palustris griseus (Brewster) in Georgia salt marshes. Publ. Nuttall 

Ornith. Club No. 5. 

Leonard, M. L.; Picman, J. (1986) Why are nesting marsh wrens and yellow-headed 

blackbirds spatially segregated? Auk 103: 135-140. 

Leonard, M. L.; Picman, J. (1987) Nesting mortality and habitat selection by marsh wrens. 

Auk 104: 491-495. 

Leonard, M. L.; Picman, J. (1988) Mate choice by marsh wrens: the influence of male and 

territory quality. Anim. Behav. 36: 517-528. 

Meeh, K. (1879) Oberflachenmessungen des mensclichen Korpers. Z. Biol. 15: 426-458. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

National Geographic Society. (1987) Field guide to the birds of North America. Washington, 

DC: National Geographic Society. 

Orians, G. H.; Wilson, M. F. (1964) Interspecific territories of birds. Ecology 45: 736-745. 

Picman, J. (1977) Intraspecific nest destruction in the long-billed marsh wren, 

Telmatodytes palustris plustris. Can. J. Zool. 55: 1997-2003. 

2-191 Marsh Wren 
Rubner, M. (1883) Uber den Einfluss der Korpergrosse auf Stoff- und Kraftweschsel. Z. 

Biol. 19: 535-562. 

Verner, J. (1964) Evolution of polygamy in the long-billed marsh wren. Evolution 18: 

252-261. 

Verner, J. (1965) Breeding biology of the long-billed marsh wren. Condor 67: 6-30. 

Verner, J. (1971) Survival and dispersal of male long-billed marsh wrens. Bird-Banding 42: 

92-98. 

Verner, J.; Engelsen, G. H. (1970) Territories, multiple nest building, and polygamy in the 

long-billed marsh wren. Auk 87: 557-567. 

Walsberg, G. E.; King, J. R. (1978) The relationship of the external surface area of birds to 

skin surface area and body mass. J. Exp. Biol. 76: 185-189. 

Welter, W. A. (1935) The natural history of the long-billed marsh wren. Wilson Bull. 47: 3-34. 

2-192 Marsh Wren 
2.1.15. American Robin (thrushes) 

Order Passeriformes, Family Muscicapidae, Subfamily Turdinae. Thrushes are 

common, medium-sized birds that eat worms, insects, and fruit. They live in a variety of 

habitats, including woodlands, swamps, suburbs, and parks. Most thrushes build nests of 

mud and vegetation on the ground or in the crotches of trees or shrubs; bluebirds nest in 

holes in trees and posts or in nest boxes. This group forages primarily on the ground and 

in low vegetation by probing and gleaning. Some thrushes are neotropical migrants while 

others reside year-round in North America. Thrushes range in size from the eastern and 

western bluebirds (18 cm from bill tip to tail tip) to the American robin (25 cm). Male and 

female plumages are similar in most thrushes, although in some species, such as the 

bluebirds, the males are more brightly colored. 

Selected species 

The American robin (Turdus migratorius) occurs throughout most of the continental 

United States and Canada during the breeding season and winters in the southern half of 

the United States and in Mexico and Central America. The breeding range of the robin has 

expanded in recent times with the increasing area covered by lawns and other open 

habitats (Howell, 1942; Martin et al., 1951; James and Shugart, 1974). 

Body size. The sexes are similar in size and appearance. Their size varies slightly 

geographically; the smallest robins are found in the eastern United States and along the 

Pacific coast, and the largest ones occur in the Rocky Mountains, northern Great Plains, 

and northern deserts (Aldrich and James, 1991).d The size of robins tends to increase with 

latitude in eastern North America but does not in western North America (Aldrich and 

James, 1991). Fledglings attain adult size at approximately 6 weeks of age (Howell, 1942). 

Habitat. Access to fresh water, protected nesting sites, and productive foraging 

areas are important requirements for breeding robins (Speirs, 1953). Breeding habitats 

include moist forests, swamps, open woodlands, orchards, parks, and lawns. Robins 

forage on the ground in open areas, along habitat edges, or the edges of streams; they 

also forage above ground in shrubs and within the lower branches of trees (Paszkowski, 

1982; Malmborg and Willson, 1988). Nests in wooded areas are usually near some type of 

opening such as the forest edge or a treefall gap (Young, 1955; Knupp et. al., 1977). During 

the nonbreeding season, robins prefer moist woods or fruit-bearing trees and shrubs 

(Robbins et al., 1983). In the fall, flocks of migratory robins are often found along forest 

edges or clearings where fruits are most plentiful (Baird, 1980). 

Food habits. Robins forage by hopping along the ground in search of grounddwelling invertebrates and by searching for fruit and foliage-dwelling insects in shrubs and 

low tree branches (Malmborg and Willson, 1988; Paszkowski, 1982). In the months 

preceding and during the breeding season, robins feed mainly (greater than 90 percent 

volume) on invertebrates and on some fruits; during the remainder of the year, their diet 

d

Based on linear measurements of museum study skins. 

2-193 American Robin 
consists primarily (over 80 to 99 percent by volume) of fruits (Martin et al., 1951; Gochfeld 

and Burger, 1984; Wheelwright, 1986). Robins eat a wide variety of both plant and animal 

foods; in a compilation of diet records collected throughout the United States and southern 

Canada, Wheelwright (1986) found that robins consumed fruits from 51 genera and 

invertebrates from 107 families. Commonly eaten fruits include plums, dogwood, summac, 

hackberries, blackberries, cherries, greenbriers, raspberries, and juniper (Martin et al., 

1951; Wheelwright, 1986); common invertebrates include beetles, caterpillars, moths, 

grasshoppers, spiders, millipedes, and earthworms (Martin et al., 1951; Wheelwright, 1986; 

Paszkowski, 1982). Wheelwright (1986) has compiled seasonal changes in the proportion 

of plants and invertebrates consumed by robins in three different sections of the United 

States (see table). Wheelwright (1986) also has summarized the average occurrence of 

fruits of various plant families in the stomachs of robins by month for these sections. 

Martin et al. (1951) have summarized the occurrence of fruits of various plant families in 

more specific areas of the United States (see Appendix). 

Wheelwright (1986) found no differences between the sexes in the proportion or 

types of invertebrates and fruits eaten. Very young robins (up to at least 35 days of age) 

feed almost entirely on insects and other invertebrates (Howell, 1940). Older juveniles tend 

to eat a higher proportion of fruit and easy-to-capture prey than adults (Gochfeld and 

Burger, 1984; Wheelwright, 1986). In a given area, robins often show food preferences: a 

population in central New York seemed to prefer northern arrowwood and spice bush fruits 

over most other plants (Wheelwright, 1988); in Illinois, a group ate predominantly frost 

grapes and Virginia creeper in the late summer and fall (Malmborg and Willson, 1988). 

During seasons when fruits dominate the diet, robins may need to consume 

quantities in excess of their body weight to meet their metabolic needs each day (see 

table). Robins as well as other fruit-eating birds exhibit a low digestive efficiency for fruits; 

Karasov and Levey (1990) estimated the metabolizable energy coefficient (MEC) (i.e., the 

proportion of food energy that actually is assimilated) for robins eating a mixed fruit diet to 

be only 55 percent, perhaps because of the low retention time of the digested matter in the 

gut (Levey and Karasov, 1992). The short retention time might actually be an adaptation to 

eating fruit because large quantities of fruit must be processed to obtain an adequate 

protein intake. In contrast, when eating insects, robins (as well as other bird species) 

exhibit a higher digestive efficiency of approximately 70 percent (Levey and Karasov, 

1989). Moreover, the energy content of insects tends to be higher than that of most fruits, 

particularly on a wet-weight basis (see Chapter 4). Thus, during the spring when robins 

are consuming insects, they should consume a smaller amount relative to their body 

weight than when eating fruits (Chapter 4 provides approaches that can be used to 

estimate insect ingestion rates for robins). 

Molt. Postjuvenile and postbreeding (prebasic) molts occur from late July to 

October (Wheelwright, 1986; Sharp, 1990). During this molt, robins are consuming largely 

fruits and other plant materials, which contain limited proteins. This may contribute to 

larger fruit consumption rates at this time. During the prebreeding (prealternate) molt, 

robins are feeding primarily on insects and other invertebrates (letter 

2-194 American Robin 
from N.T. Wheelright, Department of Biology, Bowdoin College, Brunswick, ME, to Sue 

Norton, March 18, 1992). 

Migration. Most robins nesting in the northern United States and Canada winter in 

the Gulf Coast States and the Carolinas (Speirs, 1953; Dorst, 1962, as cited in Henny, 

1972). Wintering robins are most abundant between 30 and 35 degrees N latitude (Speirs, 

1953). Robin flocks migrate during the day (Robbins et al., 1983); most northern robins 

leave their breeding grounds from September to November and return between February 

and April (Howell, 1942; Young, 1951; Fuller, 1977). 

Breeding activities and social organization. The onset of the breeding season is 

later at higher latitudes (approximately 3 days for each additional degree in the east) and 

altitudes, but mating and egg laying generally occur in April or May (James and Shugart, 

1974; Knupp et al., 1977). Males arrive on the breeding grounds before females to 

establish territories; females pair with established males, usually for the duration of the 

breeding season (Young, 1951). The female primarily builds the nest out of mud, dried 

grass, weedy stems, and other materials, constructing it on horizontal limbs, tree-branch 

crotches, within shrubs, or on any one of a number of man-made structures with horizontal 

surfaces (Howell, 1942; Klimstra and Stieglitz, 1957). First clutches usually contain three 

or four eggs; later clutches tend to contain fewer eggs (Young, 1955). The female does all 

of the incubating, which continues for 10 to 14 days following the laying of the second egg 

(Klimstra and Stieglitz, 1957; Young, 1955). Both males and females feed the nestlings 

(Young, 1955). Following fledging, the brood often divides, with the male and female each 

feeding half of the fledglings for another 2 weeks (Weatherhead and McRae, 1990). 

Females may start another brood before the current one is independent, leaving the male 

to feed all of the fledglings (Young, 1955). After reaching independence, juveniles often 

form foraging flocks in areas of high food availability (Hirth et al., 1969). 

Early in the breeding season, robins often roost communally. Males can continue to 

use these roosts throughout the breeding season, whereas females stop once they begin 

incubating eggs (Howell, 1940; Pitts, 1984). As fall approaches and their diet turns more 

toward fruits, robins in many areas begin to roost communally again and may join other 

species, such as common grackles and European starlings, in large roosts (Morrison and 

Caccamise, 1990). 

Home range and resources. During the breeding season, male robins establish 

breeding territories, which the female helps to defend against other robins. Nonetheless, 

the territories of different pairs often overlap where neither pair can establish dominance 

(Young, 1951). Most foraging during the breeding season is confined to the territory, but 

adults sometimes leave to forage in more productive areas that are shared with other 

individuals (Howell, 1942; Young, 1951; Pitts, 1984). In some prime nesting areas (e.g., 

dense coniferous forest), where robin densities are high, territories are small and the birds 

might often forage elsewhere (Howell, 1942). Adult robins often return to the same territory 

in succeeding years (Young, 1951). During the nonbreeding roosting period, robins are 

likely to return to the same foraging sites for many weeks and to join roosts within 1 to 3 

km of these foraging areas (Morrison and Caccamise, 1990). 

2-195 American Robin 
�

�

�

�

Population density. Nesting population density varies with habitat quality. Densely 

forested areas that provide well-protected nest sites have been found to support high 

densities of nesting robins; however, the relatively small territories found in these areas 

might not be used as much for foraging as those containing open areas (Howell, 1942). In 

the nonbreeding season, robins often join single- or mixed-species roosts that can include 

tens of thousands of birds (Morrison and Caccamise, 1990). Wintering robins are most 

common in pine or oak pine communities of the southeastern and southcentral United 

States, and decrease in abundance in drier, less forested areas westward (Speirs, 1953). 

Population dynamics. Robins first attempt to breed the year after they hatch 

(Henny, 1972) and will raise multiple broods in a season (Howell, 1942). Predation is often 

a major source of mortality for both eggs and nestlings (Knupp et al., 1977; Klimstra and 

Stieglitz, 1957). Approximately half of the adult birds survive from year to year (Farner, 

1949; Henny, 1972); the average longevity of a robin that survives to its first January is 

from 1.3 to 1.4 years (Farner, 1949). 

Similar species (from general references) 

� The wood thrush (Hylocichla mustelina), which is smaller than the robin (18 

cm), co-occurs with the robin in some woodland habitats but is only present 

in the eastern United States. This species nests primarily in the interiors of 

mature forests and has been decreasing in abundance over the past decade 

as forested habitats in North America become increasingly fragmented 

(Robbins et al., 1989; Terborgh, 1989). This species is also primarily a 

summer resident, wintering in Florida and the neotropics. 

� The hermit thrush (Catharus guttatus) is found in coniferous and mixed 

woodlands at northerly latitudes or high elevations and winters primarily in 

the southern half of the United States. This species is also significantly 

smaller (15 cm) than the robin. 

� Swainson's thrush (Catharus ustulatus) is present in the western and 

northeastern United States during the summer months, wintering in the 

neotropics. It is also smaller than the robin (16 cm). 

� The varied thrush (Ixoreus naevius) occurs in moist coniferous forests of the 

Pacific Northwest. This bird is similar in size (21 cm) to the robin. 

General references 

Howell (1942); Young (1955); National Geographic Society (1987); Robbins et al. 

(1983); Sharp (1990). 

2-196 American Robin 
American Robin (Turdus migratorius) 

2-197 American Robin 

Factors 

Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referenc

Body Weight A B all seas. 77.3 ± 0.36 SE 63.5 - 103 Pennsylvania Clench & 

(g) 

A M nonbreed. 86.2 ± 6.1 SD New York Wheelwr

A F nonbreed. 83.6 ± 6.4 SD A M breeding 77.4 New York Wheelwr

A F breeding 80.6 

nestlings: 

at hatching 5.5 4.1 - 6.7 New York/forest Howell, 1

day 2 12.6 8.4 - 17.5 

day 4 24.3 17.9 - 32.3 

day 6 39.4 32.5 - 45.9 day 8 50.9 42.0 - 59.3 day 10 55.2 49.0 - 63.2 day 14 55.0 51.8 - 58.2 

Egg Weight (g) 6.26 4.6 - 8.4 New York Howell, 1

Metabolic Rate A B basal 259 estimate

(kcal/kg-day) 

- B existence 344 Kansas Hazelton 

A B free-living 713 (336 - 1,513) estimate

(estimate

Food Ingestion A B free-living 1,070 ± 220 SD 760 - 1,330 Kansas Hazelton 

Rate (kcal/kgday) 

Food Ingestion B B free-living 0.89 ± 0.73 SD California Skorupa 

Rate (g/g-day) 

- B free-living 1.52 ± 0.25 SD 1.22 - 1.96 Kansas Hazelton 

Water A B 0.14 estimate

Ingestion 

Rate (g/g-day) 
American Robin (Turdus migratorius) 

Factors 

Age/Sex/ Range or Location or 

Cond./Seas. Mean (95% CI of mean) subspecies Referenc

Surface Area A B 198 Walsberg 

(cm )2 

A B 182 estimate

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

nestlings/fledglings: south central New Howell, 1

earthworms 15.0 York/forest 

sowbugs 1.7 

spiders 2.3 (% wet weight; stomach 

millipedes 3.1 contents) 

short-horned grasshoppers 4.9 (age of robins ranged from 3 

beetles 11.6 to 35 days after hatching; 

lepidopteran larvae 24.7 presence of grass is likely to ants 3.2 be accidental - carried along 

unidentified animal 5.2 with prey) 

grass (all parts) 19.5 

mulberries 3.2 

honeysuckle seeds 2.4 

unidentified plants 4.2 

adults: eastern United States Wheelwr

fruit 7 68 92 83 (% volume; 

invertebrates 93 32 8 17 stomach contents) 

adults: central United States Wheelwr

fruit 8 41 76 73 (% volume; 

invertebrates 92 59 24 27 stomach contents) 

adults: western United States Wheelwr

fruit 17 29 63 70 (% volume; 

invertebrates 83 71 37 30 stomach contents) 

2-198 American Robin 
American Robin (Turdus migratorius) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Range Location/Habitat Referenc

Territory spring 

Size (ha) A B 0.42 0.12 - 0.84 Tennessee/campus Pitts, 198

A B 0.11 New York/dense conifers Howell, 1

A B 0.21 /unspecified forest 

Foraging summer, Home Range adults (ha) feeding: 

nestlings 0.15 ± 0.021 SE Ontario/deciduous forest Weather

fledglings 0.81 ± 0.13 SE 

Population spring Density A B 1.98 ± 0.48 SD 1.39 - 2.54 Tennessee/campus Pitts, 198

(pairs/ha) 

A B 8.6 New York/dense conifers Howell, 1

A B 4.9 /unspecified forest 

Clutch Size 3.17 1 - 5 Illinois/suburban Klimstra 

3.45 ± 0.59 SD 1 - 5 Wisconsin/park Young, 1

Clutches/Year 2 1 - 3 New York/forest Howell, 1

Days 12.5 ± 0.14 SE 10 - 14 Wisconsin/park Young, 1

Incubation Age at B 13.4 ± 0.13 SE Wisconsin/park Young, 1

Fledging (days) Number 5.6 Wisconsin/park Young, 1

Fledge per 3.9 New York/forest Howell, 1

Breeding Pair 1.5 ± 0.45 SE Ontario/deciduous forest Weather

Number five areas 2.9 2.4 - 3.4 Wisconsin/park Young, 1

Fledge per (over 5 areas) Successful 2.5 ± 0.15 SD Maine/forest Knupp e

Nest 

2-199 American Robin 
American Robin (Turdus migratorius) 

Population 

Dynamics 

Age/Sex 

Cond./Seas. Mean Range Location/Habitat Referenc

Age at B 1 year NS Henny, 1Sexual Maturity Annual A B 51 ± 0.5 SE North America Henny, 1

Mortality Rates J B 78 - 82 

(percent) Longevity after Jan. 1 of 1.3 - 1.4 up to 9 North America Farner, 1

(years) first year 

Seasonal 

Activity Begin Peak End Location Referenc

Mating/Laying early April mid-April late April Illinois Klimstra 

late April mid-July south central New York Howell, 1

early May late May early July n Maine Knupp e

Hatching early May west: California, New James & 

early May east: VA, WV, DC, NY James & 

mid-May northeast: VT, NH, CT James & 

mid-April Kentucky James & 

early June Colorado James & 

Mexico 

Molt fall July & August North America Wheelwr

Migration fall mid-Sept. mid-October early November migrating through Fuller, 19

spring February March Howell, 1

mid-March mid-April arriving New York Young, 1

early November Minnesota Howell, 1

leaving New York 

arriving Wisconsin 

1 As cited in Dunning (1984). 

2-200 American Robin 2 Estimated using equation 3-27 (Lasiewski and Dawson, 1967) and body weights from Clench and Leberman (1978). 3 Hazelton et al. (1984) estimate using Kendeigh's (1969) equations for a 55-g bird. 4 Estimated using equation 3-36 (Nagy, 1987) and body weights from Clench and Leberman (1978).
American Robin (Turdus migratorius) 

5 Estimated kcal consumed in feeding trials. Diet consisted of paired offerings of fruit (to test preferences) over a 2-d

Fruit included strawberries (2.29 kcal/g), cherries (4.34 kcal/g), green grapes (2.59 kcal/g), and purple grapes (5.85 kc

birds = 55 g. 

6 Based on gizzard contents of robins caught foraging in vineyards; diet 85 percent (wet weight) grapes, 11.5 percent 

other plants. Mean weight of the birds = 82.3 g. 

7 Based on same study described in note 5 and estimated weights of fruits consumed. 

8 Estimated using equation 3-15 (Calder and Braun, 1983) and body weights from Clench and Leberman (1978). 

9 Beak surface area 3.1 cm2; leg surface area 14.0 cm2. 

10 Estimated using equation 3-21 (Meeh, 1879 and Rubner, 1883, as cited in Walsberg and King, 1978) and body weigh

(1978). 

11 The U.S. Biological Survey and U.S. Fish and Wildlife Service records on which this study is based have several lim

collected in agricultural and suburban than natural areas; seasons and time of day of collection were convenient to 

digested foods such as earthworms and other soft-bodied insects are underrepresented. 

12 Birds nesting in high densities in dense coniferous forest probably foraged elsewhere more of the time than did bird

less dense forests. 

13 Also included data from Howell (1942) (Ithaca, New York) in calculations. 

2-201 American Robin 
References (including Appendix) 

Aldrich, J. W.; James, F. C. (1991) Ecogeographic variation in the American robin (Turdus 

migratorius). Auk 108: 230-249. 

Armstrong, J. T. (1965) Breeding home range in the nighthawk and other birds: its 

evolutionary and ecological significance. Ecology 46: 619-629. 

Baird, J. W. (1980) The selection and use of fruit by birds in an eastern forest. Wilson Bull. 

92: 63-73. 

Bovitz, P. (1990) Relationships of foraging substrate selection and roosting in American 

robins and European starlings [master's thesis]. New Brunswick, NJ: Rutgers 

University. 

Brackbill, H. (1952) Three-brooded American robin. Bird-Banding 23: 29. 

Butts, W. K. (1927) The feeding range of certain birds. Auk 44: 329-350. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Clench, M. H.; Leberman, R. C. (1978) Weights of 151 species of Pennsylvania birds 

analyzed by month, age, and sex. Bull. Carnegie Mus. Nat. Hist. 

Dorst, J. (1962) The migration of birds. Boston: Houghton Mifflin Co. 

Dunning, J. B., Jr. (1984) Body weights of 686 species of North American birds. Western 

Bird Banding Association, Monograph No. 1. Cave Creek, AZ: Eldon Publishing. 

Farner, D. S. (1945) Age groups and longevity in the American robin. Wilson Bull. 57: 56-74. 

Farner, D. S. (1949) Age groups and longevity in the American robin: comments, further 

discussion, and certain revisions. Wilson Bull. 61: 68-81. 

Fuller, P. (1977) Fall robin migration. Loon 49: 239-240. 

Gochfeld, M.; Burger, J. (1984) Age differences in foraging behavior of the American robin 

(Turdus migratorius). Behaviour 88: 227-239. 

Hamilton, W. J., Jr. (1940) Summer food of the robin determined by fecal analyses. Wilson 

Bull. 52: 79-82. 

Hamilton, W. J., Jr. (1943) Spring food of the robin in central New York. Auk 60: 273. 

2-202 American Robin 
Hazelton, P. K., Robel, R. J.; Dayton, A. D. (1984) Preferences and influences of paired food 

items on energy intake of American robins (Turdus migratorius) and gray catbirds 

(Dumetella carolinensis). J. Wildl. Manage 48: 198-202. 

Henny, C. J. (1972) An analysis of the population dynamics of selected avian species with 

special reference to changes during the modern pesticide era. Washington, DC: Bur. 

Sport. Fish. Wildl., Wildl. Res. Rep. 1. 

Hirth, D. H.; Hester, A. E.; Greeley, F. (1969) Dispersal and flocking of marked young robins 

(Turdus m. migratorius) after fledging. Bird-Banding 40: 208-215. 

Howell, J. C. (1940) Spring roosts of the robin. Wilson Bull. 52: 19-23. 

Howell, J. C. (1942) Notes on the nesting habits of the American robin (Turdus migratorius 

L.). Am. Midl. Nat. 28: 529-603. 

James, F. C.; Shugart, H. H. (1974) The phenology of the nesting season of the American 

robin (Turdus migratorius) in the United States. Condor 76: 159-168. 

Jung, R. E. (1992) Individual variation in fruit choice by American robins Turdus 

migratorius. Auk 109: 98-111. 

Karasov, W. H.; Levey, D. J. (1990) Digestive system trade-offs and adaptations of 

frugivorous passerine birds. Physiol. Zool. 63: 1248-1270. 

Kendeigh, S. C. (1969) Tolerance of cold and Bergmann's rule. Auk 86: 13-25. 

Klimstra, W. D.; Stieglitz, W. O. (1957) Notes on reproductive activities of robins in Iowa 

and Illinois. Wilson Bull. 69: 333-337. 

Knupp, D. M.; Owen, R. B.; Dimond, J. B. (1977) Reproductive biology of American robins in 

northern Maine. Auk 94: 80-85. 

Lasiewski, R. C.; Dawson, W. R. (1967). A reexamination of the relation between standard 

metabolic rate and body weight in birds. Condor 69: 12-23. 

Levey, D. J.; Karasov, W. H. (1989) Digestive responses of temperate birds switched to fruit 

or insect diets. Auk 106: 675-686. 

Levey, D. J.; Karasov, W. H. (1992) Digestive modulation in a seasonal frugivore: the 

American robin Turdus migratorius. Am. J. Physiol. 262: G711-G718. 

Malmborg, P. K.; Willson, M. F. (1988) Foraging ecology of avian frugivores and some 

consequences for seed dispersal in an Illinois woodlot. Condor 90: 173-186. 

Martin, A. C.; Zim, H. S.; Nelson, A. L. (1951) American wildlife and plants. New York, NY: 

McGraw-Hill Book Company, Inc. 

2-203 American Robin 
Meeh, K. (1879) Oberflachenmessungen des mensclichen Korpers. Z. Biol. 15: 426-458. 

Morrison, D. W.; Caccamise, D. F. (1990) Comparison of roost use by three species of 

communal roostmates. Condor 92: 405-412. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

National Geographic Society. (1987) Field guide to the birds of North America. Washington, 

DC: National Geographic Society. 

Paszkowski, C. A. (1982) Vegetation, ground, and frugivorous foraging of the American 

robin Turdus migratorius. Auk 99: 701-709. 

Pitts, T. D. (1984) Description of American robin territories in northwest Tennessee. 

Migrant 55: 1-6. 

Robbins, C. S.; Bruun, B.; Zim, H. S. (1983) A guide to field identification: birds of North 

America. New York, NY: Golden Press. 

Robbins, C. S.; Sauer, J. R.; Greenberg, R. S.; et al. (1989) Population declines in North 

American birds that migrate to the neotropics. Proc. Natl. Acad. Sci. USA 86: 7658-

7662. 

Rubner, M. (1883) Uber den Einfluss der Korpergrosse auf Stoff- und Kraftweschsel. Z. 

Biol. 19: 535-562. 

Sharp, M. H. (1990) America's songbird--species profile: American robin (Turdus 

migratorius). Wild Bird 4: 22-27. 

Skorupa, J. P.; Hothem, R. L. (1985) Consumption of commercially-grown grapes by 

American robins (Turdus migratorius): a field evaluation of laboratory estimates. J. 

Field Ornithol. 56: 369-378. 

Speirs, J. M. (1953) Winter distribution of robins east of the Rocky Mountains. Wilson Bull. 

65: 175-183. 

Terborgh, J. (1989). Where have all the birds gone? Princeton, NJ: Princeton University 

Press. 

Walsberg, G. E.; King, J. R. (1978) The relationship of the external surface area of birds to 

skin surface area and body mass. J. Exp. Biol. 76: 185-189. 

Weatherhead, P. J.; McRae, S. B. (1990) Brood care in American robins: implications for 

mixed reproductive strategies by females. Anim. Behav. 39: 1179-1188. 

Wheelwright, N. T. (1986) The diet of American robins: an analysis of U.S. Biological 

Survey records. Auk 103: 710-725. 

2-204 American Robin 
Wheelwright, N. T. (1988) Seasonal changes in food preferences of American robins in 

captivity. Auk 105: 374-378. 

Young, H. (1951) Territorial behavior of the eastern robin. Proc. Linnean Soc. N.Y. 58-62: 

1-37. 

Young, H. (1955) Breeding behavior and nesting of the eastern robin. Am. Midl. Nat. 53: 

329-352. 

2-205 American Robin 
2.2. MAMMALS 

Table 2-2 lists the mammalian species described in this section. For range maps, 

refer to the general references identified in the individual species profiles. The remainder 

of this section is organized by species in the order presented in Table 2-2. The availability 

of information in the published literature varies substantially among species, as is reflected 

in the profiles. Some of the selected species include two or more subspecies; these are 

indicated in the profiles when reported by the investigators. Body lengths of the mammals 

are reported for the length of the outstretched animal from the tip of the nose to the base 

of the tail. The tail measurements do not include the hairs at the tip, but only the tail 

vertebrae. Body weight is reported as fresh wet weight with pelage, unless otherwise 

noted. 

2-207
l

Table 2-2. Mammals Included in the Handbook 

Order 

Subfamily Common name Scientific name Section 

Soricidae short-tailed shrew Blarina brevicauda 2.2.1 

Canidae red fox Vulpes vulpes 2.2.2 

Procyonidae raccoon Procyon lotor 2.2.3 

Mustelidae 

Mustelinae mink Mustela vison 2.2.4 

Lutrinae river otter Lutra canadensis 2.2.5 

Phocidae harbor seal Phoca vitu ina 2.2.6 

Cricetidae 

Sigmodontinae deer mouse Peromyscus maniculatus 2.2.7 

Arvicolinae prairie vole Microtus ochrogaster 2.2.8 

meadow vole Microtus pennsylvanicus 2.2.9 

muskrat Ondatra zibethicus 2.2.10 

Leporidae eastern cottontail Sylvilagus floridanus 2.2.11 

2-208
�

�

2.2.1. Short-Tailed Shrew (shrews) 

Order Insectivora, Family Soricidae. Shrews are small insectivorous mammals that 

inhabit most regions of the United States. They have high metabolic rates and can eat 

approximately their body weight in food each day. Most species are primarily vermivorous 

and insectivorous, but some also eat small birds and mammals. 

Selected species 

The northern short-tailed shrew (Blarina brevicauda) ranges throughout the northcentral and northeastern United States and into southern Canada (George et al., 1986). It 

eats insects, worms, snails, and other invertebrates and also may eat mice, voles, frogs, 

and other vertebrates (Robinson and Brodie, 1982). Because they prey on other 

vertebrates, shrews can concentrate DDT (and presumably other bioaccumulative 

chemicals) to levels 10 times higher than either Peromyscus and Clethrionomys (Dimond 

and Sherburne, 1969). Shrews are an important component of the diet of many owls 

(Palmer and Fowler, 1975; Burt and Grossenheider, 1980) and are also prey for other 

raptors, fox, weasels, and other carnivorous mammals (Buckner, 1966). 

Body size. Short-tailed shrews are 8 to 10 cm in length with a 1.9 to 3.0 cm tail 

(Burt and Grossenheider, 1980). The short-tailed shrew is the largest member of the 

genus, with some weighing over 22 g (George et al., 1986; see table). Some studies have 

found little or no sexual dimorphism in size (Choate, 1972), while other reports show that 

males are slightly larger than females (George et al., 1986; Guilday, 1957). 

Metabolism. Short-tailed shrews are active for about 16 percent of each 24-hour 

period (Martinsen, 1969), in periods of around 4.5 minutes at a time (Buckner, 1964). The 

shrew's metabolism is inversely proportional to the ambient temperature, within the range 

of 0 to 25�C (Randolph, 1973). Sleeping metabolism is half that associated with normal, 

exploring activity (Randolph, 1973). Randolph (1973) developed a regression equation for 

meta e bolism (cc O2/g-hour) during (1) interrupted sleep:

(Winter) Y = 4.754 - 0.0869 (X - 16.4305) 

(Summer) Y = 5.3448 - 0.1732 (X - 16.2310) 

and (2) normal exploring activity: 

(Winter) Y = 6.5425 - 0.0516 (X - 12.0600) 

(Summer) Y = 7.949 - 0.2364 (X - 16.9554) where X= ambient temperature 

in �C. 

Randolph (1973) also developed a regression equation for overall metabolism (cal/animalhour) for shrews spending equal amounts of time sleeping and exploring (cal/animal-hour) 

as a function of ambient temperature: 

e

Randolph's (1973) equations could be simplified to match that of Deavers and Hudson (1981;

next page) in form; however, we report the equations as Randolph reported them. 

2-209 Short-Tailed Shrew 
�

(Winter) Y = 583.83 - 7.53 (X - 13.68)

(Summer) Y = 544.86 - 20.37 (X - 16.33), where X= ambient temperature in �C.

Deavers and Hudson (1981) found a linear increase in standard (near basal) 

metabolism with decreasing temperature that is similar to that for interrupted sleep 

described above (Y = standard metabolism in cc O2/g-hour): 

Y = 8.84 - 0.22 (X) where X= ambient temperature. 

Deavers and Hudson (1981) found that within the thermoneutral zone, the standard 

metabolic rate of the short-tailed shrew is approximately 190 percent the metabolic rate 

predicted from body weight. 

Habitat. Short-tailed shrews inhabit a wide variety of habitats and are common in 

areas with abundant vegetative cover (Miller and Getz, 1977). Short-tailed shrews need 

cool, moist habitats because of their high metabolic and water-loss rates (Randolph, 1973). 

Food habits. The short-tailed shrew is primarily carnivorous. Stomach analyses 

indicate that insects, earthworms, slugs, and snails can make up most of the shrew's food, 

while plants, fungi, millipedes, centipedes, arachnids, and small mammals also are 

consumed (Hamilton, 1941; Whitaker and Ferraro, 1963). Small mammals are consumed 

more when invertebrates are less available (Allen, 1938; Platt and Blakeley, 1973, cited in 

George et al., 1986). Shrews are able to prey on small vertebrates because they produce a 

poison secretion in their salivary glands that is transmitted during biting (Pearson, 1942, 

cited in Eadie, 1952). The short-tailed shrew stores food, especially in the autumn and 

winter (Hamilton, 1930; Martin, 1984). Robinson and Brodie (1982) found that short-tailed 

shrews cached most (86.6 percent) of the prey captured; only 9.4 percent was consumed 

immediately. Short-tailed shrews consume approximately 40 percent more food in winter 

than in summer (Randolph, 1973). The shrew must consume water to compensate for its 

high evaporative water loss, despite the fact that it obtains water from both food and 

metabolic oxidation (Chew, 1951). Deavers and Hudson (1981) indicated that the shorttailed shrew's evaporative water loss increases with increasing ambient temperature even 

within its thermoneutral zone. Short-tailed shrews' digestive efficiency is about 90 percent 

(Randolph, 1973). 

Temperature regulation and molt. The short-tailed shrew does not undergo torpor 

but uses nonshivering thermogenesis (NST) to compensate for heat loss during cold 

stress in winter (Zegers and Merritt, 1987). The short-tailed shrew exhibits three molts. 

Two are seasonal molts, the first in October/November replaces summer with winter 

pelage and occurs in first- and second-year shrews. The spring molt can occur any time 

from February to October. The third molt occurs in postjuveniles that have reached adult 

size (Findley and Jones, 1956). 

Breeding activities and social organization. The short-tailed shrew probably breeds 

all year, including limited breeding in winter even in the northern portions of its range 

(Blus, 1971). In Illinois, males were found to be most active from January to July, females 

from March to September (Getz, 1989). There are two peak breeding periods, in 

2-210 Short-Tailed Shrew 
�

�

�

�

the spring and in late summer or early fall (Blair, 1940). The home ranges of short-tailed 

shrews in summer overlap both within and between sexes (Blair, 1940), although females 

with young do exhibit some territoriality (Platt, 1976). Nomadic shrews are either young of 

the year or adults moving to areas with more abundant prey (Platt, 1976). 

Home range and resources. Short-tailed shrews inhabit round, underground nests 

and maintain underground runaways, usually in the top 10 cm of soil, but sometimes as 

deep as 50 cm (Hamilton, 1931; and Jameson, 1943, cited in George et al., 1986). Winter, 

nonbreeding home ranges can vary from 0.03 to 0.07 ha at high prey densities to 1 to 2.2 

ha during low prey densities with a minimum of territory overlap. In the summer, ranges of 

opposite sex animals overlap, but same sex individuals do not; females with young exclude 

all others from their area (Platt, 1976). 

Population density. Population densities vary by habitat and season (Getz, 1989; 

Jackson, 1961; Platt, 1968). In east-central Illinois, population density was higher in 

bluegrass than in tallgrass or alfalfa (Getz, 1989). In all three of these habitats, the shorttailed shrew exhibited annual abundance cycles, with peak densities ranging from 2.5 to 45 

shrews per hectare, depending on the habitat (Getz, 1989). The peaks occurred from July 

to October (12.9/ha average for all three habitats), apparently just following peak 

precipitation levels (Getz, 1989). 

Population dynamics. Winter mortality up to 90 percent has been reported for the 

short-tailed shrew (Barbehenn, 1958; Gottschang, 1965; Jackson, 1961, cited in George et 

al., 1986); however, Buckner (1966) suggests that mortality rates in winter may be closer to 

70 percent, which is similar to the average monthly mortality rate he found for subadult 

animals. Several litters, averaging four to five pups, are born each year (George et al., 

1986). 

Similar species (from general references) 

� The masked shrew (Sorex cinereus) (length 5.1 to 6.4 cm; weight 3 to 6 g) is 

smaller than the short-tailed shrew and is the most common shrew in moist 

forests, open country, and brush of the northern United States and 

throughout Canada and Alaska. It feeds primarily on insects. 

� Merriam's shrew (Sorex merriami) (5.7 to 6.4 cm) is found in arid areas and 

sagebrush or bunchgrass of the western United States and is smaller than 

the short-tailed shrew. 

� The smokey shrew (Sorex fumeus) (6.4 to 7.6 cm; 6 to 9 g), smaller than the 

short-tailed, prefers birch and hemlock forests with a thick leaf mold on the 

ground to burrow in. It uses burrows made by small mammals or nests in 

stumps, logs, and among rocks. Range is limited to the northeast United 

States and east of the Great Lakes in Canada. 

� The southeastern shrew (Sorex longirostris) (5.1 to 6.4 cm; 3 to 6 g) prefers 

moist areas. Found mostly in open fields and woodlots, its range is limited 

2-211 Short-Tailed Shrew 
�

�

�

�

�

�

to the southeastern United States. It nests in dry grass or leaves in a 

shallow depression. 

� The long-tailed shrew (Sorex dispar) (7.0 cm; 5 to 6 g) inhabits cool, moist, 

rocky areas in deciduous or deciduous-coniferous forests of the northeast, 

extending south to the North Carolina and Tennessee border. 

� The vagrant shrew (Sorex vagrans) (5.9 to 7.3 cm; 7 ± g) inhabits marshy 

wetlands and forest streams. Its range is confined to the western United 

States, excluding most of California and Nevada. In addition to insects, it 

also eats plant material. 

� The Pacific shrew (Sorex pacificus) (8.9 cm) is slightly larger than the shorttailed shrew. It is limited to redwood and spruce forests, marshes, and 

swamps of the northern California and southern Oregon coasts. 

� The dwarf shrew (Sorex nanus) (6.4 cm) is rare throughout its limited range 

in the western United States. 

� The least shrew (Cryptotis parva) (5.6 to 6.4 cm; 4 to 7 g) is easily 

distinguished from other shrews by its cinnamon color. It inhabits grassland 

and marsh; its range is similar to the short-tailed shrew but does not extend 

as far north. 

� The desert shrew (Notiosorex crawfordi) (Gray shrew) (5.1 to 6.6 cm) is 

rarely seen and is found only in the arid conditions, chaparral slopes, alluvial 

fans, and around low desert shrubs of the extreme southwest. It nests 

beneath plants, boards, or debris. 

General references 

Burt and Grossenheider (1980); George et al. (1986). 

2-212 Short-Tailed Shrew 
Short-Tailed Shrew (Blarina brevicauda) 

2-213 Short-Tailed Shrew 

Factors 

Age/Sex/ Range Cond./Seas. Mean or (95% CI) Location Referenc

Body Weight A B 15.0 ± 0.78 SD New Hampshire Schlesin

(g) 

M summer 19.21 ± 0.42 SD 17.0 - 22.0 w Pennsylvania Guilday, 

F summer 17.40 ± 0.48 SD 14.0 - 21.0 

M fall 16.87 ± 0.21 SD 13.0 - 22.0 

M fall 15.58 ± 0.23 SD 12.5 - 22.5 

neonate 0.67 - 1.29 Maryland/lab Blus, 197

Metabolic basal 82 80 - 84 Pennsylvania/lab Pearson

Rate average daily 125 106 - 150 (lO /kg-day) 2 

average daily 127 ± 15.3 SD 94 - 218 NS/lab Morrison

+ 20�C 126.5 Ontario, CAN/lab Randolp

- 20�C 207.1 

Metabolic Rate basal 390 Pennsylvania/lab Pearson

(kcal/kg-day) average daily 600 

average daily 680 Wisconsin/lab Morrison 

Food Ingestion A B: 22 - 23�C 7.95 ±0.17 g/d SD Ohio/lab Barrett & 

Rate 0.49 g/g-day 

A B: 25�C Wisconsin/lab Morrison 

0.62 g/g-day 

Water A B 0.223 Illinois/lab Chew, 19

Ingestion 

Rate (g/g-day) 

Inhalation A B 0.026 estimate

Rate (m /day) 3 

Surface Area A B 54 Pennsylvania/lab Pearson

(cm )2 

A B 84 estimate
Short-Tailed Shrew (Blarina brevicauda) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

earthworms 31.4 New York/NS Whitaker 

slugs & snails 27.1 

misc. animals 8.1 (% volume; stomach 

Endegon (fungi) 7.7 contents) 

beetles 5.9 vegetation 5.4 (June through October 

lepidopteran 4.3 collections combined) 

larvae 

chilopoda 1.8 

other 8.6 

insects 77.6 eastern United States Hamilton

annelids 41.8 (primarily New York)/NS 

vegetable matter 17.1 

centipedes 7.4 (% frequency of 

arachnids 6.1 occurrence; stomach 

snails 5.4 contents) 

small mammals 5.2 (all seasons combined) 

crustacea 3.7 

undetermined 2.4 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Location/Habitat Refere

Home Range A F summer < 0.1 - 0.36 s Michigan/bluegrass Blair, 

Size (ha) A M summer < 0.1 - 1.8 

B B all 0.39 ± 0.036 SD s Manitoba/tamarack bog Buckn

B B winter (a) 0.03 - 0.07 c New York/old field Platt, 1

B B winter (b) 0.10 - 0.22 

Range 

2-214 Short-Tailed Shrew 
Short-Tailed Shrew (Blarina brevicauda) 

Population 

Dynamics 

Age/Sex/ Cond./Seas. Mean Location/Habitat Refere

Population winter 2.3 ec Illinois/alfalfa Getz, 1

Density (N/ha) spring 5.9 

summer 11.4 

fall 10.0 B B 0.06 - 0.16 Manitoba, Canada/ Buckn

1.6 - 121 Wisconsin/beech-maple Jacks

tamarack bog 

1936 

Litter 5.4 2 - 8 Indiana/NS Frenc

Size 

4.7 ± 0.2 SE 1 - 8 Maryland/lab Blus, 

Litters several NS/NS Georg

/Year 

Days 21 - 22 Maryland/lab Blus, 

Gestation Age at 25 - 30 Maryland/lab Blus, 

Weaning (days) Age at M > 65 days Maryland/lab Blus, 

Sexual Maturity M > 83 days NS/NS Pears

F < 1 year Indiana/NS Frenc

Annual B B 93 % MD, PA, NY, MA/NS Pears

Mortality 

Longevity M 4.6 months Maryland/lab Blus, 

F 4.4 months 

B 20 months c New York/woods, field Dapso

Range 

<

2-215 Short-Tailed Shrew 
�

�

�

�

Short-Tailed Shrew (Blarina brevicauda) 

Seasonal 

Activity Begin Peak End Location Refere

Mating late February April - May mid-September Indiana Frenc

Parturition May - June c New York Dapso

Molt fall October November NS Findle

spring February July NS Findle

1 Ambient temperatures 25 to 30�C; mean weight of shrews = 21.2 g. 

2 Ambient temperatures 15 to 25�C; mean weight of shrews = 21 g. 

2-216 Short-Tailed Shrew 

3 Calculated from oxygen consumption rate; mean weight of shrews = 21.2 g. Basal metabolism is 186 percent highe

equations 3-42 or 3-43, in agreement with the finding of Deavers and Hudson (1981). Average daily metabolism was 

period at 25 to 30�C and is 146 percent higher than the free-living metabolic rate predicted on the basis of equation 

4 Calculated from average food consumption rate (liver; 1.22 kcal/g wet weight) at 25�C. This value is 167 percent hig

metabolic rate predicted on the basis of equation 3-47 (Nagy, 1987). 

5 Diet of mealworms estimated to provide 2.33 kcal/g live weight. Assimilation efficiency for shrews consuming mealw

6 Diet of beef liver; mean weight of shrews = 21 g. 

7 Estimated using equation 3-20 (Stahl, 1967) and adult male summer body weights from Guilday (1957). 

8 Estimate for 21.2-g shrew. 9 Estimated using equation 3-22 (Stahl, 1967) and adult male summer body weights from Guilday (1957). 

10 (a) At high prey density; (b) at low prey density.

11 Cited in George et al. (1986).

12 From pairing to parturition.

13 Mean longevity of animals that survived to weaning.
References (including Appendix) 

Allen, D. L. (1938) Ecological studies on the vertebrate fauna of a 500-acre farm in 

Kalamazoo County, Michigan. Ecol. Monogr. 8: 347-436. 

Barbehenn, K. R. (1958) Spatial and population relationships between Microtus and Blarina. 

Ecology 39: 293-304. 

Barrett, G. W.; Stueck, K. L. (1976) Caloric ingestion rate and assimilation efficiency of the 

short-tailed shrew, Blarina brevicauda. Ohio J. Sci. 76: 25-26. 

Blair, W. F. (1940) Notes on home ranges and populations of the short-tailed shrew. 

Ecology 21: 284-288. 

Blair, W. F. (1941) Some data on the home ranges and general life history of short-tailed 

shrews, red-backed voles and woodland jumping mice in northern Michigan. Am. 

Midl. Nat. 25: 681-685. 

Blus, L. J. (1971) Reproduction and survival of short-tailed shrews (Blarina brevicauda) in 

captivity. Lab. Anim. Sci. 21: 884-891. 

Buckner, C. H. (1964) Metabolism, food capacity, and feeding behavior in four species of 

shrews. Can. J. Zool. 42: 259-279. 

Buckner, C. H. (1966) Populations and ecological relationships of shrews in tamarack bogs 

of southeastern Manitoba. J. Mammal. 47: 181-194. 

Burt, W. H.; Grossenheider, R. P. (1980) A field guide to the mammals of North America 

north of Mexico. Boston, MA: Houghton Mifflin Co. 

Chew, R. M. (1951) The water exchanges of some small mammals. Ecol. Monogr. 21: 

215-225. 

Choate, J. R. (1972) Variation within and among populations of short-tailed shrews, Blarina 

brevicauda. J. Mammal. 53: 116-128. 

Dapson, R. W. (1968) Reproduction and age structure in a population of short-tailed 

shrews, Blarina brevicauda. J. Mammal. 49: 205-214. 

Deavers, D. R.; Hudson, J. W. (1981) Temperature regulation in two rodents (Clethrionomys 

gapperi and Peromyscus leucopus) and a shrew (Blarina brevicauda) inhabiting the 

same environment. Physiol. Zool. 54: 94-108. 

Dimond, J. B.; Sherburne, J. A. (1969) Persistence of DDT in wild populations of small 

mammals. Nature 221: 486-487. 

2-217 Short-Tailed Shrew 
Eadie, R. W. (1952) Shrew predation and vole populations on a localized area. J. Mammal. 

33: 185-189. 

Findley, J. S.; Jones, J. K., Jr. (1956) Molt of the short-tailed shrew, Blarina brevicauda. 

Am. Midl. Nat. 56: 246-249. 

French, T. W. (1984) Reproduction and age structure of three Indiana shrews. Proc. Indiana 

Acad. Sci. 94: 641-644. 

George, S. B.; Choate, J. R.; Genoways, H. H. (1986) Blarina brevicauda. American Society 

of Mammalogists; Mammalian Species 261. 

Getz, L. L. (1989) A 14-year study of Blarina brevicauda populations in east-central Illinois. 

J. Mammal. 70: 58-66. 

Gottschang, J. L. (1965) Winter populations of small mammals in old fields of southwestern 

Ohio. J. Mammal. 46: 44-52. 

Guilday, J. E. (1957) Individual and geographic variation in Blarina brevicauda from 

Pennsylvania. Ann. Carnegie Mus. 35: 41-68. 

Hamilton, W. J., Jr. (1929) Breeding habits of the short-tailed shrew, Blarina brevicauda. J. 

Mammal. 10: 125-134. 

Hamilton, W. J., Jr. (1930) The food of the Soricidae. J. Mammal. 11: 26-39. 

Hamilton, W. J., Jr. (1931) Habits of the short-tailed shrew, Blarina brevicauda (Say). Ohio 

J. Sci. 31: 97-106. 

Hamilton, W. J., Jr. (1941) The foods of small forest mammals in eastern United States. J. 

Mammal. 22: 250-263. 

Jackson, H. H. T. (1961) Mammals of Wisconsin. Madison, WI: University of Wisconsin 

Press. 

Jameson, E. W., Jr. (1943) Notes on the habits and siphanapterous parasites of the 

mammals of Welland County, Ontario. J. Mammal. 24: 194-197. 

Lomolino, M. V. (1984) Immigrant selection, predation, and the distribution of Microtus 

pennsylvanicus and Blarina brevicauda on islands. Am. Nat. 123: 468-483. 

Martin, I. G. (1984) Factors affecting food hoarding in the short-tailed shrew Blarina 

brevicauda. Mammalia 48: 65-71. 

Martinsen, D. L. (1969) Energetics and activity patterns of short-tailed shrews (Blarina) on 

restricted diets. Ecology 50: 505-510. 

2-218 Short-Tailed Shrew 
Miller, H.; Getz, L. L. (1977) Factors influencing local distribution and species diversity of 

forest small mammals in new England. Can. J. Zool. 55: 806-814. 

Morrison, P. R. (1948) Oxygen consumption in several small wild mammals. J. Cell. Comp. 

Physiol. 31: 69-96. 

Morrison, P. R.; Pierce, M.; Ryser, F. A. (1957) Food consumption and body weight in the 

masked and short-tailed shrews (genus Blarina) in Kansas, Iowa, and Missouri. Ann. 

Carnegie Mus. 51: 157-180. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Mono. 57: 111-128. 

Neal, C. M.; Lustick, S. I. (1973) Energetics and evaporative water loss in the short-tailed 

shrew Blarina brevicauda. Physiol. Zool. 46: 180-185. 

Palmer, E. L.; Fowler, H. S. (1975) Fieldbook of natural history. New York, NY: McGraw-Hill 

Book Co. 

Pearson, O. P. (1942) The cause and nature of a poisonous action produced by the bite of a 

shrew (Blarina brevicauda). J. Mammal. 23: 159-166. 

Pearson, O. P. (1944) Reproduction in the shrew (Blarina brevicauda Say). Am. J. Anat. 75: 

39-93. 

Pearson, O. P. (1945) Longevity of the short-tailed shrew. Am. Midl. Nat. 34: 531-546. 

Pearson, O. P. (1947) The rate of metabolism of some small mammals. Ecology 29: 

127-145. 

Platt, A. P. (1968) Differential trap mortality as a measure of stress during times of 

population increase and decrease. J. Mammal. 49: 331-335. 

Platt, W. J. (1974) Metabolic rates of short-tailed shrews. Physiol. Zool. 47: 75-90. 

Platt, W. J. (1976) The social organization and territoriality of short-tailed shrew (Blarina 

brevicauda) populations in old-field habitats. Anim. Behav. 24: 305-318. 

Platt, W. J.; Blakeley, N. R. (1973) Short-term effects of shrew predation upon invertebrate 

prey sets in prairie ecosystems. Proc. Iowa Acad. Sci. 80: 60-66. 

Randolph, J. C. (1973) Ecological energetics of a homeothermic predator, the short-tailed 

shrew. Ecology 54: 1166-1187. 

Richardson, J. H. (1973) Locomotory and feeding activity of the shrews, Blarina brevicauda 

and Suncus murinus. Am. Midl. Nat. 90: 224-227. 

2-219 Short-Tailed Shrew 
Robinson, D. E.; Brodie, E. D. (1982) Food hoarding behavior in the short-tailed shrew 

Blarina brevicauda. Am. Midl. Nat. 108: 369-375. 

Schlesinger, W. H.; Potter, G. L. (1974) Lead, copper, and cadmium concentrations in small 

mammals in the Hubbard Brook Experimental Forest. Oikos 25:148-152. 

Stahl, W. R. (1967) Scaling of respiratory variables in mammals. J. Appl. Physiol. 22: 

453-460. 

Whitaker, J. O., Jr.; Ferraro, M. G. (1963) Summer food of 220 short-tailed shrews from 

Ithaca, New York. J. Mammal. 44: 419. 

Williams, A. B. (1936) The composition and dynamics of a beech-maple climax community. 

Ecol. Monogr. 6: 317-408. 

Zegers, D. A.; Merritt, J. F. (1987) Adaptations of Peromyscus for winter survival in an 

Appalachian montane forest. J. Mammal. 69: 516-523. 

2-220 Short-Tailed Shrew 
2.2.2. Red Fox (foxes and coyotes) 

Order Carnivora, Family Canidae. Unlike the more social wolves, foxes and coyotes 

tend to hunt alone, although coyotes may hunt larger prey in pairs. Foxes and coyotes are 

primarily carnivorous, preying predominantly on small mammals, but they also may eat 

insects, fruits, berries, seeds, and nuts. Foxes are found throughout most of the United 

States and Canada, including the arctic, as are coyotes with the exception of the 

southeastern United States. Foxes and coyotes are active primarily at night. 

Selected species 

Red foxes (Vulpes vulpes) are present throughout the United States and Canada 

except in the southeast, extreme southwest, and parts of the central states. Red fox prey 

extensively on mice and voles but also feed on other small mammals, insects, hares, game 

birds, poultry, and occasionally seeds, berries, and fruits (Palmer and Fowler, 1975). 

Twelve subspecies are recognized in North America (Ables, 1974). 

Body size. The dog-sized red fox has a body about 56 to 63 cm in length, with a 35 

to 41 cm tail (Burt and Grossenheider, 1980). They weigh from 3 to 7 kg, with the males 

usually outweighing the females by about 1 kg (Voigt, 1987; see table). 

Habitat. As the most widely distributed carnivore in the world, the red fox can live 

in habitats ranging from arctic areas to temperate deserts (Voigt, 1987). Red foxes utilize 

many types of habitat--cropland, rolling farmland, brush, pastures, hardwood stands, and 

coniferous forests (MacGregor, 1942; Eadie, 1943; Cook and Hamilton, 1944; Ables, 1974). 

They prefer areas with broken and diverse upland habitats such as occur in most 

agricultural areas (Ables, 1974; Samuel and Nelson, 1982; Voigt, 1987). They are rare or 

absent from continuous stands of pine forests in the southeast, moist conifer forests along 

the Pacific coast, and semiarid grasslands and deserts (Ables, 1974). 

Food habits. The red fox feeds on both animal and plant material, mostly small 

mammals, birds, insects, and fruit (Korschgen, 1959; Samuel and Nelson, 1982). Meadow 

voles are a major food in most areas of North America; other common prey include mice 

and rabbits (Korschgen, 1959; Voigt, 1987). Game birds (e.g., ring-necked pheasant and 

ruffed grouse) and waterfowl are seasonally important prey in some areas (Pils and Martin, 

1978; Sargeant, 1972; Voigt and Broadfoot, 1983). Plant material is most common in red 

fox diets in summer and fall when fruits, berries, and nuts become available (Johnson, 

1970; Major and Sherburne, 1987). Red foxes often cache food in a hole for future use 

(Samuel and Nelson, 1982). They also are noted scavengers on carcasses or other refuse 

(Voigt, 1987). Most activity is nocturnal and at twilight (Nowak and Paradiso, 1983). 

Temperature regulation and molt. In winter, foxes do not undergo hibernation or 

torpor; instead, they are active year-round. They undergo one molt per year, which usually 

begins in April and is finished by June. The winter coat is regrown by October or 

November in northern latitudes (Voigt, 1987). 

2-221 Red Fox 
Breeding activities and social organization. Breeding occurs earlier in the south 

than in the red fox's northern ranges (Samuel and Nelson, 1982) (see table). A mated pair 

maintains a territory throughout the year, with the male contributing more to its defense 

than the female (Preston, 1975). Pups are born and reared in an underground den, and the 

male assists the female in rearing young, bringing food to the den for the pups (Samuel 

and Nelson, 1982). Pups first emerge from the den when 4 to 5 weeks old (Samuel and 

Nelson, 1982). Once considered solitary, red foxes now are reported to exhibit more 

complex social habits (MacDonald and Voigt, 1985). A fox family, the basic social unit, 

generally consists of a mated pair or one male and several related females (MacDonald, 

1980; Voigt, 1987). The additional females are usually nonbreeders that often help the 

breeding female (Voigt, 1987). 

Home range and resources. The home ranges of individuals from the same family 

overlap considerably, constituting a family territory (Sargeant, 1972; Voigt and MacDonald, 

1984). Territories of neighboring red fox families are largely nonoverlapping and 

contiguous, usually resulting in all parts of a landscape being occupied by foxes. Territory 

sizes range from less than 50 to over 3,000 ha (see table). Territories in urban areas tend 

to be smaller than those in rural areas (Ables, 1969). Adults visit most parts of their 

territory on a regular basis; however, they tend to concentrate their activities near to their 

dens, preferred hunting areas, abundant food supplies, and resting areas (Ables, 1974; 

Keenan, 1981). Territory boundaries often conform to physical landscape features such as 

well-traveled roads and streams (Ables, 1974). Territory defense is primarily by 

nonaggressive mechanisms involving urine scent-marking and avoidance behaviors. 

Scent marking occurs throughout the territory; there is little patrolling of territory 

boundaries. Each fox or family usually has a main underground den and one or more other 

burrows within the home range (Nowak and Paradiso, 1983). Most dens are abandoned 

burrows of other species (e.g., woodchucks, badgers) (Samuel and Nelson, 1982). Tunnels 

are up to 10 m in length and lead to a chamber 1 to 3 m below the surface (Nowak and 

Paradiso, 1983). Pup-rearing dens are the focal point of fox activity during spring and early 

summer. Foxes have some rest sites and usually forage away from the den (Voigt, 1987). 

Population density. One red fox family per 100 to 1,000 ha is typical (Voigt, 1987; 

see table). Red foxes have larger home ranges where population densities are low and in 

poorer habitats (Voigt, 1987). Most young foxes, especially males, disperse before the age 

of 1 (Voigt, 1987), usually during September to March, with peaks in dispersal in October 

and November (Phillips et al., 1972; Storm et al., 1976). 

Population dynamics. Foxes usually produce pups their first year, except in 

extremely high density areas and in some years in northern portions of their range where 

they may delay breeding until the next season (Allen, 1984; Harris, 1979; Storm et al., 1976; 

Voigt and MacDonald, 1984). Litter size generally averages four to six pups (see table). 

The pups leave the den about 1 month after birth, and they are weaned by about 8 to 10 

weeks of age (Ables, 1974). Red foxes incur high mortality rates as a result of shooting, 

trapping, disease, and accidents (e.g., roadkills) (Storm et al., 1976). Two factors that tend 

to limit red fox abundance are competition with other canids, especially coyotes, and 

seasonal limits on food availability (Voigt, 1987). Fecundity is higher in areas of high 

mortality and low population densities (Voigt, 1987). 

2-222 Red Fox 
�

�

�

�

�

Similar species (from general references) 

� The arctic fox (Alopex lagopus) is smaller than the red fox (body length 

approximately 51 cm; weight 3.2 to 6.7 kg) and is restricted in its distribution 

to the arctic, found in the United States only in Alaska. This species 

primarily scavenges for food but also eats lemmings, hares, birds, and eggs 

as well as berries in season. 

� The swift fox (Vulpes velox) is smaller than the red fox (body length 38 to 51 

cm; weight 1.8 to 2.7 kg) and inhabits the deserts and plains of the southwest 

and central United States. It dens in ground burrows and feeds on small 

mammals and insects. 

� The kit fox (Vulpes macrotis) is similar in size to the swift fox and is 

considered by some to be the same species, although it has noticeably 

larger ears. It inhabits the southwestern United States and prefers open, 

level, sandy areas and low desert vegetation. It feeds on small mammals and 

insects. 

� The gray fox (Urocyon cinereoargenteus) is similar in size (body length 53 to 

74 cm; weight 3.2 to 5.8 kg) to the red fox and ranges over most of the United 

States except the northwest and northern prairies, inhabiting chaparral, open 

forests, and rimrock regions. Secretive and nocturnal, gray foxes will climb 

trees to evade enemies. They feed primarily on small mammals but also eat 

insects, fruits, acorns, birds, and eggs. 

� The coyote (Canis latrans) is much larger (body length 81 to 94 cm; weight 9 

to 22 kg) than the red fox and is found throughout most of the United States 

(except possibly eastern), western Canada, and Alaska. It inhabits prairies, 

open woodlands, brushy and boulder-strewn areas, and dens in the ground. 

Coyotes share some feeding habits with the red fox but also scavenge and 

hunt larger prey in pairs. 

General references 

Ables (1974); Burt and Grossenheider (1980); Palmer and Fowler (1975); Voigt 

(1987). 

2-223 Red Fox 
Red Fox (Vulpes vulpes) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referenc

Body Weight A M spring 5.25 ± 0.18 SE 4.54 - 7.04 Illinois Storm et 

(kg) A F spring 4.13 ± 0.11 SE 3.27 - 4.72 

A M fall 4.82 ± 0.081 SE 4.13 - 5.68 Iowa Storm et 

A F fall 3.94 ± 0.079 SE 2.95 - 4.59 

neonate B 0.102 ± 0.12 SD 0.071 - 0.109 Wisconsin Storm & 

at weaning B 0.70 North Dakota Sargean

Pup Growth birth to 15.9 North Dakota/lab Sargean

Rate (g/day) weaning 

Metabolic Rate J summer 193 ± 56 SD Ohio/lab Vogtsbe

(kcal/kg-day) 

A M basal 47.9 estimate

A F basal 51.1 A M free-living 161 (68 - 383) estimate

A F free-living 

168 (71 - 400) 

Food Ingestion J 5-8 wks 0.16 North Dakota/lab Sargean

Rate (g/g-day) J 9-12 wks 0.12 

J 13-24 wks 0.11 

A before 0.075 North Dakota/captive Sargean

whelp F after whelp 0.14 A 0.069 North Dakota/captive Sargeant

nonbreeding 

Water A M 0.084 estimateIngestion A F 0.086 Rate (g/g-day) 

Inhalation A M 2.0 estimate

Rate (m /day) A F 1.7 3 

2-224 Red Fox 
Red Fox (Vulpes vulpes) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referenc

Surface Area A M 3,220 estimate

(cm ) A F 2,760 2 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

rabbits 44.4 Nebraska/statewide Powell & 

small mammals 33.0 pheasant 8.4 (% wet volume; stomach 

other birds 11.2 contents) 

misc. 2.0 

not accounted for 1.0 mammals 92.2 37.1 61.7 65.0 Illinois/farm and woods Knable, 1

birds 2.4 43.2 0.2 8.6 arthropods 0.2 11.6 4.2 <0.1 

plants 4.6 6.3 31.1 26.1 (% wet weight; stomach 

unspecified/other 0.6 1.8 2.8 0.3 contents) 

rabbits 24.8 10.7 36.5 38.7 Missouri Korschg

mice/rats 24.2 6.2 21.3 22.5 other mammals 4.0 1.4 8.1 8.2 (% wet volume; stomach 

poultry 21.0 45.0 16.3 11.6 contents) 

carrion 12.9 13.0 6.5 7.4 

livestock 9.8 0.3 2.0 5.4 

birds 0.6 1.2 1.1 3.8 

invertebrates trace 15.3 1.6 trace 

plant foods 2.7 6.9 6.6 2.1 

mammals 81.4 Maryland/Appalachian Hockma

birds 4.8 Province (fall & winter) 

arthropods 2.8 

plants 7.0 (% wet weight; stomach 

unspecified/other 4.0 contents) 

2-225 Red Fox 
Red Fox (Vulpes vulpes) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Location/Habitat Referenc

Territory size A B summer 1,611 277 - 3,420 nw British Columbia/ Jones & 

(ha) A M summer 1,967 514 - 3,420 alpine and subalpine 

A F summer 1,137 277 - 1,870 A F spring 699 ± 137 SD 596 - 855 ec Minnesota/woods, fields, Sargeant

A M all year 717 Wisconsin/diverse Ables, 19

A F all year 96 57 - 170 

swamp 

Population B B spring 0.001 Canada/northern boreal Voigt, 19

Density (N/ha) forests/arctic tundra 

B B spring 0.01 s Ontario, Canada/southern Voigt, 19

B B 0.046 - 0.077 "good fox range" in Ables, 19

habitats North America 

Litter 5.5 s Wisconsin/farm, marsh, Pils & Ma

Size pasture 

6.8 2 - 9 Illinois/farm and woods Storm et 

6.7 3 - 12 Iowa/farm and woods Storm et 

4.2 upper Michigan/NS Switzenb

4.1 North Dakota/prairie Allen, 19

potholes 

Litters/Year 1 NS/NS Samuel & 

Days 51 - 54 New York/NS Sheldon

Gestation 

Age at 8 - 10 weeks NS/NS Ables, 19

Weaning Age at F 10 months Illinois, Iowa/farm woods Storm et 

Sexual Maturity 

Range 

2-226 Red Fox 
1

234567

Red Fox (Vulpes vulpes) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Location/Habitat Referenc

Annual B B 79.4 s Wisconsin/various Pils & Ma

Mortality Rates (percent) J M 83 Illinois/Iowa/ Storm et 

J F 81 farms and woods 

A F 74 

A B 77 

Longevity < 1.5 yrs up to 6 yrs NS/NS Storm et 

Seasonal 

Activity Begin Peak End Location Referenc

Mating early Dec. late January late February Iowa Storm et 

late December Jan. - Feb. March New York Layne & 

late January early February southern Ontario, Canada Voigt, 19

February March northern Ontario, Canada Voigt, 19

Sheld

Parturition March southern CAN Voigt, 19

late March, April e North Dakota Sargean

Molt April June NS/NS Voigt, 19

Disperal late March Illinois, Iowa Storm et 

September 

Range 

2-227 Red Fox 

Estimated using extrapolation equation 3-45 (Boddington, 1978) and body weights from Storm et al. (1976) (Illinois). 

Estimated using extrapolation equation 3-47 (Nagy, 1987) and body weights from Storm et al. (1976) (Illinois). 

Food consumption of an adult pair for 11 days prior to whelping (i.e., parturition) and of the adult female for the first 

Estimated using extrapolation equation 3-17 (Calder and Braun, 1983) and body weights from Storm et al. (1976) (Illi

Estimated using extrapolation equation 3-20 (Stahl, 1967) and body weights from Storm et al. (1976) (Illinois).

Estimated using extrapolation equation 3-22 (Stahl, 1967) and body weights from Storm et al. (1976) (Illinois).

Litter size determined from embryo count. Using placental scars generally overestimates litter size, and counting liv

litter size (Allen, 1983; Lindstrom, 1981).

8 Method of determining litter size not specified. 

9 Cited in Samuel and Nelson (1982). 
References (including Appendix) 

Ables, E. D. (1969) Home range studies of red foxes (Vulpes vulpes). J. Mammal. 50: 

108-120. 

Ables, E. D. (1974) Ecology of the red fox in North America. In: Fox, M. W., ed. The wild 

canids. New York, NY: Van Nostrand Reinhold; pp. 148-163. 

Allen, S. H. (1983) Comparison of red fox litter sizes determined from counts of embryos 

and placental scars. J. Wildl. Manage. 47: 860-863. 

Allen, S. H. (1984) Some aspects of reproductive performance in the red fox in North 

Dakota. J. Mammal. 65: 246-255. 

Allen, S. H.; Gulke, J. (1981) The effect of age on adult red fox body weights. Prairie Nat. 

13: 97-98. 

Asdell, S. A. (1946) Patterns of mammalian reproduction. Ithaca, NY: Comstock Publ. Co. 

Boddington, M. J. (1978) An absolute metabolic scope for activity. J. Theor. Biol. 75: 443-

449. 

Burt, W. H.; Grossenheider, R. P. (1980) A field guide to the mammals of North America 

north of Mexico. Boston, MA: Houghton Mifflin Co. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Cook, D. B.; Hamilton, W. J., Jr. (1944) The ecological relationship of red fox food in 

eastern New York. Ecology 24: 94-104. 

Dalke, P. D.; Sime, P. R. (1938) Home and seasonal ranges of the eastern cottontail in 

Connecticut. Trans. N. Amer. Wildl. Conf. 3: 659-669. 

Dekker, D. (1983) Denning and foraging habits of red foxes, Vulpes vulpes, and their 

interaction with coyotes, Canis latrans, in central Alberta. Can. Field-Nat. 97: 

303-306. 

Eadie, W. R. (1943) Food of the red fox in southern New Hampshire. J. Wildl. Manage. 7: 

74-77. 

Green, J. S.; Flinders, J. T. (1981) Diets of sympatric red foxes and coyotes in southeastern 

Idaho. Great Basin Nat. 41: 251-254. 

Halpin, M. A.; Bissonette, J. A. (1983) Winter resource use by red fox (Vulpes vulpes) 

(abstract only). Trans. Northeast Sect. Wildl. Soc. 40: 158. 

2-228 Red Fox 
Hamilton, W. J., Jr. (1935) Notes on food of red foxes in New York and New England. J. 

Mammal. 16: 16-21. 

Harris, S. (1979) Age-related fertility and productivity in red foxes, Vulpes vulpes, in 

suburban London. J. Zool. (London) 187: 195-199. 

Harris, S.; Smith, G. C. (1987) Demography of two urban fox (Vulpes vulpes) populations. J. 

Appl. Ecol. 24: 75-86. 

Hockman, J. G.; Chapman, J. A. (1983) Comparative feeding habits of red foxes (Vulpes 

vulpes) and gray foxes (Urocyon cinereoargentus) in Maryland. Am. Midl. Nat. 110: 

276-285. 

Hoffman, R. A.; Kirkpatrick, C. M. (1954) Red fox weights and reproduction in Tippecanoe 

County, Indiana. J. Mammal. 55: 504-509. 

Johnson, W. J. (1970) Food habits of the red fox in Isle Royale National Park, Lake 

Superior. Am. Midl. Nat. 84: 568-572. 

Johnson, D. H.; Sargeant, A. B. (1977) Impact of red fox predation on the sex ratio of prairie 

mallards. Washington, DC: U.S. Fish Wildl. Serv.; Wildl. Res. Rep. 6. 

Jones, D. M.; Theberge, J. B. (1982) Summer home range and habitat utilization of the red 

fox (Vulpes vulpes) and gray foxes (Urocyon cinereoargentus) in Maryland. Am. 

Midl. Nat. 110: 276-285. 

Keenan, R. J. (1981) Spatial use of home range among red foxes (Vulpes vulpes) in southcentral Ontario. In: Chapman, J. A.; Pursley, D., eds. Worldwide furbearer 

conference proceedings, August, 1980; Frostburg, Maryland; pp. 1041-1063. 

Knable, A. E. (1970) Food habits of the red fox (Vulpes fulva) in Union County, Illinois. 

Trans. Ill. State Acad. Sci. 63: 359-365. 

Knable, A. E. (1974) Seasonal trends in the utilization of major food groups by the red fox 

(Vulpes fulva) in Union County, Illinois. Trans. Ill. State Acad. Sci. 66: 113-115. 

Korschgen, L. J. (1959) Food habits of the red fox in Missouri. J. Wildl. Manage. 23: 

168-176. 

Kuehn, D. W.; Berg, W. E. (1981) Notes on movements, population statistics, and foods of 

the red fox in north-central Minnesota. Minn. Wildl. Res. Q. 41: 1-10. 

Layne, J. N.; McKeon, W. H. (1956) Some aspects of red fox and gray fox reproduction in 

New York. N.Y. Fish and Game J. 3: 44-74. 

Lindstrom, E. (1981) Reliability of placental scar counts in the red fox (Vulpes vulpes L.) 

with special reference to fading of the scars. Mammal Rev. 11: 137-49. 

2-229 Red Fox 
Llewellyn, L. M.; Uhler, F. M. (1952) The foods of fur animals of the Patuxent Research 

Refuge, Maryland. Am. Midl. Nat. 48: 193-203. 

MacDonald, D. W. (1980) Social factors affecting reproduction amongst red foxes (Vulpes 

vulpes L. 1758). In: Zimen, E., ed. The red fox, biogeographica: v. 18. The 

Netherlands: W. Junk, The Hague; pp. 123-175. 

MacDonald, D. W.; Voigt, D. R. (1985) The biological basis of rabies models. In: Bacon, P. 

J., ed. Population dynamics of rabies in wildlife. London, UK: Academic Press; pp. 

71-107. 

MacGregor, A. E. (1942) Late fall and winter foods of foxes in central Massachusetts. J. 

Wildl. Manage. 6: 221-224. 

Major, J. T.; Sherburne, J. A. (1987) Interspecific relationships of coyotes, bobcats, and red 

foxes in western Maine. J. Wildl. Manage. 51: 606-616. 

Maurel, D. (1980) Home range and activity rhythm of adult male foxes during the breeding 

season. In: Amlaner, C. J.; MacDonald, D. W., eds. A handbook on biotelemetry and 

radio tracking. Edmonds, WA: The Franklin Press; pp. 697-702. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Mono. 57: 111-128. 

Nowak, R. M.; Paradiso, J. L. (1983) Foxes. In: Walker's mammals of the world. 4th ed. 

Baltimore, MD: Johns Hopkins University Press; pp. 932-980. 

Palmer, E. L.; Fowler, H. S. (1975) Fieldbook of natural history. New York, NY: McGraw-Hill 

Book Co. 

Phillips, R. L.; Andrews, R. D.; Storm, G. L.; et al. (1972) Dispersal and mortality of red 

foxes. J. Wildl. Manage. 36: 237-248. 

Pils, C. M.; Martin, M. A. (1978) Population dynamics, predator-prey relationships and 

management of the red foxes in Wisconsin. Madison, WI: Wisc. Dept. Nat. Resour. 

Tech. Bull. No. 105; 56 pp. 

Pils, C. M.; Martin, M. A.; Lange, E. (1981) Harvest, age structure, survivorship, productivity 

of red foxes in Wisconsin. Madison, WI: Wisc. Dept. Nat. Resour. Tech. Bull. No. 

125; 19 pp. 

Powell, D. G.; Case, R. M. (1982) Food habits of the red fox in Nebraska. Trans. Nebr. Acad. 

Sci. and Affil. Soc. 10: 13-16. 

Preston, E. M. (1975) Home range defense in the red fox, Vulpes vulpes L. J. Mammal. 56: 

645-652. 

2-230 Red Fox 
Richards, S. H.; Hine, R. L. (1953) Wisconsin fox populations. Madison, WI: Wisc. Cons. 

Dept. Tech. Wildl. Bull. No. 6; 78 pp. 

Samuel, D. E.; Nelson, B. B. (1982) Foxes. In: Chapman, J. A.; Feldhammer, G. A., eds. Wild 

mammals of North America. Baltimore, MD: Johns Hopkins University Press; pp. 

475-490. 

Sargeant, A. B. (1972) Red fox spatial characteristics in relation to waterfowl predation. J. 

Wildl. Manage. 36: 225-236. 

Sargeant, A. B. (1978) Red fox prey demands and implications to prairie duck production. 

J. Wildl. Manage. 42: 520-527. 

Sargeant, A. B.; Pfeifer, W. K.; Allen, S. H. (1975) A spring aerial census of red foxes in 

North Dakota. J. Wildl. Manage. 39: 30-39. 

Sargeant, A. B.; Allen, S. H.; Fleskes, J. P. (1986) Commercial sunflowers: food for red 

foxes in North Dakota. Prairie Nat. 18: 91-94. 

Sargeant, A. B.; Allen, S. H.; Hastings, J. O. (1987) Spatial relations between sympatric 

coyotes and red foxes in North Dakota. J. Wildl. Manage. 51: 285-293. 

Sargeant, A. B.; Allen, S. H.; Johnson, D. H. (1981) Determination of age and whelping dates 

of live red fox pups. J. Wildl. Manage. 45: 760-765. 

Schoonmaker, W. J. (1938) Notes on mating and breeding habits of foxes in New York 

state. J. Mammal. 19: 375-376. 

Scott, T. G. (1943) Some food coactions of the northern plains red fox. Ecol. Monogr. 13: 

427-480. 

Sheldon, W. G. (1949) Reproductive behavior of foxes in New York state. J. Mammal. 30: 

236-246. 

Stahl, W. R. (1967) Scaling of respiratory variables in mammals. J. Appl. Physiol. 22: 

453-460. 

Stanley, W. C. (1963) Habits of the red fox in northeastern Kansas. Univ. Kansas Mus. Nat. 

Hist. Misc. Pub. 34: 1-31. 

Storm, G. L.; Ables, E. D. (1966) Notes on newborn and fullterm wild red foxes. J. Mammal. 

47: 116-118. 

Storm, G. L.; Andrews, R. D.; Phillips, R. L.; et al. (1976) Morphology, reproduction, 

dispersal and mortality of midwestern red fox populations. Wildl. Monogr. 49: 1-82. 

Switzenberg, D. F. (1950) Breeding productivity in Michigan red foxes. J. Mammal. 31: 

194-195. 

2-231 Red Fox 
Tullar, B. J. (1983) An unusually long-lived red fox. N.Y. Fish Game J. 30: 227. 

Tullar, B. J., Jr.; Berchielli, L. T. (1980) Movement of the red fox in central New York. N.Y. 

Fish Game J. 27: 197-204. 

Vogtsberger, L. M.; Barrett, G. W. (1973) Bioenergetics of captive red foxes. J. Wildl. 

Manage. 37: 495-500. 

Voigt, D. R.; MacDonald, D. W. (1984) Variation in the spatial and social behaviour of the 

red fox, Vulpes vulpes. Acta Zool. Fenn. 171: 261-265. 

Voigt, D. R.; Tinline, R. L. (1980) Strategies for analyzing radio tracking data. In: Amlaner, 

C. J., Jr.; MacDonald, D. W., eds. A handbook on biotelemetry and radio tracking. 

Oxford, United Kingdom: Pergamon Press; pp. 387-404. 

Voigt, D. (1987) Red fox. In: Novak, M.; Baker, J. A.; Obbarel, M. E.; et al., eds. Wild 

furbearer management and conservation. Pittsburgh, PA: University of Pittsburgh 

Press; pp. 379-392. 

Voigt, D. R.; Broadfoot, J. (1983) Locating pup-rearing dens of red foxes with 

radio-equipped woodchucks. J. Wildl. Manage. 47: 858-859. 

2-232 Red Fox 
2.2.3. Raccoon (raccoons, coatis, ringtails) 

Order Carnivora, Family Procyonidae. Procyonids are medium-sized omnivores 

that range throughout much of North America. Raccoons, coatis, and ringtails feed on 

insects, small mammals, birds, lizards, and fruits. Ringtails are much smaller and more 

slender than raccoons and consume a higher proportion of animal matter (Kaufmann, 

1982). Coatis are slightly smaller than racoons and are limited in their distribution in the 

United States to just north of the Mexican border. 

Selected species 

The raccoon (Procyon lotor) is the most abundant and widespread medium-sized 

omnivore in the North America. They are found throughout Mexico, Central America, the 

United States, except at the higher elevations of the Rocky Mountains, and into southern 

Canada (Kaufmann, 1982). During the last 50 years, raccoon populations in the United 

States have increased greatly (Sanderson, 1987). In suburban areas, they frequently raid 

garbage cans and dumps. Raccoons are preyed on by bobcats, coyotes, foxes, and great 

horned owls (Kaufmann, 1982). Twenty-five subspecies are recognized in the United 

States and Canada; however, most researchers do not identify the subspecies studied 

because different subspecies inhabit essentially nonoverlapping geographic ranges. 

Body size. Raccoons measure from 46 to 71 cm with a 20 to 30 cm tail. Body 

weights vary by location, age, and sex from 3 to 9 kg (Kaufmann, 1982; Sanderson, 1987). 

The largest raccoons recorded are from Idaho and nearby states, while the smallest reside 

in the Florida Keys (Lotze and Anderson, 1979). Juveniles do not reach adult size until at 

least the end of their second year (Stuewer, 1943b). In the autumn, fat reserves account 

for 20 to 30 percent or more of the raccoon's weight (Whitney and Underwood, 1952, cited 

in Kaufmann, 1982). In Minnesota, Mech et al. (1968) found that juveniles gained weight 

almost linearly until mid-November, after which they began to lose weight until April. 

Weight loss in adults and yearlings can reach 50 percent during the 4 months of winter 

dormancy (e.g., 4.3-kg loss for a 9.1-kg raccoon) (Thorkelson and Maxwell, 1974; Mech et 

al., 1968). In Alabama, where raccoons are active all year, winter weight losses are less, 16 

to 17 percent on average (Johnson, 1970). 

Habitat. Raccoons are found near virtually every aquatic habitat, particularly in 

hardwood swamps, mangroves, floodplain forests, and freshwater and saltwater marshes 

(Kaufmann, 1982). They are also common in suburban residential areas and cultivated and 

abandoned farmlands (Kaufmann, 1982) and may forage in farmyards (Greenwood, 1982). 

Stuewer (1943a) stated that a permanent water supply, tree dens, and available food are 

essential. Raccoons use surface waters for both drinking and foraging (Stuewer, 1943a). 

Food habits. The raccoon is an omnivorous and opportunistic feeder. Although 

primarily active from sunset to sunrise (Kaufmann, 1982; Stuewer, 1943a), raccoons will 

change their activity period to accommodate the availability of food and water (Sanderson, 

1987). For example, salt marsh raccoons may become active during the day to take 

advantage of low tide (Ivey, 1948, cited in Sanderson, 1987). Raccoons feed primarily on 

fleshy fruits, nuts, acorns, and corn (Kaufmann, 1982) but also eat grains, insects, frogs, 

2-233 Raccoon 
crayfish, eggs, and virtually any animal and vegetable matter (Palmer and Fowler, 1975). 

The proportion of different foods in their diet depends on location and season, although 

plants are usually a more important component of the diet. They may focus on a preferred 

food, such as turtle eggs, when it is available (Stuewer, 1943a). They also will feed on 

garbage and carrion. Typically, it is only in the spring and early summer that raccoons eat 

more animal than plant material. Their late summer and fall diets consist primarily of 

fruits. In winter, acorns tend to be the most important food, although raccoons will take 

any corn or fruits that are still available (Kaufmann, 1982; Stuewer, 1943a). 

Temperature regulation and molt. From the central United States into Canada, 

raccoons undergo a winter dormancy lasting up to 4 months (Stuewer, 1943a). It is not a 

true hibernation, however, and they can be easily awakened (Kaufmann, 1982). Animals in 

the south are active year-round (Goldman, 1950). Snow cover, more than low 

temperatures, triggers winter dormancy (Stuewer, 1943a; Mech et al., 1966; Kaufmann, 

1982). The raccoon's annual molt begins early in spring and lasts about 3 months 

(Kaufmann, 1982). 

Breeding activities and social organization. Although solitary, adult raccoons come 

together for a short time during the mating period (Kaufmann, 1982), which begins earlier 

(January to March) in their northern range than in their southern range (March to June) 

(Johnson, 1970; Sanderson, 1987). Male and female home ranges overlap freely and each 

male may mate with several females during the breeding season (Mech et al., 1966; 

Johnson, 1970; Kaufmann, 1982; Stuewer, 1943a). The most common group of raccoons is 

a mother and her young of that year. Further north in their range, a family will den together 

for the winter and break up the following spring (Kaufmann, 1982). Males are territorial 

toward one another but not toward females; females are not territorial (Fritzell, 1978). 

Home range and resources. The size of a raccoon's home range depends on its sex 

and age, habitat, food sources, and the season (Sanderson, 1987). Values from a few 

hectares to more than a few thousand hectares have been reported, although home ranges 

of a few hundred hectares appear to be most common (see Appendix). In general, home 

ranges of males are larger than those of females, the home range of females with young is 

restricted, and winter ranges are smaller than ranges at other times of the year for both 

sexes (Sanderson, 1987). During the winter, raccoons commonly den in hollow trees; they 

also use the burrows of other animals such as foxes, groundhogs, skunks, and badgers. 

These sites are used for sleeping during warmer periods. After wintering in one den, the 

female will choose a new den in which to bear her young (Kaufmann, 1982). Schneider et 

al. (1971) found that once the cubs leave the den, the family will not use it again that year. 

Population density. Population density depends on the quality and quantity of food 

resources and den sites. Values between 0.005 and 1.5 raccoons per hectare have been 

reported, although 0.1 to 0.2 per hectare is more common (see Appendix). Populations 

exceeding one raccoon per hectare have been reported in residential areas (Hoffman and 

Gottschang, 1977). Although raccoons may prefer tree dens over ground dens, particularly 

for raising young (Stuewer, 1943a), Butterfield (1954) found high raccoon densities in an 

area with few tree dens but numerous ground dens. 

2-234 Raccoon 
�

�

Population dynamics. Males generally are not sexually mature by the time of the 

first regular breeding season following their birth, but they may mature later that summer 

or fall (Johnson, 1970; Sanderson, 1951). Females may become pregnant in their first year 

(Johnson, 1970). In a review of several studies, Kaufmann (1982) found that up to 60 

percent of both wild and captive females mate and produce litters in their first year. In 

Illinois and Missouri, Fritzell et al. (1985) found pregnancy rates of yearlings from 38 to 77 

percent. After their first year, almost all females breed annually (Fritzell et al., 1985). 

Females produce only one litter each year, and the female alone cares for the young 

(Sanderson, 1987; Stuewer, 1943a, 1943b). With some exceptions (Bissonnette and Csech, 

1937), larger litter sizes usually occur in the raccoon's northern range (Lotze and 

Anderson, 1979). Some juveniles of both sexes disperse from the areas where they were 

born during the fall or winter of their first year, while others stay and raise young within 

their parents' home range (Stuewer, 1943a). The highest mortality rates occur within the 

first 2 years; the age structure of populations in Alabama suggests that mortality is higher 

for subadults than for juveniles (Johnson, 1970). 

Similar species (from general references) 

� The coati (Nasua nasua) is slightly smaller than the raccoon (4 to 6 kg) but 

with a much longer tail (51 to 64 cm). Ranging throughout Central America 

from Panama to Mexico (Kaufmann, 1982), the coati is rare in the United 

States where it inhabits open forests of the southwest, near the Mexican 

border. It forages primarily for grubs and tubers but also feeds on fruits, 

nuts, bird eggs, lizards, scorpions, and tarantulas. Coatis roll arthropods on 

the ground to remove wings and scales. 

� The ringtail (Bassariscus astutus) is smaller (36 to 41 cm; 0.9 to 1.13 kg) than 

the raccoon, with a tail equal to its body length. It ranges throughout the 

southwestern United States into northern California and Oregon, inhabiting 

chaparral, rocky ridges, and cliffs near water. Ringtails are omnivorous like 

the raccoon but consume a higher proportion of animal matter, feeding 

mainly on small mammals, insects, birds, and lizards as well as fruits. They 

den in caves or crevices along cliffs, hollow trees, under rocks, and in 

unused buildings. Although ringtails sometimes live in colonies, mated pairs 

are more common. More nocturnal than the raccoon, the ringtail is only 

active at dawn and dusk (Kaufmann, 1982). 

General references 

Burt and Grossenheider (1980); Goldman (1950); Johnson (1970); Kaufmann (1982); 

Palmer and Fowler (1975); Sanderson (1987). 

2-235 Raccoon 
Raccoon (Procyon lotor) 

Factors 

Age/Sex/ Range 

Cond./Seas. Mean or (95% CI) Location Referenc

Body Weight A M 7.6 7.0 - 8.3 wc Illinois Sanderso

(kg) A F parous 6.4 5.6 - 7.1 

A F nulliparous 6.0 5.1 - 7.1 

J M 5.1 4.6 - 5.7 J F 4.8 4.2 - 5.3 A M 6.76 Missouri Nagel, 19

A F 5.74 

A M 4.31 up to 8.8 Alabama Johnson

A F 3.67 up to 5.9 

neonate 0.075 w New York/captive Hamilton

Pup Growth birth to 7 days 17 w New York Hamilton

Rate (g/day) 8 to 19 days 21 

20 to 30 days 11 31 to 40 days 12 41 to 50 days 23 

birth to 6 wks 17.8 NS/lab Montgom

6 to 9 wks 3.9 10 to 16 wks 29.5 

Metabolic Winter 9.36 ± 1.68 SD Washington, DC/National Mugaas 

Rate 15-35�C Zoo 

(lO /kg-day) 2 

Metabolic Rate J B 304 Ohio/lab Teubner 

(kcal/kg-day) 

A M basal 44.8 estimate

A F basal 46.8 A M free-living 183 (83 - 400) estimate

A F free-living 187 (85 - 408) 

Food Ingestion 

Rate (g/g-day) 

2-236 Raccoon 
Raccoon (Procyon lotor) 

Factors 

Age/Sex/ Range 

Cond./Seas. Mean or (95% CI) Location Referenc

Water A M 0.082 estimate

Ingestion Rate A F 0.083 

(g/g-day) Inhalation A M 2.47 estimate

Rate (m /day) A F 2.17 3 

Surface Area A M 3,796 estimate(cm ) A F 3,414 2 Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

crayfish 37 8 aryland/forested Llewellyn 

snails 5 ottomland 

insects 40 39 18 12 

reptiles/amphibians 6 % et olume w ; ig v estive d

fish 3 2 trace 2 tract) 

rodents 7 2 trace 8 

corn 0 9 

Smilax 0 trace trace 6 acorns 0 trace 5 17 

pokeberry 0 trace 17 2 wild cherry 0 17 2 0 blackberries 0 16 trace 0 

grapes 0 trace 23 8 

persimmon 0 0 11 7 

3 9 M

5 3 6 b

5 3 7 (

1 2 1

2-237 Raccoon 
Raccoon (Procyon lotor) 

2-238 Raccoon 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

frogs 8.1 trace 0 0 Tennessee/NS Tabataba

fish 1.2 0 0 0 

birds trace 0 trace 8.4 (% wet volume; digestive 

mammals 1.7 0 1.4 0 tract) other/unspecified 7.8 6.7 1.8 7.2 

persimmon 0 35.8 57.3 27.4 corn 57.6 0 10.0 25.9 grapes 0 trace 10.2 0 pokeberry 0 20.5 4.5 0 acorns 0 0 5.4 4.2 

sugar hackberry 0 0 5.5 18.4 

cherry 0 29.5 0 0 

insects 22.0 3.5 2.4 trace 

crayfish 1.6 4.0 1.5 1.4 Mollusca 44 sw Washington/tidewater Tyson, 1

(mussels and oysters) mudflats 

Crustacea (shrimp & 25 

crabs) (% wet volume; stomach 

Pisces (goby 9 contents) 

& cabezon) 

Annelida 20 

(marine worms) 

Echiurida (worm) 1 fruits 37.9 New York/NS Hamilton

insects 8.2 mammals 14.3 (% wet volume; stomach 

grains (e.g. corn) 14.7 contents) 

earthworms 7.2 amphibians 4.4 vegetation 6.1 reptiles 3.0 molluscs 1.9 

birds 1.5 

carrion 1.5 

unspecified 0.2 
Raccoon (Procyon lotor) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Home A M spr./sum. 2,560 670 - 4,946 North Dakota/prairie Fritzell, 1

Range A F spr./sum. 806 229 - 1,632 potholes 

Size (ha) A M May - Dec 204 18.2 - 814 Michigan/riparian Stuewer, 

A F May - Dec 108 5.3 - 376 

A M all year 65 ± 18 SE Georgia/coastal island Lotze, 19

A F all year 39 ± 16 SE 

Population NS 1.46 Ohio/residential woods Hoffman 

Density (N/ha) 

spring 0.17 Lake Erie, Ohio/ Urban, 1

spring 0.022 Wisconsin/marsh Dorney, 

Sandusky Bay, marsh 

Litter 1 to 3 yrs 3.4 n Illinois/NS Fritzell e

Size 4 yrs + 3.8 

2.43 Alabama/bottomlands, Johnson

marsh 

Litters 1 most of range/NS Sanders

/Year Days 63 North America/NS Hamilton

Gestation 1987; Stu

Age at 84 63 - 112 NS/lab Montgom

Weaning (days) Age at M 15 months Alabama/NS Johnson

Sexual Maturity F 1 year IL, MO/NS Fritzell e

Annual A B 56 Missouri/NS Sanders

Mortality Rates A B 38 sw Iowa/agricultural Clark et a

(percent) J B 42 

2-239 Raccoon 
1

23456789

101112

Raccoon (Procyon lotor) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Longevity A B 3.1 years Alabama/NS Johnson

A B 1.8 years Missouri/NS Sanders

Seasonal 

Activity Begin Peak End Location Referenc

Mating February March August sw Georgia, nw Florida McKeeve

January February March n United States Johnson

Parturition April early April May Michigan Stuewer, 

April May October sw Georgia, nw Florida McKeeve

Molt summer northern latitudes Goldman

Torpor late March/April ec Minnesota Whitney 

November 

Estimated using equation 3-43 (Boddington, 1978) and body weights from Nagel (1943). 

Estimated using equation 3-45 (Nagy, 1987) and body weights from Nagel (1943). 

2-240 Raccoon 

See Chapters 3 and 4 for methods for calculating food ingestion rates from free-living metabolic rate and diet.

Estimated using equation 3-17 (Calder and Braun, 1983) and body weights from Nagel (1943).

Estimated using equation 3-20 (Stahl, 1967) and body weights from Nagel (1943).

Estimated using equation 3-22 (Stahl, 1967) and body weights from Nagel (1943).

Collections from April through October.

Measured from April through July.

Based on radiotracking.

Average of three methods of estimating density.

Hunted population.Cited in Schneider et al. (1971).
References (including Appendix) 

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Brown, C. E. (1936) Rearing wild animals in captivity, and gestation periods. J. Mammal. 17: 

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Burt, W. H.; Grossenheider, R. P. (1980) A field guide to the mammals of North America 

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Cauley, D. L.; Schinner, J. R. (1973) The Cincinnati raccoons. Nat. Hist. 82: 58-60. 

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Iowa raccoon population. J. Wildl. Manage. 53: 982-990. 

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and Goldman) in the northern part of its range [Ph.D. dissertation]. Grand Forks, 

ND: University of North Dakota. 

2-241 Raccoon 
Cunningham, E. R. (1962) A study of the eastern raccoon, Procyon lotor (L.), on the Atomic 

Energy Commission Savannah River Plant [master's thesis]. Athens, GA: University 

of Georgia. 

Dew, R. D. (1978) Biology of the raccoon, Procyon lotor; I. Genic variation. II. Population 

age structure and average litter size [master's thesis]. Memphis, TN: Memphis State 

University. 

Dorney, R. S. (1954) Ecology of marsh raccoons. J. Wildl. Manage. 18: 217-225. 

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Fritzell, E. K.; Hubert, G. F., Jr.; Meyen, B. E.; et al. (1985) Age-specific reproduction in 

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Greenwood, R. J. (1982) Nocturnal activity and foraging of prairie raccoons (Procyon lotor) 

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Hamilton, W. J., Jr. (1940) The summer food of minks and raccoons on the Montezuma 

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Hamilton, W. J., Jr. (1951) Warm weather foods of the raccoon in New York state. J. 

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Hoffman, C. O.; Gottschang, J. L. (1977) Numbers, distribution, and movements of a 

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290-291. 

Johnson, A. S. (1970) Biology of the raccoon (Procyon lotor varius Nelson and Goldman) in 

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2-242 Raccoon 
Kaufmann, J. H. (1982) Raccoon and allies. In: Chapman, J. A.; Feldhamer, G. A., eds. Wild 

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McKeever, S. (1958) Reproduction in the raccoon in the southeastern United States. J. 

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determined by telemetry. J. Mammal. 47: 450-466. 

Mech, L. D.; Barnes, D. M.; Tester, J. R. (1968) Seasonal weight changes, mortality, and 

population structure of raccoons in Minnesota. J. Mammal. 49: 63-73. 

Montgomery, G. G. (1969) Weaning of captive raccoons. J. Wildl. Manage. 33: 154-159. 

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2-243 Raccoon 
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2-244 Raccoon 
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Tennessee. J. Tenn. Acad. Sci. 63: 89-94. 

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2-245 Raccoon 
2.2.4. Mink (mink, weasels, ermine) 

Order Carnivora, Family Mustelidae. Although varied in size, most members of this 

family have long, slender bodies and short legs. Throughout the family, the male is usually 

larger than the female. The more terrestrial species feed primarily on small mammals and 

birds. Mustelids that live around lakes and streams feed on aquatic prey such as fish, 

frogs, and invertebrates (Burt and Grossenheider, 1980). 

Selected species 

The mink (Mustela vison) is the most abundant and widespread carnivorous 

mammal in North America. Mink are distributed throughout North America, except in the 

extreme north of Canada, Mexico, and arid areas of the southwestern United States. It is 

common throughout its range but often overlooked because of its solitary nature and 

nocturnal activity. Mink are particularly sensitive to PCBs and similar chemicals, and have 

been found to accumulate PCBs in subcutaneous fat to 38 to 200 times dietary 

concentrations, depending on the PCB congener (Hornshaw et al., 1983). 

Body size. Body size varies greatly throughout the species' range, with males 

weighing markedly more than females (in some populations, almost twice as much, see 

table). Males measure from 33 to 43 cm with a 18 to 23 cm tail. Females measure from 30 

to 36 cm with a 13 to 20 cm tail (Burt and Grossenheider, 1980). Farm-raised mink tend to 

be larger than wild mink (letter from R.J. Aulerich, Department of Animal Science, Michigan 

State University, East Lansing, MI, to Susan Norton, January 7, 1992). 

Metabolism. Harper et al. (1978) evaluated the energy requirements of growing 

farm-raised male mink during a 21-day period when about 20 percent of their total growth 

would occur. They expressed food intake on the basis of metabolic body size (MBS) 

instead of body weight (BW) where MBS = BW(kg)

0.73. Metabolizable energy (ME) 

requirements were 147.8 ± 6.06 (kcal/kgMBS-day). Accounting for assimilation efficiency, 

this corresponded to a gross energy (GE) intake of approximately 203 (kcal/kgMBS-day). 

Iversen (1972) found that basal metabolic rate for mink and other mustelids 

weighing 1 kg or more could be expressed by the equation: 

BMR = 84.6Wt

0.78 (±0.15), 

where BMR = basal metabolic rate in kcal/day and Wt = body weight in kilograms. This 

model reflects the finding that the larger mustelids have a slightly (10 to 15 percent) higher 

basal metabolic rate than expected for mammals in general.

f Free-living metabolic rates 

would be expected to be three to five times higher (see table). 

Habitat. Mink are found associated with aquatic habitats of all kinds, including 

waterways such as rivers, streams, lakes, and ditches, as well as swamps, marshes, and 

f

Mustelid species much smaller than 1 kg (i.e., the stoat and weasel) have much higher basal 

metabolic rates than predicted for mammals in general. 

2-247 Mink 
backwater areas (Linscombe et al., 1982). Mink prefer irregular shorelines to more open, 

exposed banks (Allen, 1986). They also tend to use brushy or wooded cover adjacent to 

the water, where cover for prey is abundant and where downfall and debris provide den 

sites (Allen, 1986). 

Food habits. Mink are predominantly nocturnal hunters, although they are 

sometimes active during the day. Shorelines and emergent vegetation are the mink's 

principal hunting areas (Arnold, 1986, cited in Eagle and Whitman, 1987). Mink are 

opportunistic feeders, taking whatever prey is abundant (Hamilton, 1936, 1940; Errington, 

1954; Sargeant et al., 1973). Mammals are the mink's most important prey year-round in 

many parts of their range (Eagle and Whitman, 1987), but mink also hunt aquatic prey such 

as fish, amphibians, and crustaceans and other terrestrial prey such as bird, reptiles, and 

insects, depending on the season (Linscombe et al., 1982). In marsh habitats in summer, 

muskrats can be an important food source depending on their population density and 

vulnerability (e.g., health) (Hamilton, 1940; Sealander, 1943; Errington, 1954). Mink diet 

also can depend on marsh water level; Proulx et al. (1987) found that with high water 

levels, mink captured predominantly crayfish and meadow voles, but during periods of low 

water, the mink preyed on aquatic birds and muskrats deeper in the marsh. Similarly, 

Errington (1939) found that mink predation on muskrats in the prairie pothole region can 

increase dramatically in times of drought as the muskrat burrows become more exposed. 

Also in this region, ducklings and molting adult ducks that frequent shorelines are 

particularly vulnerable to mink predation (Arnold and Fritzell, 1987; Sargeant et al., 1973). 

In winter, mink often supplement their diet with fish (Eagle and Whitman, 1987). Females 

tend to be limited to smaller prey than males, who are able to hunt larger prey such as 

rabbits and muskrats more successfully (Birks and Dunstone, 1985; Sealander, 1943). 

Temperature regulation and molt. In winter, mink do not undergo hibernation or 

torpor; instead, they are active year-round. Mink replace their summer coat in mid to late 

fall with a darker more dense coat and molt again in the spring (Eagle and Whitman, 1987; 

Linscombe et al., 1982). 

Breeding activities and social organization. Mating occurs in late winter to early 

spring (Eagle and Whitman, 1987). Variation in the length of mating season with different 

subspecies reflects adaptations to different climates (Linscombe et al., 1982). Ovulation is 

induced by mating, and implantation is delayed (Eagle and Whitman, 1987). Parturition 

generally occurs in the late spring, and the mink kits are altricial (helpless) at birth 

(Linscombe et al., 1982). Mink are generally solitary, with females only associating with 

their young of the year. Female home ranges generally do not overlap with the home 

ranges of other females, nor do the home ranges of males overlap with each other (Eagle 

and Whitman, 1987). The home range of a male may overlap the home range of several 

females, however, particularly during the breeding season (Eagle and Whitman, 1987). 

Home range and resources. The home range of mink encompasses both their 

foraging areas around waterways and their dens. When denning, mink use bank burrows 

of other animals, particularly muskrats, as well as cavities in tree roots, rock or brush 

piles, logjams, and beaver lodges (Melquist et al., 1981; Birks and Linn, 1982; Eagle and 

Whitman, 1987). Individual mink may use several different dens within their home range, 

males more so than females (Birks and Linn, 1982). Melquist et al. (1981) found that den 

2-248 Mink 
�

�

�

�

sites in Idaho were 5 to 100 m from the water, and they never observed mink more than 200 

m from water. The shape of mink home ranges depends on habitat type; riverine home 

ranges are basically linear, whereas those in marsh habitats tend to be more circular (Birks 

and Linn, 1982; Eagle and Whitman, 1987). Home range size depends mostly on food 

abundance, but also on the age and sex of the mink, season, and social stability (Arnold, 

1986; Birks and Linn, 1982; Eagle and Whitman, 1987; Linn and Birks, 1981; Mitchell, 1961). 

In winter, mink spend more time near dens and use a smaller portion of their home range 

than in summer (Gerell, 1970, cited in Linscombe et al., 1982). Adult male home ranges are 

generally larger than adult female home ranges (Eagle and Whitman, 1987), particularly 

during the mating season when males may range over 1,000 ha (Arnold, 1986). 

Population density. Population density depends on available cover and prey. 

Population densities typically range from 0.01 to 0.10 mink per hectare (see table). In 

riverine environments, it can be more meaningful to measure densities in terms of number 

of mink per unit length of shoreline covered rather than in terms of number per hectare. 

Population dynamics. Mink reach sexual maturity at 10 months to a year and may 

reproduce for 7 years, possibly more (Enders, 1952; Ewer, 1973). Female mink can 

reproduce once per year and usually give birth to their first litters at the age of 1 year 

(Eagle and Whitman, 1987). Females often live to the age of 7 years in captivity (Enders, 

1952). 

Similar species (from general references) 

� The long-tailed weasel (Mustela frenata) is smaller (males 23 to 27 cm, 200 to 

340 g; females 20 to 23 cm, 85 to 200 g) than the mink. It is considered 

beneficial in agriculture because it kills small rodents, but it does not harm 

poultry. Although it does not range as far north as the mink, the long-tailed 

weasel does inhabit parts of the southwest. 

� The least weasel (Mustela nivalis) is smaller than the mink (males 15 to 17 

cm, 39 to 63 g; females 14 to 15 cm, 38 to 40 g) and inhabits meadows, fields, 

and wooded areas. The least weasel feeds extensively on mice and insects. 

Its habitat is limited to the north central United States and Canada. 

� The ermine (Mustela erminea), or shorttail weasel, is smaller (males 15 to 17 

cm, 71 to 170 g; females 13 to 19 cm, 28 to 85 g) than the mink. The ermine 

inhabits woody areas near water and feeds primarily on small mammals. 

The ermine's range is limited to the northern and western United States and 

Canada. 

� The black-footed ferret (Mustela nigripes) is larger (36 to 46 cm; up to 1.1 kg) 

than the mink and inhabits western prairies in the United States, although it 

now is an endangered species. It feeds on prairie dogs and other small 

animals. 

2-249 Mink 
General references 

Burt and Grossenheider (1980); Eagle and Whitman (1987); Hall (1981); Linscombe 

et al. (1982); Palmer and Fowler (1975). 

2-250 Mink 
Mink (Mustela vison) 

2-251 Mink 

Range or 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean Location eren

Weight A M < 2,300 western races Harding

(g) A M < 1,400 eastern races Harding

A M spring 1,734 ± 350 SD Michigan (farm-raised) Hornsh

A F spring 974 ± 202 SD 

A M summer 1,040 Montana Mitchel

J M summer 777 

A M fall 1,233 

J M fall 952 

A F summer 550 Montana Mitchel

J F summer 533 A F fall 586 J F fall 582 

neonate 6 - 10 NS Eagle & 

neonate 8.3 ± 1.54 SD Michigan (farm-raised) Hornsh

Pup Growth 0-30 days; M 7.0 NS/(farm-raised) Wehr e

Rate (g/day) 31-90 d; M 21 

91-120 d; M 15 121-150 d; M 9.0 151-180 d; M 4.3 0-30 days; F 6.5 

31-90 d; F 13 

91-120 d; F 6.7 121-150 d; F 1.7 151-180 d; F 0.6 

Ref
Mink (Mustela vison) 

Range or 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean Location eren

Metabolic Rate A F basal 96 estimat(kcal/kg-day) A M basal 84 

A F ranch cage 258 (farm-raised) Farrell & 

A F free-living 258 (110 - 507) estimat

A M free-living 236 (121 - 550) 

Food Ingestion A M summer 0.13 (captive) Arnold 

Rate (g/g-day) 

A M winter 0.12 ± 0.0048 SE Michigan (farm-raised) Bleavin

A F winter 0.16 ± 0.0075 SE 

A M yr-round 0.22 estimat

Water A F 0.11 estimat

Ingestion A M 0.099 

Rate (g/g-day) A F 0.028 (farm-raised) Farrell 

Inhalation A F 0.33 estimat

Rate (m /day) A M 0.55 3 

Surface Area A F 743 estimat(cm ) A M 1,120 2 Dietary Composition Spring Summer Fall Winter (measure) Referen

Location/Habitat 

ducks 5.2 32.5 Manitoba, Can/aspen Arnold 

other birds 18.8 21.6 parklands of prairie 

eggs 3.3 14.5 potholes 

muskrats 42.0 2.1 

ground squirrels 14.2 0.5 (% dry weight in scats; 

other mammals 15.5 25.3 male mink only) 

insects 1.0 3.5 

Ref

2-252 Mink 
Mink (Mustela vison) 

Dietary Composition Spring Summer Fall Winter (measure) Referen

Location/Habitat 

(habitat/season) (stream; year-round) (river; year-round) Michigan/stream, river Alexand

trout 52 56 

non-trout fish 6 26 (% wet weight; stomach 

unidentified fish 3 3 contents) crustaceans 11 4 

amphibians 2 3 

birds/mammals 5 6 

vegetation 17 1 

unidentified 4 1 

(sex of mink) (M) (F) Michigan/NS Sealand

muskrat 43 14 

cottontail 16 12 (% volume; stomach 

small mammals 5 17 contents) 

large birds 18 11 

small birds trace 

snakes 2 2 

frogs 10 37 

fish 5 4 crayfish 1 3 

frogs 24.9 Missouri/statewide Korsch

mice & rats 23.9 

fish 19.9 

rabbits 10.2 (% dry volume; stomach 

crayfish 9.3 contents) 

birds 5.6 

fox squirrels 2.2 

muskrats 1.3 

other 2.7 

2-253 Mink 
Mink (Mustela vison) 

Population 

Dynamics 

Age/Sex/ Cond./Seas. Mean Location/Habitat Refere

Home Range 259 - 380 ha North Dakota/prairie Eagle 

Size potholes 

A M 770 ha Manitoba, Canada/prairie Arnold 

A F 7.8 ha heavy vegetation 

A F 20.4 ha sparse vegetation 

A M 2.63 km 1.8 - 5.0 km Sweden/stream Gerell

J M 1.23 km 1.1 - 1.4 km 

A F 1.85 km 1.0 - 2.8 km 

potholes 

Montana/riverine: Mitche

Population 0.03 - 0.085 N/ha Montana/river Mitche

Density 

A F winter 0.006 N/ha Michigan/river Marsh

A F winter 0.6 N/km river 

Litter 4.2 Michigan/(farm-raised) Horns

Size 4 2 - 8 Montana/river Mitche

4 - 10 North America/NS Hall & 

Litters 1 North America/NS Hall & 

/Year 

Days 39 - 76 North America/NS Hall & 

Gestation 51 40 - 75 United States/(farm-raised) Ender

Age at eat meat 37 days Louisiana/NS Svilha

Weaning fully 

homeothermic 7 weeks NS/NS Kostro

Age at B 10 months United States/(farm-raised) Ender

Sexual B 1 year NS/NS Ewer, 

Maturity Longevity maximum 10 years NS/zoo Eisenb

F 7 maximum 11 years NS/(farm-raised) Ender

Range 

2-254 Mink 
Mink (Mustela vison) 

Seasonal 

Activity Begin Peak End Location Referen

Mating April Alaska Burns, 1

March Montana Mitchell

fall Florida, Cypress Swamp Humphr

Parturition April June most areas (except south) Eagle & 

Molt mid- to late fall NS Eagle & 

1 Cited in Linscombe et al. (1982).

2 Cited in NRC (1982).

3 Estimated using Iversen's (1972) model and summer body weights from Mitchell (1961); equation 3-43 (Boddington, 

Mitchell (1961) yield slightly lower estimates (see text). 

4 Estimated using equation 3-47 (Nagy 1987) and body weights from Mitchell (1961). 

5 Arnold and Fritzell (1987) estimated that mink require 180 g of prey per day by assuming a male body mass of 1,420 

Cowan et al. (1957) derived from measures of prey requirements for captive mink. 

6 Diet of whole chicken (20 percent), commercial mink cereal (17 percent), ocean fish scraps (13 percent), and beef pa

powdered milk. Moisture content of feed = 66.2 percent. 

7 Estimated using equation 3-47 (Nagy, 1987), summer body weights from Mitchell (1961), and dietary composition of 

Chapter 4, Figure 4-7 for the calculations. 

8 Estimated using equation 3-17 (Calder and Braun, 1983) and body weights from Mitchell (1961). 

9 Diet contained 65 percent water. 

10 Estimated using equation 3-20 (Stahl, 1967) and body weights from Mitchell (1961).

11 Estimated using equation 3-22 (Stahl, 1967) and body weights from Mitchell (1961).

12 Collected from fur buyers.13 Cited in Allen (1986).14 Cited in Eagle and Whitman (1987).

15 Cited in Eisenberg (1981).

2-255 Mink 
References (including Appendix) 

Alexander, G. (1977) Food of vertebrate predators on trout waters in north central lower 

Michigan. Michigan Academician 10: 181-195. 

Allen, A. W. (1986) Habitat suitability index models: mink. U.S. Fish Wildl. Serv. Biol. Rep. 

82(10.127). 

Arnold, T. W. (1986) The ecology of prairie mink during the waterfowl breeding season 

[master's thesis]. Columbia, MO: University of Missouri. 

Arnold, T. W.; Fritzell, E. K. (1987) Food habits of prairie mink during the waterfowl 

breeding season. Can. J. Zool. 65: 2322-2324. 

Birks, J. D.; Dunstone, N. (1985) Sex-related differences in the diet of the mink Mustela 

vison. Holarctic Ecol. 8: 245-252. 

Birks, J. D.; Linn, I. J. (1982) Studies of home range of the feral mink, Mustela vison. Symp. 

Zool. Soc. Lond. 49: 231-257. 

Bleavins, M. R.; Aulerich, R. J. (1981) Feed consumption and food passage in mink 

(Mustela vison) and European ferrets (Mustela putorius furo). Lab. Anim. Sci. 31: 

268-269. 

Boddington, M. J. (1978) An absolute metabolic scope for activity. J. Theor. Biol. 75: 443-

449. 

Burgess, S. A.; Bider, J. R. (1980) Effects of stream habitat improvements on invertebrates, 

trout populations, and mink activity. J. Wildl. Manage. 44: 871-880. 

Burns, J. J. (1964) The ecology, economics, and management of mink in the 

Yukon-Kuskokwim Delta, Alaska [master's thesis]. Anchorage, AK: University of 

Alaska. 

Burt, W. H.; Grossenheider, R. P. (1980) A field guide to the mammals of North America 

north of Mexico. Boston, MA: Houghton Mifflin Co. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Chanin, P. R.; Linn, I. (1980) The diet of the feral mink (Mustela vison) in southwest Britain. 

J. Zool. (London) 192: 205-223. 

Cowan, I. M.; Wood, A. J.; Kitts, W. D. (1957) Feed requirements of deer, beaver, bear, and 

mink for growth and maintenance. Trans. North Am. Wildl. Conf. 22: 179-188. 

2-256 Mink 
Cowan, W. F.; Reilly, J. R. (1973) Summer and fall foods of mink on the J. Clark Salyer 

National Wildlife Refuge. Prairie Nat. 5: 20-24. 

Eagle, T. C.; Whitman, J. S. (1987) Mink. In: Novak, M.; Baker, J. A.; Obbarel, M. E.; et al., 

eds. Wild furbearer management and conservation. Pittsburgh, PA: University of 

Pittsburgh Press; pp. 615-624. 

Eberhardt, L. E. (1974) Food habits of prairie mink (Mustela vison) during the waterfowl 

breeding season [master's thesis]. St. Paul, MN: University of Minnesota. 

Eisenberg, J. F. (1981) The mammalian radiations. Chicago, IL: University of Chicago 

Press. 

Enders, R. K. (1952) Reproduction of the mink (Mustela vison). Proc. Am. Philos. Soc. 96: 

691-755. 

Errington, P. L. (1939) Reactions of muskrat populations to drought. Ecology 20: 168-186. 

Errington, P. L. (1954) The special responsiveness of minks to epizootics in muskrat 

populations. Ecol. Monogr. 24: 377-393. 

Ewer, R. F. (1973) The carnivores. Ithaca, NY: Cornell University Press. 

Farrell, D. J.; Wood, A. J. (1968a) The nutrition of the female mink (Mustela vison). I. The 

metabolic rate of the mink. Can. J. Zool. 46: 41-46. 

Farrell, D. J.; Wood, A. J. (1968b) The nutrition of the female mink (Mustela vison). II. The 

energy requirement for maintenance. Can. J. Zool. 46: 47-52. 

Farrell, D. J.; Wood, A. J. (1968c) The nutrition of the female mink (Mustela vison). III. The 

water requirement for maintenance. Can. J. Zool. 46: 53-56. 

Gerell, R. (1970) Home ranges and movements of the mink Mustela vison Schreber in 

southern Sweden. Oikos 20: 451-460. 

Gilbert, F. F.; Nancekivell, E. G. (1982) Food habits of mink (Mustela vison) and otter (Lutra 

canadensis) in northeastern Alberta. Can. J. Zool. 60: 1282-1288. 

Guilday, J. E. (1949) Winter food of Pennsylvania mink. Pennsylvania Game News 20: 

12-32. 

Hall, E. R. (1981) The mammals of North America. 2nd ed. New York, NY: John Wiley and 

Sons. 

Hall, E. R.; Kelson, K. R. (1959) The mammals of North America. 1st ed. New York, NY: The 

Ronald Press Co. 

Hamilton, W. J., Jr. (1936) Food habits of the mink in New York. J. Mammal. 17: 169. 

2-257 Mink 
Hamilton, W. J., Jr. (1940) The summer food of minks and raccoons on the Montezuma 

Marsh, New York. J. Wildl. Manage. 4: 80-84. 

Hamilton, W. J., Jr. (1959) Foods of mink in New York. N.Y. Fish and Game J. 6: 77-85. 

Harding, A. R. (1934) Mink trapping. Columbus, OH: A. R. Harding. 

Harper, R. H.; Travis, H. F.; Glinsky; M. S. (1978) Metabolizable energy requirement for 

maintenance and body composition of growing farm raised male mink (Mustela 

vison). J. Nutr. 108: 1937-1943. 

Hornshaw, T. C.; Aulerich, R. J.; Johnson, H. E. (1983) Feeding Great Lakes fish to mink: 

effects on mink and accumulation and elimination of PCBs by mink. J. Toxicol. 

Environ. Health 11: 933-946. 

Humphrey, S. R.; Zinn, T. L. (1982) Seasonal habitat use by river otters and everglades 

mink. J. Wildl. Manage. 46: 375-381. 

Iversen, J. A. (1972) Basal energy metabolism of mustelids. J. Comp. Physiol. 81: 341-344. 

Korschgen, L. J. (1958) December food habits of mink in Missouri. J. Mammal. 39: 521-527. 

Kostron, K.; Kukla, F. (1970) Changes in thermoregulation in mink kits within the 45 days of 

ontogenesis. Acta Univ. Agric., Facultas Agronomica, Sbornik Vysoke Skoly 

Zemedelske (Brunn) (rada A) 18: 461-469. 

Linn, I. J.; Birks, J. D. (1981) Observations on the home ranges of feral American mink 

(Mustela vison) in Devon, England, as revealed by radio-tracking. In: Chapman, 

J. A.; Pursley, D., eds. Proceedings worldwide furbearer conference: v. 1. August 

1980; Frostburg, MD; pp. 1088-1102. 

Linscombe, G.; Kinler, N.; Aulerich, R. J. (1982) Mink. In: Chapman, J. A.; Feldhammer, G. 

A., eds. Wild mammals of North America. Baltimore, MD: Johns Hopkins University 

Press; pp. 329-643. 

Marshall, W. H. (1936) A study of the winter activities of the mink. J. Mammal. 17: 382-392. 

McCabe, R. A. (1949) Notes on live-trapping mink. J. Mammal. 30: 416-423. 

McDonnell, J. A.; Gilbert, F. F. (1981) The responses of muskrats (Ondatra zibethicus) to 

water level fluctuations at Luther Marsh, Ontario. In: Chapman, J. A.; Pursley, D., 

eds. Proceedings worldwide furbearer conference: v. 1. August 1980; Frostburg, 

MD; pp. 1027-1040. 

Melquist, W. E.; Whitman, J. S.; Hornocker, M. G. (1981) Resource partitioning and 

coexistence of sympatric mink and river otter populations. In: Chapman, J. A.; 

Pursley, D., eds. Proceedings worldwide furbearer conference: v. 1. August 1980; 

Frostburg, MD; pp. 187-220. 

2-258 Mink 
Mitchell, J. L. (1961) Mink movements and populations on a Montana river. J. Wildl. 

Manage. 25: 48-54. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

National Research Council (NRC) (1982) Nutrient requirements of mink and foxes. In: 

Nutrient requirements of domestic animals series, No. 7. Washington, DC: National 

Academy of Sciences, National Academy Press. 

Palmer, E. L.; Fowler, H. S. (1975) Fieldbook of natural history. New York, NY: McGraw-Hill 

Book Co. 

Pendleton, G. W. (1982) A selected annotated bibliography of mink behavior and ecology. 

Brookings, SD: South Dakota State University; Tech. Bull. No. 3. 

Perel'dik, N. S.; Milovanov, L. V.; Erin, A. T. (1972) Feeding fur bearing animals. 

Washington, DC: Translated from Russian by the Agricultural Research Service, 

U.S. Department of Agriculture and the National Science Foundation. 

Proulx, G.; McDonnell, J. A.; Gilbert, F. F. (1987) The effect of water level fluctuations on 

muskrat, Ondatra zibethicus, predation by mink, Mustela vison. Can. Field-Nat. 101: 

89-92. 

Sargeant, A. B.; Swanson, G. A.; Doty, H. (1973) Selective predation by mink, Mustela 

vison, on waterfowl. Am. Midl. Nat. 89: 208-214. 

Sealander, J. A. (1943) Winter food habits of mink in southern Michigan. J. Wildl. Manage. 

7: 411-417. 

Stahl, W. R. (1967) Scaling of respiratory variables in mammals. J. Appl. Physiol. 22: 

453-460. 

Svilha, A. (1931) Habits of the Louisiana mink (Mustela vison vulgivagus). J. Mammal. 12: 

366-368. 

Williams, T. M. (1980) A comparison of running and swimming energetics in the mink 

(abstract). Am. Zool. 20: 909. 

Williams, T. M. (1983) Locomotion in the North American mink, a semi-aquatic mammal. I. 

Swimming energetics and body drag. J. Exp. Biol. 103: 155-168. 

2-259 Mink 
2.2.5. River Otter 

Order Carnivora, Family Mustelidae. Mustelids have long, slender bodies, short 

legs, and anal scent glands. Throughout the family, the male is usually larger than the 

female. The more terrestrial species of this family occupy various habitats and feed 

primarily on small mammals and birds. Mustelids that live around lakes and streams feed 

primarily on aquatic species such as fish, frogs, and invertebrates (Palmer and Fowler, 

1975; Burt and Grossenheider, 1980). 

Selected species 

The northern river otter (Lutra canadensis) historically lived in or near lakes, 

marshes, streams, and seashores throughout much of the North American continent (Hall, 

1981). Currently, many populations along the coastal United States and Canada are stable 

or increasing, but this species is rare or extirpated throughout much of the midwestern 

United States (Toweill and Tabor, 1982). The river otter dens in banks and hollow logs. 

Individuals range over large areas daily, feeding primarily on fish. Although otters have 

few natural predators, while on land, they may be taken by coyotes, fox, or dogs (Melquist 

and Hornocker, 1983). Otters clean themselves frequently by rubbing and rolling in any dry 

surface (Toweill and Tabor, 1982). Otters appear to undergo bradycardia while submerged 

and can stay underwater for up to 4 minutes (Melquist and Dronkert, 1987). Because of its 

piscivorous diet and high trophic level, the river otter is a noteworthy indicator of 

bioaccumulative pollution in aquatic ecosystems (Melquist and Dronkert, 1987). 

Body size. River otters measure 66 to 76 cm with a 30 to 43 cm tail. Sexual 

dimorphism in size is seen among all subspecies (Harris, 1968; van Zyll de Jong, 1972, 

cited in Toweill and Tabor, 1982), and adult males (5 to 10 kg) outweigh females (4 to 7 kg) 

by approximately 17 percent (Melquist and Hornocker, 1983; see Table). Full adult weight 

generally is not attained until sexual maturity after 2 years of age (Melquist and Hornocker, 

1983). Along the Pacific Coast, there is some evidence that size decreases from north to 

south (Toweill and Tabor, 1982). 

Metabolism. Iversen (1972) found that basal metabolic rate of otters and other 

mustelids weighing 1 kg or more could be expressed by the equation: 

BMR = 84.6Wt

0.78 (±0.15), 

where BMR = basal metabolic rate in kcal/day and Wt = body weight in kilograms. Freeliving metabolic rates would be expected to be three to five times higher (see table). 

Habitat. Almost exclusively aquatic, the river otter is found in freshwater, estuarine, 

and some marine environments all the way from coastal areas to mountain lakes (Toweill 

and Tabor, 1982). They are found primarily in food-rich coastal areas, such as the lower 

portions of streams and rivers, estuaries, nonpolluted waterways, the lakes and tributaries 

that feed rivers, and areas showing little human impact (Mowbray et al., 1979; Tabor and 

Wight, 1977). 

2-261 River Otter 
Food habits. Otters usually are active in the evening and from dawn to midmorning, 

although they can be active any time of day (Melquist and Hornocker, 1983). The bulk of 

the river otter's diet is fish; however, otters are opportunistic and will feed on a variety of 

prey depending on availability and ease of capture. River otters take different fish species 

according to their availability and how well the fish can escape capture (Loranger, 1981). 

Depending on availability, otters also may consume crustaceans (especially crayfish), 

aquatic insects (e.g., stonefly nymphs, aquatic beetles), amphibians, insects, birds (e.g., 

ducks), mammals (e.g., young beavers), and turtles (Burt and Grossenheider, 1980; Lagler 

and Ostenson, 1942; Liers, 1951b; Melquist and Hornocker, 1983; Palmer and Fowler, 1975; 

Toweill and Tabor, 1982). Gilbert and Nancekivell (1982) observed that otters consume 

more waterfowl in the northerly latitudes than in the south, probably because of the ease of 

capturing the waterfowl during their molt in the north. Otters probe the bottoms of ponds 

or streams for invertebrates and may ingest mud or other debris in the process (Liers, 

1951b). Otters in captivity required 700-900 g of food daily (Harris, 1968, cited in Toweill 

and Tabor, 1982). 

Temperature regulation and molt. Seasonal patterns in otters are not well 

understood. Otters are active throughout the year (Toweill and Tabor, 1982), with the most 

intense activity levels during the winter (Larsen, 1983; Melquist and Hornocker, 1983). 

They undergo a gradual molt in spring and fall (Melquist and Dronkert, 1987). 

Breeding activities and social organization. Adult males are usually solitary; an 

adult female and two or three pups make up a typical family group (Melquist and Dronkert, 

1987). River otters breed in late winter or early spring over a period of 3 months or more. 

Birth of a litter follows mating by about 1 year; however, implantation is delayed for 

approximately 10 months, and active gestation lasts only 2 months (Pearson and Enders, 

1944, cited in Toweill and Tabor, 1982; Melquist and Dronkert, 1987). Newborn otters are 

born blind but fully furred and depend on their mother for milk until 3 to 5 months of age 

(Johnstone, 1978; Liers, 1951b). Family groups disperse about 3 months after the pups are 

weaned (Melquist and Hornocker, 1983). 

Home range and resources. The river otter's home range encompasses the area 

needed for foraging and reproduction (Melquist and Dronkert, 1987). The shape of the 

home range varies by habitat type; for example, near rivers or coastal areas, it may be a 

long strip along the shoreline (measured in kilometers), but in marshes or areas with many 

small streams, the home range may resemble a polygon (measured in hectares; Melquist 

and Dronkert, 1987). All parts of a home range are not used equally; instead, several 

activity centers may be interconnected by a stream or coast (Melquist and Hornocker, 

1983). Food has the greatest influence on habitat use, but adequate shelter in the form of 

temporary dens and resting sites also plays a role (Anderson and Woolf, 1987a; Melquist 

and Hornocker, 1983). River otters use dens dug by other animals or natural shelters such 

as hollow logs, logjams, or drift piles (Toweill and Tabor, 1982; Melquist and Dronkert, 

1987). Beaver bank dens and lodges accounted for 38 percent of resting sites used by 

radio-tracked otters in Idaho (Melquist and Hornocker, 1983). River otters appear to prefer 

flowing water habitats (e.g., streams) over more stationary water (e.g., lakes, ponds) (Idaho 

study; Melquist and Hornocker, 1983). 

2-262 River Otter 
�

River otters maintain distinct territories within their home ranges: females maintain 

a feeding area for their families, males for breeding purposes (Toweill and Tabor, 1982). 

Individuals tend to avoid confrontation through mutual avoidance (Melquist and Hornocker, 

1983). Home ranges are most restricted for lactating females (Melquist and Dronkert, 

1987). Adult and subadult males have larger, more variable home ranges than females. 

Population density. River otter populations show variable spacing in relation to 

prey density and habitat (Hornocker et al., 1983). This characteristic, along with their 

secretive habits and use of several den sites, makes it difficult to estimate river otter 

populations (Melquist and Dronkert, 1987). Population density of otters often is expressed 

in terms of number per kilometer of waterway or coastline because of their dependence on 

aquatic habitats. Densities between one otter every kilometer to one otter every 10 km of 

river or shoreline are typical (see table). 

Population parameters. Otters generally are not sexually mature until 2 years of 

age (Liers, 1951b; Hamilton and Eadie, 1964; Tabor and Wight, 1977; Lauhachinda, 1978). 

Adult females appear to reproduce yearly in Oregon (based on a pregnancy rate of almost 

100 percent; Tabor and Wight, 1977), but Lauhachinda (1978) concluded that they breed 

every other year in Alabama and Georgia. Litters usually consist of two to three pups, 

although litters as large as six pups occur (see table). As adults, river otter mortality rates 

are low, between 15 and 30 percent per year (Lauhachinda, 1978; Tabor and Wight, 1977). 

Similar species (from general references) 

� The sea otter (Enhydra lutris) (76 to 91 cm body and 28 to 33 cm tail; weight 

13 to 38 kg) inhabits kelp beds and rocky shores from the Aleutian Islands to 

California. Its diet includes fish, abalones, sea urchins, and other marine 

animals. 

General references 

Burt and Grossenheider (1980); Melquist and Dronkert (1987); Palmer and Fowler 

(1975); Toweill and Tabor (1982). 

2-263 River Otter 
River Otter (Lutra canadensis) 

Factors 

Age/Sex/ (95% CI of 

Cond./Seas. Mean mean) Location erenc

Range or 

Weight A B 5.0 - 15 throughout range Melquist 

(kg) 

A M 8.13 ± 1.15 SD 5.84 - 10.4 Alabama, Georgia Lauhach

A F 6.73 ± 1.00 SD 4.74 - 8.72 

Y M 6.36 ± 0.98 SD 4.41 - 8.31 

Y F 5.83 ± 1.82 SD 3.75 - 7.01 

A M 9.20 ± 0.6 SE wc Idaho Melquist 

A F 7.90 ± 0.2 SE Y M 7.90 ± 0.4 SE 

Y F 7.20 ± 0.1 SE neonate 0.132 New York Hamilton 

neonate 0.140 to 0.145 Alabama, Georgia Hill & La

Pup Growth 10 to 20 days 26.7 NS Liers, 19

Rate (g/day) 

Metabolic Rate A F basal 44.8 estimate

(kcal/kg-day) A M basal 42.6 

A F free-living 183 (83 - 400) estimateA M free-living 178 (81 - 391) 

Food Ingestion 

Rate (g/g-day) Water A F 0.082 estimate

Ingestion A M 0.080 

Rate (g/g-day) 

Inhalation A F 2.5 estimate

Rate (m /day) A M 2.9 3 

Surface Area A F 3,785 estimate(cm ) A M 4,280 2 

Ref

2-264 River Otter 
--

-- --

River Otter (Lutra canadensis) 

2-265 River Otter 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

fish 100 93 97 99 wc Idaho/mountain streams Melquist 

(sucker) (52) (47) (17) (30) and lakes 

(sculpins) (40) (31) (38) (42) 

(squawfish) ( 5) ( 4) ( 1) ( 6) (percent frequency of 

(perch) (22) ( 3) ( 7) ( 9) occurrence in scats) 

(whitefish) (21) (10) (24) (66) 

invertebrates 2 7 10 12 (most of the fish were longer 

birds <1 12 1 <1 than 30 cm) 

mammals 1 4 3 1 

reptiles 0 1 0 0 

invertebrates 41.6 44.2 33.3 26.3 nw Montana/ Greer, 19

(aquatic insects) 19.6 19.2 10.7 4.0 lakes and streams 

(fr water shrimp) 14.3 8.9 10.7 4.0 

fishes 91.4 92.9 100 100 (percent frequency of 

(trout) 23.7 9.8 33.3 29.3 occurrence in scats) 

(sculpin) 20.5 20.9 21.3 25.3 

(sunfish) 47.1 72.8 60.0 33.3 

frog 19.6 19.2 10.7 9.1 

salamander 0.3 0.7 1.3 

snake 0.2 0.7 

birds 6.7 4.1 1.3 1 

mammals 8.1 5.3 2.7 4.0 

fish 97 69 98 99 nw Illinois/Mississippi River Anderso

(sunfish) (31) (31) (80) (52) 

(minnow/carp) (52) ( 0) (17) (44) (percent frequency of 

(herring) (49) (38) (10) (40) occurrence in scats) 

(bass) (26) ( 0) ( 5) (14) 

frogs 3 6 11 16 crayfish 12 50 8 7 

dragonfly nymphs 2 birds 4 13 3 1 

0 6 2 
River Otter (Lutra canadensis) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

game & pan fish 32 Michigan/habitat NS Lagler & 

forage fish 17.6 

fish remains 3.0 (% volume; stomach 

amphibians 16.1 contents) 

other invertebrates 25.8 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Home Range A B 400 - 1,900 ha Missouri/marsh, streams Erickson 

Size (ha or km 

river) A B 2,900 - 5,700 ha Colorado (fall-spr)/NS Mack, 19

A M 400 ha se Texas/coastal marsh Foy, 198

A F 295 ha yearling M 43 ± 20 SD km 10 - 78 km wc Idaho/river drainage Melquist 

yearling F 32 ± 6.2 SD km 25 - 40 km (no trends seen with 

adult F 31 ± 9.2 SD km 23 - 50 km season) B B 28 ± 7.5 SD km 15 - 39 km 

Population B B 0.26/km 0.17 - 0.37/km wc Idaho/river drainage Melquist 

Density A F breeding 0.05/km 

(N/ha or N/km A M breeding 0.019/km 

shoreline) yearling B 0.071/km 

B B 0.85/km se Alaska/coastal - island Wooling

B B 0.0094 - 0.014 /ha se Texas/coastal marsh Foy, 198

A B 0.0025/ha Missouri/marsh, streams Erickson 

2-266 River Otter 
River Otter (Lutra canadensis) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Litter 2.73 ± 0.77 SD 1 - 4 Maryland/wetlands Mowbray 

Size 2.68 ± 0.71 SD 1 - 4 Alabama, Georgia/NS Hill & La

1 yr old 0.53 ± 0.91 SD 0 - 3 Maine/NS Docktor 

2 yr old 0.87 ± 0.96 SD 0 - 3 

3 yr old 1.60 ± 1.42 SD 0 - 4 

4 yr old 2.29 ± 1.25 SD 1 - 5 

5 to 12 yrs old 2.67 ± 1.40 SD 0 - 6 

2.1 ± 0.7 SD New York/NS Hamilton 

Litters 1 NS Trippens/Year 

Days total 290 - 380 Wisconsin/captive Liers, 19

Gestation 

active 60-63 NS Lancia & 

Age at > 90 days NS Harris, 1

Weaning Age at F 2 yrs New York/NS Hamilton 

Sexual M 2 yrs 

Maturity Annual birth - 1 yr 32 Oregon/NS Tabor & 

Mortality 1 - 2 yrs 54 

Rates (percent) 2 - 11 yrs 27 

A M 17.8 Alabama, Georgia/riverine Lauhach

A F 20.3 

Longevity A B < 15 yrs Alabama, Georgia/riverine Lauhach

2-267 River Otter 
1

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10111213

River Otter (Lutra canadensis) 

Seasonal 

Activity Begin Peak End Location Referenc

Mating January March to April May Michigan Hooper & 

March April New York Hamilton 

winter late winter spring AL, FL, GA Lauhach

Parturition mid-March mid-May Maryland, Chesapeake Bay Mowbray 

late March early April wc Idaho Melquist 

late January May Alabama Lauhach

Dispersal April to May wc Idaho Melquist 

2-268 River Otter 

Summary of studies discussed by Hall (1981) and Woolington (1984).

Cited in Toweill and Tabor (1982).

Estimated using equation 3-43 (Boddington, 1978) and adult body weights from Lauhachinda (1978).

Estimated using equation 3-47 (Nagy, 1987) and adult body weights from Lauhachinda (1978).

See Chapters 3 and 4 for methods of estimating food ingestion rates.

Estimated using equation 3-17 (Calder and Braun, 1983) and adult body weights from Lauhachinda (1978).

Estimated using equation 3-20 (Stahl, 1967) and adult body weights from Lauhachinda (1978).

Estimated using equation 3-22 (Stahl, 1967) and adult body weights from Lauhachinda (1978).

Cited in Melquist and Dronkert (1987).

Determined from implanted embryo counts.

Determined from corpora lutea counts.

Total gestation period (including preimplantation).

Active gestation period (postimplantation), cited in Melquist and Dronkert (1987).

14 Cited in Toweill and Tabor (1982). 

15 Dispersal at age 12 to 13 months. 
References (including Appendix) 

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Michigan. Michigan Academician 10: 181-195. 

Anderson, K. L. (1981) Population and reproduction characteristics of the river otter in 

Virginia and tissue concentrations of environmental contaminants [master's thesis]. 

Blacksburg, VA: Virginia Polytechnic Institute. 

Anderson, K. L.; Scanlon, P. F. (1981) Reproduction and population characteristics of river 

otters in Virginia. Virginia J. Sci. 32: 87. 

Anderson, E. A.; Woolf, A. (1987a) River otter habitat use in northwestern Illinois. Trans. 

Illinois Acad. Sci. 80: 107-114. 

Anderson, E. A.; Woolf, A. (1987b) River otter food habits in northwestern Illinois. Trans. 

Illinois Acad. Sci. 80: 115-118. 

Boddington, M. J. (1978) An absolute metabolic scope for activity. J. Theor. Biol. 75: 443-

449. 

Burt, W. H.; Grossenheider, R. P. (1980) A field guide to the mammals of North America 

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Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Chabreck, R. H.; Holcombe, J. E.; Linscombe, R. G.; et al. (1982) Winter foods of river 

otters from saline and fresh environments in Louisiana. Proc. Annu. Conf. 

Southeast Assoc. Fish Wildl. Agencies 36: 473-483. 

Docktor, C. M.; Bowyer, T. R.; Clark, A. G. (1987) Number of corpora lutea as related to age 

and distribution of river otter in Maine. J. Mammal. 68: 182-185. 

Eisenberg, J. F. (1981) The mammalian radiations; an analysis of trends in evolution, 

adaptation, and behavior. Chicago, IL: University of Chicago Press. 

Erickson, D. W.; McCullough, C. R.; Porath, W. R. (1984) River otter investigations in 

Missouri. Missouri Dept. Conserv.; Pittman-Robertson Proj. W-13-R-38, Final Report. 

Foy, M. K. (1984) Seasonal movement, home range, and habitat use of river otter in 

southeastern Texas [master's thesis]. College Station, TX: Texas A&M University. 

Gilbert , F. F.; Nancekivell, E. G. (1982) Food habits of mink (Mustela vison) and otter (Lutra 

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2-269 River Otter 
Greer, K. R. (1955) Yearly food habits of the river otter in the Thompson Lakes region, 

Northwestern Montana, as indicated by scat analyses. Am. Midl. Nat. 54: 299-313. 

Greer, K. R. (1956) Fur resources and investigations: study of the otter food habits along a 

segment of the Gallatin River. Montana Fish and Game Dept.; Job Comp. Rep. 

W-049-R-06:35-59. 

Grenfell, W. E., Jr. (1974) Food habits of the river otter in Suisin Marsh, central California 

[master's thesis]. Sacramento, CA: California State University. 

Grinnell, J.; Dixon, J. S.; Linsdale, J. M. (1937) Fur-bearing mammals of California. 

Berkeley, CA: University of California Press. 

Hall, E. R. (1981) The mammals of North America. 2nd ed. New York, NY: John Wiley and 

Sons. 

Hall, E. R.; Kelson, K. R. (1959) The mammals of North America. 1st ed. New York, NY: The 

Ronald Press Co. 

Hamilton, W. J., Jr. (1961) Late fall, winter and early spring foods of 141 otters from New 

York. N. Y. Fish and Game J. 8: 106-109. 

Hamilton, W. J., Jr.; Eadie, W. R. (1964) Reproduction in the otter, Lutra canadensis. J. 

Mammal. 45: 242-252. 

Harris, C. J. (1968) Otters: a study of the recent Lutrinae. London, U.K.: Weidenfield & 

Nicolson. 

Harris, J. (1969) Breeding the Canadian otter Lutra c. canadensis in a private collection. Int. 

Zoo Yearbook 9: 90-91. 

Hill, E. P.; Lauhachinda, V. (1981) Reproduction in river otters from Alabama and Georgia. 

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v. 1. August 1980; Frostburg, MD. 

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Hornocker, M. G.; Messick, J. P.; Melquist, W. E. (1983) Spacial strategies in three species 

of Mustelidae. Acta Zool. Fenn. 174: 185-188. 

Humphrey, S. R.; Zinn, T. L. (1982) Seasonal habitat use by river otters and Everglades 

mink. J. Wildl. Manage. 46: 375-381. 

Iversen, J. A. (1972) Basal energy metabolism of Mustelids. J. Comp. Physiol. 81: 341-344. 

Johnstone, P. (1978) Breeding and rearing the Canadian otter (Lutra canadensis) at Mole 

Hall Wildlife Park, 1966-1977. Int. Zoo Yearbook 18: 143-147. 

2-270 River Otter 
Knudsen, G. J.; Hale, J. B. (1968) Food habits of otters in the Great Lakes region. J. Wildl. 

Manage. 32: 89-93. 

Lagler, K. F.; Ostenson, B. T. (1942) Early spring food of the otter in Michigan. J. Wildl. 

Manage. 6: 244-254. 

Lancia, R. A.; Hair, J. D. (1983) Population status of bobcat (Felis rufus) and river otter 

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E-1; 65 pp. 

Larsen, D. N. (1983) Habitats, movements, and foods of river otters in coastal southeastern 

Alaska [master's thesis]. Fairbanks, AL: University of Alaska. 

Larsen, D. (1984) Feeding habits of river otters in coastal southeastern Alaska. J. Wildl. 

Manage. 48: 1446-1452. 

Lauhachinda, V. (1978) Life history of the river otter in Alabama with emphasis on food 

habits [Ph.D. dissertation]. Auburn, AL: University of Alabama. 

Liers, E. E. (1951a) My friends the land otters. Nat. Hist. 60: 320-326. 

Liers, E. E. (1951b) Notes on the river otter (Lutra canadensis). J. Mammal. 32: 1-9. 

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longevity records of beavers Castor canadensis. Int. Zoo Yearbook 6: 171-172. 

Loranger, A. J. (1981) Late fall and early winter foods of the river otter (Lutra canadensis) 

in Massachusetts, 1976 - 1978. In: Chapman, J. A.; Pursley, D., eds. Worldwide 

furbearer conference proceedings, v 1; August 3-11, 1980; Frostburg, MD; pp. 599-

605. 

MacFarlane, R. (1905) Notes on mammals collected and observed in the northern 

Mackenzie River District. Proc. U.S. Natl. Mus. 23: 716-717. 

Mack, C. M. (1985) River otter restoration in Grand County, Colorado [master's thesis]. Fort 

Collins, CO: Colorado State University. 

McDaniel, J. C. (1963) Otter population study. Proc. Annu. Conf. Southeast. Assoc. Game 

and Fish Comm. 17: 163-168. 

Melquist, W. E.; Dronkert, A. E. (1987) River otter. In: Novak, M.; Baker, J. A.; Obbarel, M. 

E.; et al., eds. Wild furbearer management and conservation. Pittsburgh, PA: 

University of Pittsburgh Press; pp. 627-641. 

Melquist, W. E.; Hornocker, M. G. (1983) Ecology of river otters in west central Idaho. In: 

Kirkpatrick, R. L., ed. Wildlife monographs: v. 83. Bethesda, MD: The Wildlife 

Society; 60 pp. 

2-271 River Otter 
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coexistence of sympatric mink and river otter populations. In: Chapman, J. A.; 

Pursley, D., eds. Worldwide furbearer conference proceedings, v 1; August 3-11, 

1980; Frostburg, MD; pp. 187-220. 

Modafferi, R.; Yocom, C. F. (1980) Summer food of river otter in north coastal California 

lakes. Murrelet 61: 38-41. 

Mowbray, E. E.; Pursley, D.; Chapman, J. A. (1979) The status, population characteristics 

and harvest of the river otter in Maryland. Waverly Press; Maryland Wildl. Admin., 

Publ. Wildl. Ecol. 2; 16 pp. 

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birds. Ecol. Mono. 57: 111-128. 

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Book Co. 

Pearson, O. P.; Enders, R. K. (1944) Duration of pregnancy in certain Mustelids. J. Exp. 

Zool. 95: 21-35. 

Pierce, R. M. (1979) Seasonal feeding habits of the river otter (Lutra canadensis) in ditches 

of the Great Dismal Swamp [master's thesis]. Norfolk, VA: Old Dominion University. 

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[master's thesis]. Calgary, Canada: University of Calgary. 

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Scheffer, V. B. (1958) Long life of a river otter. J. Mammal. 39: 591. 

Sheldon, W. G.; Toll, W. G. (1964) Feeding habits of the river otter in a reservoir in central 

Massachusetts. J. Mammal. 45: 449-455. 

Shirley, M. G. (1985) Spring food habits of river otter in southwestern Louisiana (abstract 

only). Proc. La. Acad. Sci. 48: 138. 

Stahl, W. R. (1967) Scaling of respiratory variables in mammals. J. Appl. Physiol. 22: 

453-460. 

Stenson, G. B.; Badgero, G. A.; Fisher, H. D. (1984) Food habits of the river otter Lutra 

canadensis in the marine environment of British Columbia. Can. J. Zool. 62: 88-91. 

Tabor, J. E.; Wight, H. M. (1977) Population status of river otter in western Oregon. J. Wildl. 

Manage. 41: 692-699. 

2-272 River Otter 
Toll, W. G. (1961) The ecology of the river otter (Lutra canadensis) in the Quabbin 

Reservation of central Massachusetts [master's thesis]. Amherst, MA: University of 

Massachusetts. 

Toweill, D. E. (1974) Winter food habits of river otters in western Oregon. J. Wildl. Manage. 

38: 107-111. 

Toweill, D. E.; Tabor, J. E. (1982) River otter. In: Chapman, J. A.; Feldhammer, G. A., eds. 

Wild mammals of North America. Baltimore, MD: Johns Hopkins University Press; 

pp. 688-703. 

Trippensee, R. E. (1953) Wildlife management: fur bearers, waterfowl, and fish. New York, 

NY: McGraw-Hill. 

Tumlison, R.; Shalaway, S. (1985) An annotated bibliography on the North American river 

otter Lutra canadensis. Stillwater, OK: Okla. Fish Wildl. Res. Unit & Dept. Zool., 

Oklahoma State University. 

van Zyll de Jong, C. G. (1972) A systematic review of the nearctic and neotropical river 

otters (Genus Lutra, Mustelidae, Carnivora). Ontario, Canada: R. Ontario Mus., Life 

Sci. Contr. 80. 

Wilson, K. A. (1959) The otter in North Carolina. Proc. Southeast. Assoc. Fish and Game 

Comm. 13: 267-277. 

Wilson, K. A. (1985) The role of mink and otter as muskrat predators in northeastern North 

Carolina. Proc. Annu. Conf. Southeast. Assoc. Game Fish Comm. 18: 199-207. 

Woolington, J. D. (1984) Habitat use and movements of river otters at Kelp Bay, Baranof 

Island, Alaska [master's thesis]. Fairbanks, AK: University of Alaska. 

2-273 River Otter 
2.2.6. Harbor Seal (hair seals) 

Order Carnivora, Family Phocidae. Seals, sea lions, and walruses are collectively 

referred to as pinnipeds (Latin for wing-footed). Pinnipeds are divided into three families: 

otarids (sea lions and fur seals); phocids (hair seals, also called true seals or earless 

seals); and walruses. Most pinnipeds feed on marine species such as fish, squid, and 

other invertebrates (Burt and Grossenheider, 1980). Unlike fur seals, which are protected 

from the cold marine environment by a dense layer of underfur, phocids rely only on a 

thick blubber layer for insulation (Pierotti and Pierotti, 1980). Phocids include both the 

smallest (ring seals) and the largest (elephant seals) of the pinnipeds. The geographic 

range of most phocid species is from the arctic Atlantic and Pacific south to the coasts of 

Canada and Alaska, although some do inhabit warmer water (Burt and Grossenheider, 

1980). Most phocids, with the exception of the elephant seal, do not exhibit the large 

disparity in size between the sexes, which is characteristic of otarids (sea lions and fur 

seals) (Burt and Grossenheider, 1980). 

Selected species 

In North America, harbor seals (Phoca vitulina) range from Alaska to Baja California, 

Mexico, along the Pacific coast (subspecies richardsi; Hoover, 1988), and from 

Newfoundland to eastern Long Island along the Atlantic coast (subspecies concolor; Payne 

and Selzer, 1989). They are one of the most commonly seen pinniped species, in part due 

to their tendency to inhabit coastal areas (Hoover, 1988). Harbor seals can be found along 

the Pacific coast on a year-round basis (except during stormy periods in winter), but 

Atlantic populations winter offshore when coastal ice has formed in their usual haul-out 

areas (Boulva and McLaren, 1979). The recent increases in harbor seal populations in New 

England waters appear to be due to a southward dispersal of seals from rookeries in Maine 

following the termination of a Massachusetts bounty on harbor seals (1962) and the 

passage of the Marine Mammal Protection Act (1972) (Payne and Schneider, 1984). 

The spotted or largha seal (Phoca largha) is a closely related species that until 

recently was considered a subspecies of the harbor seal. It is similar in size, appearance, 

and feeding habits to the Pacific harbor seal, but it tends to inhabit colder waters along the 

Pacific coasts (Ashwell-Erickson and Elsner, 1981). In North America, it seldom ventures 

further south than the northern coast of Alaska (Ashwell-Erickson and Elsner, 1981). The 

spotted seal requires ice for breeding haul-outs and gives birth about 2 months earlier than 

the Pacific harbor seal (Ashwell-Erickson and Elsner, 1981; Boulva and McLaren, 1979). 

The harbor seal, in contrast, breeds on land (Boulva and McLaren, 1979). 

Body size. The length and weight of harbor seals vary geographically, but sexually 

mature adults tend to be about 1.5 m in length and weigh from 65 to 90 kg (AshwellErickson and Elsner, 1981; Pitcher and Calkins, 1979). Harbor seals exhibit some sexual 

dimorphism, the male being larger (Pitcher and Calkins, 1979). Body length usually is used 

to measure size because weight can vary substantially with factors such as season, food 

availability, and molting (Ronald et al., 1982). Newborn pups are around 80 cm long and 

weigh from 8.6 to almost 15 kg, with females often weighing less than males (Newby, 1973; 

Pitcher and Calkins, 1979; Rosen, 1989). Harbor seal pups are highly precocial and are 

2-275 Harbor Seal 
able to swim within hours of birth (Boulva and McLaren, 1979; Lawson and Renouf, 1987). 

Seal milk consists of about half fat, and the pups more than double their weight before they 

are weaned at approximately 30 days (Bigg, 1969a, as cited in Pitcher and Calkins, 1979). 

Harbor seals continue to grow with age for several years beyond the age of sexual maturity 

(Boulva and McLaren, 1979; Pitcher and Calkins, 1979). Body fat varies seasonally with 

food intake, while total body weight and lean body mass increase with age (AshwellErickson and Elsner, 1981). Harbor seals, unlike many other pinnipeds, do not fast for 

extended periods during the molting period or breeding season (Boulva and McLaren, 

1979; Pierotti and Pierotti, 1980). 

Habitat. Harbor seals inhabit a variety of environments and are able to tolerate a 

wide range of temperatures and water salinities (Boulva and McLaren, 1979; Hoover, 1988). 

In its eastern range, the harbor seal inhabits inlets, islets, reefs, and sandbars (Boulva and 

McLaren, 1979). In western North America, the harbor seal inhabits tidal mud flats, sand 

bars, shoals, river deltas, estuaries, bays, coastal rocks, and offshore islets (Johnson and 

Jeffries, 1977), even ranging up rivers into freshwater areas in search of food (Roffe and 

Mate, 1984). Harbor seals also inhabit some freshwater lakes (Power and Gregoire, 1978). 

Habitats used for haul-outs include cobble and sand beaches, tidal mud flats, offshore 

rocks and reefs, glacial and sea ice, and man-made objects such as piers and log booms 

(Hoover, 1988). 

Food habits. Harbor seals' diet varies seasonally and includes bottom-dwelling 

fishes (e.g., flounder, sole, eelpout), invertebrates (e.g., octopus), and species that can be 

caught in periodic spawning aggregations (e.g., herring, lance, squid) (Everitt et al., 1981; 

Lowry and Frost, 1981; Pitcher and Calkins, 1979; Roffe and Mate, 1984).g Harbor seals are 

opportunistic, consuming different prey in relation to their availability and ease of capture 

(Pitcher and Calkins, 1979; Pitcher, 1980; Shaffer, 1989). They may move into rivers on a 

seasonal basis in pursuit of prey (e.g., eulachon in the Columbia River during winter; 

Brown et al., 1989). They hunt alone or in small groups (Hoover, 1988). Fish species 

consumed range between 40 and 280 mm, with mean values of between 60 and 180 mm 

(Brown and Mate, 1983). Recently weaned pups tend to feed on prey that are more easily 

captured than fish, such as shrimp or other crustaceans (Hoover, 1988; Pitcher and 

Calkins, 1979). During the breeding and molting seasons, when harbor seals spend more 

time on land, adults rely on their blubber layer as an additional source of energy (AshwellErickson and Elsner, 1981). During this time, they may be more susceptible to lipophilic 

contaminants (e.g., PCBs) that may have accumulated in their blubber (Hoover, 1988). 

g Studies of harbor seal diet often rely on counts of fish sagittal otoliths found in scats or stomach

contents. These otoliths can be identified to the level of species, annuli on the otoliths counted to 

determine age, and fish weights and lengths estimated from otolith dimensions. However, partial 

or complete digestion of otoliths, particularly of small fish species, may result in significant 

underestimates of the proportion of these prey in seal diets, particularly from scat analysis (da 

Silva and Neilson, 1985; Harvey, 1989). Studies of stomach contents of stranded seals also may 

present a biased picture of dietary composition due to extended periods of fasting prior to 

stranding (Selzer et al., 1986). 

2-276 Harbor Seal 
�

In general, food consumption by adult seals is highest in winter and lowest in the 

summer (Ashwell-Erickson and Elsner, 1981; Ashwell-Erickson et al., 1979). Innes et al. 

(1987) estimated allometric equations for maintenance food ingestion rates (IR; wet-weight 

biomass) with body weight (BW, kg) for phocids: 

IRmaint(kg/day) = 0.079 BW(kg)

0.71 adult (N = 11; r2 = 0.84); 

IRmaint(kg/day) = 0.032 BW(kg)

1.00 juveniles (N = 19; r2 = 0.68); and 

IRmaint(kg/day) = 0.068 BW(kg)

0.78 both adults and juveniles (N = 30; r2 = 0.68). 

Allometric equations for food ingestion rates of growing animals (IR; wet-weight 

biomass) with body weight (BW, kg) for phocids also have been estimated (Innes et al., 

1987): 

IRgrowth(kg/day) = 0.0919 BW(kg)

0.84 adult (N = 11; r2 = 0.84); and 

IRgrowth(kg/day) = 0.0547 BW(kg)

0.84 juveniles (N = 19; r2 = 0.68). 

Innes et al. (1987) found that growing juvenile phocid seals ingested 1.7 times more 

biomass per day than a similar-sized growing adult and 1.4 times more than juvenile 

phocids that were not growing. 

Boulva and McLaren (1979) estimated a relationship between body weight and daily 

food ingestion for harbor seals from eastern Canada: 

IRfree-living(kg/day) = 0.089 BW(kg)

0.76 adults (N = 26). 

Perez (1990) estimated the average energy value of the harbor seal's diet to be 1.4 kcal/g 

wet weight. Ashwell-Erickson and Elsner (1981) provide age-specific estimates of food 

ingestion rates for the closely related spotted seal (see Appendix) and summarize studies 

in which food ingestion rates for harbor and spotted seals have been estimated. 

Temperature regulation and molt. Harbor seals can maintain their heat balance 

while diving in water as low as 13�C without increased muscle activity or metabolic rate 

(Ronald et al., 1982). For seals in general, molting is simply part of an ongoing pelage 

cycle that is influenced by the seal's environment, physiology, and behavior (Ling, 1974). 

Phocids get an entirely new coat with each annual molt (Ling, 1970), a process that takes 

about 5 weeks (Scheffer and Slipp, 1944, as cited in Ashwell-Erickson and Elsner, 1981). 

During their molt, they spend more time hauled and exhibit a slower metabolic rate (e.g., 83 

percent of premolt levels), which decreases their food requirements (Ashwell-Erickson and 

Elsner, 1981). After molting, harbor seals increase their fat reserves (and weight) for the 

winter and early spring; metabolic rates also might be lowered during this time to conserve 

energy (Renouf, 1989). 

Breeding activities and social organization. The timing of reproduction in harbor 

seals varies with location. Mating and pupping are initiated earlier in the year in more 

2-277 Harbor Seal 
�

southern latitudes, but within populations, breeding is synchronized (Hoover, 1988; Slater 

and Markowitz, 1983). Harbor seals may form large breeding aggregations on land in areas 

where food resources are plentiful (Slater and Markowitz, 1983); however, pupping 

activities are not restricted to large, discrete rookeries (Pitcher and Calkins, 1979). Mating 

occurs soon after weaning, which is 3 to 6 weeks after birth (Ashwell-Erickson and Elsner, 

1981). It is likely that harbor seals are promiscuous (Pierotti and Pierotti, 1980), although 

there is some evidence that they are mildly polygynous, with males defending territories at 

the haul-out sites (Boulva and McLaren, 1979; Perry, 1989; Slater and Markowitz, 1983). 

Following mating, implantation is delayed for 1.5 to 3 months, during which time the female 

molts (Bigg, 1969a; Hoover, 1988; Pitcher and Calkins, 1979). At other times of the year, 

harbor seals also can be found in groups of 30 to 80 in some haul-out areas (Hoover, 1988). 

Home range and resources. Harbor seals generally inhabit highly productive 

coastal areas, with upwelling ocean currents that bring nutrients to the surface supporting 

abundant marine life (e.g., the California current system, the Gulf of Alaska, and the Gulf of 

Maine; Ronald et al., 1982). Harbor seals also require adequate places to haul out, and 

their distribution is influenced by the availability of suitable sites (Boulva and McLaren, 

1979). In general, seals stay near particular haul-out sites with only local movements 

(Brown and Mate, 1983; Pitcher and Calkins, 1979; Slater and Markowitz, 1983). Haul-out 

patterns are determined by several factors, including weather, tidal pattern, time of day, 

season, and human proximity (Slater and Markowitz, 1983). Harbor seals are considered 

fairly sedentary, with individuals showing year-round site fidelity, although some seasonal 

movement associated with pupping and long-distance movements are recorded (Pitcher 

and Calkins, 1979; Slater and Markowitz, 1983). Data on likely daily or monthly foraging 

distances are lacking. 

Population density. Harbor seals are found principally in coastal areas within 20 km 

of shore; they tend to concentrate in estuaries and protected waters (Hoover, 1988). Their 

distribution is highly patchy, and local population densities in haul-out areas with favorable 

food resources nearby can be quite high (Pitcher and Calkins, 1979). 

Population dynamics. Females are sexually mature by 3 to 5 years of age, whereas 

males are sexually mature later, at 4 to 6 years of age (Boulva and McLaren, 1979; Pitcher 

and Calkins, 1979). Females only produce one pup per year (Hoover, 1988). Three major 

causes of preweaning pup mortality are stillbirth, desertion by the mother, and shark kills 

(Boulva and McLaren, 1979). Mortality from birth to 4 years of age was estimated to be 74 

percent for females and 79 percent for males in one study, after which it remained at about 

10 percent per year (Pitcher and Calkins, 1979). Life expectancy for harbor seals is about 

30 years (Newby, 1978). 

Similar species (from general references) 

� The ringed seal (Phoca hispida) is smaller (1.4 m length; weight to 90 kg) 

than the harbor seal and inhabits colder waters. It feeds mainly on marine 

invertebrates. 

2-278 Harbor Seal 
�

�

�

The harp seal (Phoca groenlandicus) (1.8 m; weight to 180 kg) inhabits deep, 

icy water. It ranges from the Arctic Atlantic south to Hudson Bay; it is only 

rarely found further south. It feeds on macroplankton and fish. 

� The largha or spotted seal (Phoca largha) (1.5 m) is a closely related species 

that until recently was considered a subspecies of the harbor seal. Its 

characteristics are compared with those of the harbor seal under Selected 

species. 

� The ribbon seal (Phoca fasciata) (1.6 m; males to 90 kg, females to 76 kg) 

lives near pack ice in the Bering Sea and feeds on bottom invertebrates, fish, 

and octopus and squid. 

General references 

Ashwell-Erickson and Elsner (1981); Burt and Grossenheider (1980); Hoover (1988); 

Pitcher and Calkins (1979); Ronald et al. (1982). 

2-279 Harbor Seal 
Harbor Seal (Phoca vitulina) 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean Location Referen

Range or 

Body Weight A M (> 7 yrs) 84.6 ± 11.3 SD Gulf of Alaska Pitcher 

(kg) A F (> 7 yrs) 76.5 ± 17.7 SD 

J M 2 yrs 49 Aleutian Ridge and Pribilof Ashwel

J M 4 yrs 70 Islands, Bering Sea, Alaska 1981 

J M 6 yrs 84 

A M 8 yrs 95 A M 12 yrs 110 A M 16 yrs 120 A M 24 yrs 124 J F 2 yrs 40 J F 4 yrs 56 J F 6 yrs 67 A F 8 yrs 76 A F 12 yrs 90 A F 16 yrs 101 A F 24 yrs 112 neonate M 12.0 ± 0.51 SE Alaska Pitcher 

neonate F 11.5 ± 0.31 SE 

at weaning B 24.0 British Columbia, Canada Bigg, 1

Pup Growth birth to Gulf of St. Lawrence/island Rosen, 

Rate (g/day) weaning marine 

M 520 F 790 

Metabolic J B resting 7.3 California/lab Davis e

Rate A F resting 6.6 

(lO /kg-day) 2 

2-280 Harbor Seal 
Harbor Seal (Phoca vitulina) 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean Location Referen

Range or 

Metabolic Rate 1 to 4 yrs old/ 57.5 Bering Sea, Alaska Ashwel

(kcal/kg-day) basal 1981 

A F basal 24.3 estimatA M basal 22.4 A F free-living 131 (57 - 300) estimat

A M free-living 129 (56 - 296) 

Food Ingestion A B 0.05 e Canada/marine Boulva 

Rate (g/g-day) 

A B 0.06 to 0.08 review of several studies Ashwel

A F lact./gest. 0.10 1981 

J B 1st year 0.13 Bering Sea (1 harbor & Ashwel

1 spotted seal) 1981 

Water A B 0.0048 0.0028 - 0.0091 seawater ingestion (most Depoca

Ingestion water obtained from food) 

Rate (g/g-day) A B 0.064 estimat

Inhalation A M 18.6 estimat

Rate (m /day) A F 17.2 3 

Surface Area A M 19,620 estimat

(cm ) A F 18,380 2 

2-281 Harbor Seal 
Harbor Seal (Phoca vitulina) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

walleye pollock 3.7 27.3 32.2 1.3 Washington/ Everitt et 

English sole 37.0 0.0 27.0 0 coastal island 

shiner perch 0.0 0.0 0.5 63.6 

Pacific herring 0 54.6 3.9 28.6 (% of total otoliths 

Pacific cod 0 0 10.1 0 recovered from scat 

rex sole 37 9.1 2.9 0 samples) 

Pacific tomcod 3.7 0 4.7 0 

rockfish 3.7 0 4.7 0 

Dover sole 3.7 0 3.4 2.6 

Petrale sole 7.4 0 1.8 0 

other fish 3.8 9.0 8.8 3.9 

octopus 17.6 17.7 30.4 Kodiak Island, Alaska/ Pitcher & 

salmon 5.4 0.0 0.0 coastal marine 

capelin 20.3 4.8 5.4 

Pacific cod 6.8 8.1 10.7 (% frequency of occurrence; 

walleye pollock 12.2 9.7 14.3 stomach contents) 

Pacific sandlance 4.1 21.0 0.0 

squid & octopus 20 Gulf of Alaska/ Pitcher, 

shrimp, crabs 3.7 coastal marine 

herring 6.4 salmonids 4.4 (% wet volume; stomach 

osmerids 22.5 contents) 

cod, tomcod, 26.0 

walleye, pollock all seasons combined 

other 14.1 

2-282 Harbor Seal 
Harbor Seal (Phoca vitulina) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Location/Habitat Referenc

Foraging A B 5 km unknown California/Bay Stewart e

Radius (km) A B 30 to 55 km unknown Washington/Columbia River Beach et 

Population summer 0.0305 0.00394 - 0.0611 Maine/coastal marine Richards

Density (N/ha) highly clumped throughout range and Pitcher a

distrib. habitats 

Litter 1 throughout range and Hoover, Size habitats Litters 1 throughout range and Hoover, 

/Year habitats 

Months 10.5 to 11 NS/NS FAO Adv

Gestation Age at B 30 days e Canada/marine Boulva & 

Weaning B 35 days c California/coastal marine Slater & 

Age at F 5.5 ± 0.23 SE 4 - 9 Gulf of Alaska/coastal Pitcher & 

Sexual M 5 - 7 marine 

Maturity (years) F 3 to 4 e Canada/marine Boulva & 

M 

Annual A B 17.5 e Canada/marine Boulva & 

Mortality Rates (percent) birth to 4 yrs 77/4 yrs Gulf of Alaska/coastal Pitcher & 

4 to 5 yrs old 11/yr marine 

7 to 14 yrs old 8 to 9/yr 

> 20 yrs old 14/yr 

Longevity A B < 30 e Pacific/NS Newby, 1

A M < 26 Gulf of Alaska/coastal Pitcher & 

A F < 31 marine 

Range 

6 

2-283 Harbor Seal 
Harbor Seal (Phoca vitulina) 

Seasonal 

Activity Begin Peak End Location Referenc

Mating early April July Nova Scotia, Canada Boulva & 

February Mexico Bigg, 196

July Bering Sea Bigg, 196

Parturition mid-May mid-June late June Tugidak Island, Alaska Pitcher & 

late April early May c California Riedman

early February Mexico late June September Canada 

May early June June Washington Johnson 

August September Washington, Puget Sound 

Molt early June early September Scotland Thompso

2-284 late June late July September/October Gulf of Alaska Pitcher & Harbor Seal 

1 Estimated from graph of growth curve. 

2 Cited in Boulva and McLaren (1979). Weight doubled from birth. 

3 Juvenile is a yearling; weight 33 kg. Adult female weight 63 kg. 

4 Estimated using equation 3-43 (Boddington, 1978) and body weights from Pitcher and Calkins (1979). Caution must 

pinnipeds were not included in the data set from which the allometric model was derived. 

5 Estimated using equation 3-47 (Nagy, 1987) and body weights from Pitcher and Calkins (1979). Caution must be use

pinnipeds were not included in the data set from which the allometric model was derived. Mean values are somewh

with food ingestion rate estimates and data from the spotted seal (see Appendix). 

6 Estimated using equation 3-17 (Calder and Braun, 1983) and body weights from Pitcher and Calkins (1979). Caution 

because pinnipeds were not included in the data set from which the allometric model was derived. 

7 Estimated using equation 3-20 (Stahl, 1967) and body weights from Pitcher and Calkins (1979). Caution must be use

pinnipeds were not included in the data set from which the allometric model was derived. 

8 Estimated using equation 3-22 (Stahl, 1967) and body weights from Pitcher and Calkins (1979). Caution must be use

pinnipeds were not included in the data set from which the allometric model was derived. 

9 Satellite telemetry of one seal. Foraging radius depends on distribution and abundance of prey. 

10 Seventy-five percent of 58 seals radio-tagged in the Columbia River were relocated at haul-out sites 30 to 55 km awa11 Cited in Ronald et al. (1982). 12 Postweaning mortality. 13 Cited in Hoover (1988). 14 Nineteen to 33 days to complete molt. 
References (including Appendix) 

Allen, S. G.; Huber, H. R.; Ribic, C. A.; et al. (1989) Population dynamics of harbor seals in 

the Gulf of the Farallones, California. Calif. Fish Game 75: 224-232. 

Angell-James, J. E.; Elsner, R.; de Burgh Daly, M. (1981) Lung inflation: effects on heat 

rate, respiration, and vagal afferent activity in seals. Am. J. Physiol. 240: H190-H198. 

Ashwell-Erickson, S.; Elsner, R. (1981) The energy cost of free existence for Bering Sea 

harbor and spotted seals. In: Hood, D. W.; Calder, J. A., eds. The Eastern Bering Sea 

shelf: oceanography and resources. v. 2. Washington, DC: Department of 

Commerce; pp. 869-899. 

Ashwell-Erickson, S.; Elsner, R.; Wartzol, D. (1979) Metabolism and nutrition of Bering Sea 

harbor and spotted seals. Proc. Alaska Sci. Conf. 29: 651-665. 

Beach, R.J.; Geiger, A.; Jeffries, S. J., et al. (1985) Marine mammals and their interactions 

with fisheries of the Columbia River and adjacent waters, 1980-1982. Seattle, WA: 

Third Ann. Rept. to U.S. Dept. Commerce, NOAA, Natl. Mar. Fish. Serv. 

Bigg, M. A. (1969a) The harbour seal in British Columbia. Fish. Res. Board Can.; Bull. 172. 

Bigg, M. A. (1969b) Clines in the pupping season of the harbour seal, Phoca vitulina. J. 

Fish. Res. Board Can. 26: 449-455. 

Boddington, M. J. (1978) An absolute metabolic scope for activity. J. Theor. Biol. 75: 443-

449. 

Boulva, J.; McLaren, I. A. (1979) Biology of the harbor seal, Phoca vitulina, in eastern 

Canada. Quebec, Canada: Fish. Res. Board Can. Bull. 200. 

Brown, R. F.; Mate, B. R. (1983) Abundance, movements, and feeding habits of harbor 

seals, Phoca vitulina, at Nearts and Tillamook Bays, Oregon. U.S. Natl. Mar. Fish. 

Serv. Fish. Bull. 81: 291-301. 

Brown, R. F.; Jeffries, S. J.; Harvey, J. T. (1989) Seasonal abundance and winter feeding 

ecology of harbor seals in the Columbia River (abstract). In: 8th Biennial Conference 

on the Biology of Marine Mammals; December 7-11, 1989; Pacific Grove, CA; p. 9. 

Bryden, M. M. (1972) Growth and development of marine mammals. In: Harrison, R. J., ed. 

Functional anatomy of marine mammals. New York, NY: Academic Press; pp. 2-79. 

Burt, W. H.; Grossenheider, R. P. (1980) A field guide to the mammals of North America 

north of Mexico. Boston, MA: Houghton Mifflin Co. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

2-285 Harbor Seal 
Craig, A. B., Jr.; Pasche, A. (1980) Respiratory physiology of freely diving harbor seals 

(Phoca vitulina). Physiol. Zool. 53: 419-432. 

da Silva, J.; Neilson, J. D. (1985) Limitations of using otoliths recovered in scats to 

estimate prey consumption in seals. Can. J. Fish. Aquat. Sci. 42: 1439-1442. 

Davis, R. W.; Williams, T. M.; Kooyman, G. L. (1985) Swimming metabolism of yearling and 

adult harbor seals (Phoca vitulina). Physiol. Zool. 58: 590-596. 

Depocas, F.; Hart, J. S.; Fisher, H. D. (1971) Sea water drinking and water flux in starved 

and in fed harbor seals, Phoca vitulina. Can. J. Physiol. Pharmacol. 49: 53-62. 

Everitt, R. D.; Gearin, P. J.; Skidmore, J. S.; et al. (1981) Prey items of harbor seals and 

California sea lions in Puget Sound, Washington. Murrelet 62: 83-86. 

Food and Agriculture Organization (FAO) of the United Nations, A. C. on Marine Resources 

Research. (1976) Mammals in the seas. Ad Hoc Group III on seals and marine otters, 

draft report. In: Symposium: Scientific consultation on marine mammmals; August 

13 to September 9, 1976; Food and Agric. Advis. Comm. Mar. Resour. Res., Mar. 

Mammal, Sci. Consult. Organ. of U.N., Bergen, Norway. 

Harkonen, T. J. (1988) Food-habitat relationship of harbour seals and black cormorants in 

Skagerrak and Kattegat. J. Zool. (London) 214: 673-681. 

Harvey, J. T. (1989) Assessment of errors associated with harbour seal (Phoca vitulina) 

faecal sampling. J. Zool. (Lond.) 219: 101-111. 

Hoover, A. A. (1988) Harbor seal, Phoca vitulina. In: Lentfer, J. W., ed. Selected marine 

mammals of Alaska: species accounts with research and management 

recommendations. Washington, DC: Marine Mammal Commission; pp. 125-157. 

Innes, S.; Lavigne, D. M.; Earle, W. M.; et al. (1987) Feeding rates of seals and whales. J. 

Anim. Ecol. 56: 115-130. 

Irving, L. (1972) Arctic life of birds and mammals including man. New York, NY: 

Springer-Verlag. 

Johnson, M. L.; Jeffries, S. J. (1977) Population evaluation of the harbour seal (Phoca 

vitulina richardii) in the waters of the state of Washington. U.S. Mar. Mammal 

Comm.; Rep. MMC-75/05. 

Johnson, M. L.; Jeffries, S. J. (1983) Population biology evaluation of the harbor seal 

(Phoca vitulina richardii) in the waters of the State of Washington: 1976-1977. 

Tacoma, WA: University of Puget Sound; MMC-76/25. 

Jones, R. E. (1981) Food habits of smaller marine mammals from northern California. Proc. 

Calif. Acad. Sci. 42: 409-433. 

2-286 Harbor Seal 
Klinkhart, E. G. (1967) Birth of a harbor seal pup. J. Mammal. 48: 677. 

Lawson, J. W.; Renouf, D. (1987) Bonding and weaning in harbor seals, Phoca vitulina. J. 

Mammal. 68: 445-449. 

Ling, J. K. (1970) Pelage and molting in wild animals with special reference to aquatic 

forms. Q. Rev. Bio. 45: 16-54. 

Ling, J. K. (1974) The integument of marine mammals. In: Harrison, R. J., ed. Functional 

anatomy of marine mammals: v. 2. New York, NY: Academic Press; pp. 1-44. 

Lowry, L. F.; Frost, K. J. (1981) Feeding and trophic relationships of phocid seals and 

walruses in the Eastern Bering Sea. In: Hood, D. W.; Calder, J. A., eds. The Eastern 

Bering Sea shelf: oceanography and resources: v. 2. Washington, DC: Department 

of Commerce; pp. 813-824. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Mono. 57: 111-128. 

Newby, T. C. (1973) Observations on the breeding behavior of the harbor seal in the State 

of Washington. J. Mammal. 54: 540-543. 

Newby, T. C. (1978) Pacific harbor seal. In: Haley, D., ed. Marine mammals of eastern north 

Pacific and arctic waters. Seattle, WA: Pacific Search Press; pp. 184-191. 

Payne, P. M.; Schneider, D. C. (1984) Yearly changes in abundance of harbor seals, Phoca 

vitulina, at a winter haul-out site in Massachusetts. Fish. Bull. 82: 440-442. 

Payne, P. M.; Selzer, L. A. (1989) The distribution, abundance and selected prey of the 

harbor seal, Phoca vitulina concolor, in southern New England. Mar. Mammal. Sci. 

5: 173-192. 

Perez, M. A. (1990) Review of marine mammals population and prey information for Bering 

Sea ecosystem studies. Washington, DC: U.S. Dept. Commerce, Nat. Oceanic Atm. 

Admin., Nat. Mar. Fish. Serv.; NOAA Tech. Mem. NMFS F/NWC-186. 

Perry, E. (1989) Evidence for polygyny in harbour seals, Phoca vitulina. In: 8th Biennial 

conference on the biology of marine mammals; December; Pacific Grove, CA. 

Pierotti, R.; Pierotti, D. (1980) Effects of cold climate on the evolution of pinniped breeding 

systems. Evolution 34: 494-507. 

Pitcher, K. W. (1977) Population productivity and food habits of harbor seals in the Prince 

William Sound-Copper River Delta area, Alaska. Final report to U. S. Marine Mammal 

Commission No. MMC-75103. USDC NTIS. PB-226 935. 

Pitcher, K. W. (1980) Food of the harbor seal, Phoca vitulina richardsi, in the Gulf of 

Alaska. U.S. Natl. Mar. Fish. Serv. Fish. Bull. 78: 544-549. 

2-287 Harbor Seal 
Pitcher, K. W.; Calkins, D. G. (1979) Biology of the harbor seal, Phoca vitulina richardsi, in 

the Gulf of Alaska. Final report. Outer Continental Shelf Environmental Assessment 

Program Research Unit 229, Contract No. 03-5-002-69. 

Pitcher, K. W.; McAllister, D. C. (1981) Movements and haulout behavior of radio-tagged 

harbor seals, Phoca vitulina. Can. Field-Nat. 95:292-297. 

Power, G.; Gregoire, J. (1978) Predation by freshwater seals on the fish community of 

lower Seal Lake, Quebec. J. Fish. Res. Board Can. 35: 844-850. 

Renouf, D. (1989) Weight increases in harbour seals in spite of reduced food intake and 

heightened thermal demands: adjustable metabolism? In: 8th Biennial Conference 

on the Biology of Marine Mammals; December; Pacific Grove, CA. 

Richardson, D. T. (1973) Distribution and abundance of harbor and gray seals in Acadia 

National Park. Final report to National Park Service and Maine Department of Sea 

and Shore Fisheries. State of Maine Contract No. MM4AC009. 

Richardson, D. T. (1981) Feeding habits and population studies of Maine's harbor and gray 

seals. Natl. Geogr. Soc. Res. Rep. 13: 497-502. 

Riedman, M. (1990) The pinnipeds: seals, sea lions, and walruses. Berkeley, CA: University 

of California Press. 

Roffe, T. J.; Mate, B. R. (1984) Abundances and feeding habits of pinnipeds in the Rogue 

River, Oregon. J. Wildl. Manage. 48: 1262-1274. 

Ronald, K.; Selley, J.; Healey, P. (1982) Seals. In: Chapman, J. A.; Feldhammer, G. A., eds. 

Wild mammals of North America. Baltimore, MD: Johns Hopkins University Press; 

pp. 769-827. 

Rosen, D. A. (1989) Neonatal growth rates and behaviour in the Atlantic harbour seal, 

Phoca vitulina (abstract). In: 8th Biennial Conference on the Biology of Marine 

Mammals; December 7-11, 1989; Pacific Grove, CA; p. 57. 

Scheffer, V. B.; Slipp, J. W. (1944) The harbor seal in Washington state. Am. Midl. Nat. 32: 

373-416. 

Schneider, D. C.; Payne, P. M. (1983) Factors affecting haul-out of harbor seals at a site in 

southeastern Massachusetts. J. Mammal. 64: 518-520. 

Selzer, L. A.; Early, G.; Fiorelli, P. M.; et al. (1986) Stranded animals as indicators of prey 

utilization by harbor seals, Phoca vitulina concolor, in southern New England. Fish. 

Bull. 84: 217-220. 

Shaffer, K. E. (1989) Seasonal and size variations in diets of harbor seals, Phoca vitulina 

(abstract). In: 8th Biennial Conference on the Biology of Marine Mammals; 

December 7-11, 1989; Pacific Grove, CA; p. 62. 

2-288 Harbor Seal 
Slater, L. M.; Markowitz, H. (1983) Spring population trends in Phoca vitulina richardi in two 

central California coastal areas. Calif. Fish Game 69: 217-226. 

Stahl, W. R. (1967) Scaling of respiratory variables in mammals. J. Appl. Physiol. 22: 

453-460. 

Stewart, B. S.; Leatherwood, S.; Yochem, P. K.; et al. (1989) Harbor seal tracking and 

telemetry by satellite. Mar. Mamm. Sci. 5: 361-375. 

Stutz, S. S. (1966) Moult and pelage patterns in the Pacific harbor seal, Phoca vitulina 

[master's thesis]. Vancouver, Canada: University of British Columbia. 

Thompson, P; Rothery, P. (1987) Age and sex differences in the timing of moult in the 

common seal, Phoca vitulina. J. Zool. (London) 212: 597-603. 

Wilson, S. C. (1978) Social organization and behavior of harbor seals Phoca vitulina 

concolor in Maine. Final report to Marine Mammal Commission, Contract No. GPO 

PB 280-3188. NTIS PB 280 188. 

2-289 Harbor Seal 
2.2.7. Deer Mouse (deer and white-footed mice) 

Order Rodentia, Family Muridae (Genus Peromyscus).

h New world mice (family 

Muridae) are small, ground-dwelling rodents that live in a large variety of habitats including 

woodlands, prairies, rocky habitats, tundra, and deserts. All are nocturnal and are preyed 

on by owls, hawks, snakes, and carnivorous mammals. Most species eat primarily seeds, 

but some also regularly eat small invertebrates. Many species store food. The genus 

Peromyscus is the most widespread and geographically variable of North American 

rodents (MacMillen and Garland, 1989). 

Selected species 

The deer mouse (Peromyscus maniculatus) is primarily granivorous and has the 

widest geographic distribution of any Peromyscus species (Millar, 1989; Brown and Zeng, 

1989). It is resident and common in nearly every dry-land habitat within its range, including 

alpine tundra, coniferous and deciduous forest, and grasslands as well as deserts. There 

are many recognized subspecies or races of the deer mouse associated with different 

locations or insular habitats, including artemisiae, austerus, bairdii, balaclavae, blandus, 

borealis, carli, cooledgei, gambelii, gracilis, labecula, maniculatus, oreas, nebrascensis, 

nubiterrae, rufinus, and sonoriensis (MacMillen and Garland, 1989; Millar, 1982) 

Body size. Deer mice range from 7.1 to 10.2 cm in length, with a 5.1 to 13 cm tail, 

and adults weigh from 15 to 35 g (Burt and Grossenheider, 1980; see table). Body size 

varies somewhat among populations and subspecies throughout the species' range. Body 

weight also varies seasonally, being lower in autumn and winter and a few grams higher in 

spring and summer (Zegers and Merritt, 1988). There may (Fleharty et al., 1973) or may not 

(Millar and Schieck, 1986) be seasonal differences in fat content. 

Habitat. Deer mice inhabit nearly all types of dry-land habitats within their range: 

short-grass prairies, grass-sage communities, coastal sage scrub, sand dunes, wet 

prairies, upland mixed and cedar forests, deciduous forests, ponderosa pine forests, other 

coniferous forests, mixed deciduous-evergreen forests, juniper/piñon forests, and other 

habitats (Holbrook, 1979; Kaufman and Kaufman, 1989; Ribble and Samson, 1987; Wolff 

and Hurlbutt, 1982). Few studies have found microhabitat features that distinguish the 

deer mouse, and some studies have come to different conclusions regarding habitat 

structure preferences (Ribble and Samson, 1987). For example, Vickery (1981) found that 

deer mice appeared to prefer areas with moderate to heavy ground and mid-story cover to 

more open ground areas, whereas others have found more deer mice in more open than in 

more vegetated areas (see Kaufman and Kaufman, 1989). 

Food habits. Deer mice are omnivorous and highly opportunistic, which leads to 

substantial regional and seasonal variation in their diet. They eat principally seeds, 

arthropods, some green vegetation, roots, fruits, and fungi as available (Johnson, 1961; 

Menhusen, 1963; Whitaker, 1966). The nonseed plant materials provide a significant 

h

Peromyscus is considered a member of the family Cricetidae by some mammalogists. 

2-291 Deer Mouse 
�

�

proportion of the deer mouse's daily water requirements (MacMillen and Garland, 1989). 

Food digestibility and assimilation for most of their diet have been estimated to be as high 

as 88 percent (Montgomery, 1989). Deer mice may cache food during the fall and winter in 

the more northern parts of their range (Barry, 1976; Wolff, 1989). They are nocturnal and 

emerge shortly after dark to forage for several hours (Marten, 1973). 

Temperature regulation. The deer mouse has a metabolic rate about 1.3 times 

higher than the other species in the genus (MacMillen and Garland, 1989; Morris and 

Kendeigh, 1981; see table). Its metabolic rate is substantially higher in winter than in 

summer (Morris and Kendeigh, 1981; Stebbins, 1978; Zegers and Merritt, 1988). Outside 

the thermoneutral zone (25 to 35�C), metabolic rate varies according to the following 

equation: 

VO2 = 0.116 - 0.003(Ta) + 0.0304 (V0.5) 

where VO2 = volume oxygen consumed (ml/g-min); Ta = ambient temperature; and V = wind 

speed (Chappell and Holsclaw, 1984). Deer mice can enter torpor (body temperature, 19 to 

30�C) to reduce metabolic demands in the winter and also in response to brief food 

shortages (Tannenbaum and Pivorun, 1988, 1989). The deer mouse uses nonshivering 

thermogenesis (NST) to quickly awaken from torpor and to maintain body temperature 

during the winter (Zegers and Merritt, 1987). The deer mouse may burrow in soils to assist 

thermoregulation; one study measured the burrow dimensions to be 24 cm deep (range 13 

to 50 cm) and 132 cm long (range 30 to 470 cm) (Reynolds and Wakkinen, 1987). 

Breeding activities and social organization. The duration of the reproductive 

season varies with latitude and longitude according to the regression equation: 

Y = -33.0 + 2.79 X + 0.0748 Z - 0.0370 X2 

where Y = duration of the breeding season in weeks, X = latitude, and Z = longitude (r = 

0.58; Millar, 1989). Lactating females have longer gestation periods than nonlactating 

females. Newborn deer mice are highly altricial (Layne, 1968). Several studies have 

indicated that daily food consumption increases over 15 percent during early pregnancy 

and more than doubles during lactation (Glazier, 1979; Millar, 1975, 1978, 1979, 1982, 1985; 

Millar and Innes, 1983; Stebbins, 1977). Deer mice are promiscuous; in one study, 19 to 43 

percent of litters resulted from multiple inseminations (Birdsall and Nash, 1973, as cited in 

Millar, 1989). 

Home range and resources. Deer mice tend to occupy more than one nest site, 

most frequently in tree hollows up to 8 m from the ground (Wolff and Durr, 1986) but also 

among tree roots and under rocks and logs (Wolff and Hurlbutt, 1982; Wolff, 1989). At low 

densities, home ranges are maintained by mutual avoidance, but at higher densities, 

females may defend a core area or territory (Wolff, 1989). The home range of female deer 

mice encompasses both their foraging areas and their nests. Male home ranges are larger 

and overlap the home ranges of many females (Cranford, 1984; Taitt, 1981; Wolff, 1985a, 

1986; Wolff et al., 1983). 

2-292 Deer Mouse 
�

�

�

�

�

Population density. Population density varies considerably over space and time 

and is often positively correlated with food abundance (Taitt, 1981; Wolff, 1989), moisture 

content of plants (Bowers and Smith, 1979), and vegetative cover (van Horne, 1982) as well 

as season (Montgomery, 1989; Taitt, 1985). Interspecific competition also can play a role in 

determining population densities (Kaufman and Kaufman, 1989). 

Population dynamics. Although laboratory and field studies have demonstrated that 

females can produce their first litter by 3 months of age, females of the more northern 

populations do not mature under natural conditions until the spring after the year of their 

birth. First litters are consistently smaller than subsequent litters (Millar, 1989), and 

latitude and elevation explain a significant amount of the variation in litter size among P. 

maniculatus populations (Smith and McGinnis, 1968, as cited in Millar, 1989). Millar (1989) 

estimated the relationship between litter size and latitude and longitude to be 

Y = -1.62 + 0.0103X + 0.106Z + 0.0004X2 - 0.0005Z2 

where Y is the mean litter size; X, the latitude; and Z, the longitude. The largest litters are 

produced in northwestern North America. Pups wean within about 3 weeks, and females 

may have up to four litters per year in the more southern parts of the species' range (Millar, 

1989). Mortality rates are high, and most deer mice live for less than 1 year (Millar and 

Innes, 1983). 

Similar species (from general references) 

� The cactus mouse (Peromyscus eremicus), almost the same size as the deer 

mouse (8.1 to 9.1 cm; 17 to 40 g), is found only in low deserts of the extreme 

southwest and Mexico. It may feed on green vegetation, seeds, and berries 

and can climb trees for food. 

� The California mouse (Peromyscus californicus) (9.6 to 11.7 cm; 42 to 50 g) 

is found in southwestern California and lives among oaks and dense 

chaparral. It stores acorns in nests made of twigs and sticks. 

� The canyon mouse (Peromyscus crinitus) (7.6 to 8.6 cm) is limited to the 

western United States. It lives in rocky canyons and on lava-covered slopes, 

nesting among rocks. 

� The oldfield mouse (Peromyscus polionotus), smaller than the deer mouse 

(4.1 to 6.1 cm), is limited to the extreme southeastern United States, where it 

inhabits sandy beaches and fields and feeds on seeds and berries. Females 

may be territorial during the breeding season. 

� The white-footed mouse (Peromyscus leucopus) is approximately the same 

size as the deer mouse (9.1 to 10.7 cm; 14 to 31 g). Its range extends north 

into Canada and west to Arizona but does not extend as far north and west 

as the deer mouse's range. Like the deer mouse, the white-footed mouse's 

diet consists mainly of arthropods, seeds, and other vegetation, and it 

usually nests off the ground. It is most abundant in habitat that includes a 

2-293 Deer Mouse 
�

�

canopy, such as brushy fields and deciduous woodlots in northern regions 

and riparian areas and ravines in prairie and semidesert regions. 

� The cotton mouse (Peromyscus gossypinus) (9.1 to 11.7 cm; 28 to 51 g) is 

found in the southeastern United States where it inhabits wooded areas, 

swampland, stream banks, and field edges. This tree climber nests in trees, 

under logs, and in buildings. 

� The brush mouse (Peromyscus boylii) (9.7 to 10.7 cm; 22 to 36 g) is limited 

to chaparral and rocky areas of the arid and semiarid west and southwest 

United States. A good climber, it lives under rocks and debris and in 

crevices. It feeds on pine nuts, acorns, seeds, and berries. 

General references 

Burt and Grossenheider (1980); Kirkland and Lane (1989); Millar (1985, 1989); 

Wolff (1989). 

2-294 Deer Mouse 
Deer Mouse (Peromyscus maniculatus) 

2-295 Deer Mouse 

Factors 

Age/Sex (95% CI of 

Cond./Seas. Mean mean) Location (subspecies) Reference 

Range or 

Body Weight A M 22 North America Millar, 198

(g) A F 20 

A M 15.7 NS (austerus) Fordham, 

A F 14.8 A M 22.3 NS (blandus) Dewsbury 

A F 21.1 A B 19.6 ± 0.71 SE New Hampshire Schlesing

A F nonbreed. 20.3 ± 0.42 SE NS (borealis) lab Millar & In

A F gestat. 31.5 ± 0.43 SE 

A F lactat. 24.5 ± 0.37 SE 

neonate 1.8 1.6 - 2.8 North America Millar, 198

neonate 1.7 ± 0.02 SE Alberta, Canada Millar, 198

at weaning 8.8 7.7 - 11.2 North America Millar, 198

at weaning 9.3 ± 0.10 SE Northwest Territories, Canada Millar, 197

Pup Growth B 0.38 ± 0.01 SE 0.30 - 0.95 Alberta, Canada Millar, 198

Rate (g/day) (nebrascensis) 

M 0.27 ± 0.06 SE Millar & In

F 0.22 ± 0.05 SE Alberta, Canada (borealis) 

Metabolic F resting 50 40 - 61 North America MacMillen 

Rate (lO /kg-day) M avg daily: 2 

winter 138 ± 5.3 SE Alberta, Canada lab Stebbins e

spring 102 ± 7.2 SE 

summer 75 ± 3.4 SE 
Deer Mouse (Peromyscus maniculatus) 

Factors 

Age/Sex (95% CI of 

Cond./Seas. Mean mean) Location (subspecies) Reference 

Range or 

Metabolic Rate M avg daily: Alberta, Canada lab Stebbins e

(kcal/kg-day) winter 668 ± 25 SE 

spring 623 ± 35 SE 

summer 360 ± 17 SE 

B free-living: Illinois lab Morris & K

winter 790 summer 592 

A M free-living 547 (259 - 1,153) estimated 

A F free-living 574 (271 - 1,212) 

Food A F nonbreed. 0.19 Manitoba, Canada Millar, 197

Ingestion (maniculatus) lab 

Rate A F nonbreed. 0.18 Alberta, Canada Millar & In

(g/g-day) (borealis) lab 

A F lactating 0.45 Manitoba, Canada Millar, 197

A F lactating 0.38 Alberta, Canada Millar & In

A F nonbreed. 0.19 Virginia lab Cronin & B

A M nonbreed. 0.22 

J M 0.21 ± 0.01 SE South Dakota lab Nelson & 

(maniculatus) lab 

(borealis) lab 

Water A B 0.19 (sonoriensis) lab Ross, 193

Ingestion A B 0.19 0.123 - 0.287 Illinois (bairdii) lab Dice, 1922 

Rate (g/g-day) J M 0.34 ± 0.02 SE South Dakota lab Nelson & 

0.15 estimated 

Inhalation A M 0.025 estimated 

Rate (m /day) A F 0.023 3 

Surface Area A M 91 estimated 

(cm ) A F 86 2 

2-296 Deer Mouse 
Deer Mouse (Peromyscus maniculatus) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location (subspecies)/Habitat 

nuts/seeds 0 24 23 Virginia (nubiterrae)/ Wolff et a

arthropods 56 30 46 oak-maple-hickory forest 

Lepidopt. larvae 4 trace 2 

Lepidopt. adults 3 26 7 (% frequency of occurrence; 

green veg. 5 12 18 stomach contents) 

fungus 7 trace 1 

fruit 25 

unknown 1 4 3 

Lepidopt. larvae 20.6 34.5 16.7 4.8 Indiana/several habitats Whitaker

corn 4.1 4.2 3.2 8.7 

misc. veg. 15.8 3.1 8.0 13.4 

wheat seeds 6.5 1.6 3.2 23.7 (% volume; stomach 

unident. seeds 5.4 5 8.8 8.3 contents) 

green veg. 7.6 0 4.3 3.7 

Echinochloa 

seeds 

Coleoptera 

soybeans 

Hemiptera 

0 1.2 6.4 0 

3.9 5.3 5.1 1.4 

13.4 3.1 6.9 10.7 

1.3 2.7 4.2 0.9 

beetles 14.6 23.8 9.4 4.9 Colorado/short grass prairie Flake, 19

grasshoppers 6.4 4.2 6.4 2.5 

leafhoppers 13.3 1.8 1.9 2.5 (% volume by a ranking 

Lepidopterans 21.7 12.7 1.5 1.8 method; stomach contents) 

spiders 2.6 2.7 2.5 0.3 

seeds 22.5 25.9 56.8 65.4 

forbs 4.7 10.0 5.6 4.3 

grasses & 

sedges 4.0 2.6 2.8 4.8 

shrubs 3.8 1.4 0.8 2.6 

4 1 

2-297 Deer Mouse 
Deer Mouse (Peromyscus maniculatus) 

2-298 Deer Mouse 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location (subspecies)/Habitat Refe

Home Range A M summer 0.039 ±0.0054 SD Utah/subalpine meadow Cran

Size (ha) A F summer 0.027 ±0.0047 SD snowfree 

A M winter 0.019 ±0.0065 SD Utah/subalpine meadow Cran

A F winter 0.014 ±0.0050 SD snowbound B M 0.058 ± 0.006 SE 0.054 - 0.065 Virginia/mixed deciduous Wolff

B F 0.061 ± 0.005 SE 0.054 - 0.072 forest 

A M 0.10 ± 0.0063 SE Bowe

A F 0.075 ±0.0063 SE Oregon/ponderosa pines 

A M 0.128 ± 0.012 SE Bowe

A F 0.094 ±0.0013 SE Idaho/(artemisiae­sarcobatus) 

desert 

Population B B 0.19 Arizona/desert Brow

Density (N/ha) A B summer 2.8 Colorado/subalpine meadows Vaug

B B summer 12.8 - 22.4 Utah/subalpine meadow Cran

B B winter 3.4 - 8.4 A B 12.7 - 45.5 British Columbia, Sulliv

B B 12 ± 6.7 SD 3.9 - 28 slash Metz

Canada/burnt Montana/understory near river 

Litter 3.4 Virginia (nubiterrae)/NS Wolff

Size 4.4 3.0 - 6.4 average for North America/NS Milla

5.1 ± 0.14 SE 1 - 8 Alberta, Canada Milla

(nebrascensis)/NS 

Litters/Year 2.4 average for North America/NS Milla

1.9 ± 0.1 SE Alberta, Canada Milla

(borealis)/various alpine 
Deer Mouse (Peromyscus maniculatus) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location (subspecies)/Habitat Refe

Days F non-lact. 23.6 average for United States/NS Milla

Gestation F lactating 26.9 

F non-lact. 22.4 ± 0.1 SE 22 - 23 Kansas/NS Sven

F lactating 24.1 ± 0.3 SE 22 - 27 

F non-lact. 25.5 ± 0.3 SE 23 - 26 Alberta, Canada Milla

F lactating 29.5 ± 1.4 SE 24 - 35 (nebrascensis)/lab 

Age at B 20.2 16 - 25 average for North America/NS Milla

Weaning B 24.9 Alberta, Canada Milla

(days) (borealis)/various alpine 

B 17.5 Colorado/NS Halfp

Age at M 35 days Alberta, Canada Milla

Sexual F 60 days (nebrascensis)/lab 

Maturity Mortality A F winter 100%/winter Alberta, Canada (borealis)/ Milla

Rates A M winter 33%/winter various alpine 

J F winter 56%/winter 

J M winter 70%/winter 

A B summer 20%/2 weeks Alberta, Canada (borealis)/ Milla

J B summer 19%/2 weeks various alpine 

Longevity B B < 1 yr Alberta, Canada (borealis)/ Mille

various alpine 

Seasonal 

Activity Begin Peak End Location (subspecies) Reference 

Mating April August Massachusetts Drickamer

November April Texas Blair, 1958 

March October Virginia (nubiterrae) Wolff, 198

May August California Dunmire, 1

Dispersal spring Vancouver, Canada Fairbairn, 

(males) 

2-299 Deer Mouse 
� � � � 

� � � 

�

�

� �

Deer Mouse (Peromyscus maniculatus) 

Seasonal 

Activity Begin Peak End Location (subspecies) Reference 

Torpor winter northern parts of range Tannenba

1 Cited in Montgomery (1989).

2 Growth rate of "newly emerged" pups, soon after leaving the nest.

3 Temperatures during winter averaged -17.7�C (-6 to -22�C); during spring averaged 14.5�C (8 to 22�C); during summ

4 Estimated by authors from laboratory-derived model assuming no reproduction, molt, or weight change and assumi

averaged 17.5�C above ground and 20.2�C in burrows and winter temperatures averaged -3�C above ground and 10

5 Estimated using equation 3-48 (Nagy, 1987) and body weights from Millar (1989). 

6 Diet of rat chow with 3 percent water content and 4.5 kcal/g dry weight. 

7 Diet of Purina lab chow no. 5001; composition not specified. 

8 Diet of lab chow; composition not specified. 

9 Diet of lab chow with 8 to 10 percent water content. 

10 Mean varied by subspecies; sonoriensis, eremicus, gambelii, and fraterculus tested. Dry diet prepared in lab, proba

content; air temperature 21 to 24�C. 

11 Dry air at 32 to 34�C; diet of wheat and peanuts, about 10 percent water content. 

12 Temperature 20�C ± 2�C; diet of lab chow with 8 to 10 percent water content. 

13 Estimated using equation 3-17 (Calder and Braun, 1983) and body weights from Millar (1989). 

14 Estimated using equation 3-20 (Stahl, 1967) and body weights from Millar (1989). 

15 Estimated using equation 3-22 (Stahl, 1967) and body weights from Millar (1989). 

16 Cited in Millar (1989). 

2-300 Deer Mouse 
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Peromyscus leucopus in Vigo County, Indiana. J. Mammal. 47: 473-486. 

Wolff, J. O. (1985a) The effects of density, food, and interspecific interference on home 

range size in Peromyscus leucopus and Peromyscus maniculatus. Can. J. Zool. 63: 

2657-2662. 

Wolff, J. O. (1985b) Comparative population ecology of Peromyscus leucopus and 

Peromyscus maniculatus. Can. J. Zool. 63: 1548-1555. 

Wolff, J. O. (1986) The effects of food on midsummer demography of white-footed mice, 

Peromyscus leucopus. Can. J. Zool. 64: 855-858. 

Wolff, J. O. (1989) Social behavior. In: Kirkland, G. L.; Lane, J. N., eds. Advances in the 

study of Peromyscus (Rodentia). Lubbock, TX: Texas Tech. University Press; pp. 

271-291. 

Wolff, J. O.; Durr, D. S. (1986) Winter nesting behavior of Peromyscus leucopus and 

Peromyscus maniculatus. J. Mammal. 67: 409-412. 

Wolff, J. O.; Hurlbutt, B. (1982) Day refuges of Peromyscus leucopus and Peromyscus 

maniculatus. J. Mammal. 63: 666-668. 

Wolff, J. O.; Freeberg, H.; Dueser, R. D. (1983) Interspecific territoriality in two sympatric 

species of Peromyscus (Rodentia: Cricetidae). Behav. Ecol. Sociobiol. 12: 237-242. 

Wolff, J. O.; Dueser, R. D.; Berry, D. S. (1985) Food habits of sympatric Peromyscus 

leucopus and Peromyscus maniculatus. J. Mammal. 66: 795-798. 

Zegers, D. A.; Merritt, J. F. (1987) Seasonal changes in non-shivering thermogenesis of 

three small mammals (abstract only). Bull. Ecol. Soc. Am. 68: 455. 

2-308 Deer Mouse 
Zegers, D. A.; Merritt, J. F. (1988) Adaptations of Peromyscus for winter survival in an 

Appalachian montane forest. J. Mammal. 69: 516-523. 

2-309 Deer Mouse 
2.2.8. Prairie Vole (voles) 

Order Rodentia Family Muridae (subfamily Arvicolinae). New world voles are small, 

herbivorous rodents that reside in all areas of the United States where good grass cover 

exists. Their presence is characterized by narrow runways through matted grasses. 

Microtus species are adapted to underground, terrestrial, and sometimes semiamphibious 

habitats (Johnson and Johnson, 1982). They are active by day and night and feed mainly 

on shoots, grasses, and bark (Johnson and Johnson, 1982). Voles are prey for snakes, 

raptors, and mammalian predators such as short-tailed shrews, badgers, raccoons, 

coyotes, and foxes (Eadie, 1952; Johnson and Johnson, 1982; Martin, 1956). 

Selected species 

The prairie vole (Microtus ochrogaster) represents the ground-burrowing members 

of this group. This vole is found in the north and central plains of the United States and in 

southern Canada, usually in dry places such as prairies and along fencerows and 

railroads. Its range has expanded eastward to West Virginia as a result of clear-cutting of 

forests (Jones et al., 1983). Voles are active by day or night (Johnson and Johnson, 1982). 

Although prairie and meadow voles usually occupy different habitats, where they coexist 

their population densities tend to be negatively correlated (Klatt, 1985; Krebs, 1977). 

Body size. The prairie vole measures from 8.9 to 13 cm in length and has a 3.0- to 

4.1-cm tail (Burt and Grossenheider, 1980). After reaching sexual maturity, voles continue 

to grow for several months (Johnson and Johnson, 1982). Adults weigh from 30 to 45 g 

(see table). Prairie voles maintain a relatively constant proportion of their body weight as 

fat (15 to 16 percent on a dry-weight basis) throughout the year (Fleharty et al., 1973). 

Habitat. The prairie vole inhabits a wide variety of prairie plant communities and 

moisture regimes, including riparian, short-grass, or tall-grass communities (Kaufman and 

Fleharty, 1974). Prairie voles prefer areas of dense vegetation, such as grass, alfalfa, or 

clover (Carroll and Getz, 1976); their presence in a habitat depends on suitable cover for 

runways (Kaufman and Fleharty, 1974). They will tolerate sparser plant cover than the 

meadow vole because the prairie vole usually nests in burrows at least 50 mm 

underground or in grass nests under logs or boards (Klatt and Getz, 1987). 

Food Habits. Meadow voles, as other voles, are largely herbivorous, consuming 

primarily green succulent vegetation but also roots, bark, seeds, fungi, arthropods, and 

animal matter (Johnson and Johnson, 1982; Lomolino, 1984; Stalling, 1990). Voles have 

masticatory and digestive systems that allow them to digest fibrous grasses such as 

cereals (Johnson and Johnson, 1982). Diet varies by season and habitat according to plant 

availability, although meadow and other voles show a preference for young, tender 

vegetation (Johnson and Johnson, 1982; Martin, 1956). Voles can damage pastures, 

grasslands, crops such as hay and grain, and fruit trees (by eating bark and roots) 

(Johnson and Johnson, 1982). 

2-311 Prairie Vole 
�

�

Temperature regulation and molt. Unlike some other mammals, prairie voles do not 

hibernate or exhibit torpor (Johnson and Johnson, 1982). They overwinter without using 

their lipid reserves, finding food to meet their metabolic requirements year-round (Fleharty 

et al., 1973). Prairie voles use burrows, runways, nests, and snow cover to help maintain 

their body temperature. They also modify when they are active to avoid excessively hot or 

cold temperatures (Johnson and Johnson, 1982). Voles undergo three molts (juvenile, 

subadult, and adult), and molting may occur at any time during the year (Jameson, 1947, as 

cited in Stalling, 1990). The subadult-to-adult molt occurs between 8 and 12 weeks of age 

(Martin, 1956). 

Breeding activities and social organization. Prairie voles are monogamous; a 

mated pair occupies the same home range (Thomas and Birney, 1979). Reproduction 

occurs throughout the year, and gestation lasts approximately 3 wk (Martin, 1956; Keller, 

1985; Nadeau, 1985). Both sexes care for the young; paternal activities include runway 

construction, food caching, grooming, retrieving, and brooding the young (Thomas and 

Birney, 1979). The young are weaned by about 3 weeks of age (Thomas and Birney, 1979). 

Reproductive activity peaks from May to October, coinciding with high moisture availability 

(Martin, 1956; Keller, 1985). Monogamous family units apparently defend territories against 

other family groups (Ostfeld et al., 1988; Johnson and Johnson, 1982; Thomas and Birney, 

1979). 

Home range and resources. Prairie voles excavate underground nests that are 

used as nurseries, resting areas, and as shelter from severe weather (Klatt and Getz, 

1987). They spend very little time away from this nest (Barbour, 1963). In thick vegetation, 

prairie voles move about in surface runways, and the number of runways is proportional to 

population density (Carroll and Getz, 1976). Female home range size decreases with 

increasing prairie vole density according to the following regression equation (Gaines and 

Johnson, 1982): 

Y= �0.23X + 20.16 where Y= home range length in meters and X= minimum 

number alive per 0.8 ha grid. 

Abramsky and Tracy (1980) found a similar correlation using both sexes according to the 

equation: 

Y= �0.20X + 27.12 where Y= home range length in meters and X=number of 

individuals per hectare. 

Population dynamics. Female prairie voles can reach sexual maturity in about 35 d, 

males in 42 to 45 d (Gier and Cooksey, 1967, as cited in Stalling, 1990). Martin (1956) found 

in Kansas that females mature within about 6 wk in the summer, but may require 15 wk or 

more to mature if born in the fall. Male prairie voles tend to disperse from their natal site; 

approximately twice as many females as males mature near their birthplace (Boonstra et 

al., 1987). Populations tend to fluctuate with available moisture (Gier, 1967, as cited in 

Stalling, 1990). Mortality rates in prairie vole postnestling juveniles and young adults are 

similar and higher than adult mortality rates; nestlings have the lowest mortality rate 

(Golley, 1961). Average life expectancy in the field is about 1 yr (Martin, 1956). 

2-312 Prairie Vole 
�

�

Similar species (from general references) 

� The pine vole (Microtus pinetorum) (7 to 11 cm), despite its name, usually 

inhabits deciduous forest floors, among a thick layer of duff, where it tunnels 

through loose soil near the surface. It is found in the eastern half of the 

United States, except Florida; in the south, it inhabits pine forests. In 

addition to feeding on bark, it burrows for bulbs, tubers, and corms. 

� See also similar species listed for the meadow vole in this chapter. 

General references 

Burt and Grossenheider (1980); Johnson and Johnson (1982); Stalling (1990); 

Tamarin (1985). 

2-313 Prairie Vole 
Prairie Vole (Microtus ochrogaster) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referenc

Body Weight A B 41.6 ne Colorado Abramsk

(g) 

A B summer 41.9 ne Colorado Abramsk

A B fall 44.2 

A B winter 39.0 

A B spring 41.3 

A M 31.3 ± 0.35 SE s Indiana Myers & 

A F 33.3 ± 0.30 SE 

neonate B 2.8 ± 0.4 SD ne Kansas Martin, 1

Metabolic Rate A winter 51.8 ± 8.2 SD NS/lab Wunder 

(lO /kg-d) 2 

A summer 41.8 ± 4.8 SD 

Metabolic Rate A B basal 177 estimate

(kcal/kg-d) 

A B free-living 399 (190 - 833) estimate

Food Ingestion A B at 21�C 0.13 - 0.14 Illinois/lab Dice, 192

Rate (g/g-d) A B at 28�C 0.09 - 0.10 

Water A B 0.37 NS/lab Chew, 19

Ingestion Rate 

(g/g-d) A B 0.29 ± 0.02 SE Kansas/lab Dupre, 1

A B 0.21 0.15 to 0.26 Illinois/lab Dice, 192

A B 0.14 estimate

Inhalation A B 0.043 estimate

Rate (m /d) 3 

Surface Area A B 139 estimate(cm )2 

2-314 Prairie Vole 
Prairie Vole (Microtus ochrogaster) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

Sporobolus asper 

Kochia scoparia 

Bouteloua gracilis 

Bromus japonicus 

Rumex crispus 

Triticum aestivum 

Carex sp. 

other 

(grasses) 

(forbs) 

19.5 Kansas/forb and grass field Fleharty 

22.5 

6.5 (% volume; stomach 

8.5 contents) 9.2 3.4 (Items less than 2% of 

2.0 volume were combined as 

28.3 "other") 

(53.5) (46.5) 

Festuca arundinacea 

Dactylis glomerata 

Phleum pratense 

Tridens flavus 

Setaria viridis 

Taraxacum officinale 

Lamium amplexicaule 

Bromus tectorum 

Setaria faberi 

Capsella bursa­past. 

Trifolium stolonifera 

arthropods animal material 

other 

20.5 25.0 10.6 28.9 Missouri/old field Cook et a

6.7 1.7 1.1 4.2 

8.3 2.0 2.1 5.3 (mean number of food 

17.1 11.1 1.9 11.0 items; stomach contents) 

6.7 6.2 1.7 6.2 

5.8 4.8 3.9 1.5 (Plant parts consumed: leaf, 

3.9 2.9 5.2 3.4 stem, and seeds of Festuca 

2.8 4.7 2.5 4.8 and Bromus; leaf and stem 

5.6 3.9 0.7 21.0 of Tridens and Setaria 

2.7 1.2 0.5 0.6 faberi; leaf and seeds of 

2.4 0.8 0.5 1.4 Dactylis and Seteria viridis; 

0.2 0.3 0.0 0.1 and leaves only of all other 

0 0.2 0.2 0.0 plant species) 

3.9 1.4 1.5 0.9 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Location/Habitat Referen

Home A B all yr 0.098 ± 0.012 SE Illinois/bluegrass Jike et a

Range Size (ha) A M all yr 0.037 ± 0.0029 SE Kansas/NS Swihart 

A F all yr 0.024 ± 0.0018 SE 

A M 0.011 ne Colorado/short-grass Abrams

A F 0.0073 prairie 

Range 

2-315 Prairie Vole 
Prairie Vole (Microtus ochrogaster) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Location/Habitat Referen

Population summer 25 - 35 w Nebraska/xeric prairie Meserv

Density winter 12 (N/ha) 

spring 78 - 118 Illinois/alfalfa field Carroll 

summer 81 - 104 summer 168 - 234 ne Kansas/grassland Martin, 

winter 160 - 197 spring 203 - 247 fall 94 - 123 

Litter 3.18 ± 0.24 SD ne Kansas/grassland Martin, 

Size 3.4 1 - 7 Kansas/NS Jameso

4.25 Illinois/NS Cole & 

Litters/Year several NS/NS Johnso

Days 21 ne Kansas/grassland Martin, 

Gestation 21 NS/NS Keller, 1

Pup Growth days 1 to 10 0.6 ne Kansas/grassland Martin, 

Rate (g/d) days 11 to 30 1.0 

> 30 d until 0.5 

growth stops (highly variable) 

Age at 21 days NS/lab Thomas 

Weaning Age at F 35 days NS/NS Gier & C

Sexual M 42 to 45 d 

Maturity Annual B 93 % ne Colorado/short-grass Abrams

Mortality prairie 

Longevity B 1 yr up to 1.8 yr ne Kansas/grassland Martin, 

Range 

2-316 Prairie Vole 
�

�

Prairie Vole (Microtus ochrogaster) 

Seasonal 

Activity Begin Peak End Location Referen

Mating May to Oct NS Keller, 1

Parturition May to Oct NS Keller, 1

Molt any time NS Jameso

1 Estimated using equation 3-43 (Boddington, 1978) and body weights (summer) from Abramsky and Tracy (1980). 

2 Estimated using equation 3-48 (Nagy, 1987) and body weights (summer) from Abramsky and Tracy (1980). 

2-317 Prairie Vole 

3 Estimated from ingestion rate for diet of oats (74 to 78 percent of total weight of diet) and dry grass, assuming 31 to 3

in water (probably less than 10 percent). 

4 Measured water drunk from water bottles; diet consisted of rolled oats with sunflower seeds; temperature 28�C. 

5 Measured water drunk; diet of dry food. 

6 Temperature 21�C; dry air. 

7 Estimated using equation 3-17 (Calder and Braun, 1983) and body weights (summer) from Abramsky and Tracy (1980)

8 Estimated using equation 3-20 (Stahl, 1967) and body weights (summer) from Abramsky and Tracy (1980). 

9 Estimated using equation 3-22 (Stahl, 1967) and body weights (summer) from Abramsky and Tracy (1980). 

10 Determined from pup count, which may underestimate litter size at birth.

11 Cited in Keller (1985); embryo or pup count.

12 Cited in Keller (1985); embryo or placental scar count.

13 Cited in Stalling (1990).
References (including Appendix) 

Abramsky, Z.; Tracy, C. R. (1980) Relation between home range size and regulation of 

population size in Microtus ochrogaster. Oikos 34: 347-355. 

Agnew, W. J.; Uresk, D. W.; Hansen; et al. (1988) Arthropod consumption by small 

mammals on prairie dog colonies and adjacent ungrazed mixed grass prairie in 

western South Dakota. In: Uresk, D. W.; Schenbeck, G. L.; Cefkin, R., tech. coord. 

Eighth Great Plains wildlife damage control workshop proceedings; April 28-30, 

1987; Rapid City, South Dakota. Fort Collins, CO: U.S. Department of Agriculture, 

Forest Service, Rocky Mountain Forest and Range Experiment Station; pp. 81-87. 

Barbour, R. W. (1963) Microtus: a simple method of recording time spent in the nest. 

Science 141: 41. 

Boddington, M. J. (1978) An absolute metabolic scope for activity. J. Theor. Biol. 75: 443-

449. 

Boonstra, R.; Krebs, C. J.; Gaines, M. S.; et al. (1987) Natal philopatry and breeding 

systems in voles (Microtus spp.). J. Anim. Ecol. 56: 655-673. 

Bradley, S. R. (1976) Temperature regulation and bioenergetics of some microtine rodents 

[Ph.D. dissertation]. Ithaca, NY: Cornell University. 

Burt, W. H.; Grossenheider, R. P. (1980) A field guide to the mammals of North America 

north of Mexico. Boston, MA: Houghton Mifflin Co. 

Calder, W. A.; Braun, E. J. (1983) Scaling of osmotic regulation in mammals and birds. Am. 

J. Physiol. 244: R601-R606. 

Carroll, D.; Getz, L. L. (1976) Runway use and population density in Microtus ochrogaster. 

J. Mammal. 57: 772-776. 

Chew, R. M. (1951) The water exchanges of some small mammals. Ecol. Monogr. 21: 

215-225. 

Cole, F. R.; Batzli, G. O. (1978) Influence of supplemental feeding on a vole population. J. 

Mammal. 59: 809-819. 

Colvin, M. A.; Colvin, D. V. (1970) Breeding and fecundity of six species of voles (Microtus). 

J. Mammal. 51: 417-419. 

Cook, J. C.; Topping, M. S.; Stombaugh, T. A. (1982) Food habits of Microtus ochragaster 

and Peromyscus maniculatus in sympatry. Trans. Missouri Acad. Sci. 16: 17-23. 

Corthum, D. W., Jr. (1967) Reproduction and duration of placental scars in the prairie vole 

and the eastern vole. J. Mammal. 48: 287-292. 

2-318 Prairie Vole 
Dice, L. R. (1922) Some factors affecting the distribution of the prairie vole, forest deer 

mouse, and prairie deer mouse. Ecology 3: 29-47. 

Dupre, R. K. (1983) A comparison of the water relations of the hispid cotton rat, Sigmodon 

hispidus, and the prairie vole, Michrotus ochrogaster. Comp. Biochem. Physiol. 

75A: 659-663. 

Eadie, R. W. (1952) Shrew predation and vole populations on a localized area. J. Mammal. 

33: 185-189. 

Fitch, H. S. (1957) Aspects of reproduction and development in the prairie vole (Microtus 

ochrogaster). Univ. Kansas Publ., Mus. Nat. Hist. 10: 129-161. 

Fleharty, E. D.; Olson, L. E. (1969) Summer food habits of Michrotus ochrogaster and 

Sigmodon hispidus. J. Mammal. 50: 475-486. 

Fleharty, E. D.; Krause, M. E.; Stinnett, D. P. (1973) Body composition, energy content, and 

lipid cycles of four species of rodents. J. Mammal. 54: 426-438. 

Gaines, M. S.; Johnson, M. L. (1982) Home range size and population dynamics in the 

prairie vole, Microtus ochrogaster. Oikos 39: 63-70. 

Gaines, M. S.; Rose, R. K. (1976) Population dynamics of Microtus ochrogaster in eastern 

Kansas. Ecology 57: 1145-1161. 

Getz, L. L.; Hofmann, J. E.; Klatt, B. J.; et al. (1987) Fourteen years of population 

fluctuations of Microtus ochrogaster and M. pennsylvanicus in east central Illinois. 

Can. J. Zool. 65: 1317-1325. 

Gier, H. T. (1967) The Kansas small mammal census: terminal report. Trans. Kansas Acad. 

Sci. 70: 505-518. 

Gier, H. T.; Cooksey, B. F., Jr. (1967) Michrotus ochrogaster in the laboratory. Trans. 

Kansas Acad. Sci. 70: 256-265. 

Golley, F. B. (1961) Interaction of natality, mortality and movement during one annual cycle 

in a Microtus population. Am. Midl. Nat. 66: 152-159. 

Harvey, M. J.; Barbour, R. W. (1965) Home range of Microtus ochrogaster as determined by 

a modified minimum area method. J. Mammal. 46: 398-402. 

Jameson, E. W., Jr. (1947) Natural history of the prairie vole (mammalian genus Michrotus). 

Misc. Publ. Mus. Nat. Hist. Univ. Kansas 1: 125-151. 

Jike, L.; Batzli, G. O.; Getz, L. L. (1988) Home ranges of prairie voles as determined by 

radiotracking and by powdertracking. J. Mammal. 69: 183-186. 

2-319 Prairie Vole 
Johnson, M. L.; Johnson, S. (1982) Voles (Microtus species). In: Chapman, J. A.; 

Feldhamer, G. A., eds. Wild mammals of North America. Baltimore, MD: Johns 

Hopkins University Press; pp. 326-353. 

Jones, J. K. Jr.; Armstrong, R. S.; Hoffman, R. S.; et al. (1983) Mammals of the Great 

Northern Plains. Lincoln, NE: University of Nebraska Press. 

Kaufman, D. W.; Fleharty, E. D. (1974) Habitat selection by nine species of rodents in 

north-central Kansas. Southwest. Nat. 18: 443-451. 

Keller, B. L. (1985) Reproductive patterns. In: Tamarin, R. H., ed. Biology of new world 

Microtus. American Society of Mammalogists; Special Publication No. 8; pp. 

725-778. 

Keller, B. L.; Krebs, C. J. (1970) Microtus population biology. III. Reproductive changes in 

fluctuating populations of M. ochrogaster and M. pennsylvanicus in southern 

Indiana, 1965-1967. Ecol. Monogr. 40: 263-294. 

Kenney, A. M.; Evans, R. L.; Dewsbury, D. A. (1977) Postimplantation pregnancy disruption 

in Microtus orchogaster, Microtus pennsylvanicus, and Peromyscus maniculatis. J. 

Reprod. Fert. 49: 365-367. 

Klatt, B. J. (1985) The role of habitat preference and interspecific competition in 

determining the local distribution of Microtus pennsylvanicus and M. ochrogaster in 

central Illinois (abstract). Bull. Ecol. Soc. Am. 66: 209. 

Klatt, B. J.; Getz, L. L. (1987) Vegetation characteristics of Microtus ochragaster and M. 

pennsylvanicus habitats in east-central Illinois. J. Mammal. 68: 569-577. 

Krebs, C. J. (1977) Competition between Microtus pennsylvanicus and Microtus 

ochragaster. Am. Midl. Nat. 97: 42-49. 

Kruckenberg, S. M.; Gier, H. T.; Dennis, S. M. (1973) Postnatal development of the prairie 

vole, Microtus ochrogaster. Lab. Anim. Sci. 23: 53-55. 

Lomolino, M. V. (1984) Immigrant selection, predation, and the distribution of Microtus 

pennsylvanicus and Blarina brevicauda on islands. Am. Nat. 123: 468-483. 

Martin, E. P. (1956) A population study of the prairie vole (Michrotus ochragaster) in 

northeastern Kansas. Univ. Kansas Publ. Mus. Nat. Hist. 8: 361-416. 

Martin, E. P. (1960) Distribution of native mammals among the communities of the mixed 

prairie. Fort Hays Stud. N. S. Sci. Ser. 1: 1-26. 

Meserve, P. L. (1971) Population ecology of the prairie vole, Microtus ochrogaster, in the 

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2-320 Prairie Vole 
Morrison, P. R.; Dieterich, R.; Preston, D. (1976) Breeding and reproduction of fifteen wild 

rodents maintained as laboratory colonies. Lab. Anim. Care 26: 237-243. 

Myers, J. H.; Krebs, C. J. (1971) Genetic, behavioral, and reproductive attributes of 

dispersing field voles Microtus pennsylvanicus and Michrotus ochrogaster. Ecol. 

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Nadeau, J. H. (1985) Ontogeny. In: Tamarin, R. H., ed. Biology of new world Microtus. Spec. 

Publ. Amer. Soc. Mammal. 8; pp. 254-285. 

Nagy, K. A. (1987) Field metabolic rate and food requirement scaling in mammals and 

birds. Ecol. Monogr. 57: 111-128. 

Ostfeld, R. S.; Pugh, S. R.; Seamon, J. O.; et al. (1988) Space use and reproductive success 

in a population of meadow voles. J. Anim. Ecol. 57: 385-394. 

Quick, F. W. II (1970) Small mammal populations in an old field community [Ph.D. 

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Richmond, M. E. (1967) Reproduction of the vole, Microtus orchogaster [Ph.D. 

dissertation]. Columbia, MO: University of Missouri. 

Richmond, M. E.; Conaway, C. H. (1969) Management, breeding and reproductive 

performance of the vole, Microtus ochrogaster in a laboratory colony. Lab. Anim. 

Care 19: 80-87. 

Rolan, R. G.; Gier, H. T. (1967) Correlation of embryo and placental scar counts of 

Peromyscus maniculatis and Microtus orchogaster. J. Mammal. 48: 317-319. 

Rose, R. K.; Gaines, M. S. (1978) The reproductive cycle of Microtus orchogaster in eastern 

Kansas. Ecol. Monogr. 48: 21-42. 

Stahl, W. R. (1967) Scaling of respiratory variables in mammals. J. Appl. Physiol. 22: 

453-460. 

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Species No. 355; 9 pp. 

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Microtus ochrogaster. J. Mammal. 70: 816-820. 

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Thomas, J. A.; Birney, E. C. (1979) Parental care and mating system of the prairie vole, 

Microtus ochrogaster. Behav. Ecol. Sociobiol. 5: 171-186. 

Wooster, L. D. (1939) An ecological evaluation of predatees on a mixed prairie area in 

western Kansas. Trans. Kans. Acad. Sci. 42: 515-517. 

2-321 Prairie Vole 
Wunder, B. A. (1985) Energetics and thermoregulation. In: Tamarin, R. H., ed. Biology of 

new world Microtus. Spec. Publ. Amer. Soc. Mammal. 8; pp. 812-844. 

Wunder, B. A.; Dobkin, D. S.; Gettinger, R. D. (1977) Shifts of thermogenesis in the prairie 

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Mammal. 46: 605-612. 

2-322 Prairie Vole 
2.2.9. Meadow Vole (voles) 

Order Rodentia Family Muridae (subfamily Arvicolinae). New world voles are small, 

herbivorous rodents that reside in all areas of Canada and the United States where there is 

good grass cover. Their presence is characterized by narrow runways through matted 

grasses. Microtus species are adapted to underground, terrestrial, and sometimes 

semiamphibious habitats (Johnson and Johnson, 1982). They are active by day and night, 

feeding mainly on shoots, grasses, and bark. Voles are prey for hawks and owls as well as 

several mammalian predators such as short-tailed shrews, badgers, and foxes (Johnson 

and Johnson, 1982; Eadie, 1952). 

Selected species 

The meadow vole (Microtus pennsylvanicus) makes its burrows along surface 

runways in grasses or other herbaceous vegetation. It is the most widely distributed small 

grazing herbivore in North America and is found over most of the northern half of the 

United States. Meadow voles have been used in bioassays to indicate the presence of 

toxins in their foods (Kendall and Sherwood, 1975, cited in Reich, 1981; Schillinger and 

Elliot, 1966). Although primarily terrestrial, the meadow vole also is a strong swimmer 

(Johnson and Johnson, 1982). 

Body size. The meadow vole measures 8.9 to 13 cm in length (head and body) and 

has a 3.6- to 6.6-cm tail. They weigh between 20 and 40 g depending on age, sex, and 

location (see table). Mature males are approximately 20 percent heavier than females 

(Boonstra and Rodd, 1983). Meadow voles lose weight during the winter, reaching a low 

around February, then regain weight during spring and summer, reaching a high around 

August in many populations (see table; Iverson and Turner, 1974). 

Habitat. The meadow vole inhabits grassy fields, marshes, and bogs (Getz, 1961a). 

Compared with the prairie vole, the meadow vole prefers fields with more grass, more 

cover, and fewer woody plants (Getz, 1985; Zimmerman, 1965). The meadow vole also 

tends to inhabit moist to wet habitats, whereas the prairie vole is relatively uncommon in 

sites with standing water (Getz, 1985). 

Food habits. Meadow voles consume green succulent vegetation, sedges, seeds, 

roots, bark, fungi, insects, and animal matter (see table). They are agricultural pests in 

some areas, feeding on pasture, hay, and grain (Johnson and Johnson, 1982; Burt and 

Grossenheider, 1980). At high population densities, the meadow vole has been known to 

girdle trees, which can damage orchards (Byers, 1979, cited in Reich, 1981). In seasonal 

habitats, meadow voles favor green vegetation when it is available and consume other 

foods more when green vegetation is less available (Johnson and Johnson, 1982; Riewe, 

1973; Getz, 1985). Although Zimmerman (1965) found some evidence of food selection, he 

found that meadow voles generally ate the most common plants in their habitat. Meadow 

voles living on prairies consume more seeds and fewer dicots and monocots than voles in 

a bluegrass habitat (Lindroth and Batzli, 1984). The meadow vole's large cecum allows it to 

have a high digestive efficiency of 86 to 90 percent (Golley, 1960). Coprophagy (eating of 

feces) has been observed in this species (Ouellete and Heisinger, 1980). 

2-323 Meadow Vole 
�

Temperature regulation and molt. In winter, Microtus species do not undergo 

hibernation or torpor; instead, they are active year round (Didow and Hayward, 1969; 

Johnson and Johnson, 1982). Behaviors that help meadow voles to maintain their body 

temperature include the use of burrows, runways, nests, and snow cover for insulation. 

They also can change when they are active; when temperatures exceed 20�C, meadow 

voles are most active at night (Getz, 1961b; Johnson and Johnson, 1982). In winter, 

meadow voles increase their brown fat content (a major site of thermoregulatory heat 

production). Mature individuals average 0.5 percent brown fat in summer, increasing to 1.7 

percent in early winter; juveniles average 1.0 percent in the summer, increasing to 2.3 

percent in the winter (Didow and Hayward, 1969). Voles undergo three molts: juvenile, 

postjuvenile, and adult. The timing varies by species (Johnson and Johnson, 1982). Adult 

Arvicolinae also undergo winter and summer molts (Johnson and Johnson, 1982). 

Breeding activities and social organization. Meadow voles are polygynous 

(McShea, 1989). Males form a hierarchy in which the most dominant male voles breed 

(Boonstra and Rodd, 1983). Voles produce litters throughout the breeding season, the 

number of litters per season increases with decreasing latitude (Johnson and Johnson, 

1982). 

Home range and resources. The area encompassed by a meadow vole's home 

range depends on season, habitat, population density, and the age and sex of the animal. 

Summer ranges tend to be larger than winter ranges, and ranges in marshes tend to be 

larger than ranges in meadows (Getz, 1961c; Reich, 1981). Home range size also declines 

with increasing population density (Getz, 1961c; Tamarin, 1977a). Female meadow voles 

defend territories against other females, whereas male home ranges are larger and overlap 

with home ranges of both sexes (Madison, 1980; Ostfeld et al., 1988; Wolff, 1985). Meadow 

voles build runways in grasses and vegetation at the ground's surface and use the 

runways for foraging about 45 percent of the time, depending on weather and other factors 

(Gauthier and Bider, 1987). The meadow vole exhibits daytime activity where dense cover 

is available and becomes more crepuscular with less cover (Graham, 1968, cited in Reich, 

1981). All Microtus species apparently do some burrowing, excavating underground nests 

that are used as nurseries, resting areas, and as shelter from severe weather (Johnson and 

Johnson, 1982). Nests are built with the use of dead grass in patches of dense, live grass; 

widened spaces, called forms, are used off main runways (Ambrose, 1973). 

Population density. Meadow vole population densities fluctuate widely from season 

to season and year to year, sometimes crashing to near zero before recovering in a few 

years to densities of several hundred per hectare (Boonstra and Rodd, 1983; Lindroth and 

Batzli, 1984; Getz et al., 1987; Myers and Krebs, 1971; Taitt and Krebs, 1985). Krebs and 

Myers (1974) noted population cycles of 2 to 5 yr, whereas Tamarin (1977b) reported 3- to 

4-year population cycles in southeastern Massachusetts. However, Getz et al. (1987) found 

no indication of multiannual abundance cycles in their three habitat study (i.e., bluegrass, 

tallgrass prairie, and alfalfa) in east central Illinois. Meadow voles avoid short-tailed 

shrews (Fulk, 1972), and the vole population density decreases as the number of shorttailed shrews in the area increases (Eadie, 1952). 

2-324 Meadow Vole 
�

�

�

�

�

�

Population dynamics. Voles reach sexual maturity usually within several weeks 

after birth, with females maturing before males, but still continue to grow for several 

months (Johnson and Johnson, 1982). Innes (1978) reported that litter size is independent 

of latitude or elevation. However, summer litters were, on average, 14 percent larger than 

litters produced during other seasons, and larger females produced larger litters (Keller 

and Krebs, 1970). Young from the spring and early summer litters reached adult weight in 

about 12 wk (Brown, 1973). Mortality rates are highest in postnestling juveniles and young 

adults and lowest in nestlings (ages 1 to 10 d) (Golley, 1961). Dispersing meadow voles 

(predominantly young males) tend to weigh less than resident meadow voles (Boonstra et 

al., 1987; Myers and Krebs, 1971; Boonstra and Rodd, 1983; Brochu et al., 1988). 

Similar species (from general references) 

� The California vole (Microtus californicus) is larger than the meadow vole (12 

to 14 cm head and body) and is found throughout California and southern 

Oregon. It inhabits freshwater and saltwater marshy areas, wet meadows, 

and grassy hillsides from the seashore to the mountains and feeds on green 

vegetation. 

� Townsend's vole (Microtus townsendii) usually is found near water in moist 

fields, sedges, tules, and meadows (from tidewater to alpine meadows). Its 

range is limited to extreme northwestern California, western Oregon and 

Washington, and southern British Columbia (inhabits several islands off the 

coast of Washington and British Columbia). It is easily distinguished by its 

large size (12 to 16 cm) and black-brown color. 

� The montane vole (Microtus montanus) (mountain vole) is slightly larger (10 

to 14 cm) than the meadow vole and is found in valleys of the mountainous 

Great Basin area of the western and northwestern United States. 

� The long-tailed vole (Microtus longicaudus) (tail 5 to 9 cm) is slightly larger 

(11 to 14 cm) than the meadow vole. It is found in the western United States 

and Canada to Alaska and lives along streambanks, in mountain meadows, 

sometimes in dry situations, and in brushy areas during winter. In addition 

to grasses and bark, it feeds on bulbs. It nests above ground in winter and 

burrows in summer. 

� The creeping vole (Microtus oregoni) (Oregon vole) (10 to 11 cm) is an 

inhabitant of western Oregon and Washington and extreme northwest 

California. Seldom above ground, it spends most of its time burrowing 

through forest floor duff or grass roots. It lives in forests, brush, and grassy 

areas. 

� The sagebrush vole (Lagurus curtatus) (9.7 to 11 cm) lives in loose soil and 

arid conditions and feeds on green vegetation, especially sagebrush. It also 

burrows around sagebrush; a vole found living in sagebrush is almost 

certainly this species. 

2-325 Meadow Vole 
General references 

Burt and Grossenheider (1980); Reich (1981); Johnson and Johnson (1982); Tamarin 

(1985). 

2-326 Meadow Vole 
Meadow Vole (Microtus pennsylvanicus) 

2-327 Meadow Vole 

Factors 

Age/Sex/ (95% CI of 

Cond./Seas. Mean mean) Location Referenc

Range or 

Body Weight A M summer 40.0 ± 8.3 SE Quebec, Canada Brochu e

(g) A F summer 33.4 ± 8.2 SE 

A M spring 52.4 Ontario, Canada Boonstra 

A F spring 43.5 

A M & F Manitoba, Canada Anderso

spring 26.0 summer 24.3 fall 17.0 winter 17.5 

A M avg. all yr 35.5 ± 0.1 SE south Indiana Myers & 

A F avg. all yr 39.0 ± 0.3 SE 

neonate M & F 2.1 1.6 - 3.0 not specified Hamilton

neonate M & F 2.3 ± 0.1 SD Innes & M

Pup Growth birth - 21 days 0.95 south Michigan/old field Golley, 1

Rate (g/d) 22 - 33 days 0.81 

34 - 54 days 0.45 55 - 103 days 0.19 

Body Fat (g) summer: Alberta, Canada Millar, 19

J F 0.37 ± 0.04 SE 

A F gestating 1.20 ± 0.15 SE 

A F lactating 0.60 ± 0.09 SE 

Metabolic basal 60.0 lab Wiegert, 

Rate average daily 82.8 ± 12 SD 43.2 - 146 lab Morrison

(lO /kg-d) 2 

Metabolic Rate A M basal 166 estimate(kcal/kg-d) A F basal 175 

A B avg. daily 395 lab 25-30�C PearsonA M free-living 357 (170 - 747) estimateA F free-living 485 (231 - 1,020) 
Meadow Vole (Microtus pennsylvanicus) 

2-328 Meadow Vole 

Factors 

Age/Sex/ (95% CI of 

Cond./Seas. Mean mean) Location Referenc

Range or 

Food Ingestion Rate (g/g-d) 0.30 - 0.35 Russia Ognev, 1

(cal/g-d) A M short-day 370 ± 20 SE NS Dark et a

A M long-day 410 ± 10 SE 

Water A B 0.21 ± 0.02 SE NS Ernst, 19

Ingestion 

Rate (g/g-d) A B 0.14 estimate

Inhalation A M 0.052 estimate

Rate (m /d) A F 0.044 3 

Surface Area A M 161 estimate(cm ) A F 143 2 Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

dicot shoots 41 60 66 12 Illinois/bluegrass Lindroth 

monocot 50 26 9 40 

shoots 

seeds 1 9 1 13 (% volume; stomach 

roots 0 1 12 34 contents) 

fungi 6 4 10 0 

insects 2 0 2 1 

dicot shoots 53 65 41 41 Illinois/tallgrass prairie Lindroth 

monocot 23 29 12 5 

shoots (% volume; stomach 

seeds 7 1 16 36 contents) 

roots 4 0 6 17 

fungi 12 1 20 0 

insects 1 4 5 1 
Meadow Vole (Microtus pennsylvanicus) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Location/Habitat Refere

Home Range A M summer 0.019 ± 0.011 SD Virginia/old field Madis

Size (ha) A F summer 0.0069 ±0.0039 SD 

A B summer 0.014 Montana/alluvial bench Dougl

A B winter 0.0002 

A M summer 0.083 ± 0.037 SD Massachusetts/grassy Ostfel

A F summer 0.037 ± 0.020 SD meadow 

Population A B 96 - 549 Ontario, Canada/grassland Boons

Density A B 2 - 28 Illinois/bluegrass Lindro

(N/ha) A B 25 - 163 Indiana/grassland Myers 

fall 28 - 51 Michigan/grass-sedge Getz, 

winter 20 - 51 marsh spring 22 - 53 summer 38 - 64 

Litter 3.82 1 - 11 Manitoba, Canada/NS Iverso

Size 4.46 1 - 9 Indiana/NS Corth

6.05 1 - 8 Pennsylvania/NS Goin, 

Litters/Year several NS/NS Bailey

Days 21.0 ± 0.2 SD NS/NS Kenne

Gestation Age at 21 s Michigan/NS Golley

Weaning (d) 

Age at F at least 3 wk NS/NS Johns

Sexual M at least 6-8 wk 

Maturity Mortality nestlings (0-10 g) 50% south Michigan/old field Golley

Rates juveniles (11-20 g) 61% 

young adults (21-30 g) 58% 

adults (31-50 g) 53% 

old adults (>50 g) 100% 

Range 

2-329 Meadow Vole 
1

234 �

56789

101112131415

Meadow Vole (Microtus pennsylvanicus) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Location/Habitat Refere

Longevity 2-3 mo NS Beer & 

< 24 mo NS Johns

Seasonal 

Activity Begin Peak End Location Referenc

Mating early April mid-October Manitoba, Canada Mihok, 1

Oct. - Nov. Michigan (fall-winter peak) Getz, 196

April - June Michigan (spring-summer Getz, 196

peak) 

Dispersal fall/winter Indiana/grassland Myers & 

summer (females) Massachusetts/coastal field Tamarin, 

winter (males) 

Range 

Cited in Reich (1981) and Johnson and Johnson (1982). 

Cited in Nadeau (1985). 

2-330 Meadow Vole 

Body weight 35.6 g; temperature not specified; cited in Deavers and Hudson (1981).

Temperature 15 to 25�C; weight 26.2 to 32 g.

Estimated using equation 3-43 (Boddington, 1978) and body weights from Anderson et al. (1984).

Estimated using equation 3-48 (Nagy, 1987) and body weights from Anderson et al. (1984).

Cited in Johnson and Johnson (1982).

Short-day photoperiod = 10 h of light, 14 of dark; long-day photoperiod = 14 h of light, 10 of dark.

Cited in Reich (1981).

Estimated using equations 3-17 (Calder and Braun, 1983) and 3-18 and body weights from Anderson et al. (1984).

Estimated using equation 3-20 (Stahl, 1967) and body weights from Anderson et al. (1984).

Estimated using equation 3-22 (Stahl, 1967) and body weights from Anderson et al. (1984).

Cited in Keller (1985).

Cited in Johnson and Johnson (1982).

Cited in Getz (1961b).
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Publ. Am. Soc. Mammal. 8; pp. 340-372. 

Wunder, B. A. (1985) Energetics and thermoregulation. In: Tamarin, R. H., ed. Biology of 

new world Microtus. Spec. Publ. Amer. Soc. Mammal. 8; pp. 812-844. 

Zimmerman, E. G. (1965) A comparison of habitat and food of two species of Microtus. J. 

Mammal. 46: 605-612. 

2-336 Meadow Vole 
2.2.10. Muskrat (water rats and muskrats) 

Order Rodentia Family Muridae. Water rats and muskrats are the most aquatic of 

this family of rodents, with most of their lives spent in or near bogs, marshes, lakes or 

streams. These two rodents feed mostly on aquatic vegetation. Only one species exists in 

each genus (Burt and Grossenheider, 1980). 

Selected species 

The muskrat (Ondatra zibethicus) is indigenous and common throughout most of 

the United States (except in the extreme southeast, central Texas, and most of California) 

and Canada (except in the extreme north) (Burt and Grossenheider, 1980). Muskrats feed 

primarily on aquatic plants. They are prey for hawks, minks, otters, raccoons, owls, red 

fox, dogs, snapping turtles, and water snakes (Bednarik, 1956; Errington, 1939a; Wilson, 

1985), and are more vulnerable to predation during times of drought when low water levels 

leave their dens or lodges more exposed (Errington, 1939a). Many vertebrates use 

muskrat homes for shelter or to find food (Kiviat, 1978). The muskrat is one of the most 

valuable fur animals in North America (Dozier, 1953; Perry, 1982). Including the 

Newfoundland muskrat, formerly Ondatra obscurus, 16 recognized subspecies of O. 

zibethicus exist in North America (Perry, 1982). Of these, O. z. zibethicus (eastern United 

States, southeastern Canada), O. z. osoyoosensis (Rocky Mountains, southwestern 

Canada), and O. z. rivalicius (southern Louisiana, coasts of Mississippi, western Alabama, 

and eastern Texas) are most often studied. 

Body size. The muskrat measures 25 to 36 cm (head and body) with a 20- to 25- cm 

tail (Burt and Grossenheider, 1980), and adult weights can range from 0.5 kg to over 2 kg 

(see Appendix). Willner et al. (1980) reported no sexual dimorphism, whereas Dozier 

(1950), Parker and Maxwell (1984), and others (see Appendix) reported that males are 

slightly heavier than females. Muskrats tend to be larger and heavier in northern latitudes 

(Perry, 1982), although the smallest muskrats are found in Idaho (Reeves and Williams, 

1956). Fat levels in adult males increase from spring through fall, and subsequently 

decrease from winter to spring (Schacher and Pelton, 1975). In nonpregnant females, fat 

levels decrease from winter through summer; in pregnant females, body fat increases from 

spring to summer (Schacher and Pelton, 1975). 

Habitat. Muskrats inhabit saltwater and brackish marshes and freshwater creeks, 

streams, lakes, marshes, and ponds (Dozier, 1953; Johnson, 1925; Kiviat, 1978; O'Neil, 

1949). Muskrats that live along the banks or shores of waterways generally excavate dens 

in the banks, whereas muskrats living in ponds with ample plant material construct lodges 

(Johnson, 1925; Perry, 1982). When available, bank dens seem preferred over constructed 

lodges (Johnson, 1925). 

Food habits. Muskrats are primarily herbivorous, but some populations are more 

omnivorous (Dozier, 1953; Errington, 1939b). Muskrats usually feed at night, diving to 

gnaw on aquatic vegetation growing near their houses (Dozier, 1953; Johnson, 1925; Perry, 

1982). The roots and basal portions of aquatic plants make up most of the muskrat's diet, 

although shoots, bulbs, tubers, stems, and leaves also are eaten (Dozier, 

2-337 Muskrat 
1950, 1953; Willner et al., 1980; Svihla and Svihla, 1931). Marsh grasses and sedges 

(Svihla and Svihla, 1931) and cattails (Johnson, 1925; Willner et al., 1975) seem to be 

important muskrat foods; in Maryland, green algae is also important (Willner et al., 1975). 

Although muskrats forage near their dens or lodges, they show preferences for some plant 

species (e.g., cattails, bulrushes) over others (Bellrose, 1950). Muskrats are a major 

consumer of marsh grasses (Kiviat, 1978). They also dig for food on lake and pond 

bottoms (Bailey, 1937; Dozier, 1953; Hanson et al., 1989). Among the animals that 

muskrats consume are crayfish, fish, frogs, turtles, and young birds (Errington, 1939b; 

Johnson, 1925; Willner et al., 1980). Molluscs are an important component of the diet of 

some populations (Convey et al., 1989; Neves and Odom, 1989; Parmalee, 1989; Willner et 

al., 1980). Young muskrats feed more on bank vegetation than do adults (Warwick, 1940, 

cited in Perry, 1982). 

Temperature regulation and molt. Active year-round (Kiviat, 1978), muskrats 

usually begin their annual molt in the summer, with fur reaching its minimum density 

during August (Willner et al., 1980). Muskrats use their dens or lodges to insulate 

themselves from summer heat and winter cold (O'Neil, 1949; Willner et al., 1980). During 

extreme cold, muskrats may freeze to death if they are unable to plug their den entrances 

(Errington, 1939a). 

Breeding activities and social organization. Muskrats are solitary or form breeding 

pairs that remain in a home range exclusive of other pairs (Errington, 1963; Proulx and 

Gilbert, 1983). They are territorial, particularly during peak reproductive activity, with their 

houses usually spaced at least 8 m apart (Johnson, 1925; Sather, 1958; Trippensee, 1953). 

In southern parts of their range, muskrats breed throughout the year, with late fall and 

early spring peaks (O'Neil, 1949; Svihla and Svihla, 1931; Wilson, 1955). In northern 

latitudes, breeding occurs only in the spring and summer, with first litters born in late April 

or early May (Mathiak, 1966; Beer, 1950; Errington, 1937b; Gashwiler, 1950). Errington 

(1937b) found that postpartum estrus occurs in the muskrat, and suggested that the period 

between litters is about 30 d. Neonates are almost hairless but by age 2 wk are covered 

with fur and able to swim (Errington, 1963). 

Home range and resources. Muskrats have relatively small home ranges that vary 

in configuration depending on the aquatic habitat (Perry, 1982; Willner et al., 1980). They 

build two different types of houses: a main dwelling and a feeding house (feeder) that is 

smaller than the main house (Dozier, 1953; Johnson, 1925; Sather, 1958). The feeder 

provides protection from the elements and predators when feeding in prime foraging areas, 

as well as access to oxygen during frozen conditions. The house provides a dry nest and 

stable temperatures. Muskrats usually forage within 5 to 10 m of a house (Willner et al., 

1980). Using radiotelemetry, MacArthur (1978) found muskrats within 15 m of their primary 

dwelling 50 percent of the time and only rarely more than 150 m. Mathiak (1966) reported 

other experiments showing that muskrats remain close to their dwellings. 

In the winter, muskrats build pushups, which are cavities formed in 30 to 46 cm high 

piles of vegetation pushed up through holes in the ice of a marsh (Perry, 1982). Muskrats 

use pushups as resting places during frozen conditions to minimize their exposure to cold 

water (Fuller, 1951). In the summer, muskrats often change the use of their home range in 

response to water levels; during droughts they will move if the area 

2-338 Muskrat 
�

around the house dries up, which can lead to intense aggression in the more favorable 

habitat (Errington, 1939a). Usually only a minor proportion of drought-evicted muskrats 

can find new homes (Errington, 1939a). In the winter, droughts can result in severe 

mortality (Errington, 1937a). 

Population density. Bellrose and Brown (1941, cited in Perry, 1982) concluded that 

cattail communities support more muskrat houses than other plant types in the Illinois 

River valley. Cattail communities also support high densities of muskrats in other areas 

(Errington, 1963; Dozier, 1950). In pond and lake habitats, shoreline length is a more 

important factor than overall habitat area in determining muskrat density (Glass, 1952, 

cited in Perry, 1982). Many investigators estimate muskrat densities by counting the 

number of houses or push-ups and multiplying by a factor ranging from 2.8 (Lay, 1945, 

cited in Boutin and Birkenholz, 1987) to 5.0 (Dozier et al., 1948), although this method is 

questionable (Boutin and Birkenholz, 1987). 

Population dynamics. The age at first breeding varies but usually occurs during the 

first spring after birth (Errington, 1963; Perry, 1982). Southern populations produce more 

litters but with fewer pups in each than do northern populations (Boyce, 1977; Perry, 1982; 

see table). Muskrats in lower quality habitats have both smaller litter sizes and fewer litters 

than muskrats in better quality areas (Neal, 1968). They disperse in the spring to establish 

breeding territories or to move into uninhabited areas (Errington, 1963). Muskrat 

population cycles of 5, 6, and 10 y have been reported (Butler, 1962; Willner et al., 1980); 

Perry (1982) summarized several studies that reported cycles ranging from 10 to 14 yr or 

more. Butler (1962) found that muskrats follow a 10-yr cycle in most parts of Canada. 

Similar species (from general references) 

� The Florida water rat (Neofiber alleni) is much smaller (20 to 22 cm) than the 

muskrat, with a rounded tail (11 to 17 cm) to distinguish it further. The 

Florida water rat inhabits bogs, marshes, weedy lake borders, and savanna 

streams, though its range is limited to Florida. It feeds on aquatic plants and 

crayfish. 

General references 

Boutin and Birkenholz (1987); Burt and Grossenheider (1980); Perry (1982); Willner 

et al. (1980). 

2-339 Muskrat 
Muskrat (Ondatra zibethicus) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Refere

Body Weight B M winter 1,480 1,400 - 1,520 New York Dozie

(g) B F winter 1,350 1,300 - 1,400 

B M winter 1,326 ± 45.9 SE e Tennessee Schac

B F winter 1,221 ± 54.2 SE B M winter 1,180 730 - 1,550 Nebraska, nc Kansas Sathe

B F winter 1,090 770 - 1,450 A M spring 909 Idaho Reeve

A F spring 837 

neonate 21.3 16 - 28 Iowa Erring

neonate 20 - 25 New York Dean, 

at weaning 200 112 - 184 Iowa Erring

at weaning New Brunswick, Canada Parke

Pup Growth 0 to 30 d 5.4 4.3 - 5.6 Iowa/marsh Erring

Rate (g/d) weaning to 1st 

fall; M 7.5 New Brunswick, Canada/ Parke

F 7.1 marsh 

Metabolic floating 21 ± 7.9 SE lab (water temperature 25 C) Fish, 1

Rate swimming 38 (lO /kg-d) 2 

o 

Metabolic Rate floating 101 lab (water temperature 25 C) Fish, 1

(kcal/kg-d) swimming 182 

A M basal 71.6 estima

A F basal A M free-living 213 (90 - 505) estima

A F free-living 216 (91 - 513) 

o 

2-340 Muskrat 
Muskrat (Ondatra zibethicus) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Refere

Food greens 0.34 Louisiana, captive Svihla 

Ingestion greens & corn 0.26 (rivalicius) 

Rate (g/g-d) 

Water A M 0.97 estima

Ingestion A F 0.98 

Rate (g/g-d) 

Inhalation A M 0.61 estima

Rate (m /d) A F 0.57 3 

Surface Area A M 1,221 estima(cm ) A F 1,159 2 Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

cattail 25 - 50 ne United States/NS Martin et 

bulrush 10 - 25 

burreed 5 - 10 (rough approximation of % 

waterstarwort 2 - diet; stomach contents) 

pondweed 2 - 5 

arrowhead 2 - 5 

corn 2 - 5 

cattail 59 Somerset Co., MD/brackish Willner e

rush 17 marsh 

millet 8 algae 5 (% of diet; stomach 

grass 4 contents) 

cord grass 4 

seeds 2 other 3 

5 

2-341 Muskrat 
Muskrat (Ondatra zibethicus) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

green algae 77 Montgomery Co., MD/ Willner e

3-square rush 8 freshwater 

switch grass 8 

soft rush 4 (% of diet; stomach 

water willow 2 contents) grass 1 

(Graminae) 

other <1 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Home Range summer 0.17 ± 0.0078 SD Ontario, Canada/marsh Proulx & 

Size (ha) early summer 0.048 ± 0.024 SD Ontario, Canada/bay Proulx & 

late summer 0.11 ± 0.084 SD 

B M 0.17 Iowa/marsh Neal, 196

B F 0.17 

Population A B spring 9.3 ± 1.3 SE/ha ne Iowa/open water riverine Clay & C

Density A B summer 2.6 ± 0.3 SE/ha 

A B fall 6.3 ± 1.1 SE/ha 

B M 18.7/ha Virginia/fringe marsh Halbrook

B M 2.1/ha Virginia/marsh B B 28.3/ha 1 - 74 Louisiana/Scirpus olneyi O'Neil, 19

B B summer 23/km river Pennsylvania/riverine (little Brooks & 

B B summer 48/km river Massachusetts/wetland, Brooks & 

marsh vegetation) river (sedges) 

Litter 3.46 Louisiana/marsh O'Neil, 19

Size 4.65 3 - 6 Virginia/marsh Halbrook

7.1 ± 0.2 SE Iowa/riverine Clay & C

7.3 1 - 12 Wisconsin/marsh Mathiak, 

2-342 Muskrat 
Muskrat (Ondatra zibethicus) 

Population 

Dynamics 

Age/Sex/ 

Cond./Seas. Mean Range Location/Habitat Referenc

Litters/Year 1.7 Idaho/marsh Reeves & 

2.1 Maine/wildlife refuge - NS Gashwile

5 - 6 < 7 - 8 Louisiana/NS O'Neil, 19

Days 29 - 30 > 22 - 23 nw Iowa/marsh Errington

Gestation Maine/wildlife refuge - NS Gashwile

Age at B 28 d 21 - 30 d Iowa/marsh Errington

Weaning Age at 6 mo Louisiana/marsh Svihla & 

Sexual Maturity Annual adult 87 ne Iowa/riverine Clay & C

Mortality juvenile 90 

Rates juvenile 67 Missouri/NS Schwartz 

(%) Longevity < 5 yr Ontario, Canada/marsh Proulx & 

Seasonal 

Activity Begin Peak End Location Referenc

Mating year-round winter southern latitudes O'Neil, 19

spring-summer northern latitudes Chambe

1931 Gashwi

William

Parturition late April June late August Iowa Errington

early May late August Maine Gashwile

late May early July mid-August Idaho Reeves & 

Dispersal fall Ontario, Canada McDonn

spring Iowa Errington

2-343 Muskrat 
1

23

4567

Muskrat (Ondatra zibethicus) 

Estimated using equation 3-43 (Boddington, 1978) and body weights from Sather (1958).

Estimated using equation 3-46 (Nagy, 1987) and body weights from Sather (1958).

Based on wet weight of food; greens included Panicum hemitomum, P. virgatum, and Spartina patens.

Estimated using equation 3-17 (Calder and Braun, 1983) and body weights from Sather (1958).

Estimated using equation 3-20 (Stahl, 1967) and body weights from Sather (1958).

Estimated using equation 3-22 (Stahl, 1967) and body weights from Sather (1958).

Cited in Perry (1982.)

2-344 Muskrat 
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Svihla, A. (1931) The field biologist's report. In: Arthur, S. C., compil. The fur animals of 

Louisiana. New Orleans, LA: Louisiana Dept. Conserv., Bull. 18 (rev.); 439 pp. 

Svihla, A.; Svihla, R. D. (1931) The Louisiana muskrat. J. Mammal. 12: 12-28. 

Trippensee, R. E. (1953) Muskrats. In: Wildlife management: fur bearers, waterfowl, and 

fish: v. 2. New York, NY: McGraw-Hill; pp. 126-139. 

Walker, E. P.; et al. (1975) In: Paradiso, J. L., ed. Mammals of the world: v. 2. 3rd ed. 

Baltimore, MD: Johns Hopkins University Press; pp. 645-1500. 

Warwick, T. (1940) A contribution to the ecology of the muskrat (Ondatra zibethica) in the 

British Isles. Proc. Zool. Soc. London, Ser. A 110: 165-201. 

Willner, G. R.; Chapman, J. A.; Goldsberry, J. R. (1975) A study and review of muskrat food 

habits with special reference to Maryland. Maryland Wildl. Adm. Publ. Wildl. Ecol. 1; 

25 pp. 

Willner, G. R.; Feldhamer, G. A.; Zucker, E. E.; et al. (1980) Ondatra zibethicus. Mammalian 

species. No. 141. Amer. Soc. Mammal.; 8 pp. 

Wilson, K. A. (1954) Litter production of coastal North Carolina muskrats. Proc. Annu. Conf. 

Southeast. Assoc. Game and Fish Comm. 8: 13-19. 

Wilson, K. A. (1955) A compendium of the principal data on muskrat reproduction. Raleigh, 

NC: North Carolina Wildl. Resour. Comm., Game Div.; Fed. Aid Wildl. Restoration 

Proj. W-6-R. 

Wilson, K. A. (1956) Color, sex ratios, and weights of North Carolina muskrats. Raleigh, NC: 

North Carolina Wildl. Resour. Comm.; Fed. Aid in Wildl. Restoration Proj. W-6-R-15; 

20 pp. 

Wilson, K. A. (1985) The role of mink and otter as muskrat predators in northeastern North 

Carolina. Proc. Annu. Conf. Southeast. Assoc. Fish and Wildl. Agencies 18: 199-207. 

2-350 Muskrat 
2.2.11. Eastern Cottontail (rabbits) 

Order Lagomorpha Family Leporidae. Rabbits and hares are medium-sized grazing 

herbivores found throughout North America. Most species are nocturnal and crepuscular. 

Many are social, travelling in small groups. Rabbits are prey for large carnivorous birds 

and mammals. Most species also are important game animals. 

Selected species 

The eastern cottontail (Sylvilagus floridanus) is the most widely distributed of the 

medium-sized rabbits (Chapman et al., 1982). It is found over most of the eastern half of 

the United States and southern Canada and has been widely introduced into the western 

United States (Chapman et al., 1980). North of Mexico, 14 subspecies are recognized 

(Chapman et al., 1982). The eastern cottontail feeds on green vegetation in summer and 

bark and twigs in winter. The cottontail is active from early evening to late morning and is 

preyed on by owls, hawks, and carnivorous mammals (Palmer and Fowler, 1975; Burt and 

Grossenheider, 1980). 

Body size. The eastern cottontail measures 35 to 43 cm in length and weighs 0.7 to 

1.8 kg (Lord, 1963; see table) with females slightly larger than the males (Nowak and 

Paradiso, 1983; see table). Cottontail body weight varies seasonally, increasing during 

spring and summer and declining during winter in some areas; different patterns occur in 

other areas (Chapman et al., 1982; Pelton and Jenkins, 1970). 

Habitat. The eastern cottontail is unique to the genus because of the large variety 

of habitats that it occupies, including glades and woodlands, deserts, swamps, prairies, 

hardwood forests, rain forests, and boreal forests (Nowak and Paradiso, 1983). Open 

grassy areas generally are used for foraging at night, whereas dense, heavy cover typically 

is used for shelter during the day (Chapman et al., 1982). During winter, cottontails rely 

more on woody vegetation for adequate cover (Allen, 1984). 

Food habits. During the growing season, cottontails eat herbaceous plants (e.g., 

grasses, clover, timoth, alfalfa). During the winter in areas where herbaceous plants are 

not available, they consume woody vines, shrubs, and trees (e.g., birch, maple, apple) 

(Chapman et al., 1982). In Ohio, bluegrass and other grasses made up a large portion of 

the eastern cottontail's diet, except during snow cover (Chapman et al., 1982). During the 

winter in Connecticut, the principle diet of eastern and New England cottontails consists of 

bark and twigs, shrubs and vines, berries, and willow (Dalke and Sime, 1941). In 

agricultural areas, corn, soybeans, wheat, and other crops may comprise a large portion of 

their diet (Chapman et al., 1982). Younger rabbits prefer the more succulent weedy forbs 

that contain more digestible energy and protein (Chapman et al., 1982). Coprophagy 

(ingestion of feces) has been reported in S. floridanus (Kirkpatrick, 1956). 

Temperature regulation and molt. Eastern cottontails do not undergo hibernation or 

torpor; they are active all year, showing peaks of daily activity at dawn and dusk (Chapman 

et al., 1980). Adults molt gradually over about 9 mo of the year, with two peak molting 

periods (Spinner, 1940). In Connecticut, the spring peak occurs in May and 

2-351 Eastern Cottontail 
June and the fall peak occurs in September and October (Spinner, 1940). In Texas, spring 

and fall molts peak in April and October, respectively (Bothma and Teer, 1982). 

Breeding activities and social organization. Breeding activity begins later at higher 

elevations and at higher latitudes (Conaway et al., 1974), by January in Alabama and by late 

March in southern Wisconsin (Chapman et al., 1980). Several studies have shown that 

continued harsh winter weather may delay the onset of the breeding season (Hamilton, 

1940; Conaway and Wight, 1962; Wight and Conaway, 1961). Breeding seasons are longer 

in the southern states (Lord, 1960). The onset of breeding varies between different 

populations and within the same population from year to year (Chapman et al., 1980). 

Males may fight to establish dominance hierarchies for access to females (Chapman and 

Ceballos, 1990; Nowak and Paradiso, 1983). Lagomorphs in general are induced ovulators, 

and cottontails in particular demonstrate a synchronized breeding season, with conception 

immediately after the birth of a litter (Chapman et al., 1982). 

Home range and resources. Cottontails are found in a variety of habitats that 

contain weedy forbs and perennial grasses; they prefer thick, short, woody perennials that 

provide escape sites (Chapman and Ceballos, 1990). Cottontails usually do not defend 

territories; the home ranges of different age and sex groups tend to overlap, especially in 

fall and winter when they look for areas offering a combination of food and cover 

(Chapman et al., 1980, 1982). Home ranges are smaller when thick vegetation provides 

abundant food and larger in habitats with less food (Chapman et al., 1982). Home ranges 

also are smaller during severe winter weather than at other times (Chapman et al., 1982). 

During the breeding season, females build elaborate nests within slanting holes in the 

ground where they give birth to their altricial (helpless) young. These burrows are 

vulnerable to flooding (Chapman et al., 1982). The size of male home ranges during the 

breeding season can be more than double that in winter (Nowak and Paradiso, 1983; Trent 

and Rongstad, 1974). 

Population density. Population density depends on the availability of resources 

(e.g., food, cover) in an area, and tends to cycle over a period of several years (Chapman 

and Ceballos, 1990). Usual densities range from 1 to 5 animals per hectare, although 

values as high as 14 per hectare have been reported (Chapman and Ceballos, 1990; 

Chapman et al., 1982). 

Population dynamics. The eastern cottontail exhibits the highest fecundity of the 

genus; they often produce 25 to 35 young per year (Chapman and Ceballos, 1990). 

Gestation lasts approximately 1 mo (Chapman et al., 1982). Females may produce five to 

seven litters per year, and juvenile breeding has been reported (Chapman et al., 1982). The 

first and last litters of the year are usually the smallest (Chapman et al., 1977). Cottontails 

have more litters with fewer young each in the southern states (Lord, 1960). Young leave 

the nest when about age 14 to 16 d, although they may not be fully weaned until a few 

weeks later (Ecke, 1955). Female cottontails are capable of breeding by age 5 mo, and 

males as early as 3 mo (Bothma and Teer, 1977). Adult mortality is high, from 

approximately 65 to 75 percent per year in some places (Eberhardt et al., 1963). Juvenile 

mortality is even higher, between 85 and 90 percent in the same areas (Eberhardt et al., 

1963). 

2-352 Eastern Cottontail 
�

� �

�

�

�

�

�

�

�

Similar species (from general references) 

� The mountain cottontail (Sylvilagus nuttallii) (Nuttall's cottontail) is smaller 

(30 to 36 cm in length and 0.7 to 1.3 kg) than the eastern cottontail. The only 

cottontail through most of its range � the western United States � it lives in 

thickets and sagebrush, around loose rocks, cliffs, and mountains. In the 

southwest, it lives in forests. 

� The New England cottontail (Sylvilagus transitionalis) is similar in size to the 

eastern cottontail and inhabits brushy areas, open forests, and mountain 

terrain in New England, extending down the Appalachians into the southern 

United States. In recent years, it has disappeared throughout much of the 

northeastern United States, apparently because of competition with S. 

floridanus. 

� The desert cottontail (Sylvilagus audubonii) (Audubon's cottontail) (30 to 38 

cm in length and 0.6 to 1.2 kg) is common in valleys in the arid southwest, 

although its range extends south to Mexico and north into the Rocky 

Mountains. It inhabits open plains, foothills, and low valleys and also areas 

of grass, sagebrush, pinyons and junipers. It is most active from late 

afternoon throughout the night. 

� The brush rabbit (Sylvilagus bachmani) (28 to 33 cm; 0.6 to 0.8 kg) is usually 

seen around thick cover and rarely uses a burrow. It feeds on green 

vegetation, including lawns when in suburban areas. The species is found 

along the Pacific coast from the Columbia River in the north to the tip of Baja 

California in the south. 

� The marsh rabbit (Sylvilagus palustris) is similar in size to the eastern 

cottontail and ranges from southeastern North Carolina to Florida. As the 

name implies, it inhabits swamps and hummocks, as well as wet 

bottomlands. Mostly nocturnal, it feeds on marsh vegetation, rhizomes, and 

bulbs. 

� The swamp rabbit (Sylvilagus aquaticus) is similar in size to the eastern 

cottontail and is a good swimmer found in swamps, marshes, and wet 

bottomlands. It ranges primarily in the south, from Texas eastward. It nests 

beneath logs or in the bases of stumps, rarely using a burrow and may harm 

crops near swamps. 

� The pygmy rabbit (Sylvilagus idahoensis) is markedly smaller (22 to 28 cm; 

0.2 to 0.5 kg) than the eastern cottontail, lacks a conspicuous tail, and is 

considered by some to be a distinct genus (Brachylagus). Its range is 

limited to several western states, where it inhabits clumps of tall sagebrush. 

It is mostly nocturnal. 

� The white-tailed jackrabbit (Lepus townsendii), larger (46 to 56 cm; 2.2 to 4.5 

kg) than the eastern cottontail, is limited to the northern United States 

2-353 Eastern Cottontail 
�

�

west of the Great Lakes, into southern Canada. It inhabits open, grassy, or 

sagebrush plains and may damage hay crops and small trees. 

� The black-tailed jackrabbit (Lepus californicus) (43 to 53 cm; 1.3 to 3.1 kg) is 

the most common jackrabbit in the grasslands and open areas of the 

western United States, where it inhabits open prairies and deserts with little 

vegetation. It is mostly nocturnal. 

� The snowshoe hare (Lepus americanus) (33 to 46 cm; 0.9 to 1.8 kg) inhabits 

swamps, forests, and thickets in the northern United States and Canada. 

During summer, it feeds on succulent vegetation and during winter on twigs, 

buds, and bark. Its home range is about 4 ha, but populations fluctuate 

widely. 

General references 

Allen (1984); Burt and Grossenheider (1980); Chapman et al. (1980, 1982); Lord 

(1963); Nowak and Paradiso (1983); and Palmer and Fowler (1975). 

2-354 Eastern Cottontail 
Eastern Cottontail (Sylvilagus floridanus) 

2-355 Eastern Cottontail 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location (subspecies) Referen

Body Weight A M 1,134 ± 122 SD 801 - 1,411 w Maryland, West Virginia Chapm

(g) A F 1,244 ± 165 SD 842 - 1,533 

A B inter 1,176 793 - 1,671 Georgia Pelton 

A B ing 1,286 898 - 1,630 all areas combined 

A B mer 1,197 910 - 1,608 

A B all 1,255 886 - 1,669 A B not breed. 1,229 ± 113 SD 1,093 - 1,461 mountain Pelton 

A B not breed. 1,313 ± 141 SD 986 - 1,671 coastal 

A B not breed. 1,132 ± 136 SD 793 - 1,579 Piedmont A B 1,231 ± 164 700 - 1,800 Illinois Lord, 19

neonate 42.2 36.0 - 49.0 Alabama Hill, 197

age: 

10 d 58 Illinois Lord, 1

30 d 159 50 d 401 

101 d 822 149 d 1,106 

Georgia 

Growth Rate day 0 - 30 3.2 Illinois Lord, 19

(g/d) day 11 - 30 3.7 

day 31 - 50 8.8 day 51 - 100 11.3 day 101 - 150 6.4 

Metabolic Rate A B basal 71 estimat

(kcal/kg-d) 

A B free-living 203 (77 - 535) estimat

Food Ingestion 

Rate (g/g-d) Water A B 0.097 estimat

Ingestion 

Rate (g/g-d) 

wsprsumf
Eastern Cottontail (Sylvilagus floridanus) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location (subspecies) Referen

Inhalation A B 0.63 estimat

Rate (m /d) 3 

Surface Area A B 1,254 estimat(cm )2 Dietary Composition Spring Summer Fall Winter Habitat(measure) Referen

Location (subspecies)/ 

trees 13 2 7 39 Connecticut (mallarus)/ Dalke & 

shrubs & vines 4 2 27 40 various (85% f

herbs 44 23 34 5 subsp

grasses, sedges, (% frequence of occurrence; remai

rushes 26 56 30 6 observations of feeding on speci

crops 13 17 2 10 plants) 

woody plants 17 23 20 100 Maryland/forest Spence

forbs 19 30 46 

grasses 64 47 34 (% frequency of occurrence; 

stomach contents) 

bluegrass 34 34 25 32 Ohio (mearnsi)/NS Dusi, 19

orchard grass 4 1 - 1 

timothy grass 5 12 7 1 (% frequency of occurrence; 

Nodding wild rye 5 11 8 4 scats) 

Canada goldenrod - - 3 -red clover - - 6 - (in winter, woody tissues 

unidentified 52 42 51 62 predominated in the 

unidentified category) 

2-356 Eastern Cottontail 
Eastern Cottontail (Sylvilagus floridanus) 

Population 

Dynamics 

Age/Sex/ Location (subspecies)/Habitat 

Cond./Seas. Mean Range Refere

Home Range A M winter 3.05 ± 0.72 SE Wisconsin/woodlot Dixon 

Size (ha) A F winter 2.99 ± 0.28 SE 

A M winter 3.2 c Pennsylvania/mixed Althof

A M spring 7.2 

A M summer 7.8 

A M fall 3.1 

A F winter 2.1 c Pennsylvania/mixed Althof

A F spring 2.8 A F summer 2.4 

A F fall 1.5 A M spring 2.8 sw Wisconsin/woodlot Trent 

A M 

early summer 4.0 

late summer 1.5 

A F spring 1.7 A F summer 0.8 

Population fall 1.1 ± 0.41 SD 0.41 to 2.08 c Michigan/woods, Eberh

Density marsh, fields 

(N/ha) fall 3.0 - 5.9 Illinois/old field Lord & 

winter 0.67 - 1.5 

summer 4.2 sw Wisconsin/farm Trent 

fall 10.1 spring 3.7 

Litter 3.5 ± 0.042 SE Alabama/across six habitats Hill, 19

Size 5.3 Illinois/NS Lord, 

6.0 Missouri/wildlife area Conaw

Litters/Year 4.6 w Maryland/NS Chapm

5 - 7 several locations and Chapm

habitats 

Days 28 25 - 35 several locations and Chapm

Gestation habitats 

2-357 Eastern Cottontail 
Eastern Cottontail (Sylvilagus floridanus) 

Population 

Dynamics 

Age/Sex/ Location (subspecies)/Habitat 

Cond./Seas. Mean Range Refere

Age at 20 - 25 days Illinois/NS Ecke, 

Weaning Age at F 3 - 6 months s Texas/grassland Lord, 

Sexual M 3 - 6 months Missouri/NS Conaw

Maturity Annual B B 80 sw Wisconsin/farm Trent 

Mortality Rates (%) B B 65 ± 7 SD Illinois/sanctuary Lord, 

Longevity B 1.25 Kentucky/NS Bruna

Seasonal 

Activity Begin Peak End Location Refere

Mating mid-March mid-September Connecticut Dalke, 

year-round January - April s Texas Bothm

Parturition April May - July August wc New York Hamilt

Molt fall August October December s Texas Bothm

spring February April July s Texas Bothm

September Sept. - Oct. November Connecticut Spinn

March May - June August Connecticut Spinn

2-358 Eastern Cottontail 

1 Estimated using equation 3-43 (Boddington, 1978) and body weights from Lord (1963).

2 Estimated using equation 3-46 (Nagy, 1987) and body weights from Lord (1963).

3 See Chapters 3 and 4 for approaches to estimating food ingestion rates.

4 Estimated using equation 3-17 (Calder and Braun, 1983) and body weights from Lord (1963).

5 Estimated using equation 3-20 (Stahl, 1967) and body weights from Lord (1963).

6 Estimated using equation 3-22 (Stahl, 1967) and body weights from Lord (1963).

7 Summary of several studies.

8 Cited in Conaway and Wight (1963).

9 Cited in Chapman et al. (1980).

10 Cited in Chapman et al. (1982).
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464-469. 

Allen, D. L. (1939) Michigan cottontails in winter. J. Wildl. Manage. 3: 307-322. 

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Biol. Rep. 82(10.66); 23 pp. 

Althoff, D. P.; Storm, G. L. (1989) Daytime spatial characteristics of cottontail rabbits in 

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47: 129-130. 

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2-359 Eastern Cottontail 
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2-360 Eastern Cottontail 
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2-361 Eastern Cottontail 
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2-362 Eastern Cottontail 
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an ecological principle. Proc. Annu. Conf. Southeast. Assoc. Game and Fish Comm. 

24: 268-277. 

Pelton, M. R.; Jenkins, J. H. (1971) Productivity of Georgia cottontails. Proc. Annu. Conf. 

Southeast. Assoc. Game and Fish Comm. 25: 261-268. 

Pelton, M. R.; Provost, E. E. (1972) Onset of breeding and breeding synchrony by Georgia 

cottontails. J. Wildl. Manage. 36: 544-549. 

Peterson, R. L. (1966) The mammals of eastern Canada. Toronto, Canada: Oxford 

University Press. 

Pils, C. M.; Martin, M. A. (1978) Population dynamics, predator-prey relationships and 

management of the red foxes in Wisconsin. Wisc. Dept. Nat. Resour.; Tech. Bull. 

105; 56 pp. 

Prouty, J. (1937) Cottontails of Massachusetts [master's thesis]. MA: Massachusetts State 

College. 

Rongstad, O. J. (1966) Biology of penned cottontail rabbits. J. Wildl. Manage. 30: 312-319. 

Sandt, J. L.; McKee, R. M. (1978) Upland wildlife investigations. Unpublished Federal Aid 

Performance Report (Maryland); W-47-7; 4 pp. 

Schierbaum, D. (1967) Job completion report, evaluation of cottontail rabbit productivity. 

Albany, NY: Pittman-Robertson Proj. W-84-R-12; 21 pp. 

Seton, E. T. (1929) Lives of game animals. Garden City, NY: Doubleday, Doran and Co., Inc. 

Sheffer, D. E. (1957) Cottontail rabbit propagation in small breeding pens. J. Wildl. Manage. 

21: 90. 

Spencer, R. K.; Chapman, J. A. (1986) Seasonal feeding habits of New England and eastern 

cottontails. Proc. Penn. Acad. Sci. 60: 157-160. 

Spinner, G. P. (1940) Molting characteristics in the eastern cottontail rabbits. J. Mammal. 

21: 429-434. 

Stahl, W. R. (1967) Scaling of respiratory variables in mammals. J. Appl. Physiol. 22: 

453-460. 

Trent, T. T.; Rongstad, O. S. (1974) Home range and survival of cottontail rabbits in 

southwestern Wisconsin. J. Wildl. Manage. 38: 459-472. 

2-363 Eastern Cottontail 
Trethewey, D. E.; Verts, B. J. (1971) Reproduction in eastern cottontail rabbits in western 

Oregon. Am. Midl. Nat. 86: 463-476. 

Wainright, L. C. (1969) A literature review on cottontail reproduction. Colo. Div. Game, Fish 

Parks, Spec. Rep. No. 19; 24 pp. 

Wight, H. M.; Conaway, C. H. (1961) Weather influences on the onset of breeding in 

Missouri cottontails. J. Wildl. Manage. 25: 87-89. 

2-364 Eastern Cottontail 
2.3. REPTILES AND AMPHIBIANS 

Table 2-3 summarizes the species of reptiles and amphibians included in this 

section. For range maps, refer to the general references identified in the individual species 

profiles. The remainder of this section is organized by species in the order presented in 

Table 2-3. The availability of information in the published literature varies substantially 

among species, which is reflected in the profiles. The measures used to describe body 

length are included in each species profile. Body weight is reported as fresh wet weight 

(including the shell for turtles), unless otherwise noted. 

Unlike birds and mammals for which a single common name usually covers all 

subspecies, many reptile and amphibian subspecies are recognized by different common 

names. For example, there are two subspecies of Rana clamitans: the green frog and the 

bronze frog (Section 2.3.7). There are four subspecies of Terrapene carolina: eastern box 

turtle, three-toed box turtle, Florida box turtle, and Gulf Coast box turtle (Section 2.3.3). In 

this case, other species exist that are also known as box turtles: the ornate and desert box 

turtles belong to the species T. ornata. For species that could be confused with other 

species unless a subspecies common name is used, we selected the common name of the 

most widespread subspecies to use in the tables and titles of the species profile. As with 

the other species in the Handbook, however, the profile covers all subspecies for the 

selected species that were represented in the literature reviewed. 

In these profiles, we use the word hibernation for the period of dormancy that 

reptiles and amphibians undergo during winter, when they change their metabolism to 

accommodate the low (often near freezing) temperatures and lack of food (and oxygen). 

Use of the word for this group is controversial, however, because the word was developed 

initially to describe mammalian winter dormancy. Some investigators argue that a different 

word, brumation, should be established to describe the overwintering dormancy and 

associated metabolic changes for reptiles and amphibians (Hutchison, 1979). Others 

disagree, because significant physiological changes also occur in reptiles and amphibians 

during winter dormancy. They argue that, although the physiological changes are different 

from those in mammals, the word hibernation is a general term that does not specify what 

2-365
Table 2-3. Reptiles and Amphibians Included in the Handbook 

Order Common name Scientific name Section 

Chelydridae snapping turtle Chelydra serpentina 2.3.1 

Emydidae painted turtle Chrysemys picta 2.3.2 

eastern box turtle Terrapene carolina carolina2.3.3 a 

Colubridae racer Coluber constrictor 2.3.4 

northern water snake Nerodia sipedon sipedon 2.3.5 a 

Salamandridae eastern newt Notophthalmus viridescens2.3.6 

Ranidae green frog Rana clamitans clamitans 2.3.7 a 

bullfrog Rana catesbeiana 2.3.8 

a

Additional subspecies also are included in the profile. 

metabolic changes occur to allow overwintering in a dormant state (Gatten, 1987). We 

have chosen this latter interpretation for the Handbook. 

References 

Gatten, R. E., Jr. (1987) Cardiovascular and other physiological correlates of hibernation in 

aquatic and terrestrial turtles. Am. Zool. 27: 59-68. 

Hutchison, V. H. (1979) Thermoregulation. In: Harless, M.; Morlock, H., eds. Turtles: 

perspectives and research. Toronto, Canada: John Wiley and Sons; pp. 207-227. 

2-366
2.3.1. Snapping Turtle (snapping turtles) 

Order Testudines, Family Chelydridae. Snapping turtles are among the largest of 

the freshwater turtles. They are characterized by large heads with powerful hooked jaws. 

There are only two species of this family in North America (the snapping turtle, including 

both the common and Florida snapping turtles, and the alligator snapping turtle). 

Selected species 

The snapping turtle (Chelydra serpentina) is primarily aquatic, inhabiting freshwater 

and brackish environments, although they will travel overland (DeGraaf and Rudis, 1983; 

Ernst and Barbour, 1972; Smith, 1961). There are two subspecies recognized in North 

America that are primarily distinguished by range: C. s. serpentina (the common snapping 

turtle, which is the largest subspecies, primarily occupies the United States east of the 

Rockies, except for the southern portions of Texas and Florida), and C. s. osceola (the 

Florida snapping turtle, found in the Florida peninsula) (Conant and Collins, 1991). In this 

profile, studies refer to the serpentina subspecies unless otherwise noted. 

Body size. Adult snapping turtles are large, 20 to 37 cm in carapace length, and 

males attain larger sizes than females (Congdon et al., 1986; Ernst and Barbour, 1972; 

Galbraith et al., 1988). In a large oligotrophic lake in Ontario Canada, adult males averaged 

over 10 kg, whereas the females averaged 5.2 kg (Galbraith et al., 1988). In other 

populations, the difference in size between males and females often is less (Congdon et al., 

1986; Galbraith et al., 1988; Hammer, 1969). They reach sexual maturity at approximately 

200 mm in carapace length (Mosimann and Bider, 1960). The cool, short activity season in 

more northern areas results in slower growth rates and longer times to reach sexual 

maturity (Bury, 1979). 

Habitat. In the east, snapping turtles are found in and near permanent ponds, lakes, 

and marshes. However, in the arid west, the species is primarily found in larger rivers, 

because these are the only permanent water bodies (Toner, 1960, cited in Graves and 

Anderson, 1987). They are most often found in turbid waters with a slow current (Graves 

and Anderson, 1987). They spend most of their time lying on the bottom of deep pools or 

buried in the mud in shallow water with only their eyes and nostrils exposed. Froese 

(1978) observed that young snapping turtles show a preference for areas with some 

obstructions that may provide cover or food. 

Food habits. Snapping turtles are omnivorous. In early spring, when limited 

aquatic vegetation exists in lakes and ponds, they may eat primarily animal matter; 

however, when aquatic vegetation becomes abundant, they become more herbivorous 

(Pell, 1941, cited in Graves and Anderson, 1987). Young snapping turtles are primarily 

carnivorous and prefer smaller streams where aquatic vegetation is less abundant (Lagler, 

1943; Pell, 1941, cited in Graves and Anderson, 1987). Snapping turtles consume a wide 

variety of animal material including insects, crustaceans, clams, snails, earthworms, 

leeches, tubificid worms, freshwater sponges, fish (adults, fry, and eggs), frogs and toads, 

salamanders, snakes, small turtles, birds, small mammals, and carrion and plant material 

including various algae (Alexander, 1943; Graves and Anderson, 1987; Hammer, 1969; 

2-367 Snapping Turtle 
�

Punzo, 1975). Budhabatti and Moll (1988) observed no difference between the diets of 

males and females who fed at the surface, midpelagic, and benthic levels. Bramble (1973) 

suggested that the pharyngeal mechanism of feeding (i.e., drawing water with food objects 

into the mouth) prevents snapping turtles from ingesting food above the air-water 

interface. 

Temperature regulation and daily activities. Snappers are most active at night. 

During the day, they occasionally leave the water to bask on shore, but basking is probably 

restricted by intolerance to high temperatures and by rapid loss of moisture (Ernst and 

Barbour, 1972). In a study in Ontario, Canada, Obbard and Brooks (1981) found that the 

turtles were active in the early morning and early evening and basked in the afternoon but 

were rarely active at night. Active turtles were found in deeper waters than inactive 

snappers (Obbard and Brooks, 1981). Cloacal temperatures of 18.7 to 32.6�C were 

reported for snapping turtles captured in the water in Sarasota County, Florida, between 

May and October (Punzo, 1975). 

Hibernation. Snapping turtles usually enter hibernation by late October and emerge 

sometime between March and May, depending on latitude and temperature. To hibernate, 

they burrow into the debris or mud bottom of ponds or lakes, settle beneath logs, or retreat 

into muskrat burrows or lodges. Snapping turtles have been seen moving on or below the 

ice in midwinter. Large congregations sometimes hibernate together (Budhabatti and Moll, 

1988; Ernst and Barbour, 1972). 

Breeding activities and social organization. Mating occurs any time turtles are 

active from spring through fall, depending on latitude (Ernst and Barbour, 1972). Some 

investigators believe that male snapping turtles are territorial (Kiviat, 1980; Pell, 1941, cited 

in Galbraith et al., 1987), but Galbraith et al. (1987) doubts that males defend their home 

ranges against other males. Sperm may remain viable in the female for several years 

(Smith, 1956). Nesting occurs from late spring to early fall, peaking in June (Ernst and 

Barbour, 1972). Hammer (1969) observed that larger, older females nested earlier in the 

season than did smaller, younger ones. Females often move up small streams to lay eggs 

(Ewert, 1976, cited in Graves and Anderson, 1987). The nest site may be in the soil of 

banks or in muskrat houses but more commonly is in the open on south-facing slopes and 

may be several hundred meters from water (DeGraaf and Rudis, 1983). The turtle digs a 4-

to 7-in cavity on dry land, preferably in sand, loam, or vegetable debris. The duration of 

incubation is inversely related to soil temperature (Ernst and Barbour, 1972; Yntema, 1978, 

cited in Graves and Anderson, 1987). In more northerly populations, hatchlings may 

overwinter in the nest (DeGraaf and Rudis, 1983). 

Home range and resources. Most turtles stay primarily within the same marsh or in 

one general area from year to year ((Hammer, 1969; Obbard and Brooks, 1981). The 

summer home range includes a turtle's aquatic foraging areas, but females may need to 

travel some distance outside of the foraging home range to find a suitable nest site 

(DeGraaf and Rudis, 1983). Obbard and Brooks (1980) found that females tagged at their 

nesting site moved an average of 5.5 km (± 1.8 SD) from the nest site afterwards. Lonke 

and Obbard (1977) observed that 91.9 percent of the turtles in one population returned to 

the same nesting site a year after having been tagged there. Home ranges overlap both 

between and within sexes (Obbard and Brooks, 1981). Young snapping turtles use 

2-368 Snapping Turtle 
�

different habitats than adults; they tend to remain in small streams until shortly before 

maturity, when they migrate to habitats preferred by adults (e.g., ponds, marshes, lakes) 

(Hammer, 1971; Minton, 1972, cited in Graves and Anderson, 1987). 

Population density. The density of snapping turtles appears to be positively 

correlated with the productivity of the surface water body (e.g., density in a eutrophic 

surface water body is higher than in an oligotrophic lake) (Galbraith et al., 1988). Specific 

habitat characteristics and intraspecific interactions contribute to the variability of 

observed population densities in snapping turtles (Froese and Burghardt, 1975). 

Population dynamics. Females do not begin laying eggs until age 6 to 19 yr 

depending on latitude and when they reach an appropriate size (approximately 200 mm 

carapace) (Galbraith et al. 1989; Mosimann and Bider, 1960). Males mature a few years 

earlier than females (see table). Females may lay one or two clutches per season (Minton, 

1972, cited in Graves and Anderson, 1987). Clutch size increases with female body size; 

Congdon et al. (1987) calculated the relationship between clutch size (CS) and plastron 

length (PL in mm) for a population in southeastern Michigan: 

CS = -21.227 + 0.242 PL, (r2 = 0.409, n = 65). 

Clutch size has also been positively correlated with latitude (Petokas and Alexander, 1980). 

Hammer (1969) found that mammalian predators destroyed over 50 percent of the turtle 

nests in a South Dakota marsh, and in undisturbed nests, hatchling success was less than 

20 percent. Petokas and Alexander (1980) observed a 94 percent predation rate of nests 

under study in northern New York. Adult mortality is low, corresponding with the long 

lives exhibited by these turtles (see table). 

Similar species (from general references) 

� The alligator snapping turtle (Macroclemys temmincki) is much larger (16 to 

68 kg; 38 to 66 cm carapace) than the common snapping turtle and is one of 

the largest turtles in the world. Its range is from northern Florida to eastcentral Texas and north in the Mississippi Valley. 

General references 

Conant and Collins (1991); DeGraaf and Rudis (1983); Ernst and Barbour (1972); 

Graves and Anderson (1987). 

2-369 Snapping Turtle 
Snapping Turtle (Chelydra serpentina) 

2-370 Snapping Turtle 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referenc

Body Weight A M summer 10.5 ± 2.85 SD Ontario, Canada/large Galbraith 

(kg) A F summer 5.24 ± 0.85 SD oligotrophic lake 

J B summer 1.15 ± 0.80 SD 

A M summer 5.52 ± 2.23 SD Ontario, Canada/eutrophic Galbraith 

A F summer 5.03 ± 1.12 SD pond 

J B summer 1.40 ± 0.20 SD 

A M 4.16 ± 0.28 SE Michigan Congdon 

A F 3.16 ± 0.20 SE 

J B 0.80 ± 0.07 SE 

at hatching 0.0057 NS Ernst & B

at hatching 0.0089 NS Ewert, 19

mm carapace: 

118 0.33 Massachusetts Graham 

127 0.44 134 0.53 167 1.03 192 1.51 220 2,362 

Egg Weight 7 - 15 NS Ernst & B

(g) 11.1 northern New York Petokas 

9.6 South Carolina Congdon 

9.3 5.7 - 13.8 New Jersey Hotaling 

Body Length age in years Michigan Gibbons

(mm carapace) 1 62 ± 4.5 SD 54 - 66 

2 102 ± 5.8 SD 83 - 108 

3 137 ± 9.4 SD 124 - 145 

4 168 ± 14.2 SD 146 - 184 

5 198 ± 13.7 SD 177 - 211 

6 222 ± 12.9 SD 204 - 238 
Snapping Turtle (Chelydra serpentina) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referenc

Metabolic Rate 7.18 kg, rest 2.54 Lynn & v(lO 2 /kg-d) 25�C

Metabolic Rate A F basal 3.2 estimate(kcal/kg-d) A M basal 3.0 

Food Ingestion B summer 0.01 - 0.016 New York/captivity Kiviat, 19

Rate (g/g-d) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

adults & juveniles: location not specified Smith, 19

plants 35 - 70 

animals 6 - 35 (% of diet; measure NS) 

adults: Tennessee/embayment Meyers-S

fish 83.7 1990 

vegetation 13.6 (% wet volume; gastroclams 0.2 intestinal tract contents) 

mud & rocks 2.5 

adults & juveniles: Connecticut/lakes, ponds, Alexande

(plants) (36.5) streams, swamps 

algae 12.8 

(animals) (54.1) (% wet volume; stomach 

crayfish 8.9 contents) 

fiddler crab 2.7 

sucker 3.2 

bullhead 6.3 

sunfish 7.5 unknown fish 12.4 

(miscellaneous) (9.4) 

2-371 Snapping Turtle 
Snapping Turtle (Chelydra serpentina) 

Population 

Dynamics 

Age/Sex/ Range or 

Cond./Seas. Mean (95% CI of mean) Location/Habitat Referenc

Home Range A M summer 0.7 ± 0.29 SD 0.24 - 1.3 Ontario, Canada/lake Galbraith 

Size (ha) 

A F summer 3.79 ± 1.46 SD 2.5 - 5.19 Ontario, Canada/lake Obbard & 

A M summer 3.21 ± 2.67 SD 0.95 - 8.38 

A B summer 3.44 ± 2.18 SD 

A M 8.9 New York/fresh tidal Kiviat, 19

A F nonbreed 7.2 wetland 

Population Ontario, Canada/ 

Density A M summer 1.5 oligotrophic lake Galbraith 

(N/ha) B B summer 2.3 ± 1.45 SD 1.0 - 4.9 oligotrophic waters Galbraith 

B B summer 60.4 40.3 - 95.0 eutrophic pond Galbraith 

B B summer 29.3 ± 27.6 SD 4.4 - 65.9 eutrophic ponds (other Galbraith 

A B summer 59 Tennessee/pond Froese & 

studies) 

Clutch Size 49.0 31 - 87 South Dakota/marsh Hammer

27.9 ± 0.76 SE 12 - 41 se Michigan/NS Congdon 

16.6 ± 1.6 SD 14 - 20 Florida/NS Iverson, 

Clutches/Yea 1 - 2 Indiana/NS Minton, 1

r > 1 NS/summarizing other Ernst & B

studies 

Days 105 90 - 119 Ontario, Canada/lake Obbard & 

Incubation 67 - 73 se Wisconsin/NS Ewert, 19

Age at Sexual F nesting 6 - 8 New York/NS Pell, 194

Maturity (yr) 

F nesting 9 - 10 Iowa/NS Christian

M 5 -

F nesting 17 - 19 at least 14 to 15 Ontario, Canada/riverine, Galbraith 

mixed forest 

4

2-372 Snapping Turtle 
�

Snapping Turtle (Chelydra serpentina) 

Population 

Dynamics 

Age/Sex/ Range or 

Cond./Seas. Mean (95% CI of mean) Location/Habitat Referenc

Length at A B 200 mm carapace Quebec, Canada/NS Mosiman

Sexual Maturity A B 145 mm plastron Tennessee/NS White & 

Annual A B 3 - 7 NS/NS Galbraith 

Mortality Rates (%) Longevity (yr) at least 24 Michigan/marsh Gibbons

at least 19 South Carolina/river Gibbons

Seasonal 

Activity Begin Peak End Location Referenc

Mating April June November depends on latitude Ernst & B

early June mid-June end of June New York Kiviat, 19

mid-June Florida Punzo, 1

Nesting May June September depends on latitude Ernst & B

late May early to mid-June late June northern New York Petokas 

early June mid-June end of June South Dakota Hammer

Hatching August October depends on latitude Ernst & B

late August September early October se Michigan Congdon 

Hibernation October March-May depends on latitude Ernst & B

late September mid-March Iowa Christian

mid-October early May Ontario, Canada Obbard & 

2-373 Snapping Turtle 

1 Cited in Sievert et al. (1988). 2 Estimated assuming temperature of 20�C, using equation 3-50 (Robinson et al., 1983) and body weights from Congd

subtracting 30 percent of body weight to eliminate the weight of the shell (Hall, 1924). More information on estimatinis provided in Congdon et al. (1982). 

3 Method of estimating percent diet not specified. 

4 Summary of six field studies, including the author's. 

5 Summary of data from various authors for eleven eutrophic ponds. 

6 Cited in Petokas and Alexander (1980). 

7 Cited in Graves and Anderson (1987). 
Snapping Turtle (Chelydra serpentina) 

8 Cited in Galbraith et al. (1989). 

9 Cited in Bury (1979). 

10 Cited in Frazer et al. (1991). 

2-374 Snapping Turtle 
References (including Appendix)

Alexander, M. M. (1943) Food habits of the snapping turtle in Connecticut. J. Wildl. Manage.

7: 278-282. 

Barbour, R. W. (1950) The reptiles of Big Black Mountain, Harlan County, Kentucky. Copeia 

1950: 100-107. 

Bramble, D. M. (1973) Media dependent feeding in turtles. Am. Zool. 13: 1342. 

Breckenridge, W. J. (1944) Reptiles and amphibians of Minnesota. Minneapolis, MN: 

University of Minnesota Press. 

Budhabhatti, J.; Moll, E. O. (1988) Diet and activity patterns of the common snapping turtle, 

Chelydra serpentina (Linnaeus) at Chain O'Lakes State Park, Lake County, Illinois 

(abstract only). Bull. Ecol. Soc. Am. Suppl. 69: 86. 

Bury, R. B. (1979) Population ecology of freshwater turtles. In: Harless, M.; Morlock, H., 

eds. Turtles: perspectives and research. Toronto, Canada: John Wiley and Sons, 

Inc.; pp. 571-602. 

Bush, F. M. (1959) Foods of some Kentucky herptiles. Herpetologica 15: 73-77. 

Cahn, A. R. (1937) The turtles of Illinois. Illinois Biol. Monogr. 35: 1-218. 

Carr, A. F. (1952) Handbook of turtles. Ithaca, NY: Comstock. 

Christiansen, J. L.; Burken, R. R. (1979) Growth and maturity of the snapping turtle 

(Chelydra serpentina) in Iowa. Herpetologica 35: 261-266. 

Conant, R.; Collins, J. T. (1991) A field guide to reptiles and amphibians - eastern and 

central North America. Boston, MA: Houghton Mifflin Co. 

Congdon, J. D.; Gibbons, J. W. (1985) Egg components and reproductive characteristics of 

turtles: relationships to body size. Herpetologica 41: 194-205. 

Congdon, J. D.; Dunham, A. E.; Tinkle, D. W. (1982) Energy budgets and life histories of 

reptiles. In: Gans, C., ed. Biology of the reptilia. v. 13. New York, NY: Academic 

Press; pp. 233-271. 

Congdon, J. D.; Greene, J. L.; Gibbons, J. W. (1986) Biomass of freshwater turtles: A 

geographic comparison. Am. Midl. Nat. 115: 165-173. 

Congdon, J. D.; Tinkle, D. W.; Rosen, P. C. (1983) Egg components and utilization during 

development in aquatic turtles. Copeia 1983: 264-268. 

2-375 Snapping Turtle 
Congdon, J. D.; Breitenbach, G. L.; van Loben Sels, R. C.; et al. (1987) Reproduction and 

nesting ecology of snapping turtles (Chelydra serpentina) in southeastern Michigan. 

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DeGraaf, R. M.; Rudis, D. D. (1983) Amphibians and reptiles of New England. Amherst, MA: 

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Ernst, C. H. (1968) A turtle's territory. Int. Turtle Tortoise Soc. J. 2: 9-34. 

Ernst, C. H. (1971) Population dynamics and activity cycles of Chrysemys picta in 

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Ewert, M. A. (1976) Nests, nesting and aerial basking of Macroclemys under natural 

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Ewert, M. A. (1979) The embryo and its egg: development and natural history. In: Harless, 

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Frazer, N. B.; Gibbons, J. W.; Greene, J. L. (1991) Growth, survivorship and longevity of 

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Froese, A. D. (1978) Habitat preferences of the common snapping turtle, Chelydra s. 

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Froese, A. D.; Burghardt, G. M. (1975) A dense natural population of the common snapping 

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Galbraith, D. A.; Brooks, R. J. (1987) Survivorship of adult females in a northern population 

of common snapping turtles, Chelydra serpentina. Can. J. Zool. 65: 1581-1586. 

Galbraith, D. A.; Chandler, M. W.; Brooks, R. J. (1987) The fine structure of home ranges of 

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Galbraith, D. A.; Bishop, C. A.; Brooks, R. J.; et al. (1988) Factors affecting the density of 

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Galbraith, D. A.; Brooks, R. J.; Obbard, M. E. (1989) The influence of growth rate on age 

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2-376 Snapping Turtle 
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Graham, T. E.; Perkins, R. W. (1976) Growth of the common snapping turtle, Chelydra s. 

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Hall, F. G. (1924) The respiratory exchange in turtles. J. Metab. Res. 6: 393-401. 

Hammer, D. A. (1969) Parameters of a marsh snapping turtle population, La-creek Refuge, 

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Hammer, D. A. (1971) The durable snapping turtle. Nat. Hist. 80: 59-65. 

Hotaling, E. C.; Wilhoft, D. C.; McDowell, S. B. (1985) Egg position and weight of hatchling 

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Hutchison, V. H. (1979) Thermoregulation. In: Harless, M.; Morlock, H., eds. Turtles: 

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Iverson, J. B. (1977) Reproduction in freshwater and terrestrial turtles of north Florida. 

Herpetologica 33: 205-212. 

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Ellenville, NY; pp. 158-168. 

Lagler, K. F. (1943) Food habits and economic relations of the turtles of Michigan with 

special reference to game management. Am. Midl. Nat. 29: 257-312. 

Lagler, K. F.; Applegate, V. C. (1943) Relationship between the length and the weight in the 

snapping turtle Chelydra serpentina Linnaeus. Am. Nat. 77: 476-478. 

Lonke, D. J.; Obbard, M. E. (1977) Tag success, dimensions, clutch size and nesting site 

fidelity for the snapping turtle, Chelydra serpentina (Reptilia, Testudines, 

Chelydridae), in Algonquin Park, Ontario, Canada. J. Herpetol. 11: 243-244. 

Lynn, W. G.; von Brand, T. (1945) Studies on the oxygen consumption and water 

metabolism of turtle embryos. Biol. Bull. 88: 112-125. 

2-377 Snapping Turtle 
Macnamara, C. (1919) Notes on turtles. Ottawa Natural. 32: 135. 

Major, P. D. (1975) Density of snapping turtles, Chelydra serpentina in western West 

Virginia. Herpetologica 31: 332-335. 

Meyers-Schone, L.; Walton, B. T. (1990) Comparison of two freshwater turtle species as 

monitors of environmental contamination. Oak Ridge, TN: Oak Ridge National Lab.; 

Environmental Sciences Division Publication No. 3454. ORNL/TM-11460. 

Minton, S. A., Jr. (1972) Amphibians and reptiles of Indiana. Indianapolis, IN: Indiana 

Academy of Science. 

Moll, E. O. (1979) Reproductive cycles and adaptations. In: Harless, M.; Morlock, H., eds. 

Turtles: perspectives and research. Toronto, Canada: John Wiley and Sons, Inc.; 

pp. 305-331. 

Mosimann, J. E.; Bider, J. R. (1960) Variation, sexual dimorphism, and maturity in a Quebec 

population of the snapping turtle, Chelydra serpentina. Can. J. Zool. 38: 19-38. 

Obbard, M. E. (1983) Population ecology of the common snapping turtle, Chelydra 

serpentina, in north-central Ontario [Ph.D. dissertation]. Guelph, Ontario Canada: 

University of Guelph. 

Obbard, M. E.; Brooks, R. J. (1980) Nesting migrations of the snapping turtle (Chelydra 

serpentina). Herpetologica 36: 158-162. 

Obbard, M. E.; Brooks, R. J. (1981) A radio-telemetry and mark-recapture study of activity 

in the common snapping turtle, Chelydra serpentina. Copeia 1981: 630-637. 

Pearse, A. S. (1923) The abundance and migration of turtles. Ecology 4: 24-28. 

Pell, S. M. (1940) Notes on the food habits of the common snapping turtle. Copeia 2: 131. 

Pell, S. M. (1941) Notes on the habits of the common snapping turtle, Chelydra serpentina 

(Linn.) in central New York [master's thesis]. Ithaca, NY: Cornell University. 

Petokas, P. J.; Alexander, M. M. (1980) The nesting of Chelydra serpentina in northern New 

York. J. Herpetol. 14: 239-244. 

Punzo, F. (1975) Studies on the feeding behavior, diet, nesting habits and temperature 

relationships of Chelydra serpentina osceola (Chelonia: Chelydridae). J. Herp. 9: 

207-210. 

Robinson, R. W.; Peters, R. H.; Zimmermann, J. (1983) The effects of body size and 

temperature on metabolic rate of organisms. Can. J. Zool. 61: 281-288. 

2-378 Snapping Turtle 
Sievert, L. M.; Sievert, G. A.; Cupp, P. V., Jr. (1988) Metabolic rate of feeding and fasting 

juvenile midland painted turtles, Chrysemys picta marginata. Comp. Biochem. 

Physiol. A Comp. Physiol. 90: 157-159. 

Smith, H. M. (1956) Handbook of amphibians and reptiles of Kansas. Univ. Kansas Mus. 

Nat. Hist. Misc. Publ. 9; pp. 134-136. 

Smith, P. W. (1961) The amphibians and reptiles of Illinois. Ill. Nat. Hist. Surv. Bull. 28: 

118-120. 

Toner, G. C. (1960) The snapping turtle. Can. Audubon 22:97-99. 

White, J. B.; Murphy, G. G. (1973) The reproductive cycles and sexual dimorphism of the 

common snapping turtle, Chelydra serpentina serpentina. Herpetologica 29: 

240-246. 

Wilhoft, D. C.; del Baglivo, M. G.; del Baglivo, M. D. (1979) Observations of mammalian 

predation of snapping turtle nests (Reptilia, Testudines, Chelydridae). J. Herpetol. 

13: 435-438. 

Yntema, C. L. (1968) A series of stages in the embryonic development of Chelydra 

serpentina. J. Morphol. 125: 219-252. 

Yntema, C. L. (1970) Observations on females and eggs of the common snapping turtle, 

Chelydra serpentina. Am. Midl. Nat. 84: 69-76. 

Yntema, C. L. (1978) Incubation times for eggs of the turtle Chelydra serpentina 

(Testudines: Chelydridae) at various temperatures. Herpetologica 34: 274-277. 

2-379 Snapping Turtle 

2.3.2. Painted Turtle (pond and marsh turtles) 

Order Testudines, Family Emydidae. Pond and marsh turtles (i.e., sliders, cooters, 

red-bellied turtles, and painted turtles) are small to medium-sized semiaquatic turtles well 

known for basking in the sun. Painted turtles are the most widespread of these in North 

America, ranging across the continent. 

Selected species 

The painted turtle (Chrysemys picta) is largely aquatic, living in shallow-water 

habitats, and is among the most conspicuous of the basking turtles. There are four 

subspecies in the United States (only one reaching slightly into Canada), distinguished by 

color variations, body size, and range: C. p. picta (eastern painted turtle; 11.5 to 15.2 cm; 

range Nova Scotia to Alabama), C. p. marginata (midland painted turtle; 11.5 to 14 cm; 

range southern Quebec and southern Ontario to Tennessee), C. p. dorsalis (southern 

painted turtle; 10 to 12.5 cm; range southern Illinois to the Gulf), and C. p. bellii (western 

painted turtle; the largest of the subspecies, 9 to 18 cm; range southwest Ontario and 

Missouri to the Pacific Northwest) (Conant and Collins, 1991). C. p. dorsalis is the smallest 

subspecies and also one of the smallest emydid turtles in North America (Moll, 1973). 

Hybridization occurs between subspecies in areas where their ranges overlap (e.g., bellii × 

marginata hybrids may occur in areas of Michigan) (Snow, 1980). 

Body size. Painted turtles are medium-sized turtles (10 to 18 cm). Males are 

smaller than females; adult males average from 170 to 190 g, whereas adult females 

average from 260 to 330 g in some populations (Congdon et al., 1986; Ernst 1971b). In 

general, the shell comprises approximately 30 percent of the total wet weight of turtles of 

this size (Hall, 1924). Frazer et al. (1991) estimated a relationship between plastron length 

(PL in mm) and age (t in years) for a population in Michigan in the 1980's using von 

Bertalanffy growth equations: 

PL = 111.8(1 - 0.792e-0.184t) for males, and 

PL = 152.2(1 - 0.852e-0.128t) for females. 

Congdon et al. (1982) reported a relationship between plastron length (PL in mm) and body 

weight (Wt in grams) for painted turtles: 

loge(Wt) = -6978 + 2.645 loge(PL). 

Eggs weigh 4 to 6 g, and neonates retain a large yolk mass that they draw on for the first 

few months of life (Cagle, 1954). 

Habitat. Painted turtle habitat requirements include soft and muddy bottoms, 

basking sites, and aquatic vegetation (Sexton, 1959). Painted turtles prefer slow-moving 

shallow water such as ponds, marshes, ditches, prairie sloughs, spring runs, canals, and 

occasionally brackish tidal marshes (Conant and Collins, 1991). They frequent areas with 

floating surface vegetation for feeding and for cover (Sexton, 1959). These areas tend to 

2-381 Painted Turtle 
�

�

� �

be warmer than more open water, which is important in the early fall as temperatures begin 

to drop (Sexton, 1959). For winter hibernation or dormancy, painted turtles seek deeper 

water (Sexton, 1959). If outlying marsh areas are dry during the summer, the turtles may 

return to the more permanent bodies of water sooner (McAuliffe, 1978). Painted turtles 

sometimes inhabit stagnant and polluted water (Smith, 1956). 

Food habits. Painted turtles are omnivorous. Depending on habitat and on age, 

painted turtles may consume predominantly vegetation or predominantly animal matter. 

Marchand (1942, cited in Mahmoud and Klicka, 1979) found in one population that juveniles 

consumed approximately 85 percent animal matter and 15 percent plant matter, whereas 

the adults were primarily herbivorous, consuming 88 percent plant matter and 12 percent 

insects and amphipods. Knight and Gibbons (1968) found oligochaets, cladocera, 

dragonfly nymphs, lepidopteran larvae, and tendipedid larvae and pupae to dominate the 

animal component of the diet and filamentous algae to dominate the plant component of 

the diet in a population living in a polluted river in Michigan. Adult painted turtles in a 

Pennsylvania population were found to consume only 40 percent plant matter (Ernst and 

Barbour, 1972), whereas in a Michigan marsh and elsewhere, painted turtles of all ages 

apparently consumed 95 to 100 percent plant matter (Cahn, 1937, cited in Smith, 1961; 

Gibbons, 1967). Some carrion also may be consumed (Mount, 1975). 

Temperature regulation and daily activities. Painted turtles are diurnal and usually 

spend their nights sleeping submerged (Ernst, 1971c). During the day, they forage in the 

late morning and late afternoon and bask during the rest of the day (Ernst, 1971c). Active 

feeding does not occur until water temperatures approach 20�C, and these turtles are most 

active around 20.7 to 22.4�C (Ernst, 1972; Ernst and Barbour, 1972; Hutchinson, 1979). 

Basking is most frequent in the spring, summer, and fall, but occasionally painted turtles 

bask during warm spells in the winter (Ernst and Barbour, 1972). Sexton (1959) divided the 

annual activity cycle of painted turtles into five parts: (1) the prevernal, which begins with 

the final melting of winter ice and lasts until late March, or when the turtles begin to move 

in mass out of the hibernation ponds; (2) the vernal, from late March to late May, when the 

submerged aquatic plants important to the turtles grow to the surface of the water (the 

initiation of feeding and mating activities and the emergence of the hatchling turtles from 

the nests of the previous year also occur during this season); (3) the aestival, extending 

from June through August, when the turtles forage, grow, nest, and return to their winter 

hibernation ponds; (4) the autumnal, including September through November or when a 

permanent ice cover forms; and (5) the winter season, which lasts while the water is 

permanently covered with ice. 

Hibernation. Most painted turtles become dormant during the colder months but 

will become active during warm periods in the winter (Ernst and Barbour, 1972). C. picta 

usually hibernates in muddy bottoms of ponds (DeGraaf and Rudis, 1983). Taylor and Nol 

(1989) found painted turtles overwintering in an Ontario pond in areas with a mean water 

depth of 0.32 m (range 0.2 to 0.48 m), mean sediment depth of 0.79 m (0.5 to 0.95 m), and 

mean sediment temperature of 4.1�C (3 to 6�C). During hibernation, painted turtles shift 

toward more anaerobic metabolism, supported by glycolysis of liver and skeletal muscle 

glycogen (Seymour, 1982). After emerging from hibernation, the turtles convert the 

accumulated lactate to glucose in the liver (using aerobic metabolism) (Seymour, 1982). 

2-382 Painted Turtle 
�

Breeding activities and social organization. Mating usually occurs in spring and 

summer but may continue into the fall (Ernst, 1971c; Gibbons, 1968a; Gist et al., 1990). 

Nesting occurs somewhat later (Cagle, 1954; Ernst and Barbour, 1972; Moll 1973). Eggs 

are often laid in high banks (DeGraaf and Rudis, 1983). The species does not appear to be 

territorial and can be found in large aggregations, particularly at favorite basking sites 

(Ernst, 1971c). 

Home range and resources. In spring, as the winter ice melts, many painted turtles 

move away from the ponds in which they hibernated to more shallow ponds and marshes 

with surface vegetation (Sexton, 1959). Movements averaging 60 to 140 meters 

characterized one population in Michigan (Sexton, 1959). The summer home range 

includes the painted turtle's foraging areas and basking sites. Females find nesting sites 

on dry land outside of the foraging range; Congdon and Gatten (1989) found nests to 

average 60 meters from the edge of a foraging marsh. Females initiate nesting migrations 

during daylight hours, and most finish their nests before dark on the same day (Congdon 

and Gatten, 1989). In winter, painted turtles generally move back to the deeper ponds for 

hibernation (DeGraaf and Rudis, 1983). 

Population density. Reported densities range from 11.1/ha in Saskatchewan 

(MacCulloch and Secoy, 1983) to 830/ha in Michigan marshes (Frazer et al., 1991). 

Accurate censuses are difficult, however (Bayless, 1975), and the distribution of painted 

turtles in summer is highly clumped, corresponding to the patches of floating aquatic 

vegetation (Sexton, 1959). 

Population dynamics. Sexual maturity is attained in about 2 to 7 years, depending 

on the sex and size of the turtle and growing season (Christiansen and Moll, 1973; Ernst 

and Barbour, 1972). Males reach sexual maturity 1 to a few years earlier than females 

(Moll, 1973). Once sexual maturity is reached, growth of painted turtles slows or 

essentially ceases (Ernst and Barbour, 1972). Older, larger females tend to produce larger 

clutch sizes and larger eggs than younger, smaller females (Mitchell, 1985). In more 

southerly populations, painted turtles produce more clutches annually with fewer eggs 

each than in more northerly populations (Moll, 1973; Snow, 1980; Schwarzkopf and Brooks, 

1986). Predation causes most nest losses, usually within the first 2 days after laying 

(Tinkle et al., 1981). The duration of the incubation period depends on soil temperature, 

and hatchlings may overwinter in the nest in more northerly populations (Gibbons and 

Nelson, 1978). 

Similar species (from general references) 

Many species of pond and marsh turtles can be found in similar habitats; however, 

there are important dietary differences among species that can affect exposure to 

environmental contaminants, as described below. Size is listed according to carapace 

length, which is longer than plastron length. 

cooters 

� The Florida cooter (Pseudemys floridana) is larger (23 to 33 cm) than the 

painted turtle. The floridana subspecies ranges from the coastal plain of 

2-383 Painted Turtle 
�

�

�

�

�

�

�

Virginia to eastern Texas and north in the Mississippi Valley to southern 

Illinois, while the peninsularis subspecies is restricted to the Florida 

peninsula. The Florida cooter resides in permanent bodies of water. In their 

first year, young cooters feed on both aquatic plant and animal life; later they 

become totally herbivorous. 

� The river cooter (Pseudemys concinna), composed of five subspecies, also 

is larger (23 to 33 cm) than the painted turtle. It inhabits coastal plains 

ranging from southeastern Virginia to Georgia, southeast into Florida, west 

into Texas and New Mexico, and north in the Mississippi Valley to southern 

Illinois. It is chiefly a resident of streams and relatively large lakes. In their 

first year, young river cooters are omnivorous; the adults are almost entirely 

herbivorous. 

� The Texas river cooter (Pseudemys texana) (18 to 25.5 cm) prefers rivers but 

can be found in smaller creeks and ditches. Its range is restricted to most of 

central and southeastern Texas. 

red-bellied turtles 

� The Florida red-bellied turtle (Pseudemys nelsoni) is larger (20 to 31 cm) 

than the painted turtle and has a range in the Florida peninsula and 

panhandle. It can be found basking on logs over fresh to moderately 

brackish water, and it prefers abundant submerged aquatic vegetation, its 

principal food. 

� The Alabama red-bellied turtle (Pseudemys alabamensis) is larger (23 to 33 

cm) than the painted turtle and is found only in the lower portion of the 

Mobile Bay drainage in Alabama. It prefers fresh to moderately brackish 

water with abundant aquatic vegetation, its principal food. 

� The red-bellied turtle (Pseudemys rubriventris) is much larger (25 to 32 cm) 

than the painted turtle and is found in the mid-Atlantic states and eastern 

Massachusetts. 

sliders 

� The pond slider (Trachemys scripta) is similar in size or a little larger (12 to 

20 cm) than the painted turtle and has three subspecies ranging from 

southeastern Virginia to northern Florida and west to New Mexico. During 

the first year, pond sliders are principally carnivorous, consuming aquatic 

insects, crustaceans, molluscs, and tadpoles. As they mature, sliders 

become herbivorous, consuming a wide variety of aquatic plants. 

� The big bend slider (Trachemys gaigeae) (12 to 20 cm) is similar to the pond 

slider in size and habits. It is abundant locally in its limited range along the 

upper Rio Grande and some of its tributaries. 

2-384 Painted Turtle 
General references 

Behler and King (1979); Conant and Collins (1991); Congdon et al. (1986); Ernst and 

Barbour (1972); Moll (1973); Sexton (1959). 

2-385 Painted Turtle 
Painted Turtle (Chrysemys picta) 

2-386 Painted Turtle 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location (subspecies) Ref

Body Weight A F 266.5 ± 60.1 SD 83.5 - 450.3 Pennsylvania (picta x Ern

(g) A M 189.1 ± 52.3 SD 102.0 - 274.5 marginata) 

A F 326.7 ± 4.95 SE Michigan Con

A M 176.9 ± 1.92 SE 

J B 64.2 ± 1.59 SE 

at hatching 3.7 ± 0.2 3.5 - 3.9 central Virginia (picta) Mitc

at hatching 4.1 ± 0.61 SD Iowa Rat

198

Body Length A F 157 ± 2.6 SE 136 - 185 Wisconsin (bellii) Mo

(mm plastron) A M 132 ± 2.9 SE 96 - 155 

(mm plastron) A F 125.1 ± 0.64 SE Michigan Con

(mm carapace) A F 134.2 ± 0.81 SE Michigan Con

A M 99.9 ± 0.48 SE 

J B 65.0 ± 0.65 SE 

A M 109.7 ± 0.54 SE 

J B 71.5 ± 0.69 SE 

Egg Weight (g) initial mass 6.17 Georgia (dorsalis) Con

initial mass 6.65 ± 0.67 SD Iowa Rat

final mass 8.62 ± 1.06 SD 198

198

Growth Rate J F - 1 yr 35 mm/yr Quebec, Canada (marginata) Chr

J F - 2 to 3 yr 19 - 20 mm/yr J F - 4 to 5 yr 12 mm/yr (measured using plastron) 

J F - 6 to 7 yr 8 - 10 mm/yr 

A F - 8 to 12 yr 3 - 6 mm/yr 

A F - > 12 yr < 3 mm/yr 

SD 
Painted Turtle (Chrysemys picta) 

2-387 Painted Turtle 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location (subspecies) Ref

Metabolic Rate adults; 25�C North Carolina Sto

(lO 2 /kg-d) land, rest 0.73 ± 0.44 SD

water, swim 0.22 ± 0.32 SD 

juv.; 25�C 0.39 ± 0.68 SD 

feeding 5.06 ± 0.42 SE 1-day fast 3.44 ± 0.29 SE NS (marginata) Sie

10-day fast 1.98 ± 0.13 SE 

19-day fast 1.57 ± 0.19 SE 

Metabolic Rate J F - yr 1 0.06 Michigan (marginata) Con

(kcal/d, J F - yr 3 0.30 

averaged over J F - yr 5 0.53 

1 year) J F - yr 7 0.77 

A F - yr 9 1.12 

A F - yr 11 1.23 

A F - yr 13 1.28 

Food Ingestion 

Rate (g/g-d) 

Water A B up to 0.025 Wisconsin (bellii) (lab) Tro

Ingestion Rate (g/g-d) A B summer 0.02 0.016 - 0.022 Pennsylvania (lab) Ern

Inhalation A B resting 0.0025 ±0.0005 SE NS (lab) Mils

Rate (m /kg-d) 3 

Dietary Composition Spring Summer Fall Winter (measure) Referen

Location/Habitat 

all ages: Michigan/marsh Gibbon

plants > 95 

(% wet weight; stomach contents) 
Painted Turtle (Chrysemys picta) 

Dietary Composition Spring Summer Fall Winter (measure) Referen

Location/Habitat 

all ages: Michigan/polluted river Knight 

plants 31.6 38.7 

animals 77.3 72.3 (% wet weight; stomach 

Oligochaeta - 30.0 contents) 

Cladocera 1.5 48.5 Odonata nymphs 60.0 38.3 

Lepidoptera larvae 1.0 50.0 

Tendipedidae larva 30.8 7.7 

Tendipedidae pupae 36.7 10.0 

detritus 7.8 1.9 

adults: 

snails 12.1 Pennsylvania (picta)/NS Ernst & 

amphipods 3.0 

crayfish 7.5 (% wet volume; stomach insects 11.5 contents) fish 13.0 other animals 14.1 season not specified 

algae 14.7 vascular plants 24.1 

other plants 0.8 

Population 

Dynamics 

Age/Sex Range or Cond./Seas. Mean (95% CI of mean) Location/Habitat Referen

Movements A B spring 63 - 144 up to 301 Michigan (marginata)/NS Sexton

(m) A B summer 86 - 91 up to 300 

A B fall 88 - 130 up to 336 

Population B B summer 11.1 Saskatchewan, Canada MacCu

Density (bellii)/river 

(N/ha) B B 98 - 410 Michigan (marginata)/ponds, Sexton

B B 590 240 - 941 Pennsylvania/pond, marsh Ernst, 1

B B 828 Michigan/lake, marsh Frazer e

marsh 

2-388 Painted Turtle 
Painted Turtle (Chrysemys picta) 

Population 

Dynamics 

Age/Sex Range or Cond./Seas. Mean (95% CI of mean) Location/Habitat Referen

Clutch Size 19.8 17 - 23 Saskatchewan, Canada MacCu

10.7 4 - 16 Wisconsin (bellii)/NS Moll, 19

7.6 2 - 11 Michigan (marginata)/NS Congdo

4.8 2 - 9 Tennessee (dorsalis × Moll, 19

(bellii)/creek 

marginata)/NS 

Clutches/Year 1 - 2 2 Ontario, Canada/NS Schwar

1 - 2 2 Michigan (bellii × marginata) Snow, 1

> 2 3 Illinois (bellii × marginata) Moll, 19

> 3 5 Tennessee, Louisiana Moll, 19

/NS /kettle ponds 

(dorsalis and d. × 

marginata)/NS 

1986 

Days 65 - 80 se Pennsylvania/NS Ernst, 1

Incubation 60 - 65 se Wisconsin/NS (natural) Ewert, 1

72 - 99 nw Minnesota/NS (natural) Ewert, 1

Age at Sexual F 5 - 6 New Mexico (bellii)/NS Christia

Maturity (yr) M 3 

F 8 Wisconsin (bellii)/NS Christia

M 4 F 6 Pennsylvania (picta)/NS Ernst & 

M 5 

F 4 - 5 Tennessee (dorsalis x Moll, 19

M 2 - 3 marginata)/NS 

2-389 Painted Turtle 
Painted Turtle (Chrysemys picta) 

Population 

Dynamics 

Age/Sex Range or Cond./Seas. Mean (95% CI of mean) Location/Habitat Referen

Length at M 90 northern Michigan Cagle, 1

Sexual F 120 - 130 (marginata, dorsalis)/NS 

Maturity (mm plastron) M 70 southern Illinois (marginata, Cagle, 1

F 120 - 125 dorsalis)/NS 

M 123 88 - 170 New Mexico (bellii)/NS Christia

F 150 132 - 205 

Annual A F 0 - 14 Saskatchewan, Canada, MI, Zweifel

Mortality Rates A M 2 - 46 NY, NE/NS 

(%) 

A B 4 - 6 Virginia/NS Mitchel

J B 54 

Longevity M up to 31 yrs Michigan/marsh Frazer e

F up to 34 yrs 

Seasonal 

Activity Begin Peak End Location (subspecies) Referen

Mating late April mid-June se Pennsylvania Ernst, 1

March April - early May May Michigan Gibbon

October Ohio Gist et 

Nesting June July se Pennsylvania Ernst, 1

June July Illinois, Kansas Smith, 

late May June late June se Michigan (marginata) Tinkle e

Hatching late summer se Michigan (marginata) Tinkle e

September spring Illinois (marginata) Cahn, 1

August September Kansas (bellii) Smith, 1

Hibernation late October late March se Michigan (marginata) Congdo

late October April Kansas (bellii) Smith, 1

2-390 Painted Turtle 
Painted Turtle (Chrysemys picta) 

1 Average mass of test animals resting on land and in water = 215 g (79 to 395 g) and of test animals swimming and m

metabolism = 143 g (79 to 297 g). 

2 Average weight of juvenile turtles = 7.7 g. 

3 Based on an annual energy budget estimated by the authors assuming that females lay one clutch of eggs per year 

4 See Chapters 3 and 4 for approaches to estimating food ingestion rates from metabolic rate and diet. 

5 Uptake of water by turtles held in tap water. 

6 Measured as evaporative water loss. 

7 Spring: from hibernation to other ponds; summer: back to hibernation ponds; fall: to deep-water areas for hiberna

8 Cited in Frazer et al., 1991. 

9 Cited in Smith, 1961. 

2-391 Painted Turtle 
References (including Appendix) 

Bayless, L. E. (1975) Population parameters for Chrysemys picta in a New York pond. Am. 

Midl. Nat. 93: 168-176. 

Behler, J. L.; King, F. W. (1979) The Audubon Society field guide to North American reptiles 

and amphibians. New York, NY: Alfred A. Knopf, Inc. 

Blanchard, F. N. (1923) The amphibians and reptiles of Dickinson County, Iowa. Univ. Iowa 

Stud. Nat. Hist. 10: 19-26. 

Breckenridge, W. J. (1944) Reptiles and amphibians of Minnesota. Minneapolis, MN: 

University of Minnesota Press. 

Breitenbach, G. L.; Congdon, J. D.; van Loben Sels, R. C. (1984) Winter temperatures of 

Chrysemys picta nests in Michigan: effects on hatchling survival. Herpetologica 40: 

76-81. 

Bury, R. B. (1979) Population ecology of freshwater turtles. In: Harless, M.; Morlock, H., 

eds. Turtles: perspectives and research. Toronto, Canada: John Wiley and Sons, 

Inc.; pp. 571-602. 

Cagle, F. R. (1954) Observations on the life cycles of painted turtles (Genus Chrysemys). 

Am. Midl. Nat. 52: 225-235. 

Cahn, A. R. (1937) The turtles of Illinois. Illinois Biol. Monogr. 1-218. 

Christens, E.; Bider, J. R. (1986) Reproductive ecology of the painted turtle (Chrysemys 

picta marginata) in southwestern Quebec. Can. J. Zool. 64: 914-920. 

Christiansen, J. L.; Moll, E. O. (1973) Latitudinal reproductive variation within a single 

subspecies of painted turtle, Chrysemys picta bellii. Herpetologica 29: 152-163. 

Conant, R.; Collins, J. T. (1991) A field guide to reptiles and amphibians - eastern and 

central North America. Boston, MA: Houghton Mifflin Co. 

Congdon, J. D.; Gatten, R. E., Jr. (1989) Movements and energetics of nesting Chrysemys 

picta. Herpetologica 45: 94-100. 

Congdon, J. D.; Gibbons, J. W. (1985) Egg components and reproductive characteristics of 

turtles: relationships to body size. Herpetologica 41: 194-205. 

Congdon, J. D.; Tinkle, D. W. (1982) Reproductive energetics of painted turtle (Chrysemys 

picta). Herpetologica 38: 228-237. 

2-392 Painted Turtle 
Congdon, J. D.; Dunham, A. E.; Tinkle, D. W. (1982) Energy budgets and life histories of 

reptiles. In: Gans, C., ed. Biology of the reptilia: v. 13. New York, NY: Academic 

Press; pp. 233-271. 

Congdon, J. D.; Greene, J. L.; Gibbons, J. W. (1986) Biomass of freshwater turtles: a 

geographic comparison. Am. Midl. Nat. 115: 165-173. 

DeGraaf, R. M.; Rudis, D. D. (1983) Amphibians and reptiles of New England. Amherst, MA: 

University of Massachusetts Press. 

Ernst, C. H. (1971a) Sexual cycles and maturity of the turtle, Chrysemys picta. Biol. Bull. 

140: 191-200. 

Ernst, C. H. (1971b) Growth of the painted turtle, Chrysemys picta, in southeastern 

Pennsylvania. Herpetologica 27: 135-141. 

Ernst, C. J. (1971c) Population dynamics and activity cycles of Chrysemys picta in 

southeastern Pennsylvania. J. Herpetol. 5: 151-160. 

Ernst, C. H. (1972) Temperature-activity relationship in the painted turtle, Chrysemys picta. 

Copeia 1972: 217-222. 

Ernst, C. H.; Barbour, R. W. (1972) Turtles of the United States. Lexington, KY: University 

Press of Kentucky. 

Ewert, M. A. (1979) The embryo and its egg: development and natural history. In: Harless, 

M.; Morlock, H., eds. Turtles: perspectives and research. Toronto, Canada: John 

Wiley and Sons, Inc.; pp. 333-413. 

Frazer, N. B.; Gibbons, J. W.; Greene, J. L. (1991) Growth, survivorship and longevity of 

painted turtles Chrysemys picta in a southwestern Michigan marsh. Am. Midl. Nat. 

125: 245-258. 

Gemmell, D. J. (1970) Some observations on the nesting of the western painted turtle, 

Chrysemys picta belli, in northern Minnesota. Can. Field-Nat. 84: 308-309. 

Gibbons, J. W. (1967) Variation in growth rates in three populations of the painted turtle, 

Chrysemys picta. Herpetologica 23: 296-303. 

Gibbons, J. W. (1968a) Reproductive potential, activity and cycles in Chrysemys picta. 

Ecology 49: 399-409. 

Gibbons, J. W. (1968b) Population structure and survivorship in the painted turtle, 

Chrysemys picta. Copeia 2: 260-268. 

Gibbons, J. W. (1987) Why do turtles live so long? BioSci. 37: 262-269. 

2-393 Painted Turtle 
Gibbons, J. W.; Nelson, D. H. (1978) The evolutionary significance of delayed emergence 

from the nest by hatchling turtles. Evolution 32: 297-303. 

Gist, D. H.; Michaelson, J. A.; Jones, J. M. (1990) Autumn mating in the painted turtle, 

Chrysemys picta. Herpetologica 46: 331-336. 

Hall, F. G. (1924) The respiratory exchange in turtles. J. Metab. Res. 6: 393-401. 

Hutchinson, V. H. (1979) Thermoregulation. In: Harless, M.; Morlock, H., eds. Turtles: 

perspectives and research. Toronto, Canada: John Wiley and Sons, Inc.; pp. 

207-227. 

Iverson, J. B. (1982) Biomass in turtle populations: a neglected subject. Oecologia (Berl.) 

55: 69-76. 

Knight, A. W.; Gibbons, J. W. (1968) Food of the painted turtle, Chrysemys picta in a 

polluted river. Am. Midl. Nat. 80: 558-562. 

Lagler, K. F. (1943) Food habits and economic relations of the turtles of Michigan with 

special reference to game management. Am. Midl. Nat. 29: 257-312. 

Legler, J. M. (1954) Nesting habits of the western painted turtle, Chrysemys picta belli 

Gray. Herpetologica 10: 137-144. 

Lynn, W. G.; von Brand, T. (1945) Studies on the oxygen consumption and water 

metabolism of turtle embryos. Biol. Bull. 88: 112-125. 

MacCulloch, R. D.; Secoy, D. M. (1983) Demography, growth, and food of western painted 

turtles, Chrysemys picta bellii (Gray), from southern Saskatchewan. Can. J. Zool. 

61: 1499-1509. 

Mahmoud, I. Y.; Klicka, J. (1979) Feeding, drinking, and excretion. In: Harless, M.; Morlock, 

H., eds. Turtles: perspectives and research. Toronto, Canada: John Wiley and Sons, 

Inc.; pp. 229-243. 

Marchand, L. J. (1942) A contribution to a knowledge of the natural history of certain 

freshwater turtles [master's thesis]. Gainesville, FL: University of Florida. 

McAuliffe, J. R. (1978) Seasonal migrational movements of a population of the western 

painted turtle (Chrysemys picta bellii) (reptilia, testudines, testudinidae). J. 

Herpetol. 12: 143-149. 

Milsom, W. K.; Chan, P. (1986) The relationship between lung volume, respiratory drive and 

breathing pattern in the turtle, Chrysemys picta. J. Exp. Biol. 120: 233-247. 

Mitchell, J. C. (1985) Female reproductive cycle and life history attributes in a Virginia 

population of painted turtles, Chrysemys picta. J. Herpetol. 19: 218-226. 

2-394 Painted Turtle 
Mitchell, J. C. (1988) Population ecology and life histories of the freshwater turtles 

Chrysemys picta and Sternotherus odoratus in an urban lake. Herpetol. Monogr. 2: 

40-61. 

Moll, E. O. (1973) Latitudinal and intersubspecific variation in reproduction of the painted 

turtle, Chrysemys picta. Herpetologica 29: 307-318. 

Morlock, H.; Herrington, S.; Oldham, M. (1972) Weight loss during food deprivation in the 

eastern painted turtle, Chrysemys picta picta. Copeia 1972: 392-394. 

Mount, R. H. (1975) The reptiles and amphibians of Alabama. Auburn, AL: Auburn 

University Agricultural Experiment Station. 

Packard, G. C.; Packard, M. J.; Boardman, T. J.; et al. (1983) Influence of water exchanges 

by flexible-shelled eggs of painted turtles Chrysemys picta on metabolism and 

growth of embryos. Physiol. Zool. 56: 217-230. 

Pearse, A. S. (1923) The abundance and migration of turtles. Ecology 4: 24-28. 

Pope, C. H. (1939) Turtles of the United States and Canada. New York, NY: Alfred A. Knopf. 

Powell, C. B. (1967) Female sexual cycles of Chrysemys picta and Clemmys insculpta in 

Nova Scotia. Can. Field-Nat. 81: 134-140. 

Ratterman, R. J.; Ackerman, R. A. (1989) The water exchange and hydric microclimate of 

painted turtle (Chrysemys pica) eggs incubating in field nests. Physiol. Zool. 62: 

1059-1079. 

Ream, C. H. (1967) Some aspects of the ecology of painted turtles, Lake Mendota, 

Wisconsin [Ph.D. dissertation]. Madison, WI: University of Wisconsin. 

Schwarzkopf, L.; Brooks, R. J. (1986) Annual variations in reproductive characteristics of 

painted turtles (Chrysemys picta). Can. J. Zool. 64: 1148-1151. 

Sexton, O. J. (1959) Spatial and temporal movements of a population of the painted turtle, 

Chrysemys picta marginata (Agassiz). Ecol. Monogr. 29: 113-140. 

Seymour, R. S. (1982) Physiological adaptations to aquatic life. In: Gans, C.; Pough, F. H., 

eds. Biology of the reptilia, physiology D; physiological ecology: v. 13. New York, 

NY: Academic Press; pp. 1-51. 

Sievert, L. M.; Sievert, G. A.; Cupp, P. V., Jr. (1988) Metabolic rate of feeding and fasting 

juvenile midland painted turtles, Chrysemys picta marginata. Comp. Biochem. 

Physiol. A Comp. Physiol. 90: 157-159. 

Smith, H. M. (1956) Handbook of amphibians and reptiles of Kansas. Univ. Kansas Mus. 

Nat. Hist. Misc. Publ. 9; 365 pp. 

2-395 Painted Turtle 
Smith, P. W. (1961) The amphibians and reptiles of Illinois. Ill. Nat. Hist. Surv. Bull. 28. 

Snow, J. E. (1980) Second clutch laying by painted turtles. Copeia 1980: 534-536. 

Snow, J. E. (1982) Predation on painted turtle nests: nest survival as a function of nest age. 

Can. J. Zool. 60: 3290-3292. 

Stockard, M. E.; Gatten, R. E. (1983) Activity metabolism of painted turtles (Chrysemys 

picta). Copeia 1983: 214-221. 

Taylor, G. M.; Nol, E. (1989) Movements and hibernation sites of overwintering painted 

turtles in southern Ontario. Can. J. Zool. 67: 1877-1881. 

Tinkle, D. W.; Congdon, J. D.; Rosen, P. C. (1981) Nesting frequency and success: 

Implications for the demography of painted turtles. Ecology 62: 1426-1432. 

Trobec, T. N.; Stanley, J. G. (1971) Uptake of ions and water by the painted turtle, 

Chrysemys picta. Copeia 1971: 537-542. 

Wade, S. E.; Gifford, C. E. (1965) A preliminary study of the turtle population of a northern 

Indiana lake. Proc. Indiana Acad. Sci. 74: 371-374. 

Wilbur, H. M. (1975a) The evolutionary and mathematical demography of the turtle 

Chrysemys picta. Ecology 56: 64-77. 

Wilbur, H. M. (1975b) A growth model for the turtle Chrysemys picta. Copeia 1975: 337-343. 

Zweifel, R. G. (1989) Long-term ecological studies on a population of painted turtles, 

Chrysemys picta, on Long Island, New York. Am. Mus. Novit. 2952: 1-55. 

2-396 Painted Turtle 
2.3.3. Eastern Box Turtle (box turtles) 

Order Testudines, Family Emydidae. Box turtles are the most terrestrial of the 

Emydid turtles, having close-fitting shells that have allowed them to adapt well to terrestrial 

life. They are found throughout the eastern and central United States and into the 

southwest. They are omnivorous. 

Selected species 

The eastern box turtle (Terrapene carolina carolina) ranges from northeastern 

Massachusetts to Georgia, west to Michigan, Illinois, and Tennessee (Conant and Collins, 

1991). There are four subspecies of T. carolina, all found within the eastern United States: 

T. c. carolina (above), T. c. major (Gulf Coast box turtle; the largest subspecies, restricted 

to the Gulf Coast), T. c. triunguis (three-toed box turtle; Missouri to south-central Alabama 

and Texas), and T. c. bauri (Florida box turtle; restricted to the Florida peninsula and keys) 

(Conant and Collins, 1991). 

Body size. The eastern box turtle is small, with adults ranging from 11.5 to 15.2 cm 

in length (plastron) and approximately 300 to over 400 g. Hatchlings weigh approximately 8 

to 10 g. Turtles continue to grow throughout their lives; however, their growth rate slows 

after reaching sexual maturity (Ernst and Barbour, 1972), and growth rings are no longer 

discernable after 18 to 20 years (Stickel, 1978). Body fat reserves in a Georgia population 

averaged 0.058 to 0.060 g of fat per gram of lean dry weight from spring through fall 

(Brisbin, 1972). 

Habitat. Typical box turtle habitats include open woodlands, thickets, and welldrained but moist forested areas (Stickel, 1950), but occasionally pastures and marshy 

meadows are utilized (Ernst and Barbour, 1972). In areas with mixed woodlands and 

grasslands, box turtles use grassland areas in times of moderate temperatures and peak 

moisture conditions; otherwise, they tend to use the more moist forested habitats (Reagan, 

1974). Many turtles are killed attempting to cross roads, and fragmentation of habitat by 

roads can severely reduce populations (DeGraaf and Rudis, 1983; Stickel, 1978). 

Food habits. Adult T. carolina are omnivorous (Ernst and Barbour, 1972). When 

young, they are primarily carnivorous, but they become more herbivorous as they age and 

as growth slows (Ernst and Barbour, 1972). They consume a wide variety of animal 

material, including earthworms, slugs, snails, insects and their larvae (particularly 

grasshoppers, moths, and beetles), crayfish, frogs, toads, snakes, and carrion; they also 

consume vegetable matter, including leaves, grass, berries, fruits, and fungi (DeGraaf and 

Rudis, 1983). A high proportion of snails and slugs may comprise the animal matter in the 

diet (Barbour, 1950), and seeds can become an important component of the plant materials 

in the late summer and fall (Klimstra and Newsome, 1960). 

Temperature regulation and daily activities. The species is diurnal and spends the 

night resting in a scooped depression or form that the turtle digs in the soil with its front 

feet (Ernst and Barbour, 1972; Stickel, 1950). T. carolina are most active in temperate, 

2-397 Eastern Box Turtle 
�

�

�

humid weather (Stickel, 1950). In the summer, they avoid high temperatures during midday 

by resting under logs or leaf litter, in mammal burrows, or by congregating in mudholes 

(Smith, 1961; Stickel, 1950). In the hottest weather, they may enter shaded shallow pools 

for hours or days (Ernst and Barbour, 1972). In the cooler temperatures, they may restrict 

their foraging activities to midday (Stickel, 1950). In the laboratory, locomotion is maximal 

between 24 and 32�C (Adams et al., 1989). In the field, their mean active body temperature 

is approximately 26�C (Brattstrom, 1965, cited in Hutchinson, 1979). 

Hibernation. In the northern parts of its range (northeastern Massachusetts, 

Michigan, Illinois), the eastern box turtle enters hibernation in late October or November 

and emerges in April. In Louisiana, Penn and Pottharst (1940, cited in Ernst and Barbour, 

1972) found that T. c. major hibernated when temperatures fell below 65�F. To hibernate, 

the box turtle burrows into loose soil and debris or mud of ponds or stream bottoms. 

Congdon et al. (1989) found a South Carolina population of box turtles to occupy relatively 

shallow burrows (less than 4 cm) compared with those occupied by box turtles in colder 

regions (up to 46 cm). Dolbeer (1971) found hibernacula of box turtles in Tennessee to be 

under 15.5 cm of leaf litter and 5.8 cm of soil on average. In southern states, during rainy 

and warm periods, box turtles may become active again (Dolbeer, 1971). In Florida, the 

box turtle may be active all year (Ernst and Barbour, 1972). 

Breeding activities and social organization. Box turtles are solitary except briefly 

during the mating season. Individuals restrict their activities to a foraging home range, but 

home ranges of different individuals can overlap substantially (Stickel, 1950). Mating 

usually occurs in the spring but may continue into fall, and eggs are laid in late spring and 

summer (Ernst and Barbour, 1972). The female digs a 3- to 4-inch cavity in sandy or loamy 

soil in which she deposits her eggs and then covers the nest with soil. Nests tend to be 

constructed several hundred meters from the female's foraging home range in the warmer 

and drier uplands (Stickel, 1989). The duration of incubation depends on soil 

temperatures, and sometimes hatchlings overwinter in the nest. The young are 

semiaquatic but seldom seen (Smith, 1956). 

Home range and resources. Measures of the foraging home range for box turtles 

range from .5 ha to just over 5 ha (Dolbeer, 1969; Schwartz et al., 1984). A female may 

need to search for suitable nest site (e.g., slightly elevated sandy soils) (Ernst and 

Barbour, 1972) outside of her foraging home range (Stickel, 1950). Winter hibernacula tend 

to be within the foraging home range (Stickel, 1989). 

Population density. Population density varies with habitat quality, but studies 

linking density to particular habitat characteristics are lacking. In some areas, population 

densities have declined steadily over the past several decades (Schwartz and Schwartz, 

1974; Stickel, 1978). Some investigators attribute the decline to increasing habitat 

fragmentation and obstacles (e.g., highways) that prevent females from reaching or 

returning from appropriate nesting areas (Stickel, 1978; DeGraaf and Rudis, 1983). 

Population dynamics. Sexual maturity is attained at about 4 or 5 years (Ernst and 

Barbour, 1972) to 5 to 10 years of age (Minton, 1972, cited in DeGraaf and Rudis, 1983). 

One to four clutches may be laid per year, depending on latitude (Oliver, 1955, cited in 

2-398 Eastern Box Turtle 
�

Moll, 1979; Smith, 1961). Clutch size ranges from three to eight eggs, averaging three to 

four in some areas (Congdon and Gibbons, 1985; Ernst and Barbour, 1972; Smith, 1956). 

Juveniles generally comprise a small proportion of box turtle populations, for example, 18 

to 25 percent in one population in Missouri (Schwartz and Schwartz, 1974) and 10 percent 

in a study in Maryland (Stickel, 1950). Some individual box turtles may live over 100 years 

(Graham and Hutchinson, 1969, cited in DeGraaf and Rudis, 1983; Oliver, 1955, cited in 

Auffenberg and Iverson, 1979). 

Similar species (from general references) 

� The ornate box turtle (Terrapene ornata ornata) and the desert box turtle 

(Terrapene ornata luteola) are similar in size and habits to the eastern box 

turtle. They occur in the western, midwestern, and southern midwestern 

states. Preferred habitats include open prairies, pastureland, open 

woodlands, and waterways in arid, sandy-soil terrains. The ornate box turtle 

and desert box turtle forage primarily on insects but also on berries and 

carrion. 

General references 

Behler and King (1979); Conant and Collins (1991); DeGraaf and Rudis (1983); Ernst 

and Barbour (1972); Stickel (1950). 

2-399 Eastern Box Turtle 
Eastern Box Turtle (Terrapene carolina) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location (subspecies) Refer

Body Weight A F fall 381 ± 29 SE Georgia (carolina), captive Brisb

(g) A M fall 398 ± 47 SE 

A F spring 388 ± 29 SE Georgia (carolina) Brisb

A M spring 369 ± 47 SE 

A F 372 South Carolina Cong

at hatching 8.8 Florida (major) Ewer

2 months 21 Tennessee Allard

1.3 years 40 3.3 years 54 

8.4 Indiana (carolina) Ewer

Body Fat B fall 0.058 ± 0.014 SE Georgia (carolina), captive Brisb

(g/g lean dry B spring 0.060 ± 0.016 SE 

weight) B summer 0.059 ± 0.006 SE 

Length A F 129 mm plastron South Carolina Cong

A up to 198 mm NS/NS Olive

at hatching 28 mm carapace carapace NS/NS Olive

Egg Weight (g) 9.02 ± 0.17 SE South Carolina Cong

6 - 11 NS/NS Ernst 

Metabolic Rate A F basal 5.4 estim

(kcal/kg-d) 

Food Ingestion 

Rate (g/g-d) 

2-400 Eastern Box Turtle 
Eastern Box Turtle (Terrapene carolina) 

Dietary Composition Spring Summer Fall Winter Habitat (measure) Referen

Location (subspecies)/ 

snails 60 Kentucky (carolina)/ Barbou

crayfish 15 Cumberland Mountains 

plants 12.5 crickets 7.5 (% volume; stomach 

unidentified seeds 5 contents) 

plant matter 35 39 20 Illinois (carolina)/forest, Klimstr

insects (adults) 18 12 12 prairie 

insects (larvae) 4 5 9 

seeds 8 16 33 (% wet volume; digestive 

Gastropoda 18 6 8 tract) 

Isopoda <1 5 3 

Diplopoda 3 2 5 

Decapoda 2 2 0 Annelida 1 1 4 mammals 2 <1 2 

reptiles 1 3 1 

birds 3 1 <1 

Population 

Dynamics 

Age/Sex/ Range or Location 

Cond./Seas. Mean (95% CI of mean) (subspecies)/Habitat Referen

Home Range summer 0.46 Tennessee (carolina)/ Dolbee

Size (ha) woodland 

B M 1.2 Maryland (carolina)/ Stickel, 

B F 1.1 bottomland forest 

B M 5.2 Missouri (triunguis)/mixed Schwar

B F 5.1 woods, fields 

Population 2.8 - 3.6 Tennessee/woodland Dolbeer

Density (N/ha) 17 - 35 Maryland (triunguis)/forest Schwar

2-401 Eastern Box Turtle 
�

Eastern Box Turtle (Terrapene carolina) 

Population 

Dynamics 

Age/Sex/ Range or Location 

Cond./Seas. Mean (95% CI of mean) (subspecies)/Habitat Referen

Clutch Size 3.4 ± 0.3 SE South Carolina/NS Congdo

4 2 - 7 Washington, DC/NS Smith, 1

Clutches/Year up to 4 Florida/NS Oliver, 1

1 Illinois/NS Smith, 1

Days 78 - 102 northwest Ewert, 1Incubation 99 69 - 161 Minnesota/(natural) Ewing, 

Washington, DC/(natural) 

Age at Sexual B 4 - 5 NS/NS Ernst & 

Maturity (yr) 

B 5 - 10 NS/NS Minton, 

Length at B 100 - 130 NS/NS Oliver, 1

Sexual Maturity (mm carapace) 

Longevity (yr) 20 up to 80 NS/NS Nichols

up to 138 captivity Oliver, 

Seasonal 

Activity Begin Peak End Location (subspecies) Referen

Mating spring northern range Ernst & 

June July ne Carolinas, Washington, DeGraa

DC Smith

Hatching September October northern range Ernst & 

August September ne Carolinas DeGraa

Hibernation November April northern range Ernst & 

October April Missouri (triunguis) Schwar

2-402 Eastern Box Turtle 

1 Cited in Ernst and Barbour (1972). 

2 Cited in Auffenberg and Iverson (1979). 

3 Estimated assuming temperature of 20�C, using Equation 3-50 (Robinson et al., 1983) and body weights of Brisbin (

30 percent of the body weight to eliminate the weight of the shell (Hall, 1924). 

4 See Chapters 3 and 4 for methods of estimating ingestion rates from metabolic rate and diet. 
Eastern Box Turtle (Terrapene carolina) 

5 Foraging home range; nest sites can be several hundred meters away from the foraging home range.

6 Cited in Moll (1979).7 Cited in Ewert (1979).8 Cited in DeGraaf and Rudis (1983).

2-403 Eastern Box Turtle 
References (including Appendix) 

Adams, N. A.; Claussen, D. L.; Skillings, J. (1989) Effects of temperature on voluntary 

locomotion of the eastern box turtle, Terrapene carolina carolina. Copeia 4: 905-915. 

Allard, H. A. (1935) The natural history of the box turtle. Sci. Monthly 41: 325-338. 

Allard, H. A. (1948) The eastern box-turtle and its behavior, part 1. J. Tenn. Acad. Sci. 23: 

307-321. 

Auffenberg, W.; Iverson, J. G. (1979) Demography of terrestrial turtles. In: Harless, M.; 

Morlock, H., eds. Turtles: perspectives and research. Toronto, Canada: John Wiley 

and Sons; pp. 541-569. 

Barbour, R. W. (1950) The reptiles of Big Black Mountain, Harlan County, Kentucky. Copeia 

1950: 100-107. 

Behler, J. L.; King, F. W. (1979) The Audubon Society field guide to North American reptiles 

and amphibians. New York, NY: Alfred A. Knopf, Inc. 

Brattstrom, B. H. (1965) Body temperatures of reptiles. Am. Midl. Nat. 73: 376-422. 

Breder, R. B. (1927) Turtle trailing: a new technique for studying the life habits of certain 

testudinata. Zoologica 9: 231-243. 

Brisbin, I. L., Jr. (1972) Seasonal variations in the live weights and major body components 

of captive box turtles. Herpetologica 28: 70-75. 

Bush, F. M. (1959) Foods of some Kentucky herptiles. Herpetologica 15: 73-77. 

Cahn, A. R. (1937) The turtles of Illinois. Illinois Biol. Monogr. 1-218. 

Carr, A. F. (1952) Handbook of turtles. Ithaca, NY: Comstock. 

Conant, R.; Collins, J. T. (1991) A field guide to reptiles and amphibians: eastern/central 

North America. Boston, MA: Houghton Mifflin Co. 

Congdon, J. D.; Gibbons, J. W. (1985) Egg components and reproductive characteristics of 

turtles: relationships to body size. Herpetologica 41: 194-205. 

Congdon, J. D.; Gatten, R. E., Jr.; Morreale, S. J. (1989) Overwintering activity of box turtles 

(Terrapene carolina) in South Carolina. J. Herpetol. 23: 179-181. 

DeGraaf, R. M.; Rudis, D. D. (1983) Box turtle. Amphibians and reptiles of New England. 

Amherst, MA: University of Massachusetts Press. 

Dickson, J. D., III (1953) The private life of the box turtle. Everglades Nat. Hist. 1: 58-62. 

2-404 Eastern Box Turtle 
Dodge, C. H.; Dimond, M. T.; Wunder, C. C. (1979) The influence of temperature on the 

incubation of box turtle eggs (abstract only). Am. Zool. 19: 981. 

Dolbeer, R. A. (1969) Population density and home range size of the eastern box turtle 

(Terrapene c. carolina) in eastern Tennessee. A.S.B. Bull. 16: 49. 

Dolbeer, R. A. (1971) Winter behavior of the eastern box turtle, Terrapene c. carolina L., in 

eastern Tennessee. Copeia 1971: 758-760. 

Ernst, C. H.; Barbour, R. W. (1972) Turtles of the United States. Lexington, KY: University 

Press of Kentucky. 

Ewert, M. A. (1979) The embryo and its egg: development and natural history. In: Harless, 

M.; Morlock, H., eds. Turtles: perspectives and research. Toronto, Canada: John 

Wiley and Sons, Inc.; pp. 333-413. 

Ewing, H. E. (1933) Reproduction in the eastern box-turtle Terrapene carolina carolina. 

Copeia 1933: 95-96. 

Graham, T. E.; Hutchinson, V. H. (1969) Centenarian box turtles. Int. Turtle Tortoise Soc. J. 

3: 24-29. 

Hall, F. G. (1924) The respiratory exchange in turtles. J. Metab. Res. 6: 393-401. 

Hutchinson, V. H. (1979) Thermoregulation. In: Harless, M.; Morlock, H., eds. Turtles: 

perspectives and research. Toronto, Canada: John Wiley and Sons, Inc.; pp. 

207-227. 

Klimstra, W. D.; Newsome, F. (1960) Some observations on the food coactions of the 

common box turtle, Terrapene c. carolina. Ecology 41: 639-647. 

Lynn, W. G.; von Brand, T. (1945) Studies on the oxygen consumption and water 

metabolism of turtle embryos. Biol. Bull. 88: 112-125. 

Minton, S. A., Jr. (1972) Amphibians and reptiles of Indiana. Indianapolis, IN: Indiana 

Academy of Science. 

Moll, E. O. (1979) Reproductive cycles and adaptations. In: Harless, M.; Morlock, H., eds. 

Turtles: perspectives and research. Toronto, Canada: John Wiley and Sons, Inc.; 

pp. 305-331. 

Nichols, J. T. (1939a) Data on size, growth and age in the box turtle, Terrapene carolina. 

Copeia 1939: 14-20. 

Nichols, J. T. (1939b) Range and homing of individual box turtles. Copeia 1939: 125-127. 

Oliver, J. A. (1955) The natural history of North American amphibians and reptiles. 

Princeton, NJ: Van Nostrand Co. 

2-405 Eastern Box Turtle 
Penn, G. H.; Pottharst, K. E. (1940) The reproduction and dormancy of Terrapene major in 

New Orleans. Herpetologica 2: 25-29. 

Reagan, D. P. (1974) Habitat selection in the three-toed box turtle Terrapene carolina 

triunguis. Copeia 2: 512-527. 

Robinson, R. W.; Peters, R. H.; Zimmermann, J. (1983) The effects of body size and 

temperature on metabolic rate of organisms. Can. J. Zool. 61: 281-288. 

Rosenberger, R. C. (1972) Interesting facts about turtles. Int. Turtle Tortoise Soc. J. 6: 4-7. 

Schwartz, C. W.; Schwartz, E. R. (1974) The three-toed box turtle in central Missouri: its 

population, home range, and movements. Missouri Dept. Conserv. Terr. Ser. No. 5; 

28 pp. 

Schwartz, E. R.; Schwartz, C. W.; Kiester, A. R. (1984) The three-toed box turtle in central 

Missouri, part II: a nineteen-year study of home range, movements and population. 

Missouri Dept. Conserv. Terr. Ser. No. 12; 29 pp. 

Smith, H. M. (1956) Handbook of amphibians and reptiles of Kansas. Univ. Kansas Mus. 

Nat. Hist. Misc. Publ. 9. 

Smith, P. W. (1961) The amphibians and reptiles of Illinois. Ill. Nat. Hist. Surv. Bull. 28: 

118-120. 

Stickel, L. F. (1950) Population and home range relationships of the box turtle, Terrapene c. 

carolina (Linnaeus). Ecol. Monogr. 20: 351-378. 

Stickel, L. F. (1978) Changes in a box turtle population during three decades. Copeia 1978: 

221-225. 

Stickel, L. F. (1989) Home range behavior among box turtles (Terrapene c. carolina) of a 

bottomland forest in Maryland. J. Herpetol. 23: 40-44. 

Stickel, L. F.; Bunck, C. M. (1989) Growth and morphometrics of the box turtle, Terrapene c. 

carolina. J. Herpetol. 23: 216-223. 

Strang, C. A. (1983) Spatial and temporal activity patterns in two terrestrial turtles. J. 

Herpetol. 17: 43-47. 

2-406 Eastern Box Turtle 
2.3.4. Racer (and whipsnakes) 

Order Squamata, Family Colubridae. All racer snakes (Coluber constrictor) and 

whipsnakes (Masticophis) belong to the family Colubridae, along with 84 percent of the 

snake species in North America. Colubrids vary widely in form and size and can be found 

in numerous terrestrial and aquatic habitats. The more terrestrial members of this family 

also include some brown and garter snakes; lined snakes; earth snakes; hognose snakes; 

small woodland snakes; green snakes; speckled racer and indigo snakes; rat snakes; 

glossy snakes; pine, bull, and gopher snakes; kingsnakes and milk snakes; scarlet, longnosed, and short-tailed snakes; ground snakes; rear-fanged snakes; and crowned and 

black-headed snakes (Conant and Collins, 1991). 

Selected species 

Racer snakes (Coluber constrictor) are slender and fast moving and are found in a 

wide variety of terrestrial habitats. They are one of the most common large snakes in 

North America (Smith, 1961). There are 11 subspecies in North America, limited to the 

United States and Mexico: C. c. constrictor (northern black racer; southern Maine to 

northeastern Alabama), C. c. flaviventris (eastern yellowbelly racer; Montana, western 

North Dakota, and Iowa south to Texas), C. c. foxii (blue racer; northwest Ohio to eastern 

Iowa and southeast Minnesota), C. c. anthicus (buttermilk racer; south Arkansas, 

Louisiana, and east Texas), C. c. etheridgei (tan racer; west-central Louisiana and adjacent 

Texas), C. c. helvigularis (brownchin racer; lower Chipola and Apalachicola River Valleys in 

Florida panhandle and adjacent Georgia), C. c. latrunculus (blackmask racer; southeast 

Louisiana along east side of Mississippi River to northern Mississippi), C. c. mormon 

(western yellow-bellied racer; south British Colombia to Baja California, east to southwest 

Montana, western Wyoming, and western Colorado), C. c. oaxaca (Mexican racer; south 

Texas and Mexico), C. c. paludicola (Everglades racer; southern Florida Everglades region 

and Cape Canaveral area), and C. c. priapus (southern black racer; southeastern states 

and north and west in Mississippi Valley). 

Body size. Adult racer snakes are usually 76 to 152 cm in total length (Conant and 

Collins, 1991). Brown and Parker (1984) developed an empirical relationship between 

snout-to-vent length (SVL)

i and body weight for male and female racers of the mormon 

subspecies in northern Utah: 

weight (g) = -100.80 + 2.93 SVL (cm) females,j and 

weight (g) = -82.65 + 2.57 SVL (cm) males. 

The equations apply only over a limited range of body sizes (40 to 70 cm) where the 

relationship is approximately linear instead of exponential. Kaufman and Gibbons (1975) 

i

Measures of SVL exclude the tail. Fitch (1963) estimated that the tail measures 28 percent of the 

SVL of young females and 31 percent of the SVL of young males. j

Females collected when nonreproductive. 

2-407 Racer 
�

determined a relationship between length and weight for both sexes of a South Carolina 

population: 

weight (g) = 0.0003 SVL (cm)2.97 (± 0.15 2SE) both sexes.k 

Racers from populations in the northeastern United States tend to be the largest, while 

those from the far west and south Texas are the smallest (Fitch, 1963). Just prior to egglaying, the eggs can account for over 40 percent of a gravid female's body weight (Brown 

and Parker, 1984). At hatching, racers weigh about 8 or 9 g. Weight gain during the first 

year is rapid, with both sexes increasing their weight after hatching by approximately 3.2 

times in the first year (Brown and Parker, 1984). One-year-old females nearly double their 

weight during their second year (Brown and Parker, 1984). By the time females are 3 years 

old (when most reach sexual maturity), they are 1.3 times heavier than the males (Brown 

and Parker, 1984). 

Habitat. Racers can be found in moist or dry areas, abandoned fields, open 

woodlands, mountain meadows, rocky wooded hillsides, grassy-bordered streams, pine 

flatwoods, roadsides, and marshes from sea level to 2,150 m in elevation (Behler and King, 

1979). Racers are partially arboreal (Behler and King, 1979; DeGraaf and Rudis, 1983). C. 

c. constrictor seems to prefer forest edges and open grassy, shrubby areas (Fitch, 1963, 

1982). In autumn, most C. constrictor move into woodlands to find rock crevices in which 

to overwinter (Fitch, 1982). 

Food habits. Racers are foraging generalists that actively seek their prey. Their 

varied diet includes small mammals (e.g., mice, voles), insects, amphibians (especially 

frogs), small birds, birds' eggs, snakes, and lizards (Brown and Parker, 1982; Fitch, 1963; 

Klimstra, 1959). In early spring, C.c. flaviventris feeds primarily on mammals and from 

May to October feeds primarily on insects (Klimstra, 1959). They often capture new prey 

before fully digesting previously captured prey (Fitch, 1982). Females, which are larger 

than males, tend to consume a higher proportion of vertebrate prey than do the males 

(Fitch, 1982). Males tend to spend more time climbing among foliage in low shrubs and 

trees and consuming insects (Fitch, 1982). 

Temperature regulation and daily activities. C. constrictor is diurnal and spends a 

good portion of the daylight hours foraging (Vermersch and Kuntz, 1986). The species is 

fast moving and may be encountered in almost any terrestrial situation (Fitch, 1982). 

Hammerson (1987) observed California racers to bask in the sun after emerging from their 

night burrows or crevices until their internal body temperature reached almost 34�C, after 

which they would begin actively foraging. When temperatures are moderate, racers will 

spend much of their time during the day in the open above ground; at high temperatures, 

racers may retreat underground (Brown and Parker, 1982). Although racers are good 

climbers, they spend most of their time on the ground (Behler and King, 1979). When 

searching for food or being pursued, the racer snake will not hesitate to climb or swim 

(Smith, 1961). 

k

95 percent confidence interval for constant (intercept in log-transform regression) = 0.00015 to 

0.00058. 

2-408 Racer 
�

�

�

Hibernation. In fall, racers move to their hibernacula fairly directly and begin 

hibernation soon thereafter (Brown and Parker, 1982; Fitch, 1963). Racers hibernate in 

congregations of tens to hundreds of snakes (Brown and Parker, 1984), sometimes with 

copperheads and rattlesnakes, often using deep rock crevices or abandoned woodchuck 

holes (Parker and Brown, 1973). They are among the earliest snakes to emerge from 

hibernation (DeGraaf and Rudis, 1983). 

Breeding activities and social organization. The species breeds in the spring or 

early summer. Racers defend home territories (DeGraaf and Rudis, 1983; Smith, 1956). 

Eggs are laid in the summer in rotting wood, stumps, decaying vegetable matter, or loose 

soil and hatch about 2 months later (Behler and King, 1979; DeGraaf and Rudis, 1983). 

More than one male may mate with one female in a breeding season. Eggs may double in 

size before hatching by absorbing water from the surrounding soil (Fitch, 1963). 

Home range and resources. C. c. constrictor appears to have a definite home range 

(Smith, 1956) and requires large tracts of mixed old fields and woodlands (M. Klemens, 

pers. comm., cited in DeGraaf and Rudis, 1983). Fitch (1963) described four types of 

movement depending on the season and activity: (1) those in areas where hibernation 

occurs (e.g., rocky ledges), (2) seasonal migration between hibernation and summer 

ranges during spring and fall, (3) daily activities within a home range during the active 

season, and (4) wandering movements during which the racer shifts its activities. 

Population density. Population densities of between 0.3 and 7 active snakes per 

hectare have been recorded in different habitats and areas (Fitch, 1963; Turner, 1977). 

Data on population densities are limited due to the difficulty in accurately censusing 

snakes. 

Population dynamics. Male racers can reach sexual maturity by 13 to 14 months, 

whereas females tend not to mature until 2 or 3 years of age (Behler and King, 1979; Brown 

and Parker, 1984). Adult females produce at most a single clutch each year (some may 

reproduce only in alternate years) (Fitch, 1963). In general, the number of eggs in a clutch 

is proportional to the size of the female and ranges from 4 to 30 eggs (Fitch, 1963). 

Incubation lasts approximately 40 days to 2 months, depending on temperature (Behler and 

King, 1979; Smith, 1956). Juvenile snakes suffer higher mortality rates (e.g., 80 percent) 

than adult snakes (e.g., 20 percent) (Brown and Parker, 1984). 

Similar species (from general references) 

� The eastern coachwhip (Masticophis flagellum flagellum) (black phase) is 

similar in size and ranges from North Carolina and south Florida to Texas, 

Oklahoma, and Kansas. 

� The western coachwhip (Masticophis flagellum testaceus) is similar in size 

to the racer. It ranges from western Nebraska south to Mexico. 

� The central Texas whipsnake (Masticophis taeniatus girardi), Schott's 

whipsnake (Masticophis taeniatus schotti), and Ruthven's whipsnake 

2-409 Racer 
�

�

�

(Masticophis taeniatus ruthveni) are all similar in size to the racer and are 

restricted to southern Texas and northern Mexico. 

� The Sonora whipsnake (Masticophis bilineatus) can be slightly larger (76 to 

170 cm) than the racer and is found from Arizona southwest to New Mexico 

and Mexico. 

� The striped racer (Masticophis lateralis) is also similar in size to the racer 

snake. It ranges from south-central Washington southeast in Great Basin to 

southern New Mexico and western and central Texas, south to west-central 

Mexico. 

� The desert striped whipsnake (Masticophis taeniatus taeniatus) is similar to 

the central Texas whipsnake. It ranges from northern Texas and northern 

California to Washington state. 

General references 

Behler and King (1979); Brown and Parker (1984); Conant and Collins (1991); 

DeGraaf and Rudis (1983); Fitch (1963). 

2-410 Racer 
Racer Snake (Coluber constrictor) 

2-411 Racer 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location (subspecies) Referenc

Body Weight males: Utah (mormon) Brown & 

(g) yrs/mm SVL 

<1 8.3 

1 27.0 2 41.0 3 49.1 4 53.4 5 60.4 6 61.2 

females: Utah (mormon) Brown & 

yrs/mm SVL 

<1 8.8 

1 28.4 2 51.6 3 66.2 4 71.4 5 79.4 6 84.0 

males: Kansas (flaviventris) Fitch, 19

yrs/mm SVL 

2 68.2 3 102.1 4 139.0 5 152.4 6 175.9 7 181.2 8 217.5 

266 

420 486 520 541 564 573 

272 

430 524 575 599 620 632 

615 706 757 806 827 845 868 
Racer Snake (Coluber constrictor) 

2-412 Racer 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location (subspecies) Referenc

Body Weight females: Kansas (flaviventris) Fitch, 19

(g) yrs/mm SVL 

(continued) 2 83.5 

3 149.4 

4 212.3 

5 209.6 

6 245.9 

7 251.3 

neonate 4.16 2.4 - 5.8 Kansas (flaviventris) Fitch, 19

215 mm SVL 

Egg Weight (g) female size: Kansas (flaviventris) Fitch, 19

892 mm SVL 5.5 4.4 - 6.0 

773 mm SVL 4.9 4.4 - 5.2 

size NS 7.8 ± 0.17 SE 5.9 - 10.8 Utah (mormon) Brown & 

Juvenile both sexes; 0.116 Kansas (flaviventris) Fitch, 19

Growth Rate 0 to 10 wks 

(g/d) 

Body A B summer 31.8 ± 0.20 SE 18.6 - 37.7 Utah (mormon) Brown, 1

Temperature 

(�C) A B summer 26 - 27 (mode) 15.5 - 32.4 Kansas (flaviventris) Fitch, 19

Metabolic Rate M basal 6.78 estimate

(kcal/kg-d) F basal 6.19 Food Ingestion B B: spring 0.02 Kansas (flaviventris) Fitch, 19

Rate (g/g-d) through fall 

644 

810 866 914 965 974 
Racer Snake (Coluber constrictor) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

insects 20 40 64 s Illinois/pastures, meadows Klimstrasmall mammals 62 27 21 

amphibians 5 13 3 (% volume; digestive tracts) 

reptiles 7 8 -

birds 4 6 8 

other 2 6 4 

small mammals 65.7 Kansas (flaviventris)/ Fitch, 19

orthopterans 14.3 locations throughout state 

lizards 9.2 

snakes 4.2 (% wet weight; scats and 

misc. insects 1.9 stomach contents) 

birds 3.5 

frogs 1.2 

mice 15.4 Kansas (flaviventris)/ Fitch, 19

orthopterans 4.6 woodland, grassland 

lizards 61.5 frogs 12.6 (% wet weight; stomach 

snakes 5.1 contents) 

crickets 0.8 

Population 

Dynamics 

Age/Sex/ Range or Location (subspecies)/ 

Cond./Seas. Mean (95% CI of mean) Habitat Referenc

Home Range A F summer 1.8 Kansas (flaviventris)/ Fitch, 19

Size (ha) A M summer 3.0 woodland, grassland 

Population A B summer 7.0 Kansas (flaviventris)/ Fitch, 19

Density upland prairie, weeds, 

(N/ha) grasses 

B B 0.32 Utah (mormon)/desert shrub Brown & 

2-413 Racer 
Racer Snake (Coluber constrictor) 

2-414 Racer 

Population 

Dynamics 

Age/Sex/ Range or Location (subspecies)/ 

Cond./Seas. Mean (95% CI of mean) Habitat Referenc

Clutch Size average 16.8 7 - 31 NS (constrictor)/NS Fitch, 19

average 12.6 7 - 21 NS (priapus)/NS Fitch, 19

average 5.28 ± 0.24 SE 4 - 8 Utah (mormon)/desert shrub Brown & 

Clutches/Year 0.5 up to 1 Kansas (flaviventris)/ Fitch, 19

woodland, grassland 

Days summer 51 43 - 63 Kansas (flaviventris)/lab Fitch, 19

Incubation 

summer 45 - 50 Utah (mormon)/desert Brown & 

Age at Sexual F 2 - 3 years Kansas (flaviventris)/ Fitch, 19

Maturity M 13 - 14 months woodland, grassland 

Annual B 2 yrs 58 Kansas (flaviventris)/ Fitch, 19

Mortality Rates B 3 - 6 yrs 25 - 30 woodland, grassland 

(%) B 7 yrs 38 

Longevity A B up to 20 Utah (mormon)/cold desert Brown & 

(yr) shrub 

Seasonal 

Activity Begin Peak End Location (subspecies) Referenc

Mating April May June Kansas (flaviventris) Fitch, 19

May early June NS (constrictor) DeGraaf 

April May Texas (flaviventris) Vermers

Nesting June July Virginia, Carolinas Martof et 

June early August Texas (flaviventris) Vermers

Hatching late August early September Kansas (flaviventris) Fitch, 19

mid-late August Utah (mormon) Brown & 
�

Racer Snake (Coluber constrictor) 

Seasonal 

Activity Begin Peak End Location (subspecies) Referenc

Hibernation late early April Kansas (flaviventris) Fitch, 19

November early October 

early May Utah (mormon) Brown & 

1 Ten-week period from hatching to hibernation. 2 Active snakes under natural conditions; cited in Brown and Parker (1982). 3 Estimated assuming temperature of 20�C using Equation 3-50 (Robinson et al., 1983) and body weights of 3-year-old 

4 Author estimated that the snakes eat approximately four times their body weight over the 213-day active season from 

5 Size of snakes not specified; captured within the range of C. c. flaviventris and C. c. priapus.

6 Author summarizing own work and unspecified other studies.

2-415 Racer 
References (including Appendix) 

Behler, J. L.; King, F. W. (1979) The Audubon Society field guide to North American reptiles 

and amphibians. New York, NY: Alfred A. Knopf, Inc. 

Brown, W. S. (1973) Ecology of the racer, Coluber constrictor mormon (Serprentes, 

Colubridae), in a cold temperate desert in northern Utah [Ph.D. dissertation]. Salt 

Lake City, UT: University of Utah. 

Brown, W. S.; Parker, W. S. (1982) Niche dimensions and resource partitioning in a great 

basin desert snake community. U.S. Fish Wildl. Serv. Wildl. Res. Rep. 13: 59-81. 

Brown, W. S.; Parker, W. S. (1984) Growth, reproduction and demography of the racer, 

Coluber constrictor mormon, in northern Utah. In: Seigel, R. A.; Hunt, L. E.; Knight, 

J. L.; et al., eds. Vertebrate ecology and systematics. Lawrence, KS: Museum of 

Natural History, The University of Kansas; pp. 13-40. 

Conant, R.; Collins, J. T. (1991) A field guide to reptiles and amphibians: eastern/central 

North America. Boston, MA: Houghton Mifflin Co. 

Corn, P. S.; Bury, R. B. (1986) Morphological variation and zoogeography of racers 

(Coluber constrictor) in the central Rocky mountains. Herpetologica 42: 258-264. 

DeGraaf, R. M.; Rudis, D. D. (1983) Racer snake. Amphibians and reptiles of New England. 

Amherst, MA: University of Massachusetts Press; pp. 68. 

Fitch, H. S. (1963) Natural history of the racer Coluber constrictor: v. 15. Lawrence, KS: 

University of Kansas Publications, Museum of Natural History; pp. 351-468. 

Fitch, H. S. (1982) Resources of a snake community in prairie woodland habitat of 

northeastern Kansas. In: Scott, N. J., Jr., ed. Herpetological communities. U.S. Fish 

Wildl. Serv. Wildl. Res. Rep. 13; pp. 83-98. 

Gibbons, J. W.; Semlitsch, R. D. (1991) Guide to the reptiles and amphibians of the 

Savannah River site. Athens, GA: The University of Georgia Press. 

Hammerson, G. A. (1987) Thermal behaviour of the snake Coluber constrictor in 

west-central California. J. Therm. Biol. 12: 195-197. 

Kaufman, G. A.; Gibbons, J. W. (1975) Weight-length relationship in thirteen species of 

snakes in the southeastern United States. Herpetologica 31: 31-37. 

Klimstra, W. D. (1959) Foods of the racer, Coluber constrictor, in southern Illinois. Copeia 

1959: 210-214. 

Martof, B. S.; Palmer, W. M.; Bailey, J. R.; et al. (1980) Amphibians and reptiles of the 

Carolinas and Virginia. Chapel Hill, NC: University of North Carolina Press. 

2-416 Racer 
Parker, W. S.; Brown, W. S. (1973) Species composition and population changes in two 

complexes of snake hibernacula in northern Utah. Herpetologica 29: 319-326. 

Pope, C. H. (1944) Amphibians and reptiles of the Chicago area. Chicago, IL: Chicago 

Natural History Museum Press. 

Robinson, R. W.; Peters, R. H.; Zimmermann, J. (1983) The effects of body size and 

temperature on metabolic rate of organisms. Can. J. Zool. 61: 281-288. 

Ruben, J. A. (1976) Aerobic and anaerobic metabolism during activity in snakes. J. Comp. 

Physiol. B: Metab. Transp. Funct. 109: 147-157. 

Smith, H. M. (1956) Handbook of amphibians and reptiles of Kansas. Univ. Kansas Mus. 

Nat. Hist. Misc. Publ. 9; 356 pp. 

Smith, P. W. (1961) The amphibians and reptiles of Illinois. Ill. Nat. Hist. Surv. Bull. 28. 

Turner, F. B. (1977) The dynamics of populations of squamates, crocodilians and 

rhynchocephalians. In: Gans, C.; Tinkle, D. W., eds. Biology of the reptilia: v. 7. New 

York, NY: Academic Press; pp. 157-264. 

Uhler, F. M.; Cottom, C.; Clarke, T. E. (1939) Food of snakes of the George Washington 

National Forest, Virginia. Trans. North Am. Nat. Resour. Wildl. Conf. No. 4; pp. 

605-622. 

Vermersch, T. G.; Kuntz, R. E. (1986) Snakes of south central Texas. Austin, TX: Eakin 

Press; pp. 18-19. 

Wright, A. H.; Wright, A. A. (1957) Handbook of snakes: v. 2. Ithaca, NY: Comstock. 

2-417 Racer 
2.3.5. Northern Water Snake (water snakes and salt marsh snakes) 

Order Squamata, Family Colubridae. Water snakes and salt marsh snakes (genus 

Nerodia) belong to the family Colubridae, along with 84 percent of the snake species in 

North America. Colubrids vary widely in form and size and can be found in numerous 

habitats, including terrestrial, arboreal, aquatic, and burrowing. The more aquatic types of 

snakes in this family include water snakes, salt marsh snakes, swamp snakes, brown 

snakes, and garter and ribbon snakes (Conant and Collins, 1991). 

Selected species 

The northern water snake (Nerodia sipedon sipedon) is largely aquatic and riparian. 

It ranges from Maine and southern Quebec to North Carolina. It also inhabits the uplands 

of western North Carolina and adjacent portions of Tennessee and Virginia, and its range 

extends west to eastern Colorado (Conant and Collins, 1991). Three additional subspecies 

are recognized, distinguished by range and habitat: N. s. pleuralis (midland water snake; 

ranges from Indiana to Oklahoma and the Gulf of Mexico and south of the mountains to the 

Carolinas, preferring fast-moving streams), N. s. insularum (Lake Erie water snake; 

inhabits islands of Put-in-Bay, Lake Erie), and N. s. williamengelsi (Carolina salt marsh 

water snake; inhabits the Outer Bank islands and mainland coast of Pamlico and Core 

sounds, North Carolina) (Behler and King, 1979; Conant and Collins, 1991). 

Body size. The northern water snake is typically 61 to 107 cm in total length 

(Conant and Collins, 1991). Island populations of the species tend to be larger than 

mainland ones (King, 1986). King (1986) estimated the relationship between snout-to-vent 

length (SVL)

l and body weight for Lake Erie water snakes (N. s. insularum): 

weight (g) = 0.0005 SVL (cm)3.07 all snakes; 

weight (g) = 0.0009 SVL (cm)2.88 females; and 

weight (g) = 0.0008 SVL (cm)2.98 males. 

Kaufman and Gibbons (1975) determined a relationship between length and weight for both 

sexes of a South Carolina population: 

weight (g) = 0.0004 SVL (cm)3.15 (± 0.12 SE) all snakes 

(95% CI for intercept = 0.00015 to 0.0011). Immediately after emergence from hibernation, 

females begin to gain weight and continue gaining weight until giving birth in late summer. 

Weight loss associated with parturition in one population ranged from 28.2 to 45.5 percent 

of the female's weight just prior to parturition (King, 1986). 

l

Measures of SVL exclude the tail. Kaufman and Gibbons (1975) estimated that the tail represents 

21.8 percent (± 0.010 SE) of the total length of a female and 25.7 percent (± 0.006 SE) of the 

total length of a male. 

2-419 Northern Water Snake 
�

�

�

Habitat. The northern water snake prefers streams but can be found in lakes and 

ponds and nearby riparian areas (King, 1986; Smith, 1961). In the Carolinas and Virginia, 

they can be found from mountain lakes and streams to large coastal estuaries (Martof et 

al., 1980). They are absent from water bodies with soft muddy bottoms which may 

interfere with foraging (Lagler and Salyer, 1945). In Lake Erie, N. s. insularum occurs in 

shoreline habitats where rocks or vegetation provide refugia (King, 1986). 

Food habits. Northern water snakes consume primarily fish and amphibians and, to 

a lesser extent, insects and small mammals (Raney and Roecker, 1947; Smith, 1961). Diet 

varies according to the age (and size) of the snake and food availability (DeGraaf and 

Rudis, 1983). Young snakes forage in shallow riffles and cobble bars, primarily waiting for 

prey to move within range (letter from K.B. Jones, U.S. Environmental Protection Agency 

Environmental Monitoring Systems Laboratory, to Susan B. Norton, January 6, 1992). m Tadpoles comprise a large proportion of the diet of young snakes in some areas (Raney

and Roecker, 1947). Adults are strong swimmers and can swim and dive for fish 

midstream, often capturing large specimens (e.g., 20 to 23 cm brown trout; 19 cm bullhead; 

20+ cm lamprey) (Lagler and Salyer, 1945). They also tend to consume bottom-dwelling 

fish species (e.g., suckers) (Raney and Roecker, 1947). In New York, Brown (1958) found 

that N. s. sipedon consumed the most food between June and August; they consumed little 

during the remaining months prior to hibernation. 

Temperature regulation and daily activities. The northern water snake is active 

both day and night but is most active between 21 and 27�C (Brown, 1958; Smith, 1961). 

During the day, they are found in areas that provide basking sites and are not found in 

heavily shaded areas (DeGraaf and Rudis, 1983; Lagler and Salyer, 1945). They may 

become inactive and seek shelter, however, if temperatures exceed 27�C (Brown, 1958; 

Lagler and Salyer, 1945). They become torpid at temperatures less than 10�C (Brown, 

1958). 

Hibernation. In autumn, the N. sipedon leaves the aquatic habitats to overwinter in 

rock crevices or in banks nearby (DeGraaf and Rudis, 1983; Fitch, 1982). 

Breeding activities and social organization. The northern water snake breeds 

primarily in early spring, and the young are born from late summer to fall (i.e., viviparous) 

(DeGraaf and Rudis, 1983). The rate of development before hatching is temperature 

dependent (Bauman and Metter, 1977). 

Home range and resources. The northern water snake usually stays in the same 

area of a stream, in the same pond, or in an adjacent pond for several years (Fraker, 1970). 

Snakes along streams have larger home ranges than snakes in ponds and lakes (Fraker, 

1970). Fraker (1970) found that for large ponds (e.g., 1,500 to 2,000 m2

), the home range of 

an individual snake is essentially the entire pond. In fish hatcheries with smaller ponds, 

individual snakes frequent more than one pond (Fraker, 1970). 

mSnakes less than 36 cm in length for this example.

2-420 Northern Water Snake 
�

�

�

�

�

�

Population density. Population density estimates for water snakes usually are 

expressed relative to a length of shoreline. Values from 34 to 380 snakes per km of 

shoreline have been reported for streams and Lake Erie islands (see table). 

Population dynamics. Northern water snakes reach sexual maturity at 2 or 3 years 

of age, with males generally maturing earlier and at a smaller size than females (Feaver, 

1977, cited in King, 1986; King, 1986). Clutch sizes vary from 5 or 10 to 50 or 60 depending 

on location and on female size (see table). The proportion of females breeding in a given 

year increases with increasing female size, as does clutch size and offspring weight (King, 

1986). King determined the relationship of litter size to female SVL for Lake Erie water 

snakes (N. s. insularum): 

litter size = -12.45 + 0.41 SVL (cm). 

Feaver (1977, cited in King, 1986) determined the relationship for a Michigan population: 

litter size = -23.55 + 0.55 SVL (cm). 

Females produce only one clutch per year (Beatson, 1976). Information on annual 

survivorship of juveniles or adults was not identified in the literature reviewed. 

Similar species (from general references) 

� The Mississippi green water snake (Nerodia cyclopion) can be slightly larger 

(76 to 114 cm) than the northern water snake and is found in quiet waters of 

the Mississippi Valley. 

� The blotched water snake (Nerodia erythrogaster transversa) is larger than 

the northern water snake (76 to 122 cm) and is found in western Missouri and 

Kansas to northeastern Mexico. 

� The northern copperbelly (Nerodia erythrogaster neglecta) is larger than the 

northern water snake (76 to 122 cm) and ranges from western Kentucky to 

southeastern Illinois and to Michigan. 

� The redbelly water snake (Nerodia erythrogaster erythrogaster) of the 

midwestern United States is close in size to the water snake. It is best suited 

to swampy areas and sluggish streams. 

� The yellowbelly water snake (Nerodia erythrogaster flavigaster) is found in 

the lower Mississippi Valley and adjacent areas. Like the redbelly, it is 

similar in size to the water snake and likely to be found in swampy areas and 

sluggish streams. 

� The banded water snake (Nerodia fasciata fasciata) is similar in size, and its 

range includes the coastal plain, North Carolina to Mississippi. 

2-421 Northern Water Snake 
�

�

�

�

�

�

�

� The broad banded water snake (Nerodia fasciata confluens) (56 to 90 cm) 

occurs in the Mississippi River delta region in marshes, swamps, and 

shallow waters, including brackish waters along the Gulf Coast. 

� The Florida water snake (Nerodia fasciata pictiventris) is similar in size to the 

northern water snake and ranges from the extreme southeast of Georgia to 

the southern tip of Florida. It lives primarily in shallow freshwater habitats. 

� Harter's water snake (Nerodia harteri) is relatively small (51 to 76 cm) and is 

found in central Texas. 

� The diamondback water snake (Nerodi rhombifer rhombifer) can be slightly 

longer (76 to 122 cm) than the northern water snake and is more thick-bodied 

than most Nerodia. Its range extends south from the Mississippi Valley into 

Mexico. 

� The Gulf salt marsh snake (Nerodia clarkii clarkii) inhabits the Gulf Coast 

from west-central Florida to southern Texas. It is abundant in coastal salt 

meadows, swamps, and marshes. 

� The Atlantic salt marsh snake (Nerodia clarkii taeniata) is restricted to 

Volusia County along the Atlantic Coast of north Florida. 

� The mangrove salt marsh snake (Nerodia clarkii compressicauda) is small 

(38 to 76 cm) and inhabits the mangrove swamps of Florida's lower coasts. 

Dietary differences are evident among these species. Mushinsky et al. (1982) found 

in Louisiana forested wetlands that N. erythrogaster and N. fasciata change from a diet of 

fish to one dominated by frogs when they exceed an SVL of 50 cm. N. rhombifer and N. 

cyclopion, on the other hand, consume primarily fish throughout their lives, although the 

species and size composition of their diet changes as they grow larger (Mushinsky et al., 

1982). As N. rhombifer exceeds 80 cm SVL, it begins to prey upon larger fish that occupy 

deeper open-water habitats. N. cyclopion eats a larger proportion of centrarchid fish as its 

body size increases. In a study of the diet of N. rhombifer, Plummer and Goy (1984) found 

a relationship between the SVL of the snakes and the standard length (SL) of the fish prey 

(defined as 80 percent of total length): 

SLfish (cm) = -5.9 + 0.23 SVLsnake (cm) for males, and 

SLfish (cm) = -3.6 + 0.17 SVLsnake (cm) for females. 

The regression lines are not significantly different, however. 

General references 

Behler and King (1979); Conant and Collins (1991); DeGraaf and Rudis (1983); King 

(1986). 

2-422 Northern Water Snake 
Water Snake (Nerodia sipedon) 

Factors 

Age/Sex/ Range or 

Cond./Seas. Mean (95% CI of mean) Location (subspecies) Referenc

Body Weight A B 207 up to 480 Kansas Fitch, 198

(g) 

J B 1 yr 7.0 ± 2.3 SD 5.3 - 10.4 New York (sipedon) Brown, 1

J B 2 yr 29.0 (N = 2) 25.2 - 32.7 J M 3 yr 53.2 (N = 1) A B 5 - 6 yr 210.0 ± 65 SD 114 - 255 neonate B 4.8 3.6 - 6.6 Ohio, Ontario (insularum) King, 198

Length A M 620 SVL Ohio, Ontario (insularum) King, 198

(mm) A F 745 SVL 

J B 1 yr 285 total New York (sipedon) Brown, 1

J B 2 yr 496 total 

J M 3 yr 607 total A B 5 - 6 yr 868 total 

neonate 181 SVL 125 - 210 SVL Ohio, Ontario (insularum) King, 198

Juvenile J 1 yr 0.18 ± 0.08 SD 0.13 - 0.27 New York (sipedon) Brown, 1

Growth Rate J 2 yr 0.42 0.40 - 0.45 

(g/d) J 3 yr 0.80 

Metabolic B resting: Oklahoma, Nerodia Gratz & H

Rate 15�C 0.607 ± 0.035 SE 0.39 - 0.94 

(lO 2 /kg-d) 25�C 3.29 ± 0.10 SE 2.81 - 4.44

35�C 7.33 ± 0.23 SE 5.70 - 9.99 

rhombifera 

(similar species) 

Food J B 1 yr 0.088 New York (sipedon) Brown, 1

Ingestion Rate J B 2 yr 0.043 

(g/g-d) J M 3 yr 0.043 

A B 5 - 6 yr 0.061 

Surface Area 155 mm SVL 131.16 Arkansas, Nerodia Baeyens 

(cm ) rhombifera (similar 2 

species) 

2-423 Northern Water Snake 
Water Snake (Nerodia sipedon) 

Dietary Composition Spring Summer Fall Winter Habitat (measure) Referenc

Location (subspecies)/ 

Esocidae 7.0 Georgia/aquatic (NS) Camp et 

Catostomidae 22.5 

Percidae 15.7 (% wet volume; 

Proteidae 51.9 stomach contents) 

Cyprinidae 1.5 

Centrarchidae 0.3 season not specified 

crawfish 1.5 

trout 64 n lower Michigan/streams Alexande

non-trout fish 7 

unidentified fish 1 (% wet weight; 

Crustacea 1 stomach contents) 

Amphibia 14 

birds & mammals 12 

unidentified 1 minnows 9.1 n lower Michigan/lakes Brown, 1

darters 1.4 

Amphibia 52.8 (% volume; stomach 

sculpin (Cottidae) 2.2 contents) 

trout perch 2.8 

(Percopsis) 14.1 

game fishes (Perca) 17.4 

burbot (Lota) 0.3 

catfish (Ictaluridae) 

Population 

Dynamics 

Age/Sex/ Location (subspecies)/ 

Cond./Seas. Mean Range Habitat Referenc

Population A B 138 22 - 381 Ohio, Ontario (insularum)/ King, 198

Density Lake Erie islands 

(N/km shore) B B summer 34 - 41 Kansas (sipedon)/stream Beatson

2-424 Northern Water Snake 
Water Snake (Nerodia sipedon) 

Population 

Dynamics 

Age/Sex/ Location (subspecies)/ 

Cond./Seas. Mean Range Habitat Referenc

Litter Size 11.8 4 - 24 Michigan (sipedon)/ponds, Feaver, 1

20.8 ± 8.2 SD 6 - 34 Ohio, Ontario (insularum)/ Camin & 

22.9 9 - 50 Ohio, Ontario (insularum)/ King, 198

33 13 - 52 Illinois (pleuralis)/NS Smith, 19

marshes Lake Erie islands Lake Erie islands 

Litters/Year 1 central Missouri Bauman 

1 Kansas (sipedon)/stream Beatson

(sipedon)/fish hatchery 

Days Gestation 58 central Missouri Bauman 

(sipedon)/fish hatchery 

Age at Sexual F 34 mo Michigan (sipedon)/ponds, Feaver, 1

Maturity (d) M 23 - 24 mo marshes 

F 3 yrs Ohio, Ontario (insularum)/ King, 198

M 2 yrs Lake Erie islands 

Length at F 476 - 649 Michigan (sipedon)/ponds, Feaver, 1

Sexual M 375 - 425 marshes 

Maturity (mm SVL) F 590 Ohio, Ontario (insularum)/ King, 198

M 430 Lake Erie islands 

Seasonal 

Activity Begin Peak End Location (subspecies) Referenc

Mating April - May Kansas (sipedon) Smith, 19

mid-May mid-June central Missouri (sipedon) Bauman 

May Michigan (sipedon) Feaver, 1

2-425 Northern Water Snake 
1

23 �

456

Water Snake (Nerodia sipedon) 

Seasonal 

Activity Begin Peak End Location (subspecies) Referenc

Parturition late August September Illinois (sipedon) Smith, 19

mid-August late September Ohio, Ontario (insularum) King, 198

late summer Virginia, Carolinas (sipedon) Martof et 

Hibernation mid-October mid-April Ohio, Ontario (insularum) King, 198

November late March Michigan (sipedon) Feaver, 1

SVL = snout-to-vent length, which excludes the tail beyond the vent.

Total = total length, from nose to tip of tail.

Snakes in captivity; mean temperatures = 23�C. Snakes fed fish (one fed frogs).

Collected whenever they were found; thought to be active in area from May to September.

Months of collection and size of snakes not specified.

Cited in King (1986). 2-426 

Northern Water Snake 
References (including Appendix) 

Aldridge, R. D. (1982) The ovarian cycle of the water snake, Nerodia sipedon, and effects of 

hypophysectomy and gonadotropin administration. Herpetologica 38: 71-79. 

Alexander, G. (1977) Food of vertebrate predators on trout waters in north central lower 

Michigan. Michigan Academician 10: 181-195. 

Baeyens, D. A.; Rountree, R. L. (1983) A comparative study of evaporative water loss and 

epidermal permeability in an arboreal snake, Opheodrys aestivus, and a 

semi-aquatic snake, Nerodia rhombifera. Comp. Biochem. Physiol. 76A: 301-304. 

Barbour, R. W. (1950) The reptiles of Big Black Mountain, Harlan County, Kentucky. Copeia 

1950: 100-107. 

Bauman, M. A.; Metter, D. E. (1977) Reproductive cycle of the northern watersnake Natrix s. 

sipedon (Reptilia. Serpentes, Colubridae). J. Herpetol. 11: 51-59. 

Beatson, R. R. (1976) Environmental and genetical correlates of disruptive coloration in the 

water snake, Natrix s. sipedon. Evolution 30: 241-252. 

Behler, J. L.; King, F. W. (1979) The Audubon Society field guide to North American reptiles 

and amphibians. New York: Alfred A. Knopf, Inc. 

Brown, E. E. (1958) Feeding habits of the northern water snake, Natrix sipedon sipedon 

Linnaeus. Zoologica (N.Y.) 43: 55-71. 

Bush, F. M. (1959) Foods of some Kentucky herptiles. Herpetologica 15: 73-77. 

Camin, J. H.; Ehrlich, P. R. (1958) Natural selection in water snakes (Natrix sipedon L.) on 

islands in Lake Erie. Evolution 12: 504-511. 

Camp, C. D.; Sprewell, W. D.; Powders, V. N. (1980) Feeding habits of Nerodia taxispilota 

with comparative notes on the foods of sympatric congeners in Georgia. J. 

Herpetol. 14: 301-304. 

Conant, R.; Collins, J. T. (1991) A field guide to reptiles and amphibians: eastern/central 

North America. Boston, MA: Houghton Mifflin Co. 

DeGraaf, R. M.; Rudis, D. D. (1983) Water snake. Amphibians and reptiles of New England. 

Amherst, MA: University of Massachusetts Press. 

Feaver, P. E. (1977) The demography of a Michigan population of Natrix sipedon with 

discussions of ophidian growth and reproduction [Ph.D. dissertation]. Ann Arbor, 

MI: University of Michigan. 

2-427 Northern Water Snake 
Fitch, H. S. (1982) Resources of a snake community in prairie woodland habitat of 

northeastern Kansas. In: Scott, N. J., Jr., ed. Herpetological communities. U.S. Fish 

Wildl. Serv. Wildl. Res. Rep. 13; pp 83-98. 

Fraker, M. A. (1970) Home range and homing in the watersnake, Natrix s. sipedon. Copeia 

1970: 665-673. 

Gratz, R. K.; Hutchinson, V. H. (1977) Energetics for activity in the diamondback water 

snake, Natrix Rhombifera. Physiol. Zool. 50: 99-114. 

Justy, G. M.; Mallory, F. F. (1985) Thermoregulatory behaviour in the northern water snake, 

Nerodia s. sipedon, and the eastern garter snake, Thamnophis s. sirtalis. Can. 

Field-Nat. 99: 246-249. 

Kaufman, G. A.; Gibbons, J. W. (1975) Weight-length relationship in thirteen species of 

snakes in the southeastern United States. Herpetologica 31: 31-37. 

King, R. B. (1986) Population ecology of the Lake Erie water snake, Nerodia sipedon 

insularum. Copeia 1986: 757-772. 

King, R. B. (1989) Body size variation among island and mainland snake populations. 

Herpetologica 45: 84-88. 

Lagler, K. F.; Salyer, J. C., II. (1945) Food and habits of the common water snake, Natrix 

sipedon, in Michigan. Pap. Michigan Acad. Sci., Arts and Letters 31: 169-180. 

Martof, B. S.; Palmer, W. M.; Bailey, J. R.; et al. (1980) Water snake. Amphibians and 

reptiles of the Carolinas and Virginia. Chapel Hill, NC: University of North Carolina 

Press. 

Mushinsky, H. R.; Hebrard, J. J.; Vodopich, D. S. (1982) Ontogeny of water snake foraging 

ecology. Ecology 63: 1624-1629. 

Plummer, M. V.; Goy, J. M. (1984) Ontogenetic dietary shift of water snakes (Nerodia 

rhombifera) in a fish hatchery. Copeia 1984: 550-552. 

Raney, E. C.; Roecker, R. M. (1947) Food and growth of two species of watersnakes from 

western New York. Copeia 1947: 171-174. 

Smith, H. M. (1956) Water snake. Handbook of amphibians and reptiles of Kansas. Univ. 

Kansas Mus. Nat. Hist. Misc. Publ. 9; 356 pp. 

Smith, P. W. (1961) The amphibians and reptiles of Illinois. Ill. Nat. Hist. Surv. Bull. 28. 

Uhler, F. M.; Cottom, C.; Clarke, T. E. (1939) Food of snakes of the George Washington 

National Forest, Virginia. Trans. North Am. Wildl. Nat. Resour. Conf. 4: 605-622. 

Wright, A. H.; Wright, A. A. (1957) Handbook of snakes: v. 2. Ithaca, NY: Comstock. 

2-428 Northern Water Snake 
2.3.6. Eastern Newt (salamanders) 

Order Caudata, Family Salamandridae. Notophthalmus, the genus comprising the 

eastern newts, inhabits eastern North America. A different genus, Taricha, comprises the 

western newts along the Pacific coast of North America. Unlike other salamanders, the 

skin of newts is rough textured, not slimy. Eastern newts are primarily aquatic; western 

newts are terrestrial. The life cycle of eastern newts is complex. Females deposit their 

eggs into shallow surface waters. After hatching, the larvae remain aquatic for 2 to several 

months before transforming into brightly colored terrestrial forms, called efts (Healy, 1974). 

Postlarval migration of efts from ponds to land may take place from July through 

November, but timing varies between populations (Hurlbert, 1970). Efts live on land (forest 

floor) for 3 to 7 years (Healy, 1974). They then return to the water and assume adult 

characteristics. In changing from an eft to an adult, the newt develops fins and the skin 

changes to permit aquatic respiration (Smith, 1961). Occasionally newts omit the 

terrestrial eft stage, especially in the species located in the southeast coastal plain (Conant 

and Collins, 1991) and along the Massachusetts coast (Healy, 1974). These aquatic 

juveniles have the same adaptations (i.e., smooth skin and flattened tail) as the aquatic 

adults but are not sexually mature (Healy, 1973). Under favorable conditions, adults are 

permanently aquatic; however, adults may migrate to land after breeding due to dry ponds, 

high water temperatures, and low oxygen tension (Hurlbert, 1969). The life cycle of 

western newts does not include the eft stage (Conant and Collins, 1991). 

Selected species 

The eastern newt (Notophthalmus viridescens) has both aquatic and terrestrial 

forms. The aquatic adult is usually yellowish-brown or olive-green to dark brown above, 

yellow below. The land-dwelling eft is orange-red to reddish-brown, and its skin contains 

tetrodotoxin, a neurotoxin and powerful emetic. There are four subspecies of eastern 

newts: N. v. viridescens (red-spotted newt; ranges from Nova Scotia west to Great Lakes 

and south to the Gulf states), N. v. dorsalis (broken-striped newt; ranges along the coastal 

plain of the Carolinas), N. v. louisianensis (central newt; ranges from western Michigan to 

the Gulf), and N. v. piaropicola (peninsula newt; restricted to peninsular Florida) (Conant n and Collins, 1991). Neoteny occurs commonly in the peninsula and broken-striped newts.

In the central newt, neoteny is frequent in the southeastern coastal plain. In the redspotted newt, neoteny is rare (Conant and Collins, 1991). 

Body size. Adult eastern newts usually are 6.5 to 10.0 cm in total length (Conant 

and Collins, 1991). In North Carolina, N. v. dorsalis efts ranged from 2.1 to 3.8 cm snout-tovent length (SVL), which excludes the tail, and adults ranged from 2.0 to 4.4 cm SVL 

(Harris, 1989; Harris et al., 1988). Healy (1973) found aquatic juveniles 1 year of age to 

range from 2.0 to 3.2 cm SVL. Adult eastern newts weigh approximately 2 to 3 g (Gill, 1979; 

Gillis and Breuer, 1984), whereas the efts generally weigh 1 to 1.5 g (Burton, 1977; Gillis 

and Breuer, 1984). 

n

Neotenic newts are mature and capable of reproduction but retain the larval form, appearance, 

and habits (Conant and Collins, 1991). 

2-429 Eastern Newt 
�

Habitat. Larval and adult eastern newts are found in ponds, especially those with 

abundant submerged vegetation, and in weedy areas of lakes, marshes, ditches, 

backwaters, and pools of shallow slow-moving streams or other unpolluted shallow or 

semipermanent water. Terrestrial efts inhabit mixed and deciduous forests (Bishop, 1941, 

cited in Sousa, 1985) and are found in moist areas, typically under damp leaves, brush 

piles, logs, and stumps, usually in wooded habitats (DeGraaf and Rudis, 1983). Adequate 

surface litter is important, especially during dry periods, because efts seldom burrow 

(Healy, 1981, cited in Sousa, 1985). 

Food habits. Adult eastern newts are opportunistic predators that prey underwater 

on worms, insects and their larvae (e.g., mayfly, caddisfly, midge, and mosquito larvae), 

small crustaceans and molluscs, spiders, amphibian eggs, and occasionally small fish. 

Newts capture prey at the surface of the water and on the bottom of the pond, as well as in 

the water column (Ries and Bellis, 1966). The shed skin (exuvia) is eaten and may 

comprise greater than 5 percent of the total weight of food items of both the adult and eft 

diets (MacNamara, 1977). Snails are an important food source for the terrestrial eft 

(Burton, 1976). Efts feed only during rainy summer periods (Behler and King, 1979; Healy, 

1973). Healy (1975) noted that in late August and September, efts often were found 

clustered around decaying mushrooms feeding on adult and larval dipterans. In a northern 

hardwood hemlock forest in New York, MacNamara (1977) found that most prey of adult 

migrants and immature efts were from the upper litter layer, soil surface, or low vegetation. 

Temperature regulation and daily activities. Adult newts are often seen foraging in 

shallow water, and efts are often found in large numbers on the forest floor after it rains 

(Behler and King, 1979). Efts may be found on the open forest floor even during daylight 

hours (Conant and Collins, 1991), but they rarely emerge if the air temperature is below 

10�C (Healy, 1975). 

Hibernation. Most adults remain active all winter underwater on pond bottoms or in 

streams (DeGraaf and Rudis, 1983). Some adults overwinter on land (Hurlbert, 1970) and 

migrate to ponds during the spring to breed (Hurlbert, 1969). If the water body freezes to 

the bottom, adults may be forced to hibernate on land or to migrate to another pool (Smith, 

1956). Efts hibernate on land, burrowing under logs and debris. Hurlbert (1969) observed 

that efts migrated to ponds for the first time in the spring and fall. 

Breeding activities and social organization. In south-central New York, breeding 

takes place in late winter or early spring, usually in lakes, ponds, and swamps (Hurlbert, 

1970). Ovulation and egg deposition occur over an extended period (McLaughlin and 

Humphries, 1978). Females overwintering on land can store sperm for at least 10 months 

(Massey, 1990). Spawning underwater, the female deposits eggs singly on leaves of 

submerged plants, hiding and wrapping each in vegetation (Gibbons and Semlitsch, 1991; 

Smith 1956). The time to hatching depends on temperature (DeGraaf and Rudis, 1983). 

Smith (1961) found typical incubation periods to be 14 to 21 days in Illinois, whereas the 

incubation period observed by Behler and King (1979) was 21 to 56 days. 

Growth and metamorphosis. In late summer or early fall, the larvae transform into 

either aquatic juveniles or terrestrial efts (Behler and King, 1979). Harris (1987) showed 

2-430 Eastern Newt 
�

�

that low larval density stimulated neoteny in larvae under experimental conditions. Larval 

growth rates were higher in ponds with low larval densities (Harris, 1987; Morin et al., 

1983). Growth rates for aquatic juveniles are highest in the spring; however, maximum 

seasonal growth for the terrestrial efts occurs between June and September when the 

temperature is optimal for active foraging (Healy, 1973). 

Home range and resources. For adult newts, Bellis (1968) found the mean distance 

between capture and recapture sites to be about 7 m, indicating small home ranges. Harris 

(1981, cited in DeGraaf and Rudis, 1983) did not find any defined home range or any 

territoriality for males. Most efts around a pond in Pennsylvania remained within 1.5 m of 

the shore (Bellis, 1968). Healy (1975) estimated the home range for terrestrial efts in a 

Massachusetts woodland to be 270 m2 and located approximately 800 m from the ponds 

where the adults and larvae were located. 

Population density. Populations of aquatic adults may reach high local densities, 

whereas terrestrial efts exhibit lower population densities. Recorded population densities 

for terrestrial efts range from 34 per hectare (ranging from 20 to 50 efts per hectare) in a 

North Carolina mixed deciduous forest (Shure et al., 1989) to 300 per hectare in a 

Massachusetts woodland (Healy, 1975). Harris et al. (1988) observed a density of 1.4 adult 

newts per m2 (14,000 adult newts per hectare) in a shallow pond in North Carolina in the 

winter, whereas the summer population density was only 0.2 adults per m2 (2,000 adults 

per hectare). 

Population dynamics. Many populations of the eastern newt reach sexual maturity 

when the eft stage returns to the water and changes to the adult form (Healy, 1974). 

However, under certain conditions such as low larval density, most of the larvae present 

have been shown to metamorphose directly into adults or even into sexually mature larvae 

(Harris, 1987). In experimental ponds, densities of 22 larvae per m2 resulted in 

metamorphosis to eft by the majority, while a density of 5.5 larvae per m2 resulted in 

metamorphosis directly to the adult form or sexual maturation without metamorphosis 

(Harris, 1987). Adult density also influences reproduction. Morin et al. (1983) found that 

doubling adult density resulted in a reduction of offspring produced to one-quarter that 

produced by adults at the lower density (i.e., from 36 offspring per female in tanks 

containing 1.1 females per m2 to 9.7 offspring per female in tanks containing 2.2 females 

per m2

). The adult life expectancy noted by Gill (1978b) was 2.1 breeding seasons for 

males and 1.7 breeding seasons for females. Amphibian blood leeches (ectoparasites) are 

likely to be a primary source of mortality for adults; they also prey directly on larvae (Gill, 

1978a). 

Similar species (from general references) 

� The black-spotted newt (Notophthalmus meridionalis) is similar in size (7.5 

to 11.0 cm) to the eastern newt. It has large black spots and is found in 

south Texas in ponds, lagoons, and swamps. There is no eft stage. 

� The striped newt (Notophthalmus perstriatus) is smaller (5.2 to 7.9 cm) than 

the eastern newt and ranges from southern Georgia to central Florida. It is 

found in almost any body of shallow, standing water. 

2-431 Eastern Newt 
�

�

The western newts (Taricha) are found along the Pacific coast. They do not 

undergo the eft stage but rather transform into land-dwelling adults that 

return to the water at breeding time. 

� Other small salamanders are similar but vary by having slimy skin and 

conspicuous costal grooves. They differ in life history, however; in the family 

Plethudontidae, all are lungless and breathe through thin, moist skin. Many 

are completely terrestrial. 

General references 

Behler and King (1979); Conant and Collins (1991); DeGraaf and Rudis (1983); 

Hurlbert (1969); Smith (1961). 

2-432 Eastern Newt 
Eastern Newt (Notophthalmus viridescens) 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean ion (subspecies) Refer

Range or 

Body Weight adult: 

(g) B 2.24 ± 0.71 SD 1.12 - 3.52 New York Gillis 

F prebreed 3.05 ± 0.06 SE Virginia Gill, 1

F postbreed 2.49 ± 0.06 SE 

M prebreed 2.49 ± 0.03 SE 

M postbreed 2.76 ± 0.03 SE 

B spring 1.71 ± 0.43 SD Massachusetts Pitkin

B summer 2.13 ± 0.44 SD 

B winter 1.94 ± 0.33 SD 

B fall 1.63 ± 0.28 SD 

larvae: 

12.8 mm SVL 0.04 ± 0.025 SD South Carolina Taylo

21.9 mm SVL 0.54 ± 0.167 SD 

eft: 

B 1.10 ± 0.40 SD 0.42 - 1.82 New York Gillis 

B 1.45 New Hampshire Burto

B summer 1.23 0.63 - 2.17 Stefa

(viridescens) 

New York 

Locat

2-433 Eastern Newt 
Eastern Newt (Notophthalmus viridescens) 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean ion (subspecies) Refer

Range or 

Length adult: 

(mm SVL) M 35.0 24 - 44 North Carolina (dorsalis) Harris 

F 35.0 20 - 42 

B summer 38.9 33 - 48 New York MacN

juvenile: 

B spring 26.1 ± 0.35 SE 20 - 32 Massachusetts (viridescens) Healy

larvae: 

B spring 12.3 s Illinois BropB fall 19.2 

eft: 

B (mm total) 50.4 ± 0.5 SE North Carolina (dorsalis) Harris 

B spring 20.5 Massachusetts (viridescens) Healy

B summer 32.7 18 - 41 New York MacN

Larval Growth high density: North Carolina Harri

Rate (g/d) -> efts 0.00310 high density: 55,000/ha 

-> adults 0.00421 

-> neonates 0.00536 

low density: 

-> efts 0.00635 low density: 220/ha 

-> adults 0.00685 -> neonates 0.00676 

Metabolic efts at 15�C: New York Stefa

Rate resting 1.47 

(lO 2 /kg-d) active 4.27

Locat

2-434 Eastern Newt 
Eastern Newt (Notophthalmus viridescens) 

Factors 

Age/Sex/ (95% CI of mean) 

Cond./Seas. Mean ion (subspecies) Refer

Range or 

Metabolic Rate basal: 

(kcal/kg-d) A M postbreed 16.2 estim

A F postbreed 16.7 

larvae (12.8 mm) 43.5 estim

eft (71.0 mm) 20.1 estim

Food Ingestion 

Rate (g/g-d) Surface Area A M 17 estim

(cm ) A F 15 2 

Dietary Composition Spring Summer Fall Winter Habitat (measure) Refer

Location (subspecies)/ 

aquatic adults: New Hampshire Burto

Ephemeroptera 7.5 7.5 (viridescens)/small 

Odonata 31.9 1.9 oligotrophic lake 

Lepidoptera 13.7 0.9 

Diptera 5.8 0.3 (% wet weight; stomach 

other insects 9.9 0.6 and gut contents) 

Cladocerans 5.1 84.1 

Amphipoda 5.6 3.1 

Pelycepoda 6.2 1.5 

N. viridescens 

larvae 11.4 0.0 

other 3.2 0.1 

Locat

2-435 Eastern Newt 
Eastern Newt (Notophthalmus viridescens) 

Dietary Composition Spring Summer Fall Winter Habitat (measure) Refer

Location (subspecies)/ 

efts: New York/leaf litter MacN

Basommatophora 5.5 surface in forest 

Stylommatophora 18.3 

Acari 13.8 (% dry weight; stomach 

Collembola 10.4 contents) 

Thysanoptera 3.4 Homoptera 4.7 

Coleoptera adult 2.3 

Coleoptera larvae 3.5 

Lepidoptera larvae 7.9 

Diptera adult 9.7 

Diptera larvae 10.6 

Hymenoptera adult 5.8 

larvae: New Hampshire Burto

Zygoptera (Odonata) 0.8 (viridescens)/small 

Chironomidae 16.2 oligotrophic lake 

(Diptera) 

Cladocera 12.7 (% wet weight; stomach Ostracoda 5.3 and gut contents) 

Hyallela azteca 55.1 

(Amphipoda) 

Sphaerium sp. 9.4 

(Pelycepoda) 

Planorbidae 0.5 

(Gastropoda) 

Rhizopoda (Protozoa) 0.01 

2-436 Eastern Newt 
Eastern Newt (Notophthalmus viridescens) 

Population 

Dynamics 

Age/Sex/ Range or Location (subspecies)/ 

Cond./Seas. Mean (95% CI of mean) Habitat Ref

Home Range eft: 

Size B 0.0087 ha 0.0028 - 0.0153 Massachusetts Hea

adult: 

summer 6.86 m Pennsylvania Bell

(viridescens)/ 

oak/pine forest 

(viridescens)/pond 

Population A B entire lake 130 - 173 New Hampshire Bur

Density A B fringe only 50 - 2,600 (viridescens)/small 

(N/ha) oligotrophic lake 

A winter 50,000 ± 9,000 SE North Carolina (dorsalis)/ Har

A summer 3,000 ± 1,000 SE shallow pond 

eft spring 300 Massachusetts Hea

eft summer 34 20 - 50 North Carolina Shu

larvae spring 21,000 0 - 350,000 South Carolina/pond, Tay

larvae spring 65,000 ± 15,000 SE North Carolina (dorsalis)/ Har

summer 25,000 ± 5,000 SE shallow pond 

fall 10,000 ± 3,000 SE 

(viridescens)/ 

oak/pine forest 

(viridescens)/mixed 

deciduous forest 

wetland 

Clutch Size 200 - 400 NS/NS Beh

(eggs) 

Days to Hatching 14 - 21 Illinois/NS Smi

21 - 56 NS/NS Beh

2-437 Eastern Newt 
Eastern Newt (Notophthalmus viridescens) 

2-438 Eastern Newt 

Population 

Dynamics 

Age/Sex/ Range or Location (subspecies)/ 

Cond./Seas. Mean (95% CI of mean) Habitat Ref

Age at larvae -> eft 2 - 3 mo Illinois Smi

Metamorphosis (louisianensis)/NS 

eft -> adult 1 - 3 yrs Gib

6 mo Hea

Massachusetts 

(viridescens)/inland 

ponds 

South Carolina/ponds 199

Age at Sexual 3 - 7 years eft 5 - 6 yrs 4 - 8 Massachusetts HeaMaturity (viridescens)/inland 

no eft stage 2 yrs coastal ponds 

ponds 

Annual A F 54.1 - 59.5 Virginia/mountain ponds Gill, 

Mortality Rates A M 45.8 - 53.1 

(%) Longevity A F 1.7 Virginia/mountain ponds Gill, 

(breeding A M 2.1 

seasons) 

Seasonal 

Activity Begin Peak End Location er

Mating/Laying February - April - May South Carolina Gibb

March 1991 

April June North Carolina Harri

Hatching June Virginia Gill, 1

late April North Carolina Harri

spring NS Behle

Ref
�

Eastern Newt (Notophthalmus viridescens) 

Seasonal 

Activity Begin Peak End Location er

Metamorphosis June September South Carolina Gibb

to eft 1991 

mid-August late November Virginia Gill, 1

mid-July August - Sept. early November New York Hurlb

Fall Migration August - Sept. November Virginia Gill, 1

(of adults to 

hibernaculae) 

Spring Migration late March late April Virginia Mass

(of adults to 

breeding ponds) 

Ref

1 "Neonates" refers to newts that become sexually mature in the larval form (i.e., neoteny). 

2-439 Eastern Newt 

2 Estimated assuming temperature of 20�C using Equation 3-50 (Robinson et al., 1983) and postbreeding body weight

Taylor et al. (1988); and (c) Gillis and Breuer (1984). The values for the larvae should be used with caution because 

than any used to develop the allometric equations. 

3 See Chapters 3 and 4 for methods of estimating food ingestion rates from metabolic rate and diet. 

4 Estimated using Equation 3-26 (Whitford and Hutchinson, 1967) and postbreeding body weights from Gill, 1979. 

5 Mean distance between capture and recapture sites, suggesting small home range size. 
References (including Appendix) 

Behler, J. L.; King, F. W. (1979) The Audubon Society field guide to North American reptiles 

and amphibians. New York, NY: Alfred A. Knopf, Inc. 

Bellis, E. D. (1968) Summer movement of red-spotted newts in a small pond. J. Herpetol. 1: 

86-91. 

Bennett, S. M. (1970) Homing, density and population dynamics in the adult newt, 

Notophthalmus viridescens Rafinesque [Ph.D. dissertation]. Hanover, NH: 

Dartmouth College. 

Bishop, S. C. (1941) The salamanders of New York. N. Y. State Mus. Bull. 324; 365 pp. 

Brophy, T. E. (1980) Food habits of sympatric larval Ambystoma tigrinum and 

Notopthalmus viridescens. J. Herpetol. 14: 1-6. 

Burton, T. M. (1976) An analysis of the feeding ecology of the salamanders (Amphibia, 

Urodela) of the Hubbard Brook Experimental Forest, New Hampshire. J. Herpetol. 

10: 187-204. 

Burton, T. M. (1977) Population estimates, feeding habits and nutrient and energy 

relationships of Notophthalmus v. viridescens, in Mirror Lake, New Hampshire. 

Copeia 1977: 139-143. 

Conant, R.; Collins, J. T. (1991) A field guide to reptiles and amphibians: eastern/central 

North America. Boston, MA: Houghton Mifflin Co. 

DeGraaf, R. M.; Rudis, D. D. (1983) Amphibians and reptiles of New England. Amherst, MA: 

University of Massachusetts Press. 

Gage, S. H. (1891) The life history of the vermillion-spotted newt. Am. Nat. 25: 1084-1103. 

Gibbons, J. W.; Semlitsch, R. D. (1991) Guide to the reptiles and amphibians of the 

Savannah River Site. Athens, GA: University of Georgia Press. 

Gill, D. E. (1978a) The metapopulation ecology of the red-spotted newt, Notophthalmus 

viridescens (Rafinesque). Ecol. Monogr. 48: 145-166. 

Gill, D. E. (1978b) Effective population size and interdemic migration rates in a 

metapopulation of the red-spotted newt, Notophthalmus viridescens. Evolution 32: 

839-849. 

Gill, D. E. (1979) Density dependence and homing behavior in adult red-spotted newts 

Notophthalmus viridescens (Rafinesque). Ecology 60: 800-813. 

2-440 Eastern Newt 
Gillis, J. E.; Breuer, W. J. (1984) A comparison of rates of evaporative water loss and 

tolerance to dehydration in the red-eft and newt of Notophthalmus viridescens. J. 

Herpetol. 18: 81-82. 

Harris, R. N. (1981) Intrapond homing behavior in Notophthalmus viridescens. J. Herpetol. 

15: 355-356. 

Harris, R. N. (1987) Density-dependent paedomorphosis in the salamander Notophthalmus 

viridescens dorsalis. Ecology 68: 705-712. 

Harris, R. N. (1989) Ontogenetic changes in size and shape of the facultatively 

paedomorphic salamander Notophthalmus viridescens dorsalis. Copeia 1989: 35-42. 

Harris, R. N.; Alford, R. A.; Wilbur, H. M. (1988) Density and phenology of Notophthalmus 

viridescens dorsalis in a natural pond. Herpetologica 44: 234-242. 

Healy, W. R. (1973) Life history variation and the growth of the juvenile Notophthalmus 

viridescens from Massachusetts. Copeia 1973: 641-647. 

Healy, W. R. (1974) Population consequences of alternative life histories in Notophthalmus 

v. viridescens. Copeia 1974: 221-229. 

Healy, W. R. (1975) Terrestrial activity and home range in efts of Notophthalmus 

viridescens. Am. Midl. Nat. 93: 131-138. 

Healy, W. R. (1981) Field test of an HSI model for the red-spotted newt (Notophthalmus 

viridescens) for the Habitat Evaluation Procedures Group [unpublished material]. 

Fort Collins, CO: U.S. Fish Wildl. Serv.; 21 pp. 

Hurlbert, S. H. (1969) The breeding migrations and interhabitat wandering of the 

vermilion-spotted newt, Notophthalmus viridescens (Rafinesque). Ecol. Monogr. 39: 

465-488. 

Hurlbert, S. H. (1970) The post-larval migration of the red-spotted newt, Notophthalmus 

viridescens (Rafinesque). Copeia 1970: 515-528. 

Logier, E. B. (1952) The frogs, toads and salamanders of eastern Canada. Toronto, Canada: 

University of Toronto Press. 

MacNamara, M. C. (1977) Food habits of terrestrial adult migrants and immature red efts of 

the red-spotted newt, Notophthalmus viridescens. Herpetologica 33: 127-132. 

Massey, A. (1990) Notes on the reproductive ecology of red-spotted newts (Notophthalmus 

viridescens). J. Herpetol. 24: 106-107. 

McLaughlin, E. W.; Humphries, A. A., Jr. (1978) The jelly envelopes and fertilization of eggs 

of the newt, Notophthalmus viridescens. J. Morphol. 158: 73-90. 

2-441 Eastern Newt 
Morin, P. J. (1986) Interactions between intraspecific competition and predation in an 

amphibian predator-prey system. Ecology 67: 713-720. 

Morin, P. J.; Wilbur, H. M.; Harris, R. N. (1983) Salamander predation and the structure of 

experimental communities: responses of Notophthalmus and Microcrustacea. 

Ecology 64: 1430-1436. 

Pitkin, R. B. (1983) Annual cycle of body size and blood parameters of the aquatic adult 

red-spotted newt, Notophthalmus viridescens. J. Exp. Zool. 226: 372-377. 

Ries, K. M.; Bellis, E. D. (1966) Spring food habits of the red-spotted newt in Pennsylvania. 

Herpetologica 22: 152-155. 

Robinson, R. W.; Peters, R. H.; Zimmermann, J. (1983) The effects of body size and 

temperature on metabolic rate of organisms. Can. J. Zool. 61: 281-288. 

Shure, D. J.; Wilson, L. A.; Hochwender, C. (1989) Predation on aposomatic efts of 

Notophthalmus viridescens. J. Herpetol. 23: 437-439. 

Smith, H. M. (1956) Handbook of amphibians and reptiles of Kansas. Univ. Kansas Mus. 

Nat. Hist. Misc. Publ. 9; 356 pp. 

Smith, P. W. (1961) The amphibians and reptiles of Illinois. Ill. Nat. Hist. Surv. Bull. 28; pp. 

118-120. 

Sousa, P. J. (1985) Habitat suitability index models: Red-spotted newt. U.S. Fish Wildl. 

Serv. Biol. Rep. 82(10.111); 18 pp. 

Stefanski, M.; Gatten, R. E.; Pough, F. H. (1989) Activity metabolism of salamanders: 

tolerance to dehydration. J. Herpetol. 23: 45-50. 

Taylor, B. E.; Estes, R. A.; Pechmann, J. H.; et al. (1988) Trophic relations in a temporary 

pond: larval salamanders and their microinvertebrate prey. Can. J. Zool. 66: 

2191-2198. 

Whitford, W. G.; Hutchinson, V. H. (1967) Body size and metabolic rate in salamanders. 

Physiol. Zool. 40: 127-133. 

2-442 Eastern Newt 
2.3.7. Green Frog (true frog family) 

Order Anura, Family Ranidae. These are typical frogs with adults being truly 

amphibious, living at the edge of water bodies and entering the water to catch prey, flee 

danger, and spawn (Behler and King, 1979). This profile covers medium-sized ranids. The 

next profile (Section 2.3.8) covers large ranids. 

Selected species 

The green frog (Rana clamitans) is usually found near shallow fresh water 

throughout much of eastern North America. Two subspecies are recognized: R. c. 

clamitans (the bronze frog; ranges from the Carolinas to northern Florida, west to eastern 

Texas, and north along the Mississippi Valley to the mouth of the Ohio River) and R. c. 

melanota (the green frog; ranges from southeastern Canada to North Carolina, west to 

Minnesota and Oklahoma but rare in much of Illinois and Indiana, introduced into British 

Columbia, Washington, and Utah) (Conant and Collins, 1991). 

Body size. The green frog is a medium-sized ranid usually between 5.7 and 8.9 cm 

snout-to-vent length (SVL) (Conant and Collins, 1991; Martof et al., 1980). Its growing 

period is primarily confined to the period between mid May and mid September (Martof, 

1956b). Females are usually larger than males (Smith, 1961). Adults typically weigh 

between 30 and 70 g (Wells, 1978). Hutchinson et al. (1968) developed an allometric 

equation relating green frog surface area (SA in cm) to body weight (Wt in grams): 

SA = 0.997 Wt

0.712. 

This equation also is presented in Chapter 3 as Equation 3-25. 

Habitat. Adult green frogs live at the margins of permanent or semipermanent 

shallow water, springs, swamps, streams, ponds, and lakes (Wells, 1977). Martof (1953b) 

found green frogs primarily to inhabitat the banks of streams. They also can be found 

among rotting debris of fallen trees (Behler and King, 1979; Conant and Collins, 1991). 

Juveniles prefer shallower aquatic habitats with denser vegetation than those preferred by 

adults (Martof, 1953b). McAlpine and Dilworth (1989) observed that green frogs inhabited 

aquatic habitats about two-thirds of the time and terrestrial habitats the remaining time. 

Similarly, Martof (1953b) found that the green frog relies on terrestrial habitats for feeding 

and aquatic habitats for refuge from desiccation, temperature extremes, and enemies. 

Ponds used by green frogs are usually more permanent than those used by other anuran 

species (Pough and Kamel, 1984). 

Food habits. Adult R. clamitans are terrestrial feeders among shoreline vegetation. 

They consume insects, worms, small fish, crayfish, other crustaceans, newts, spiders, 

small frogs, and molluscs. Stewart and Sandison (1973) found that terrestrial beetles often 

are their most important food item but noted that any locally abundant insect along the 

shoreline may be consumed in large numbers. There is a pronounced reduction in food 

consumption during the breeding period for both males and females (Mele, 1980). During 

the breeding season, males spend most of their energy defending breeding territories, and 

2-443 Green Frog 
�

�

females expend their energy producing eggs (Wells, 1977). Fat reserves acquired during 

the prebreeding period compensate for reduced food intake during the breeding period 

(Mele, 1980). Jenssen and Klimstra (1966) found that green frogs consume most of their 

food in the spring and eat little during the winter. Food eaten in the spring, summer, and 

fall consists mostly of terrestrial prey, whereas winter food is composed mostly of aquatic 

prey (Jenssen and Klimstra, 1966). Juveniles (sexually immature frogs) eat about half the 

volume of food as do adults over the course of a year (Jenssen and Klimstra, 1966). 

Tadpoles are herbivorous (DeGraaf and Rudis, 1983). Green frogs eat their cast skins 

following molting; the casting of skin is frequent during midsummer (Hamilton, 1948). 

Temperature regulation and daily activities. Martof (1953b) found that the green 

frog's activity period varies by frog size, with larger frogs being primarily nocturnal, small 

frogs being diurnal, and middle-sized frogs (5 to 7 cm SVL) being equally active during day 

and night. 

Hibernation. Adult green frogs overwinter by hibernating underground or 

underwater from fall to spring (Ryan, 1953). Martof (1956a) observed frogs hibernating in 

mud and debris at the bottom of streams approximately 1 m deep. Jenssen and Klimstra 

(1966) noted that adults usually hibernate in restricted chambers within rock piles or 

beneath plant debris, while juveniles are more often found in locations with access to 

passing prey. The frogs begin emerging when the mean daily temperature is about 4.4�C 

and the maximum temperature is about 15.6�C for 3 to 4 days (Martof, 1953b). Juvenile 

frogs enter and exit hibernation after adult frogs (Martof, 1956a). 

Breeding activities and social organization. Green frogs breed from spring through 

the summer, spawning at night (Smith, 1961; Wells, 1976). Female green frogs stay in 

nonbreeding habitat until it is time to spawn (Martof, 1956a). In preparation for breeding, 

males establish territories near shore that serve as areas for sexual display and as 

defended oviposition sites (Wells, 1977). Males establish calling sites within their 

territories where they attempt to attract females (Wells, 1977). Females visit male 

territories to mate and lay their egg masses. The masses are contained in films of jelly and 

are deposited in emergent, floating, or submerged vegetation; they hatch in about 3 to 6 

days (Behler and King, 1979; Martof, 1956a; Ryan, 1953). Adults are solitary during nonbreeding periods (Smith, 1956). 

Tadpole and metamorphosis. In the southern part of their range, green frog 

tadpoles metamorphose into frogs in the same season in which they hatched, while in the 

northern part, 1 or 2 years pass before metamorphosis (Martof, 1956b). Tadpoles that 

hatch from egg masses laid in the spring usually metamorphose that fall, while those 

hatching from summer-laid eggs typically overwinter as larvae and metamorphose the 

following spring (Pough and Kamel, 1984). Ryan (1953) found that most tadpoles are 2.6 to 

3.8 cm SVL at the time of transformation. Those that transform in late June or early July 

grow rapidly, adding 1.4 to 2.0 cm SVL in the first 2 months and 0.4 to 0.7 cm SVL more 

before hibernation. Tadpoles that transform at approximately 3.1 cm SVL may reach 

between 5.0 and 5.8 cm SVL before hibernation (Ryan, 1953). Newly transformed frogs 

often move from lakes and ponds where they were tadpoles to shallow stream banks, 

usually during periods of rain (Martof, 1953b). 

2-444 Green Frog 
�

�

�

�

Home range and resources. The species' home range includes its foraging and 

refuge areas in and around aquatic environments. During the breeding period, the male's 

home range also includes its breeding territory (Wells, 1976). Martof (1953b) found that 

roughly 80 percent of adult frogs captured in the spring and again in the fall occupied the 

same home ranges. 

Population density. During the breeding season, green frog densities at breeding 

ponds can exceed several hundred individuals per hectare (Wells, 1978). Adult male frogs 

space their breeding territories about 2 to 3 m apart (Martof, 1953a). 

Population dynamics. Sexual maturity is attained in 1 or 2 years after 

metamorphosis; individuals may reach maturity at the end of the first year but not attempt 

to breed until the next year (Martof, 1956a,b). Most females lay one clutch per year, 

although some may lay two clutches, about 3 to 4 weeks apart (Wells, 1976). In natural 

populations, green frogs can live to approximately 5 years of age (Martof, 1956b). 

Similar species (from general references) 

� The river frog (Rana heckscheri) is slightly larger than the green frog (8.0 to 

12.0 cm SVL) and is found in swamps from southeast North Carolina to 

central Florida and southern Mississippi. 

� The leopard and pickerel frogs (Rana pipiens and its relatives, and Rana 

palustris) are medium sized and strongly spotted. There are four leopard 

frogs whose ranges are mostly exclusive from each other, but overlap with 

the green frog. The pickerel frog has a similar range with gaps in the upper 

midwest and the southeast. 

� The mink frog (Rana septentrionalis) is only slightly smaller (4.0 to 7.0 cm) 

and is found on the borders of ponds and lakes, especially near waterlilies. 

It ranges from Minnesota to New York, north to Labrador. 

� The carpenter frog (Rana virgatipes) is about the same size as the green frog 

(4.1 to 6.7 cm) and is closely associated with sphagnum bogs and 

grasslands. It has a coastal plain range from New Jersey to Georgia and 

Florida. 

The bullfrog and pig frog are much larger ranid species and are covered in the next profile 

(Section 2.3.8). 

General references 

Behler and King (1979); Conant and Collins (1991); DeGraaf and Rudis (1983); Martof 

(1953a, b, 1956a, b); Smith (1956, 1961). 

2-445 Green Frog 
Green Frog (Rana clamitans) 

Factors 

Age/Sex/ Range or 

Cond./Seas. Mean (95% CI of mean) Location (subspecies) Referenc

Body Weight B 49.1 ± 20.0 SD 25.5 - 103.5 New Brunswick, Canada McAlpine 

(g) 

A breeding 44.0 ± 10.0 SD 27.0 - 66.0 New York (melanota) Wells, 19

at 3 New York Pough & 

metamorphosis 

Length A 54 - 102 NS Behler a

(mm SVL) A M 79.8 ± 8.5 SD 103 maximum s Michigan Martof, 1

A 80.3 ± 8.9 SD 105 maximum 

J 32.6 28.4 - 36.3 s Michigan Martof, 1

Metabolic basal: 

Rate A 8.08 estimate

(kcal/kg-d) at 15.8 estimate

metamorphosis 

Food Ingestion 

Rate (g/g-d) 

Surface Area A 17 estimate

(cm ) at 2 estimate

2 

metamorphosis 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location (subspecies)/Habitat 

adults: New York/lake Stewart & 

plant material 10.8 

Araneae 12.1 (% total volume; 

Coleoptera 32.8 stomach contents) 

Hemiptera 12.9 

Hymenoptera 14.4 Diptera 6.8 

Ephemeroptera 5.6 Mollusca 5.4 Lepidoptera 2.5 

B 

M

F 

B 

2-446 Green Frog 
Green Frog (Rana clamitans) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location (subspecies)/Habitat 

adults: s Illinois/swamp, stream Jenssen 

mineral - - - 2.6 

plant 5.7 8.3 4.2 0.5 (% wet volume; stomach 

Pulmonata 15.7 18.3 6.4 11.0 contents) 

Oligochaeta 2.1 0.8 2.3 6.4 

Amphipoda 1.2 0.1 - 4.6 

Isopoda 5.6 1.4 - 4.6 

Decapoda - - 4.1 -

Julioforma 7.5 0.3 1.7 -

Araneida 2.8 3.4 6.6 7.4 

Odonata 1.6 12.4 5.9 -

Orthoptera 0.9 3.0 1.5 -

Hemiptera 1.0 7.0 6.1 2.2 

Coleoptera 9.6 19.6 15.9 9.1 

Lepidoptera 25.4 7.0 25.1 -

Diptera 6.0 5.2 4.5 10.3 Hymenoptera 9.9 6.0 13.5 -

Salientia - - 3.9 -

Population 

Dynamics 

Age/Sex/ Range or Location (subspecies)/ 

Cond./Seas. Mean (95% CI of mean) Habitat Referen

Home Range A B 0.0065 ± 0.0036 SD 0.0020 - 0.020 ha s Michigan (melanota)/ Martof, 

Size nonbreeding ha shallow water 

A M breeding 4.0 - 6.0 open nearshore areas A M breeding 1.0 - 1.5 densely vegetated 

meters shoreline: New York (melanota)/ Wells, 1

meters shoreline: New York (melanota)/ Wells, 1

of ponds 

nearshore areas of 

ponds 

Population A M 476 New York (melanota)/ Wells, 1

Density A F 567 artificial pond (N/ha) 

2-447 Green Frog 
Green Frog (Rana clamitans) 

Population 

Dynamics 

Age/Sex/ Range or Location (subspecies)/ 

Cond./Seas. Mean (95% CI of mean) Habitat Referen

Clutch Size 4,100 3,800 - 4,300 s Michigan (melanota)/ Martof, 

1,000 - 7,000 New York (melanota)/ Wells, 1

3,500 - 4,000 New York (melanota)/ Wright, 

pond 

shallow ponds shallow water 

Clutches/Year 1 - 2 New York (melanota)/ Wells, 1

shallow ponds 

Days 3 - 6 Connecticut (melanota)/ Babbit, 

Incubation (d) shallow water 

3 - 5 New York/ponds, pools Ryan, 1

Age at 1 - 2 yrs New England DeGraa

Metamorphosi (melanota)/ 

s shallow water 

early eggs 3 mo Virginia, Carolinas/ Martof e

late eggs 10 - 12 mo shallow ponds 

early eggs 2.5 - 3 mo s Michigan (melanota)/ Martof, 

late eggs 11 - 12 mo shallow ponds 

Age at Sexual A M 1 - 2 s Michigan (melanota)/ Martof, 

Maturity (yr) A F 1 - 2 shallow ponds 

B New ork melanota)/ Y W ( ells, 1

pond 

1 

2-448 Green Frog 
�

�

Green Frog (Rana clamitans) 

Seasonal 

Activity Begin Peak End Location (subspecies) Referen

Mating/Laying May early June mid-August s Michigan (melanota) Martof, 

May September Illinois (melanota) Smith, 1

early June mid-August New York Wells, 1

Metamorphosis 

eggs laid early early August late September s Michigan (melanota) Martof, 

eggs laid late early June mid-July s Michigan (melanota) Martof, 

August, September New York Pough 

next spring New York Pough 

Hibernation Oct. - Nov. March - April s Michigan (melanota) Martof, 

2-449 

Oct. late March New York Ryan, 1

Green Frog 

1 Weight at metamorphosis can vary by two to four times between the smallest and largest individuals. 2 Estimated assuming temperature of 20�C using Equation 3-50 (Robinson et al., 1983) and body weights from McAlp

3 Estimated assuming temperature of 20�C using Equation 3-50 (Robinson et al., 1983) and body weights from Pough 

4 See Chapters 3 and 4 for methods of estimating food ingestion rates from metabolic rate and diet.

5 Estimated using Equation 3-25 (Hutchinson et al., 1968) and body weights from McAlpine and Dilworth (1989).

6 Estimated using Equation 3-25 (Hutchinson et al., 1968) and body weights from Pough and Kamel (1984).

7 Season not specified.8 Daily activity range of nonbreeding frogs.

9 Frogs were initially hand-captured and placed in pond; the numbers given are for those frogs that stayed.

10 Cited in DeGraaf and Rudis (1983).

11 Eggs laid before June.

12 Metamorphosed in the same year eggs were laid.

13 Metamorphosed the year following the season the eggs were laid.
References (including Appendix) 

Babbitt, L. H. (1937) The amphibia of Connecticut. Hartford, CT: State Geol. and Nat. Hist. 

Surv.; Bull. No. 57. 9-50 

Behler, J. L.; King, F. W. (1979) The Audubon Society field guide to North American reptiles 

and amphibians. New York: Alfred A. Knopf, Inc. 

Bush, F. M. (1959) Foods of some Kentucky herptiles. Herpetologica 15: 73-77. 

Conant, R.; Collins, J. T. (1991) A field guide to reptiles and amphibians. Boston, MA: 

Houghton Mifflin Co. 

DeGraaf, R. M.; Rudis, D.D. (1983) Green frog. Amphibians and reptiles of New England. 

Amherst, MA: University of Massachusetts Press. 

Hamilton, W. J., Jr. (1948) The food and feeding behavior of the green frog, Rana clamitans 

(Latreille), in New York state. Copeia 1948: 203-207. 

Hutchinson, V. H.; Whitford, W. G.; Kohl, M. (1968) Relation of body size and surface area 

to gas exchange in anurans. Physiol. Zool. 41: 65-85. 

Jenssen, T. A.; Klimstra, W. D. (1966) Food habits of the green frog, Rana clamitans, in 

southern Illinois. Amer. Midl. Nat. 76: 169-182. 

Martof, B. S. (1953a) Territoriality in the green frog, Rana clamitans. Ecology 34: 165-174. 

Martof, B. S. (1953b) Home range and movements of the green frog, Rana clamitans. 

Ecology 34: 529-543. 

Martof, B. S. (1956a) Factors influencing size and composition of populations of Rana 

clamitans. Am. Midl. Nat. 56: 224-245. 

Martof, B. S. (1956b) Growth and development of the green frog, Rana clamitans, under 

natural conditions. Am. Midl. Nat. 55: 101-117. 

Martof, B. S.; Palmer, W. M.; Bailey, J. R.; et al. (1980). Amphibians and reptiles of the 

Carolinas and Virginia. Chapel Hill, NC: University of North Carolina Press. 

McAlpine, D. F.; Dilworth, T. G. (1989) Microhabitat and prey size among three species of 

Rana (Anura: Ranidae) sympatric in eastern Canada. Can. J. Zool. 67: 2241-2252. 

Mele, J. A. (1980) The role of lipids in storage and utilization of energy for reproduction and 

maintenance in the green frog, Rana clamitans [Ph.D. dissertation]. New Brunswick, 

NJ: Rutgers University. 

2-450 Green Frog 
Pope, C. H. (1947) Amphibians and reptiles of the Chicago area. Chicago, IL: Chicago Nat. 

Hist. Mus. Press. 

Pough, F. H.; Kamel, S. (1984) Post-metamorphic physiological change in relation to anuran 

life histories. Oecologia 65: 138-144. 

Robinson, F. W.; Peters, R. H.; Zimmermann, J. (1983) The effects of body size and 

temperature on metabolic rate of organisms. Can. J. Zool. 61: 281-288. 

Ryan, R. A. (1953) Growth rates of some ranids under natural conditions. Copeia 1953:73-

80. 

Smith, H. M. (1956) Handbook of amphibians and reptiles of Kansas. Univ. Kansas Mus. 

Nat. Hist. Misc. Publ. 9. 

Smith, P. W. (1961) The amphibians and reptiles of Illinois. Ill. Nat. Hist. Surv. Bull. 28. 

Stewart, M. M.; Sandison, P. (1973) Comparative food habits of sympatric mink frogs, 

bullfrogs, and green frogs. J. Herpetol. 6: 241-244. 

Wells, K. D. (1976) Multiple egg clutches in the green frog (Rana clamitans). Herpetologica 

32: 85-87. 

Wells, K. D. (1977) Territoriality and male mating success in the green frog (Rana 

clamitans). Ecology 58: 750-762. 

Wells, K. D. (1978) Territoriality in the green frog (Rana clamitans): vocalizations and 

agonistic behaviour. Anim. Behav. 26: 1051-1063. 

Wright, A. H. (1914) North American anura: life histories of the anurans of Ithaca, New York. 

Washington, DC: Carnegie Institute; Publ. No. 197. 

2-451 Green Frog 
2.3.8. Bullfrog (true frog family) 

Order Anura, Family Ranidae. These are typical frogs with adults being truly 

amphibious. They tend to live at the edge of water bodies and enter the water to catch 

prey, flee danger, and spawn (Behler and King, 1979). This profile covers large ranids. 

Medium-sized ranids are covered in the previous profile (Section 2.3.7). 

Selected species 

The bullfrog's (Rana catesbeiana) natural range includes the eastern and central 

United States and southeastern Canada; however, it has been introduced in many areas in 

the western United States and other parts of North America. It is continuing to expand its 

range, apparently at the expense of several native species in many locations (Bury and 

Whelan, 1984). There are no subspecies for the bullfrog. 

Body size. The bullfrog is the largest North American ranid. Adults usually range 

between 9 and 15 cm in length from snout-to-vent length (SVL) and exceptional individuals 

can reach one half kilogram or more in weight (Conant and Collins, 1991; Durham and 

Bennett, 1963). Males are usually smaller than females (Smith, 1961). Frogs exhibit 

indeterminate growth, and bullfrogs continue to increase in size for at least 6 years after 

metamorphosis (Durham and Bennett, 1963; Howard, 1981a). Hutchinson et al. (1968) 

developed an allometric equation relating bullfrog surface area (SA in cm) to body weight 

(Wt in grams): 

SA = 0.953 Wt

0.725. 

This equation also is presented in Chapter 3 as Equation 3-24. 

Habitat. Adult bullfrogs live at the edges of ponds, lakes, and slow-moving streams 

large enough to avoid crowding and with sufficient vegetation to provide easily accessible 

cover (Behler and King, 1979). Small streams are used when better habitat is lacking 

(Conant and Collins, 1991). Bullfrogs require permanent bodies of water, because the 

tadpoles generally require 1 or more years to develop prior to metamorphosis (Howard, 

1981b). Small frogs favor areas of very shallow water where short grasses or other 

vegetation or debris offer cover (Durham and Bennett, 1963). Larger bullfrogs seem to 

avoid such areas (Durham and Bennett, 1963). Tadpoles tend to congregate around green 

plants (Jaeger and Hailman, 1976, cited in Bury and Whelan, 1984). 

Food habits. Adult R. catesbeiana are indiscriminate and aggressive predators, 

feeding at the edge of the water and among water weeds on any available small animals, 

including insects, crayfish, other frogs and tadpoles, minnows, snails, young turtles, and 

occasionally small birds, small mammals, and young snakes (Behler and King, 1979; 

DeGraaf and Rudis, 1983; Korschgen and Baskett, 1963). Bullfrogs often focus on locally 

abundant foods (e.g., cicadas, meadow voles) (Korschgen and Baskett, 1963). 

Crustaceans and insects probably make up the bulk of the diet in most areas (Carpenter 

and Morrison, 1973; Fulk and Whitaker, 1968; Smith, 1961; Tyler and Hoestenbach, 1979). 

Bullfrog tadpoles consume primarily aquatic plant material and some invertebrates, 

2-453 Bullfrog 
�

�

�

�

�

�

� �

�

�

�

but also scavenge dead fish and eat live or dead tadpoles and eggs (Bury and Whelan, 

1984; Ehrlich, 1979). 

Temperature regulation and daily activities. Bullfrogs forage by day (Behler and 

King, 1979). They thermoregulate behaviorally by positioning themselves relative to the 

sun and by entering or leaving the water (Lillywhite, 1970). In one study, body 

temperatures measured in bullfrogs during their normal daily activities averaged 30�C and 

ranged from 26 to 33�C (Lillywhite, 1970). At night, their body temperatures were found to 

range between 14.4 and 24.9�C (Lillywhite, 1970). Tadpoles also select relatively warm 

areas, 24 to 30�C (Bury and Whelan, 1984). Despite this narrow range of temperatures in 

which bullfrogs normally maintain themselves, they are not immobilized by moderately 

lower temperatures (Lillywhite, 1970). The metabolic rate of bullfrogs increases with 

increasing body temperature. Between 15 and 25�C, the Q10 for oxygen consumption is 

1.87; between 25 and 33�C, the Q10 is 2.41 (Burggren et al., 1983). 

Hibernation. Most bullfrogs hibernate in mud and leaves under water beginning in 

the fall, but some bullfrogs in the southern states may be active year round (Bury and 

Whelan, 1984). They emerge sometime in the spring, usually when air temperatures are 

about 19 to 24�C and water temperatures are at least 13 to 14�C (Wright, 1914; Willis et al., 

1956). Bullfrogs emerge from hibernation later than other ranid species (Ryan, 1953). 

Breeding activities and social organization. Bullfrogs spawn at night close to 

shorelines in areas sheltered by shrubs (Raney, 1940, cited in DeGraaf and Rudis, 1983). 

The timing and duration of the breeding season varies depending on the location. In the 

southern states, the breeding season extends from spring to fall, whereas in the northern 

states, it is restricted to late spring and summer (Behler and King, 1979). Males tend to be 

territorial during the breeding season, defending their calling posts and oviposition sites 

(i.e., submerged vegetation near shore) (Howard, 1978b; Ryan, 1980). Female visits to the 

pond tend to be brief and sporadic (Emlen, 1976). Some males mate with several females 

whereas others, usually younger and smaller males, may not breed at all in a given year 

(DeGraaf and Rudis, 1983). Females attach their eggs, contained in floating films of jelly, to 

submerged vegetation (Behler and King, 1979). Adults are otherwise rather solitary 

occupying their own part of a stream or pond (Smith, 1961). 

Tadpole and metamorphosis. Eggs hatch in 3 to 5 days (Clarkson and DeVos, 1986; 

Smith, 1956). Temperatures above 32�C have been shown to cause abnormalities in 

tadpoles and above 35.9�C to kill embryos (Howard, 1978a). Tadpole growth rates increase 

with increasing oxygen levels, food availability, and water temperature (Bury and Whelan, 

1984). Tadpole gill ventilation at 20�C can generate a branchial water flow of almost 0.3 

ml/g-min (Burggren and West, 1982). Metamorphosis from a tadpole to a frog can occur as 

early as 4 to 6 months in the southern parts of its range; however, most tadpoles 

metamorphose from 1 to 3 years after hatching, depending on latitude and temperature 

(DeGraaf and Rudis, 1983; Martof et al., 1980). 

Home range and resources. The species' home range includes its foraging areas 

and refuges in and around aquatic environments. Home range size decreases with 

increasing bullfrog density, and males tend to use larger home ranges than females (Currie 

and Bellis, 1969). Bullfrogs tend to stay in the same pools throughout the summer months 

2-454 Bullfrog 
�

if the water level is stable (Raney, 1940, cited in DeGraaf and Rudis, 1983). During the 

breeding season, adult males establish territories that they defend against conspecific 

males (Emlen, 1968). During the non-breeding season, Currie and Bellis (1969) found no 

evidence of territorial defense. Males often do not return to the same pond the following 

spring (Durham and Bennett, 1963). 

Population density. During the breeding season, each breeding male may defend a 

few meters of shoreline (Currie and Bellis, 1969; Emlen, 1968). The densities of females 

and non-breeding males vary with time of day and season and are difficult to estimate. 

Tadpoles can be present locally in extremely high densities (Cecil and Just, 1979). 

Population dynamics. Sexual maturity is attained in about 1 to 3 years after 

metamorphosis, depending on latitude (Howard, 1978a; Raney and Ingram, 1941, cited in 

Bury and Whelan, 1984). Only females that are at least 2 years past metamorphosis mate 

during the early breeding season; males and females 1 year past metamorphosis may 

breed during the later breeding periods (Howard, 1978a, 1981b). Also, some older females 

have been observed to mate and to lay a second clutch during the later breeding period 

(Howard, 1978a). Willis et al. (1956) estimated the minimum breeding length for females in 

Missouri to be 123 to 125 mm SVL. Mortality of tadpoles is high (Cecil and Just, 1979), and 

adult frogs are unlikely to live beyond 5 to 8 years postmetamorphosis (Howard, 1978b). In 

some areas, snapping turtles may be responsible for a large component of adult bullfrog 

mortality (Howard, 1981a). 

Similar species (from general references) 

� The pig frog (Rana grylio) is smaller than the bullfrog (8 to 14 cm) and is 

found in south South Carolina to south Florida and south Texas. 

The remaining ranid species are more similar in size to the green (or bronze) frog. See 

Section 2.3.7 for a description of these frogs. 

General references 

Behler and King (1979); Bury and Whelan (1984); Conant and Collins (1991); DeGraaf 

and Rudis (1983); Smith (1961). 

2-455 Bullfrog 
Bullfrog (Rana catesbeiana) 

2-456 Bullfrog 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referen

Body Weight B B 142.8 ± 77.4 SD 9.5 - 274.0 New Brunswick, Canada McAlpi

(g) 

A B 249 central Arkansas McKam

young tadpole 2.0 ± 1.1 SD Kentucky Viparin

1-yr tadpole 35.7 ± 5.2 SD 

postemergence: 1 month 18 13 - 42 Louisiana/lab Modzel

2 months 30 19 - 52 3 months 42 27 - 77 4 months 56 41 - 101 at metamorph. 9 (84 mm) east central Illinois Durham 

1 yr B 91 (240 mm) 2 yr B 210 (307 mm) 

3 yr B 240 (320 mm) 4 yr B 260 (335 mm) 5 yr B 290 (348 mm) 6 yr B 360 (356 mm) 

total length: 

Metabolic Rate tadpole, 25�C 2.6 ± 0.2 SE NS/lab Burggr

(lO /kg-d) 2 

adult resting, 

5�C 1.0 0.31 - 2.3 NS/NS Hutchin

Metabolic Rate basal: estimat

(kcal/kg-d) 2 mo (30 g) 9.1 

1 yr (91 g) 7.0 

B B (143 g) 6.3 

A B (249 g) 5.5 
Bullfrog (Rana catesbeiana) 

Factors 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location Referen

Food Ingestion (13 - 42 g) 0.071 Louisiana (24 - 27�C) Modzel

Rate (g/g-d) (18 - 52 g) 0.059 

(28 - 77 g) 0.040 

(40 - 100 g) 0.033 

Surface Area 2 mo (30 g) 11 estimat

(cm ) 1 yr (91 g) 25 2 

B B (143 g) 35 A B (249 g) 52 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

adults: Kentucky/NS Bush, 19

Decapoda-Astacidae 47.7 

Lepidoptera 19.0 (% wet volume; stomach 

Coleoptera 16.0 contents) 

(Lampryidae) (5.8) 

(Chrysomelidae) (5.8) 

(Carabidae) (4.1) 

Pulmonata-Zonitidae 8.3 

Chilipoda 7.7 

sand, rock, gravel 1.2 

adults: New York/mountain lake Stewart & 

plant 19.7 

animal 65.2 (% volume; stomach 

(Odonata) (8.8) contents) 

(Coleoptera) (15.8) 

(Hemiptera) (0.5) 

(Hymenoptera) (2.2) 

(Amphibia) (26.4) 

unaccounted 15.1 

2-457 Bullfrog 
Bullfrog (Rana catesbeiana) 

Dietary Composition Spring Summer Fall Winter (measure) Referenc

Location/Habitat 

adults: Missouri/bait minnow pond Corse & 

frogs 35 33 39 

tadpoles 8 11 0 (number of items found; 

shiners 305 157 25 stomach contents) 

other fish 7 2 5 

Gastropoda 55 70 26 

crayfish 22 162 18 

other crustacea 71 42 47 

Arachnida 3 23 3 

Coleoptera (adult) 31 33 15 

Diptera (larvae) 2 7 0 

Hemiptera 41 43 16 

Population 

Dynamics 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location/Habitat Referenc

Home Range A M nonbreed 2.9 0.76 - 11.3 Ontario, Canada/pond Currie & 

Size (m radius) A F nonbreed 2.4 0.61 - 10.2 

A M territory 2.7 Michigan/pond Emlen, 1

Population B B (1960) 1,376 Ontario, Canada/pond Currie & 

Density B B (1961) 892 

(N/ha) 

tadpoles: Kentucky/pond Cecil & J

November 130,000 March 69,000 

May 16,000 

Clutch Size 10,000 - 20,000 Kansas/NS Smith, 19

7,360 ± 741.7 SE New Jersey/pond Ryan, 19

Clutches/Year 93% of F 1 Michigan/pond Emlen, 1

7% of F 2 

Days to 2 - 4 Arizona, California/river Clarkson 

Hatching 4 - 5 Kansas/NS Smith, 19

2-458 Bullfrog 
Bullfrog (Rana catesbeiana) 

Population 

Dynamics 

Age/Sex/ Range or Cond./Seas. Mean (95% CI of mean) Location/Habitat Referenc

Age at B 1 yr Carolinas, Virginia/NS Martof et 

Metamor- B 1 - 2 yr Michigan/pond Collins, 1

phosis B 2 - 3 yr New York/NS Ryan, 19

B 3 yr Nova Scotia, Canada/NS Bleakney

Age at Sexual M 1 yr after metam. Michigan/pond Howard, 

Maturity F 1 - 2 yr after 

B New York/NS Ryan, 19

metam. 1 - 2 yr after metam. 

Annual A M 1 - 2 yr 58 Michigan/pond Howard, 

Mortality Rates A M 2 - 3 yr 58 

(%) A M 3 - 4 yr 48 

Mortality Rates tadpoles (to 85.5 82.4 - 88.2 Kentucky/shallow ponds Cecil & J

(%) metamorph.) 

A M 4 - 5 yr 77 

Longevity A B up to 5 - 8 Michigan/ponds Howard, 

(yr) 

Seasonal 

Activity Begin Peak End Location Referenc

Mating/Laying February October southern range in N America Behler & 

April May late June California, Arizona Clarkson 

May late June August Missouri Willis et 

late May July July northern range in N America DeGraaf 

Behler & 

Metamor- August (1st clutch) October California, Arizona Clarkson 

phosis March (2nd clutch) April California, Arizona Clarkson 

June late June-Aug. early October Missouri Willis et 

July Sept., October New York Ryan, 19

2-459 Bullfrog 
�

�

Bullfrog (Rana catesbeiana) 

Seasonal 

Activity Begin Peak End Location Referenc

Hibernation late October late March east central Illinois Durham 

mid-October March Missouri Willis et 

1 Mean snout-to-vent length (SVL) of frogs was 98 mm SVL and the range was 45 to 128 mm SVL.

2 Age postmetamorphosis; maintained at a temperature of 24 to 27�C and fed mosquitofish, crickets, and earthworms

3 Restrained, cannulated; weight 5.7 g.

4 Mean weight of frogs was 74.8 g.5 Estimated assuming temperature of 20�C using Equation 3-50 (Robinson et al., 1983). Body weights (1) for 2-month 

from Modzelewski and Culley (1974); (2) for a 1-year postmetamorphosis frog from Durham and Bennett (1963), Farrboth juveniles and adults of both sexes, McAlpine and Dilworth (1989); and (4) for adults of both sexes, McKamie an

6 Estimated using Equation 3-24 (Hutchinson et al., 1968) and body weights as described in note 5. 

7 Based on average distance between frogs. 8 Cited in Bury and Whelan (1984). 2-460 Bullf

rog 
References (including Appendix) 

Behler, J. L.; King, F. W. (1979) The Audubon Society field guide to North American reptiles 

and amphibians. New York, NY: Alfred A. Knopf, Inc. 

Bleakney, J. S. (1952) The amphibians and reptiles of Nova Scotia. Can. Field-Nat. 66: 

125-129. 

Brooks, G. R., Jr. (1964) An analysis of the food habits of the bullfrog by body size, sex, 

month, and habitat. Va. J. Sci. 15: 173-186. 

Bruneau, M.; Magnin, E. (1980) Croissance, nutrition, et reproduction des ouaouarons Rana 

catesbeiana Shaw (Amphibia Anura) des Laurentides au nord de Montreal. Can J. 

Zool. 58: 175-183. 

Burggren, W. W.; West, N. H. (1982) Changing respiratory importance of gills, lungs and 

skin during metamorphosis in the bullfrog Rana catesbeiana. Physiol. Zool. 56: 

263-273. 

Burggren, W. W.; Feder, M. E.; Pinder, A. W. (1983) Temperature and the balance between 

aerial and aquatic respiration in larvae of Rana berlandieri and Rana catesbeiana. 

Physiol. Zool. 56: 263-273. 

Bury, R. B.; Whelan, J. A. (1984) Ecology and management of the bullfrog. U.S. Fish Wildl. 

Serv. Resour. Publ. No. 155; 23 pp. 

Bush, F. M. (1959) Foods of some Kentucky herptiles. Herpetologica 15: 73-77. 

Carpenter, H. L.; Morrison, E. O. (1973) Feeding behavior of the bullfrog, Rana catesbeiana, 

in north central Texas. Bios 44: 188-193. 

Cecil, S. G.; Just, J. J. (1979) Survival rate, population density and development of a 

naturally occurring anuran larvae (Rana catesbeiana). Copeia 1979: 447-453. 

Clarkson, R. W.; DeVos, J. C., Jr. (1986) The bullfrog, Rana catesbeiana Shaw, in the lower 

Colorado River, Arizona-California. J. Herpetol. 20: 42-49. 

Cohen, N. W.; Howard, W. E. (1958) Bullfrog food and growth at the San Joaquin 

Experimental Range, California. Copeia 1958: 223-225. 

Collins, J. P. (1975) A comparative study of life history strategies in a community of frogs 

[Ph.D. dissertation]. Ann Arbor, MI: University of Michigan. 

Collins, J. P. (1979) Intrapopulation variation in the body size at metamorphosis and timing 

of metamorphosis in the bullfrog. Ecology 60: 738-749. 

2-461 Bullfrog 
Conant, R.; Collins, J. T. (1991) A field guide to reptiles and amphibians - eastern and 

central North America. Boston, MA: Houghton Mifflin Co. 

Corse, W. A.; Metter, D. A. (1980) Economics, adult feeding and larval growth of Rana 

catesbeiana on a fish hatchery. J. Herpetol. 14: 231-238. 

Currie, W.; Bellis, E. D. (1969) Home range and movements of the bullfrog, Rana 

catesbeiana (Shaw), in an Ontario pond. Copeia 1969: 688-692. 

DeGraaf, R. M.; Rudis, D. D. (1983) Amphibians and reptiles of New England. Amherst, MA: 

University of Massachusetts Press. 

Dowe, B. J. (1979) The effect of time of oviposition and microenvironment on growth of 

larval bullfrogs (Rana catesbeiana) in Arizona [master's thesis]. Tempe, AZ: Arizona 

State University. 

Durham, L.; Bennett, G. W. (1963) Age, growth, and homing in the bullfrog. J. Wildl. 

Manage. 27: 107-123. 

Ehrlich, D. (1979) Predation by bullfrog tadpoles (Rana catesbeiana) on eggs and newly 

hatched larvae of the plains leopard frog (Rana blairi). Bull. Md. Herpetol. Soc. 15: 

25-26. 

Emlen, S. T. (1968) Territoriality in the bullfrog, Rana catesbeiana. Copeia 1968: 240-243. 

Emlen, S. T. (1976) Lek organization and mating strategies of the bullfrog. Behav. Ecol. 

Sociobiol. 1: 283-313. 

Emlen, S. T. (1977) "Double clutching" and its possible significance in the bullfrog. Copeia 

1977: 749-751. 

Farrar, E. S.; Dupre, R. K. (1983) The role of diet in glycogen storage by juvenile bullfrogs 

prior to overwintering. Comp. Biochem. Physiol. A: Comp. Physiol. 75: 255-260. 

Frost, S. W. (1935) The food of Rana catesbeiana Shaw. Copeia 1935: 15-18. 

Fulk, F. D.; Whitaker, J. O., Jr. (1968) The food of Rana catesbeiana in three habitats in 

Owen County, Indiana. Indiana Acad. Sci. 78: 491-496. 

George, I. D. (1940) A study of the bullfrog, Rana catesbeiana Shaw, at Baton Rouge, 

Louisiana [Ph.D. dissertation]. Ann Arbor, MI: University of Michigan. 

Gibbons, J. W.; Semlitsch, R. D. (1991) Guide to the reptiles and amphibians of the 

Savannah River Site. Athens, GA: The University of Georgia Press. 

Glass, M. L.; Burggren, W. W.; Johansen, K. (1981) Pulmonary diffusing capacity of the 

bullfrog (Rana catesbeiana). Acta Physiol. Scand. 113: 485-490. 

2-462 Bullfrog 
Hammer, D. A.; Linder, R. L. (1971) Bullfrog food habits on a waterfowl production area in 

South Dakota. Proc. SD Acad. Sci. 50: 216-219. 

Howard, R. D. (1978a) The influence of male-defended oviposition sites on early embryo 

mortality in bullfrogs. Ecology 59: 789-798. 

Howard, R. D. (1978b) The evolution of mating strategies in bullfrogs, Rana catesbeiana. 

Evolution 32: 850-871. 

Howard, R. D. (1981a) Sexual dimorphism in bullfrogs. Ecology 62: 303-310. 

Howard, R. D. (1981b) Male age-size distribution and male mating success in bullfrogs. In: 

Alexander, R. D.; Tinkle, D. W., ed. Natural selection and social behavior: recent 

research and new theory; pp. 61-77. 

Howard, R. D. (1984) Alternative mating behaviors of young male bullfrogs. Am. Zool. 24: 

397-406. 

Hutchinson, V. H.; Whitford, W. G.; Kohl, M. (1968) Relation of body size and surface area 

to gas exchange in anurans. Physiol. Zool. 41: 65-85. 

Jaeger, R. G.; Hailman, J. P. (1976) Ontogenetic shift of spectral phototactic preferences in 

anuran tadpoles. J. Comp. Physiol. Psychol. 90: 930-945. 

Korschgen, L. J.; Baskett, T. S. (1963) Foods of impoundment and stream dwelling 

bullfrogs in Missouri. Herpetologica 19: 89-97. 

Korschgen, L. J.; Moyle, D. L. (1955) Food habits of the bullfrog in central Missouri farm 

ponds. Amer. Midl. Nat. 54: 332-341. 

Lillywhite, H. B. (1970) Behavioral temperature regulation in the bullfrog, Rana catesbeiana. 

Copeia 1970: 158-168. 

Martof, B. S.; Palmer, W. M.; Bailey, J. R.; et al. (1980) Amphibians and reptiles of the 

Carolinas and Virginia. Chapel Hill, NC: University of North Carolina Press. 

McAlpine, D. F.; Dilworth, T. G. (1989) Microhabitat and prey size among three species of 

Rana (Anura: Ranidae) sympatric in eastern Canada. Can. J. Zool. 67: 2241-2252. 

McAuliffe, J. R. (1978) Biological survey and management of sport-hunted bullfrog 

populations in Nebraska. Lincoln, NE: Nebraska Game and Parks Commission; 78 

pp. 

McKamie, J. A.; Heidt, G. A. (1974) A comparison of spring food habits of the bullfrog, Rana 

catesbeiana, in three habitats of central Arkansas. Southwest. Nat. 19: 107-111. 

Modzelewski, E. H., Jr.; Culley, D. D., Jr. (1974) Growth responses of the bullfrog, Rana 

catesbeiana fed various live foods. Herpetologica 30: 396-405. 

2-463 Bullfrog 
Oliver, J. A. (1955) The natural history of North American amphibians and reptiles. 

Princeton, NJ: Van Nostrand Co. 

Raney, E. C. (1940) Summer movements of the bullfrog, Rana catesbeiana (Shaw), as 

determined by the jaw-tag method. Am. Midl. Nat. 23: 733-745. 

Raney, E. C.; Ingram, W. M. (1941) Growth of tagged frogs (Rana catesbeiana Shaw and 

Rana clamitans Daudin) under natural conditions. Am. Midl. Nat. 26: 201-206. 

Robinson, R. W.; Peters, R. H.; Zimmermann, J. (1983) The effects of body size and 

temperature on metabolic rate of organisms. Can. J. Zool. 61: 281-288. 

Ryan, M. J. (1980) The reproductive behavior of the bullfrog (Rana catesbeiana). Copeia 

1980: 108-114. 

Ryan, R. A. (1953) Growth rates of some ranids under natural conditions. Copeia 1953: 

73-80. 

Smith, H. M. (1956) Handbook of amphibians and reptiles of Kansas. Univ. Kansas Mus. 

Nat. Hist. Misc. Publ. 9. 

Smith, P. W. (1961) The amphibians and reptiles of Illinois. Ill. Nat. Hist. Surv. Bull. 28. 

Stewart, M. M.; Sandison, P. (1973) Comparative food habits of sympatric mink frogs, 

bullfrogs, and green frogs. J. Herpetol. 6: 241-244. 

Storer, T. I. (1922) The eastern bullfrog in California. Calif. Fish and Game 8: 219-224. 

Treanor, R. R.; Nichola, S. J. (1972) A preliminary study of the commercial and sporting 

utilization of the bullfrog, R. catesbeiana Shaw in California. Calif. Dept. Fish and 

Game, Inland Fish. Admin. Rep. 72-4; 23 pp. 

Turner, F. B. (1960) Postmetamorphic growth in anurans. Am. Midl. Nat. 64: 327-338. 

Tyler, J. D.; Hoestenbach, R. D., Jr. (1979) Differences in food of bullfrogs (Rana 

catesbeiana) from pond and stream habitats in southwestern Oklahoma. Southwest. 

Nat. 24: 33-38. 

Viparina, S.; Just, J. J. (1975) The life period, growth and differentiation of Rana 

catesbeiana larvae occurring in nature. Copeia 1975: 103-109. 

Weathers, W. W. (1976) Influence of temperature acclimation on oxygen consumption, 

haemodynamics and oxygen transport in bullfrogs. Aust. J. Zool. 24: 321-330. 

Willis, Y. L.; Moyle, D. L.; Baskett, T. S. (1956) Emergence, breeding, hibernation, 

movements and transformation of the bullfrog, Rana catesbeiana, in Missouri. 

Copeia 1956: 30-41. 

2-464 Bullfrog 
Wright, A. H. (1914) North American Anura: life histories of the Anurans of Ithaca, New 

York. Washington, DC: Carnegie Institute; Publ. No. 197. 

Wright, A. H.; Wright, A. A. (1949) Handbook of frogs and toads of the United States and 

Canada. Ithaca, New York: Comstock Publishing Co. 

2-465 Bullfrog 
3. ALLOMETRIC EQUATIONS 

Values for key contact rate factors such as food and water ingestion rates have 

been measured for few wildlife species. In this section, we describe allometric equations 

that can be used to estimate several exposure factors on the basis of animal body weight 

using models derived from taxonomically similar species. We emphasize, however, that 

measured values from well-conducted studies on the species of concern are likely to be 

more accurate and to have narrower confidence limits. 

Allometry is defined as the study of the relationships between the growth and size 

of one body part to the growth and size of the whole organism; however, allometric 

relationships also exist between body size and other biological parameters (e.g., metabolic 

rate). The relationship between the physiological and physical parameters and body 

weight frequently can be expressed as: 

Y = a Wt

b

 ± SE of Y, or [3-1] 

log Y = log a + b log Wt ± SE of log Y [3-2] 

where Y is the biological characteristic to be predicted, Wt is the animal's body weight 

(mass), a and b are empirically derived constants, and SE is the standard error of the mean 

value of the parameter. 

Equation 3-2 is the log transformation of Equation 3-1. Equation 3-2 represents a 

straight line, with b equal to the slope of the line and log a equal to the Y-intercept of the 

line. Values for a and b usually are determined empirically from measured values using 

linear regression analysis. Once values are determined for a and b, Equation 3-1 can be 

used to predict a value of Y from the body weight of the animal. The SE of Y is the 

standard error of the mean Y estimated for the mean of the Wt values; the SE of log Y is 

the standard error of the mean log Y estimated for the mean of the log Wt values. 

3-1
Allometric equations can be used to estimate parameter values for species for 

which measured values are not available. The equations presented in this chapter, 

however, should not be used for taxonomic categories other than the category for which 

each was developed. For example, equations developed for iguanid lizards cannot be used 

for amphibians and should not be used for other groups of reptiles without careful 

evaluation of likely differences between the groups. It also is important to remember that 

the allometric equations presented in this chapter have been developed using mean values 

for a number of species within a taxonomic category. Individual species usually exhibit 

values somewhat different from those predicted by an allometric model based on several 

species. Furthermore, different-sized individuals within a species and individuals at 

varying stages of maturation are likely to exhibit a different allometric relationship between 

body weight and the dependent variable. For further discussion of within-species 

allometric equations related to growth and reproduction, see Reiss (1989). 

In the next five sections, we describe empirically derived allometric equations that 

relate food ingestion rates (Section 3.1), water intake rates (Section 3.2), inhalation rates 

(Section 3.3), surface area (Section 3.4), and metabolic rate (Section 3.5) to body weight. 

As discussed above, most of the allometric models differ for birds, mammals, reptiles, and 

amphibians, and many also vary within these taxonomic groups. In Section 3.6, we provide 

a summary of operations involving logarithms and powers and unit conversion factors for 

those persons who may want to modify allometric equations found in the literature. 

Finally, in Section 3.7 we describe how to estimate 95-percent confidence intervals for food 

ingestion rates and free-living metabolic rates predicted on the basis of allometric 

equations presented in this chapter. We present most equations in the untransformed 

form only. For equations for which an investigator reported standard errors for the log 

transformation of the relationship, we present the equation both ways. For those persons 

interested in estimating confidence intervals for other allometric equations, Peters (1983) 

provides a simple review of how to estimate regression statistics for equations of the form 

of Equation 3-2. Section 3.8 contains the references for this chapter. 

3-2
3.1. FOOD INGESTION RATES 

Food ingestion rates vary with many factors, including metabolic rate, the energy 

devoted to growth and reproduction, and composition of the diet. The metabolic rate of 

free-ranging animals is a function of several factors, including ambient temperature, 

activity levels, and body weight. In birds and mammals, thermoregulation can 

considerably increase an animal's metabolic requirements during the winter, whereas 

reproductive efforts can replace thermoregulation as the predominant extra metabolic 

expenditure in the spring and summer. Many reptiles and amphibians, on the other hand, 

drop their activity levels and metabolic rates in the winter. 

For homeotherms (i.e., animals that maintain a relatively constant body temperature 

such as most birds and mammals), metabolic rate generally decreases with increasing 

body mass (see Section 3.5). The smallest birds and mammals must consume quantities 

of food equal to their body weight or more daily; in contrast, the larger homeotherms may 

consume only a small fraction of their body weight in food daily. Herbivores tend to 

consume larger quantities of food than carnivores because of the lower energy content of 

their food. Ingestion rates, expressed in units of food energy normalized to body size (e.g., 

kcal/kg-day), are not significantly different for herbivores and carnivores (Peters, 1983). 

Four-legged poikilotherms (those animals whose usual body temperatures are the same as 

that of their environment, such as reptiles and amphibians) exhibit the same slope of 

decreasing ingestion rates per unit body weight with increasing body size but show a lower 

intercept (i.e., lower ingestion rate for a given body weight) than homeotherms (Nagy, 

1987). 

The rate of food consumption that an animal must achieve to meet its metabolic 

needs can be calculated by dividing its free-living (or field) metabolic rate (FMR) (see 

Section 3.5) by the metabolizable energy in its food (Nagy, 1987). Metabolizable energy 

(ME) is the gross energy (GE) in a unit of food consumed minus the energy lost in feces 

and urine. Assimilation efficiency (AE) equals the ratio ME/GE, or the fraction of GE that is 

metabolizable. AE is relatively constant among different groups of consumer species of 

mammals and birds that are all either carnivorous, insectivorous, herbivorous, or 

3-3
granivorous (Hume, 1982; Peters, 1983; Nagy, 1987; Robbins, 1983). Nagy (1987) 

calculated the mean ME (i.e., kilojoules of ME per gram of dry matter) of various diets for 

birds and mammals from average values of AE for birds and mammals and typical GE 

contents of those diets as reported by Golley (1961) and Robbins (1983). These values are 

presented in Table 3-1. (For more information on ME and AE, see Section 4.1.2.) Using the 

values presented in Table 3-1, Nagy (1987) developed allometric equations for food 

ingestion (FI) rates as a function of body weight (Wt) for birds, mammals, and lizards using 

estimated FMRs and general dietary composition. In the remainder of this section, we 

present these equations for birds (Section 3.1.1) and mammals (Section 3.1.2). Section 

3.1.3 summarizes Nagy's food ingestion allometric equations for iguanid lizards. We report 

this information even though no iguanid lizards were among our selected species because 

it is the only information of this type we identified for any amphibian or reptile. 

Nagy's (1987) estimates of FMR are based on doubly labeled water measurements 

of CO2 production in free-living animals. When performed correctly, this method is more 

accurate for estimating the metabolic rate of free-living animals than other methods 

commonly used (King, 1974). Other allometric equations for food ingestion rates that we 

identified in the open literature are based largely on captive animals without corrections for 

the additional energy requirements of free-living animals. For more accurate estimates of 

food ingestion rates by type of diet, we recommend following the procedures outlined in 

Section 4.1.2 instead of using these generic equations. 

3.1.1. Birds 

For birds, Nagy (1987) calculated FI rates (in grams dry matter per day) from ME and 

FMR and developed the following equations: 

FI (g/day) = 0.648 Wt

0.651 (g), or 

FI (kg/day) = 0.0582 Wt

0.651 (kg) 

FI (g/day) = 0.398 Wt

0.850 (g) 

all birds [3-3] 

passerines [3-4] 

3-4
Table 3-1. Metabolizable Energy (ME) of Various Diets for Birds and Mammals 

Diet 

insects 

fish 

Metabolizable Energy a a (kJ/g) (kcal/g)

18.7 = 4.47 

18.0 = 4.30 

18.7 = 4.47 

16.2 = 3.87 

Animal Group 

mammals 

birds 

mammals 

birds 

mammals 

mammals 

hummingbirds 

mammals and birds 

vegetation 10.3 = 2.26 

seeds 18.4 = 4.92 

nectar 20.6 = 4.92 

omnivory 14 = 3.35

a

g = grams dry weight. 

Source: Nagy, 1987. 

FI (g/day) = 0.301 Wt

0.751 (g) 

FI (g/day) = 0.495 Wt

0.704 (g) 

non-passerines 

seabirds 

[3-5]

[3-6]

where Wt equals the body weight (wet) of the animal in grams (g) or kilograms (kg) as 

indicated. We provide the regression statistics for these equations (including sample size 

and regression coefficient) and information required to estimate a 95-percent confidence 

interval for an FI rate predicted for a specified body weight in Section 3.7. More accurate 

estimates of food requirements can be made from estimates of FMR (Section 3.5), dietary 

composition, and AE for the species of interest, as outlined in Section 4.1.2. 

3.1.2. Mammals 

For placental mammals, Nagy (1987) calculated FI rates (in grams dry matter per 

day) from ME and FMR values and developed the following equations: 

3-5
FI (g/day) = 0.235 Wt

0.822 (g), or all mammals [3-7] 

FI (kg/day) = 0.0687 Wt

0.822 (kg) 

FI (g/day) = 0.621 Wt

0.564 (g) rodents [3-8] 

FI (g/day) = 0.577 Wt

0.727 (g) herbivores [3-9] 

We provide the regression statistics for these equations (including sample size and 

regression coefficient) and information required to estimate a 95-percent confidence 

interval for an FI rate predicted for a specified body weight in Section 3.7. More accurate 

estimates of food requirements can be made from estimates of FMR (Section 3.5), dietary 

composition, and AE for the species of interest, as outlined in Section 4.1.2. 

Herbivores tend to consume more food than carnivores or omnivores on a dryweight basis because of the lower energy content of the herbivores' diets. On an energy 

basis (e.g., kilocalories), the ingestion rates of carnivores and herbivores are not 

significantly different (Farlow, 1976): 

FI (kjoule/day) = 971 Wt

0.73 (kg) (r2 = 0.942), or herbivores [3-10] 

FI (kcal/day) = 1.518 Wt

0.73 (g) 

FI (kjoule/day) = 975 Wt

0.70 (kg) (r2 = 0.968), or carnivores [3-11] 

FI (kcal/day) = 1.894 Wt

0.70 (g) 

3.1.3. Reptiles and Amphibians 

This section summarizes food ingestion allometric equations for iguanid lizards, 

which is the only information of this type we identified for any amphibian or reptile. Nagy 

(1987) calculated FI rates (in grams dry matter per day) from ME and FMR values on spring 

and summer days and developed the following equations: 

3-6
FI (g/day) = 0.019 Wt

0.841 (g) herbivores [3-12] 

FI (g/day) = 0.013 Wt

0.773 (g) insectivores [3-13] 

Again, on an energy basis, carnivores and herbivores are not significantly different and can 

be represented by a single relationship: 

FI (kjoule/day) = 0.224 Wt

0.799 (g), or all iguanids [3-14] 

FI (kcal/day) = 0.054 Wt

0.799 (g) 

We provide the regression statistics for these equations (including sample size and 

regression coefficient) and information required to estimate a 95-percent confidence 

interval for an FI rate predicted for a specified body weight in Section 3.7. More accurate 

estimates of food requirements for these and other groups of reptiles and amphibians can 

be made from estimates of FMR (Section 3.5), dietary composition, and AE for the species 

of interest, as outlined in Section 4.1.2. 

Allometric equations for FI rates for other groups of reptiles and amphibians were 

not found. For other groups, we recommend estimating FI rates from FMR and diet, as 

described in Section 4.1.2. 

3.2. WATER INTAKE RATES 

Daily water requirements depend on the rate at which animals lose water to the 

environment due to evaporation and excretion. Loss rates depend on several factors, 

including body size, ambient temperature, and physiological adaptations for conserving 

water. Drinking water is only one way in which animals may meet their water 

requirements. All animals produce some water as a product of their metabolism. The 

degree to which metabolic water production and dietary water content can satisfy an 

animal's water requirements varies from species to species and with environmental 

conditions. Extensive literature describes the allometry of total water flux for various 

3-7
groups of animals. Allometric models to predict drinking water intake, on the other hand, 

are limited. 

3.2.1. Birds 

Based on measured body weights and drinking water values from Calder (1981) and 

Skadhauge (1975), Calder and Braun (1983) developed an equation for drinking water 

ingestion (WI) for birds: 

WI (L/day) = 0.059 Wt

0.67 (kg) all birds [3-15] 

where Wt equals the average body weight in kilograms (kg) of the bird species. This 

equation is based on data from 21 species of 11 to 3,150 g body weight. Total water 

turnover should be proportional to metabolic rate (body weight to the 3/4 power, see 

Section 3.5.2.1). The exponent for Equation 3-15 is not significantly different from 0.75 

(Calder and Braun, 1983). Additional sources of water not accounted for in this equation 

(metabolic water and water contained in food) also help to balance the animals' daily water 

losses. For allometric equations for total water flux (including water obtained from food) 

for birds, see Nagy and Peterson (1988). 

To estimate daily drinking water intake as a proportion of an animal's body weight 

(e.g., as g/g-day), the WI rate estimated above is divided by the animal's body weight in kg: 

WI (g/g-day) = WI (kg/kg-day), or [3-16] 

= WI (L/day) / Wt (kg) 

In general, birds drink less water than do mammals of equivalent body weights. 

Because of their relatively high metabolic rates, the quantity of metabolic water produced 

by birds is greater in relationship to body size than that produced by other vertebrates 

(Bartholomew and Cade, 1963). In addition, birds are able to conserve water by excreting 

nitrogen as uric acid instead of urea (as excreted by mammals); uric acid can be excreted 

3-8
�

� � �

� �

�

in a semi-solid suspension, whereas urea must be excreted in aqueous solution. On the 

other hand, birds exhibit a high rate of water loss from the respiratory system and use 

panting and evaporative water loss to prevent overheating at high ambient temperatures. 

For example, Dawson (1954) found evaporative losses in two species of towhees to 

increase fourfold between 30 and 40�C. 

Although birds may satisfy some of their water needs by oxidative food metabolism, 

it has not been demonstrated that any normally active bird can satisfy its water 

requirements with metabolic water alone (Bartholomew and Cade, 1963). The balance 

must be obtained from water contained in foods such as insects or succulent plant 

material and from drinking water. 

As would be expected, birds drink more water at warmer temperatures to make up 

for evaporative losses. Seibert (1949) found that juncos (weighing 16 to 18 g) consumed 

an average of 11 percent of their body weight in water daily at an ambient temperature of 

0�C, 16 percent at 23�C, and 21 percent at 37�C. The white-throated sparrow increased 

water consumption from 18 percent of its body weight at 0�C to 27 percent at 23�C and 44 

percent at 37�C. 

Water consumption rates per unit body weight also tend to decrease with increasing 

body weight within a species. For example, in white leghorn chickens, water intake per 

gram of body weight is highest in the youngest chicks (45 percent of the body weight at 1 

week when chicks average 62 g) and decreases with age thereafter (13 percent of the body 

weight at 16 weeks when chicks average 2.0 kg) until egg-laying, when water consumption 

increases for the production of eggs (24 percent of the body weight for laying hens) 

(Medway and Kare, 1959). 

Some species obtain more of their daily water needs from their diet and therefore 

drink less water than others; therefore, measured water ingestion values from wellconducted studies should be used when available. In the absence of measured values, 

Equation 3-15 should provide a reasonable central value. Additional information required 

to estimate a 95-percent confidence interval was not provided along with this equation. 

3-9
3.2.2. Mammals 

Based on measured body weights and drinking water values from Calder (1981) and 

Skadhauge (1975), Calder and Braun (1983) developed an allometric equation for drinking 

water ingestion (WI) for mammals: 

WI (L/day) = 0.099 Wt

0.90 (kg) all mammals [3-17] 

where Wt equals the average body weight in kilograms (kg). Additional sources of water 

not accounted for in this equation (i.e., metabolic water and water contained in food) help 

to balance the animals' daily water losses. The empirically determined exponent of 0.90 

does not suggest a simple physiological explanation. If total water turnover (metabolic 

water combined with water obtained from food) is proportional to metabolic rate (body 

weight to the 3/4 power, see Section 3.5.2.1), then drinking water ingestion would be 

expected to scale similarly, as was the case for birds (see Section 3.2.1). For allometric 

equations relating body weight to total water flux (including water obtained from food) for 

mammals, see Nagy and Peterson (1988). 

To normalize drinking water intake to body weight (e.g., as g/g-day; see Chapter 4, 

Equation 4-4), the WI rate estimated above is divided by the animal's body weight in kg: 

NWI (g/g-day) = WI (kg/kg-day), or [3-18] 

= WI (L/day) / Wt (kg) 

We present normalized drinking water intakes in the species profiles. 

3.2.3. Reptiles and Amphibians 

Allometric equations relating body weight to drinking water ingestion rates were not 

identified for reptiles and amphibians. The water balance of these groups is complex, in 

part because they can absorb water through their skin as well as drink water and extract 

water from their food (Duellman and Trueb, 1986; Minnich, 1982). The relative 

3-10
contribution of these three routes of water intake depends on the species, habitat, 

temperature, and body surface area. In general, the skin of reptiles is less permeable than 

that of amphibians. Aquatic turtles (e.g., snapping turtle, painted turtle) also may ingest 

large amounts of water when feeding on aquatic plants and animals; however, the 

magnitude of such ingestion has not been quantified (Mahmoud and Klicka, 1979). For 

further discussion of water balance for these groups, see Duellman and Trueb (1986), 

Feder and Burggren (1992), Minnich (1982), and Nagy and Peterson (1988). 

3.3. INHALATION RATES 

Inhalation rate is one of the respiratory parameters needed to estimate potential 

exposure of wildlife to airborne contaminants. Inhalation rates vary with species, body 

size, body temperature, ambient temperature, and activity levels. When inhalation rate is 

increased, either because of increased activity levels or to promote evaporative cooling, 

exposure to airborne contaminants may be increased. As discussed in Section 4.1.4, an 

inhalation toxicologist should be consulted when assessing this pathway because 

additional respiratory parameters also must be considered (see U.S. EPA, 1990). 

3.3.1. Birds 

Lasiewski and Calder (1971) developed an allometric relationship for inhalation rate 

(IR) associated with standard metabolism (i.e., post-digestive, at rest) for non-passerine 

birds (N = 6 species ranging in weight from 43 to 88,000 grams). They excluded 

passerines, which have a somewhat higher metabolic rate than non-passerines (see 

Section 3.5): 

IR (ml/min) = 284 Wt

0.77 (kg), or all non-passerines [3-19] 

IR (m3/day) = 0.4089 Wt

0.77 (kg), or 

IR (m3/day) = 0.002002 Wt

0.77 (g) 

As noted above, these inhalation rates were associated with standard metabolic rates. 

Free-living metabolic rates are likely to be higher by a factor of at least 2 or 3 (see Section 

3-11
3.5); therefore, IRs estimated from these equations should be adjusted accordingly (e.g., 

multiplied by 2 or 3) although IRs might not be directly proportional to metabolic rate. 

3.3.2. Mammals 

Using measured values from several reports of respiration rates in mammals 

(covering 691 data points), Stahl (1967) developed an allometric relationship for inhalation 

rate with body size for mammals (N = 691, r = 0.98, SE Y = 45): 

IR (ml/min) = 379 Wt

0.80 (kg), or all mammals [3-20]

IR (m3

/day) = 0.5458 Wt

0.80 (kg), or

IR (m3/day) = 0.002173 Wt

0.80 (g)

As for the equations given for birds, these IRs were associated with standard metabolic 

rates. Field metabolic rates are likely to be higher by a factor of at least 2 or 3 (see Section 

3.5); therefore, IRs determined from these equations should be adjusted accordingly (e.g., 

multiplied by 2 or 3, although IRs may not be directly proportional to metabolic rate). 

3.3.3. Reptiles and Amphibians 

In contrast to the fairly regular breathing patterns of most birds and mammals, most 

reptiles breath air in distinct episodes. They may take single breaths, or exhibit an episode 

of several breaths, and then hold their breath for varying lengths of time (Milsom and Chan, 

1986). Inhalation rate varies for reptiles and amphibians not only with body size and 

activity level, as for birds and mammals, but also with body temperature. Some gas 

exchange occurs normally through the integument of both reptiles and amphibians 

(Duellman and Trueb, 1986; Lillywhite and Maderson, 1982). Moreover, for semiaquatic 

species, a significant proportion of gas exchange can occur underwater through the skin, 

reducing the need to inspire air (Seymour, 1982). For example, in adult bullfrogs, gas 

exchange through the skin can account for 18 percent of total oxygen uptake (Burggren 

and West, 1982). Given the complexity of the subject, we refer those interested in 

3-12
inhalation exposures for reptiles or amphibians to more specific treatments of these topics 

(e.g., Duellman and Trueb, 1986; Feder and Burggren, 1992; Gans and Dawson, 1976; 

Jackson, 1979; Hutchinson et al., 1968; Lillywhite and Maderson, 1982). 

3.4. SURFACE AREAS 

The degree to which an animal may absorb contaminants through direct contact 

with its skin depends on many factors, including the surface area of the skin available for 

contact. Summarizing measured surface areas for more than 100 animals reported by 

Hemmingsen (1960), Schmidt-Nielsen (1970, 1972) determined that animals have surface 

areas that usually are approximately twice that of a sphere of the same weight (assuming a 

specific gravity of 1 for both the sphere and the animal). The permeability of an animal's 

skin to contaminants, however, depends on characteristics of the skin (e.g., presence of 

keratinized scales) as well as the contaminant (e.g., molecule size, lipophilicity). This 

section presents allometric equations for estimating skin surface area; characteristics 

affecting skin permeability are not discussed. 

3.4.1. Birds 

In studies of avian thermal biology, skin surface area is commonly estimated using 

Meeh's (1879, cited in Walsberg and King, 1978) formula with Rubner's (1883, cited in 

Walsberg and King, 1978) constant of 10: 

SAskin (cm2) = 10 Wt

0.667 (g) all birds [3-21] 

where SAskin is the skin surface area beneath the feathers and Wt is body weight (Walsberg 

and King, 1978). Although Rubner's constant of 10 was derived originally from domestic 

fowl, Drent and Stonehouse (1971) have verified the formula for birds in a variety of taxa 

and of weights spanning three orders of magnitude. For passerines, beak surface area 

tends to be about 1 percent (range 0.7 percent to 1.6 percent of 10 passerine species) of 

skin surface area, and leg surface area about 7 percent (range 5.9 percent to 

3-13
7.9 percent of 10 passerine species) (Walsberg and King, 1978). These ratios would be 

expected to vary for many non-passerines (e.g., herons, woodcock). 

3.4.2. Mammals 

Summarizing data from more than 100 mammals, Stahl (1967) developed a 

relationship between surface and body weight: 

SAskin (m2)= 0.11 Wt

0.65 (kg), or all mammals 

SAskin (cm2

) = 12.3 Wt

0.65 (g) 

[3-22]

This relationship is very similar to that developed for birds (Equation 3-21). 

3.4.3. Reptiles and Amphibians 

Surface area has been found to be a different function of body weight for adult 

amphibians than for birds or mammals (Hutchinson et al., 1968; Whitford and Hutchinson, 

1967): 

SAskin (cm2) = 1.131 Wt

0.579 

SAskin (cm2) = 0.953 Wt

0.725 

SAskin (cm2) = 0.997 Wt

0.712 

SAskin (cm2) = 8.42 Wt

0.694 

(g) all frogs 

(g) bullfrog 

(g) green frog 

(g) salamanders 

[3-23] 

[3-24] 

[3-25] 

[3-26] 

Models by which to estimate surface areas for turtles (exclusive of the shell and 

plastron) and snakes were not found. The general formula for the surface area of a 

cylinder can be used to approximate the surface area of a snake if the length and girth are 

known or estimated. 

3-14
3.5. ALLOMETRIC EQUATIONS FOR METABOLIC RATE 

The allometric equations for estimating food ingestion rates provided in Section 3.1 

were derived using very simple assumptions about the energetic content and digestibility 

of the diet for the species included in the regression equations. Consequently, the 

equations will provide only very rough estimates of food ingestion rates for any given 

species. For a site-specific exposure assessment, it may be more appropriate to evaluate 

ingestion rates for a diet that is likely to represent the species and study area. The caloric 

content and percent water, fat, and protein of wildlife diets vary not only among species, 

but also among individuals within the same species depending on factors such as location, 

time of year, age, and sex. If one can estimate the energetic requirements of the animal in 

the field and its dietary composition for a specified situation, one can estimate food 

ingestion rates for that diet and situation. In the remainder of this section, we discuss 

metabolic rate and provide allometric equations to estimate field free-living metabolic rates 

(FMRs) for wildlife species. Chapter 4 describes how to use FMR estimates and 

information about the energy content of specific diets to estimate food ingestion rates. 

Several factors influence metabolic rates of free-ranging animals, including body 

size, body temperature, and type and level of activity. For homeotherms, metabolic energy 

must be expended to keep core body temperature within relatively narrow limits. At 

moderate ambient temperatures, homeotherms lose heat to the surrounding environment 

as rapidly as they gain it and therefore need not expend extra metabolic energy to maintain 

core body temperature. That range of ambient temperatures over which an animal's 

metabolic rate is at a minimum and constant level is called the thermoneutral zone. Below 

the thermoneutral zone, the organism loses heat to the environment and must increase its 

metabolic activity to compensate. Above the thermoneutral zone, the organism gains heat 

from its environment and must increase its metabolic rate to use evaporation to cool its 

body. 

Thermoneutral zones vary somewhat among species depending upon the insulating 

properties and color of the fur or feathers, surface-to-volume ratios, and other factors. The 

degree to which metabolic rate increases with changes in ambient temperature outside of 

3-15
�

�

�

the thermoneutral zone is referred to as the temperature coefficient (TC). Temperature 

a coefficients also vary with body size, insulation, and other factors. 

There are several ways to measure and express metabolic rate, including basal 

metabolic rate (BMR), resting metabolic rate (RMR), existence metabolic rate (EMR), 

average daily metabolic rate (ADMR), and free-living or field metabolic rate (FMR). The 

different measures are distinguished by the range of animal activities included in the 

measure: 

� Basal metabolic rate (BMR), also sometimes labeled standard metabolic rate 

(SMR), represents the minimal value of heat production for homeotherms. 

BMR must be measured within the thermoneutral zone of ambient 

temperatures when the animal is at rest and in a post-absorptive state (i.e., 

all food has been digested) (Gessaman, 1973). 

� Standard metabolic rate (SMR) has been used in the literature in more than 

one way. Many authors define SMR as BMR (see above). Others use SMR if 

the thermoneutral zone has not been defined so that some cost of 

thermoregulation may be included (Bennett and Harvey, 1987). 

� Resting metabolic rate (RMR) is usually measured at temperatures below the 

thermoneutral zone when the animal is at rest, but not post-absorptive (i.e., 

the animal is eating regularly and may be expending energy to digest its 

food). The RMR exceeds the BMR by the heat liberated in the digestion of 

food (i.e., the specific dynamic action, or SDA) and by some cost of 

thermoregulation. RMR and BMR are usually measured using indirect 

calorimetry (i.e., oxygen consumption and carbon dioxide production) over a 

period of 1 to 3 hours. 

a

Water has a much higher heat conductance than air. When submerged or swimming, the degree

to which metabolic rate increases with decreasing water temperature depends on the animal's 

insulation (e.g., whether the fur traps an air layer next to the skin over part or all of the body or 

whether there is an insulative layer of blubber), duration of submergence, and body size. 

3-16 
�

�

�

Existence metabolic rate (EMR) is the metabolic rate necessary for an animal 

to maintain itself in captivity without a change in body weight. EMR is 

greater than RMR due to the cost of locomotor and other activities required 

for self-maintenance. Most researchers measure EMR on the basis of food 

consumption and energy excretion at a constant weight over the period of 

several days or weeks (Kendeigh, 1969). 

� Average daily metabolic rate (ADMR) is usually measured over 24 hours at a 

temperature similar to the animal's natural environment and with food and 

water available ad libitum. ADMR is the sum of BMR and the metabolic costs 

of thermoregulation, digestion, and daily activities. 

� Free-living or field metabolic rate (FMR) can be measured using doublylabeled water, and it represents the total daily energy requirement for an 

animal in the wild. FMR includes the costs of BMR, SDA, thermoregulation, 

locomotion, feeding, predator avoidance, alertness, posture, and other 

energy expenditures. Various models and measures have indicated that a 

constant value of approximately three times BMR is a reasonable estimate of 

FMR for birds and mammals (Lamprey, 1964; Buechner and Golley, 1967; 

Koplin et al., 1980), although more precise estimates also have been 

developed (see Sections 3.5.1.3, 3.5.2.3, and 3.5.3.2). 

FMR also has been used in the literature to represent fasting metabolic rate (e.g., 

Gessaman, 1973), but we do not discuss fasting metabolic rate estimates in this Handbook. 

The relationships between metabolic rate and body weight fall into two broad 

categories: those for homeothermic animals (i.e., most birds and mammals), and those for 

poikilothermic animals (i.e., most reptiles and amphibians). For poikilotherms, metabolic 

rate must be related to body temperature. It also is important to remember that 

poikilotherms can adjust their body temperatures relative to ambient temperatures 

3-17
 somewhat by modifying their behavior (e.g., basking in the sun, adopting postures to 

minimize or maximize absorption of solar radiation). 

Allometric models relating metabolic rate to body size for birds and mammals are 

described in Sections 3.5.1 and 3.5.2, respectively. Allometric models for reptiles and 

amphibians are described in Section 3.5.3. We have attempted to identify the most 

accurate allometric equations currently available for estimating free-living metabolic rates. 

We also present allometric equations for basal and existence metabolism, which in 

combination with appropriate information on activity budgets and energy costs can be 

used to estimate field metabolic rates. Furthermore, measures of basal and existence 

metabolism are available for considerably more species than are measures (or estimates) 

of free-living metabolic rates. Consequently, more allometric models have been developed 

that distinguish the metabolic rate-weight relationship among taxonomic groups using 

measures of basal and existence metabolism than using measures of field metabolic rates. 

We caution users to pay close attention to the units for the parameters in the allometric 

equations. For most equations, energy is expressed as kcal (with the exception of some 

equations for reptiles and amphibians). Mass may be expressed either in g or kg, 

depending on how the equation was reported. 

We emphasize that the literature on allometric relationships and metabolic rate is 

extensive and complex. We provide a very simplified overview that should be of 

assistance for screening-level exposure assessments only. For additional information on 

methods of estimating metabolic costs of free-ranging animals, please consult expert 

reviews on the subject (e.g., Bennett and Dawson, 1976; Bennett and Harvey, 1987; Ellis, 

1984; Gans and Dawson, 1976; Gessaman, 1973; Kendeigh et al., 1977; King, 1974; Peters, 

1983; Robinson et al., 1983; Wiens, 1984). 

3.5.1. Birds 

In birds, metabolic rate generally decreases with increasing body mass. Several 

authors have found passerine birds to have higher metabolic rates overall for their body 

size than non-passerines (Lasiewski and Dawson, 1967; Nagy, 1987; Kendeigh, 1970; 

3-18
Zar, 1968). In this section, we present allometric models for three measures of metabolic 

rate on the basis of body size in birds: basal metabolic rate (BMR), existence metabolic 

rate (EMR), and field metabolic rate (FMR). All equations take the general form of Y = aWt

b

, 

but can also be represented in their log-transformed form (the equation of a straight line). 

We conclude this section by discussing the influence of ambient temperature on avian 

metabolic rates. Additional information required to estimate a 95-percent confidence 

interval (CI) for a predicted FMR (the expression of metabolic rate that is generally most 

appropriate for wildlife exposure assessments) is provided in Section 3.7. 

3.5.1.1. Basal Metabolic Rate 

Several investigators have derived values for the constants a and b for the equation 

relating BMR to body weight (Wt) from empirical data on birds. Lasiewski and Dawson 

(1967) compiled body weight and BMR for almost 100 species of birds. They found BMR 

for passerines to be higher than BMR for non-passerines (i.e., the Y-intercept for 

passerines is higher than the Y-intercept for non-passerines): 

Passerines 

log BMR (kcal/day) 

BMR (kcal/day) 

Non-passerines 

log BMR (kcal/day) 

BMR (kcal/day) 

= 2.11 + 0.724 log Wt (kg) ± 0.113, or 

= 128 Wt

0.724 (kg) 

= 1.89 + 0.723 log Wt (kg) ± 0.068, or 

[3-27] 

[3-28] 

= 77.6 Wt

0.723 (kg) 

Ellis (1984) found the Y-intercept for seabirdsb to be somewhat higher than the Yintercept for non-passerines determined by Lasiewski and Dawson (1967): 

b

Seabirds included penguins, albatross, petrels, shearwaters, pelicans, skuas, gulls, terns, noddys, 

murres, cormorants, and frigatebirds. 

3-19 
�

�

�

Seabirds 

log BMR (kcal/day) = 1.96 + 0.721 log Wt (kg) (no SE provided), or [3-29] 

BMR (kcal/day) = 91.2 Wt

0.721 (kg) 

Zar (1968) reexamined the data compiled by Lasiewski and Dawson (1967) and 

developed models for relating BMR to body weight (kg) for several orders and families of 

birds (Table 3-2). These may be used to estimate whether the FMR for a species of interest 

is likely to fall above or below that predicted on the basis of the allometric equations 

derived for "all birds." 

3.5.1.2. Existence Metabolic Rates 

Kendeigh (1970) developed allometric equations for EMRs as a function of weight 

(Wt) at 30�C separately for passerines and for non-passerines. As was the case for BMRs, 

passerines showed higher EMRs than did non-passerines: 

Passerines (N = 15 species) 

log EMR (kcal/day) = 0.1965 + 0.6210 log Wt (g) ± 0.0633, or [3-30] 

EMR (kcal/day) = 1.572 Wt

0.6210 (g), or 

log EMR (kcal/day) = 2.060 + 0.6210 log Wt (kg), or 

EMR (kcal/day) = 114.8 Wt

0.6210 (kg) 

Non-passerines (N = 9 species) 

log EMR (kcal/day) = -0.2673 + 0.7545 log Wt (g) ± 0.0630, or [3-31] 

EMR (kcal/day) = 0.5404 Wt

0.7545 (g), or 

log EMR (kcal/day) = 1.996 + 0.7545 log Wt (kg), or 

EMR (kcal/day) = 99.03 Wt

0.7545 (kg), or 

The average increase of EMR at 30�C over BMR is 31 and 26 percent in passerine and nonpasserine species, respectively (Kendeigh, 1970). At 0�C, on the other hand, EMR of 

passerine and non-passerine species is similar, indicating that non-passerines are affected 

3-20
�

Table 3-2. Allometric Equations for Basal Metabolic Rate (BMR) in Birdsa 

Number SE of SE of b b 

of data mean mean 

Avian group points a log a b BMR log BMR 

Apodiformes 9 114 2.06 0.769 0.201 0.0558 

Strigiformes 7 66.4 1.82 0.69 11.1 0.0989 

Columbiformes 10 92.1 1.96 0.858 2.68 0.0491 

Galliformes 13 72.6 1.86 0.698 15.3 0.0904 

Falconiformes 5 65.3 1.82 0.648 45.3 0.108 

Anseriformes 9 95.8 1.98 0.634 23.4 0.0524 

Ciconiiformes 7 86.9 1.94 0.737 22.0 0.0464 

Passeriformes 48 129 2.11 0.724 8.71 0.0806 

Corvidae 8 126 2.10 0.709 23.3 0.147 

Ploeceidae 17 164 2.21 0.794 1.40 0.0808 

Fringillidae 19 125 2.10 0.714 1.02 0.0473 

All Nonpasserines 72 78.5 1.90 0.723 42.8 0.111 

All Species 120 86.3 1.94 0.668 52.8 0.133 

a

Values for the equation relating BMR to body weight (Wt): log BMR (kcal/day) = log a + b log Wt (kg). b

Estimated from the mean log Wt used to develop the allometric equation. 

Source: Zar, 1968. 

more by cold than passerines. Kendeigh (1970) estimated the equation for all bird species 

(N = 24) at 0�C to equal: 

All birds (24 species) 

log EMR (kcal/day) = 0.6372 + 0.5300 log Wt (g) ± 0.0613, or [3-32] 

EMR (kcal/day) = 4.337 Wt

0.5300 (g) 

3-21
�

�

The equations also indicate that smaller species are affected more by cold than are larger 

species. The slopes of the regression lines for EMR on body weight is less steep at 0�C 

than at 30�C, indicating that small birds must increase heat production more than large 

birds to regulate body temperature during cold weather. 

To normalize EMR to body weight, divide the daily EMR by body weight: 

NEMR (kcal/kg-day) = EMR (kcal/day) / Wt (kg) [3-33] 

3.5.1.3. Free-Living Metabolic Rate 

FMRs have been measured using doubly-labeled water (DLW) to measure CO2 

production in animals in the field. Based on DLW measurements with 25 species of birds, 

Nagy (1987) developed an equation relating FMR for birds to body weight: 

FMR (kjoules/day) = 10.89 Wt

0.640 (g), or all birds [3-34] 

FMR (kcal/day) = 2.601 Wt

0.640 (g) 

In birds, the slope of FMR (i.e., 0.640) does not differ significantly from the BMR slope of 

0.668 (see Table 3-2). This indicates that FMR may be a relatively constant multiple of BMR 

in birds over a large range of body mass. 

Using estimates of FMR determined for 42 species by a variety of methods, 

Walsberg (1983) found a similar relationship (r

2 = 0.98, SE Y = 0.415, SE b = 0.012): 

FMR (kjoules/day) = 13.05 Wt

0.605 (g), or all birds [3-35] 

FMR (kcal/day) = 3.12 Wt

0.605 (g) 

Separating the passerine from the non-passerine species, Nagy (1987) found a 

higher FMR among passerines than non-passerines of comparable weight (i.e., the Yintercept for passerines is higher than the Y-intercept for non-passerines), as expected on 

the basis of basal metabolic rate: 

3-22
FMR (kjoules/day) = 8.892 Wt

0.749 (g), or passerines [3-36] 

FMR (kcal/day) = 2.123 Wt

0.749 (g) 

FMR (kjoules/day) = 4.797 Wt

0.749 (g), or non-passerines [3-37] 

FMR (kcal/day) = 1.146 Wt

0.749 (g) 

FMR (kjoules/day) = 8.017 Wt

0.704 (g), or seabirds [3-38] 

FMR (kcal/day) = 1.916 Wt

0.704 (g) 

FMR (kjoules/day) = 21.13 Wt

0.440 (g), or non-seabirdsc [3-39] 

FMR (kcal/day) = 5.051 Wt

0.440 (g) 

We provide the regression statistics for Nagy's (1987) equations (including sample 

size and the regression coefficient) and information required to estimate a 95-percent 

confidence interval for an FMR in Section 3.7.

d 

Nagy (1987) estimated the accuracy of the doubly-labeled water method to be ± 8 

percent or better. Because of difficulties in recapturing birds during the nonbreeding 

season, most of the measured FMRs were for breeding birds (Nagy, 1987). 

King (1974) estimated that FMR exceeds BMR by a factor of 3.5 on average (based 

on a sample of 18 measures for species ranging from 4 to 400 g in weight). Gessaman 

(1973) summarized data on mockingbirds and purple martins from Utter (1971) that 

indicated an FMR equal to 1.6 to 2.4 times the predicted BMR for adults not actively feeding 

nestlings. Feeding nestlings increased the ratio of FMR to BMR from 2.7 to 3.4 in purple 

martins (Utter, 1971, cited in Gessaman, 1973). 

c

All of the large birds included in the database were seabirds such as noddy, kittiwake, shearwater,

albatross, tern, and petrel (Nagy, 1987). Other large birds, such as herons, hawks, and owls, were 

not included. Accordingly, non-passerine and non-seabird equations should be used with caution. d

Insufficient information is provided in Walsberg (1983) to estimate confidence intervals for a 

predicted FMR for species with body weights above or below the mean log body weight value of 

his data set. 

3-23 
� �

�

�

To normalize FMR to body weight, divide the daily FMR by body weight: 

NFMR (kcal/kg-day) = FMR (kcal/day) / Wt (kg) [3-40] 

Figure 3-1 illustrates approximate monthly variations in the total energy budget of 

an adult house sparrow in Illinois throughout the year and the relationship between BMR 

and FMR (adapted from Kendeigh et al., 1977). For this bird, FMR varies seasonally, with a 

maximum value in midwinter (28 kcal/day) and a minimum in August prior to molting (20 

kcal/day). Other species, however (e.g., willow ptarmigan), show no significant variation in 

FMR with season (King, 1974). For examples of nestling energy budgets, see Kendeigh et 

al. (1977) and Dunn (1980). For a discussion of modeling energy budgets for birds in 

general and for seabirds in particular, see Wiens (1984). 

3.5.1.4. Temperature and Metabolic Rate 

Below an animal's thermoneutral zone, metabolism increases with decreasing 

ambient temperature. Section 3.5.1.2 presented equations for EMR at 30�C and at 0�C, but 

these are not particularly helpful for estimating EMR at other temperatures. Although few 

researchers have attempted general multiple regressions of metabolic rate on both body 

size and temperature for birds, some relationships have been investigated in general terms 

(Peters, 1983): 

� Low temperatures induce a greater proportional rise in metabolic rate 

relative to basal metabolic rate in smaller birds than in larger ones.e 

� At high temperatures, metabolic rate increases to increase blood flow and 

evaporative cooling (via panting). 

e

This is because conductance and heat loss for a given thermal gradient between body temperature

and ambient temperature rise more slowly with body size than do basal metabolic rates. 

3-24 

�

Peters (1983) developed an equation relating the ratio of SMR to BMR to thermal gradient 

(i.e., the difference between ambient temperature and body temperature) for birds: 

SMR/BMR = 0.029 (thermal gradient in �C) Wt

-0.249 (kg) [3-41] 

Thus, standard metabolic costs increase relative to basal metabolism at lower 

temperatures, but less so for larger birds than for smaller birds. Despite the strong 

dependence of metabolic rate on ambient temperature, for screening-level risk 

assessments, it should not be necessary to adjust estimates of FMR for seasonal 

temperature changes. As Figure 3-1 illustrates, high metabolic demands of 

thermoregulation in the winter can be replaced by those of reproduction and molting 

during spring, summer, and fall. 

3.5.2. Mammals 

As for birds, metabolic rate in mammals generally decreases with increasing body 

size. The metabolic rates of herbivorous and carnivorous mammals are similar for 

similarly sized species. In this section, we present allometric models for three measures of 

metabolic rate on the basis of body size in mammals: basal metabolic rate (BMR), resting 

metabolic rate (RMR), and free-living metabolic rate (FMR). All equations take the general 

form of Y = aWt

b

, but also can be represented in their log-transformed form (the equation 

of a straight line). We conclude this section by discussing the influence of ambient 

temperature on mammalian metabolic rates. Additional information that allows one to 

estimate a 95-percent confidence interval for a predicted FMR, the expression of metabolic 

rate that is generally most appropriate for wildlife exposure assessments, is provided in 

Section 3.7. 

3.5.2.1. Basal Metabolic Rate 

On the basis of BMR measurements for 26 species weighing 3.5 to 600 kg, Kleiber 

(1961) estimated that BMR was related to body weight in mammals according to the 3/4 

power: 

3-26
BMR (kcal/day) = 70 Wt

0.75 (kg) ± 0.004 

Boddington's (1978) analysis produced similar results: 

[3-42] 

BMR (kcal/day) = 75 Wt [3-43] 0.73 

3.5.2.2. Resting Metabolism 

(kg) ± 0.013 

Stahl (1967) used an extensive database (349 species) to determine slightly higher 

values for RMR than had been determined for BMR (Section 2.5.2.1): 

RMR (kcal/day) = 80 Wt

0.76 

3.5.2.3. Field Metabolic Rate 

(kg) [3-44] 

Based on doubly-labeled water measurements with 23 species of placental 

mammals, Nagy (1987) developed an equation relating FMR to body weight: 

FMR (kjoules/day) = 3.35 Wt

0.813 (g), or placental mammals 

FMR (kcal/day) = 0.800 Wt

0.813 (g) 

[3-45]

The slope of 0.813 is significantly higher than the BMR slopes of 0.73 to 0.76 reported 

above. Thus, the FMR does not appear to be a constant multiple of BMR over a range of 

body sizes as was the case in birds. However, no FMR measurements have yet been made 

on shrews or other very active small mammals, and whales were included in the FMR data 

set (Nagy, 1987). 

Separating the herbivores from non-herbivores, Nagy (1987) developed two 

additional equations: 

FMR (kjoules/day) = 5.943 Wt

0.727 

FMR (kcal/day) = 1.419 Wt

0.727 

(g), or herbivores [3-46] 

(g) 

3-27
�

�

FMR (kjoules/day) = 2.582 Wt

0.862 (g), or non-herbivores [3-47] 

FMR (kcal/day) = 0.6167 Wt

0.862 (g) 

Separating rodents from other animals, Nagy (1987) found: 

FMR (kjoules/day) = 10.51 Wt

0.507 (g), or rodents [3-48] 

FMR (kcal/day) = 2.514 Wt

0.507 (g) 

Nagy (1987) estimated the accuracy of the doubly-labeled water method to be ± 8 percent 

or better. 

To normalize FMR to body weight (e.g., kcal/kg-day), divide the daily FMR by body 

weight. In Section 3.7, we provide the regression statistics for Nagy's (1987) equations 

(including sample size and the regression coefficient) and information that allows one to 

estimate a 95-percent confidence interval for an FMR value predicted for a specified body 

weight. 

3.5.2.4. Temperature and Metabolic Rate 

Few researchers have attempted general multiple regressions of metabolic rate with 

both body mass and temperature for mammals. However, several relationships have been 

investigated qualitatively (Peters, 1983): 

� Low temperatures induce a greater proportional rise in metabolic rate 

relative to basal metabolic rate in smaller mammals than in larger ones.f 

� At high temperatures, metabolic rate increases to increase blood flow and 

evaporative cooling (e.g., panting). 

f

This is because conductance and heat loss for a given thermal gradient between body temperature 

and ambient temperature rise more slowly with body size than do basal metabolic rates (Peters, 

1983). 

3-28 
�

�

�

Peters (1983) developed an equation relating the ratio of SMR to BMR to thermal gradient 

for mammals: 

SMR/BMR = 0.068 (thermal gradient in �C) Wt

-0.182 (kg) [3-49] 

Thus, standard metabolic costs increase relative to basal metabolism at lower 

temperatures, but less so for larger than for smaller mammals. 

3.5.3. Reptiles and Amphibians 

Most reptiles and amphibians tend to have much lower metabolic rates than birds or 

mammals because they are poikilothermic. For example, at temperatures similar to normal 

body temperatures of birds and mammals (around 37 to 39�C), resting metabolic rates of 

reptiles and amphibians tend to be only 10 to 20 percent of those of birds and mammals of 

similar body weight (Bennett and Dawson, 1976). In this section, we provide some 

examples of allometric equations for metabolic rate. Because metabolic rate depends on 

body temperature, which in poikilotherms can vary substantially over time, we recommend 

that those persons interested in estimating metabolic rates consult more complete 

treatments of the subject, including thermoregulation in poikilotherms (e.g., Bennett and 

Dawson, 1976; Congdon et al., 1982; Duellman and Trueb, 1986; Feder and Burggren, 1992; 

Harless and Morlock, 1979; Hutchinson, 1979). 

3.5.3.1. Basal and Resting Metabolic Rates 

Robinson et al. (1983) developed an equation for the relationship between BMR and 

body mass for reptiles and amphibians at 20�C: 

BMR (Watts) = 0.19 Wt

0.76 (kg), or [3-50] 

BMR (kcal/day) = 3.92 Wt

0.76 (kg) 

Thus, the BMR of homeotherms (Sections 3.5.1 and 3.5.2) is approximately 30 times the 

BMR of poikilotherms at this ambient temperature (Peters, 1983). The difference in 

3-29
�

�

�

metabolic rates between homeotherms and poikilotherms is lessened when poikilotherms 

modify their body temperatures by behavioral adjustments (such as basking in the sun). 

Andrews and Pough (1985) used multiple regression analysis to evaluate the 

relationship between metabolic rate and three variables—mass, temperature, and standard 

or resting metabolic state—for snakes and lizards. From a total of 226 observations on 107 

species (between 20 and 30�C for most observations), they developed the following 

equation: 

MR (ml O2/hr) = 0.013 Wt

0.80 (g) × 100.038 temperature (�C) [3-51] 

× 100.14 metabolic state 

where MR equals either SMR or RMR and metabolic state equals zero (0) for standard 

metabolismg and equals 1 for resting metabolism.

h The Q10 values for the influence of 

temperature on metabolic rate (i.e., quotient of the rate measured at one temperature 

divided by the rate measured at a temperature 10�C lower) were 2.4 for resting metabolism 

and 1.4 for standard metabolism. Thus SMR depended less on ambient temperature than 

did RMR. 

Equation 3-51 is based on adult animals and should not be used to estimate 

metabolic rates of juvenile snakes and lizards. Andrews and Pough (1985) reviewed 

allometric equations relating resting metabolic rate to body weight within species and 

found that the exponents were significantly lower than the value of 0.80 in Equation 3-51. 

See Andrews and Pough (1985) for intraspecific allometric models for this group. 

3.5.3.2. Free-Living Metabolic Rates 

Nagy (1987) developed an equation for the relationship between FMR and body size 

in iguanid lizards: 

g

Measured for fasting individuals during the period of normal inactivity (at night for most species). h

Measured for fasting individuals during the period of normal activity (daytime for most species). 

3-30 
�

�

� �

FMR (kjoules/day) = 0.224 Wt

0.799 (g), or [3-52] 

FMR (kcal/day) = 0.0535 Wt

0.799 (g) 

Bennett and Nagy (1977) estimated that the ratio of FMR to EMR for lizards is 2.0. 

Robinson et al. (1983) estimated the value to be 2.9, assuming that lizards rest at 

maintenance levels for 8 hours per day at 35�C. 

Feder (1981, 1982) presented equations relating FMR to body size of unrestrained 

ranid (frog) tadpoles at 25�C: 

dry mass (mg) = 0.047 (wet mass)1.06 (mg) [3-53] 

and 

FMR (μlO2/hr) = 2.5 (dry mass)0.878 (mg), or [3-54] 

FMR (mlO2/day) = 0.06 (dry mass)0.878 (mg) 

Assuming 1 milliliter of oxygen is metabolically equivalent to approximately 4.80 calories 

(Dawson, 1974): 

FMR (cal/day) = 0.288 (dry mass)0.878 (mg) [3-55] 

Burggren et al. (1983) estimated Q10 values for metabolic rates for bullfrog larvae of 1.87 

between temperatures of 15 and 25�C and of 2.41 between temperatures of 25 and 33�C. 

Q10 values for a second ranid species (Rana berlandieri) were similar (1.97 and 1.76, 

respectively). Thus, the metabolic rate for ranid frogs approximately doubles with each 10-

degree rise in temperature over this range of temperatures. 

The equations presented in this section show that poikilotherm metabolic rate 

depends strongly on temperature. The available literature on the subject is extensive and 

complex, and again, interested readers are encouraged to consult substantive treatments 

of the subject (see references cited in the introduction to Section 3.5.3). 

3-31
3.6. MATH PRIMER AND UNIT CONVERSIONS 

To assist readers in using or modifying allometric equations presented in this 

Handbook or in using allometric equations presented in the open literature, we provide a 

brief summary of logarithm and power functions in Sections 3.6.1 and 3.6.2. Section 3.6.3 

contains frequently used unit conversion factors. 

3.6.1. Summary of Operations Involving Logarithms 

log 1 = 0 

log (N1 N2) = log N1 + log N2 

log (N1 / N2) = log N1 - log N2 

log (1 / N1) = -log N1 

c log (N1 ) = c log N1 

= log (N1

1/c

) = (1/c) log N1 log c root of N1 

3.6.2. Summary of Operations Involving Powers 

W Wa b = Wa+b 

a b (W ) = Wab 

a a a (WW) 1 2 = W1 W2

W / a Wb = Wa-b 

W / a W = Wa-1 

1/Wb = W-b 

W =0 1

a a a (W1 / W2) = W1 /W2 

c root of Wa = (Wa)

1/c = Wa/c 

3-32
3.6.3. Unit Conversions

3.6.3.1. Approximate Factors for Metabolic Equations

1 kg dry mass 

1 kg dry mass 

1 kg wet mass 

1 kg fat 

tissue density 

1 kg wet mass 

1 kg dry mass 

1 ml O2 

= 3 to 10 kg wet mass (Peters, 1983) 

= 22 × 10 (Peters, 1983) 6 joules 

= 2 to 7 × 106 joules 

= 40 × 106 joules 

= 1 kg/liter 

= 1 × 1015 μm3 

= 0.4 kg carbon 

= 20.1 joules 

= 4.8 calories 

(Peters, 1983) 

(Peters, 1983) 

(Peters, 1983) 

(Peters, 1983) 

(Peters, 1983) 

(Peters, 1983)

(Dawson, 1974)

0.4047 hectares (ha)

259 ha

1 × 10-4 ha

100 ha

3.6.3.2. Exact Conversions 

Area 

1 acre = 

1 square mile mi2

) = 

1 square meter (m2

) = 

1 square kilometer (km2

) = 

Length 

1 inch 

1 foot = 

1 mile (mi) 

Volume 

1 m3 

Mass 

1 ounce (oz) 

1 pound (lb) 

1 lb 

= 2.54 centimeters (cm) 

0.3 meters (m) 

= 

= 

= 

= 

= 

= 

= 

30.48 cm 

1.61 kilometers (km) 

1 × 103 liters (L) 

3 1 × 106 cm

28.35 grams (g) 

453.6 g 

0.4536 kilograms (kg) 

3-33
Work and energy (force × distance) 

1 joule (J) = 1 kg-m2/s2 

= 0.239 calories (cal) 

Power (energy per unit time) 

1 watt (W) = 1 kg-m2/s3 

= 1 joule/s 

= 20.64 kcal/day 

1 ml O2/s = 0.0446 mMol O2/s 

= 1.43 mg O2/s 

3.7. ESTIMATING CONFIDENCE INTERVALS 

A commonly reported measure of the precision of estimating log Y from log Wt (or Y 

from Wt) for allometric equations is the standard error (SE) of log Y: 

log Y = log a + b log Wt ± SE of log Y [3-2] 

The SE of log Y is the standard error of the estimate of log Y from log Wt at a value of log 

Wt that represents the mean of the log Wt values used to estimate the allometric 

relationship. This value cannot be used to estimate a confidence interval (CI) for a log Y 

value predicted from log Wt values other than the mean log Wt value. The CI of a predicted 

log Y value is smallest at the mean log Y and mean log Wt values and increases as log Wt 

for the species of interest deviates from mean log Wt. Thus, to estimate the CI for a single 

predicted value of Y, one also must know the sample size and the mean of the log Wt 

values used in developing the allometric equation, which many investigators do not report. 

Nagy (1987), however, did provide sufficient statistical information to estimate a 95-

percent CI for a predicted value of Y given any value of Wt for his free-living (field) 

metabolic rate (FMR) and food ingestion (FI) rate equations. In this section, we outline 

Nagy's short-cut for estimating this CI and provide the statistical values required for each 

of Nagy's equations presented in this Handbook. 

3-34
To estimate 95-percent CIs for the predicted FMR and FI rate, use the values from 

Table 3-3 (for FI rate equations) or 3-4 (for FMR equations) in the following formula: 

______ 

2 0.5 95% CIlog y = log y ± c [d + e (log Wt - log Wt) ]

where y is FMR in kilojoules/day or FI in grams (dry weight)/day. Log Wt is the log of the 

body weight in grams of the species for which y is being estimated. Log Wt bar is the 

mean log Wt of the species used to develop the allometric equation. Values for c, d, e, and 

log Wt bar are provided in Tables 3-3 and 3-4. Tables 3-3 and 3-4 also provide sample 

sizes (N), regression coefficients (r2

), and SE estimates for b and log a in the applicable 

equations. 

3-35
Table 3-3. Regression Statistics for Nagy's (1987) Allometric Equations for Food Ingestion Rates for Free-Living Animals 

Regression Statistics for Allometric Equations for Food Ingestion (FI) Rates (Dry Matter Ingestion) Rates of Free-Living Mammals, Birds, 

and Lizards. Equations are in the form Y = aWt where Y is Food Ingestion Rate (in grams dry weight/day) and Wt is body weight of b 

species s (grams wet weight). 

______ 

95% CI = log FI ± c [d + e (log Wt - log Wt) ] log FI(species s) (species s) (species s) 

2 0.5 

Group 

subgroup 

Equation a log a (SE log a) b (SE b) N r2 ______ 

log Wt c d e 

Birds 3-3 0.64 -0.188 (0.060) 0.651 (0.028) 50 0.919 1.983 0.347 1.020 0.026 

passerines 3-4 0.40 -0.400 (0.075) 0.850 (0.053) 26 0.915 1.378 0.158 1.038 0.480 

non-passerines 3-5 0.30 -0.521 (0.132) 0.751 (0.048) 24 0.919 2.638 0.401 1.042 0.061 

seabirds 3-6 0.49 -0.306 (0.187) 0.704 (0.061) 15 0.911 2.958 0.399 1.067 0.109 

Eutherian Mammals 

(i.e., placental) 

3-7 0.23 -0.629 (0.065) 0.822 (0.026) 46 0.958 2.196 0.425 1.022 0.015 

rodents 3-8 0.62 -0.207 (0.194) 0.564 (0.119) 33 0.421 1.598 0.434 1.030 0.313 

herbivores 3-9 0.58 -0.239 (0.109) 0.727 (0.039) 17 0.960 2.566 0.405 1.059 0.041 

Iguanids 

herbivores 3-12 0.019 -1.713 (0.123) 0.841 (0.059) 5 0.985 1.896 0.358 1.200 0.278 

insectivores 3-13 0.012 -1.890 (0.037) 0.773 (0.038) 20 0.958 0.870 0.151 1.050 0.279 

3-36

Source: Nagy, 1987. 
Table 3-4. Regression Statistics for Nagy's (1987) Allometric Equations for Free-Living (Field) Metabolic Rates 

Regression Statistics for Allometric Equations for Free-Living Metabolic Rates (FMR) of Free-Living Mammals, Birds, and Lizards. 

Equations are in the form Y = aWt where Y is FMR (in kilojoules/day) and Wt is body weight of species s (grams wet weight). b 

______ 

95% CI = log FMR ± c [d + e (log Wt - log Wt) ] log FMR(species s) (species s) (species s) 

2 0.5 

Group 

subgroup 

Equation a log a (SE log a) b (SE b) N r2 ______ 

log Wt c d e 

Birds 3-34 10.9 1.037 (0.064) 0.640 (0.030) 50 0.907 1.983 0.368 1.020 0.026 

passerines 3-36 8.89 0.949 (0.059) 

non-passerines 3-37 4.79 0.681 (0.102) 

seabirds 3-38 8.02 0.904 (0.187) 

non-seabirds 3-39 21.1 1.325 (0.081) 

0.749 (0.037) 26 0.899 1.378 2.014 0.026 

24 0.899 2.638 2.014 0.026 

15 0.911 2.958 0.399 1.067 

35 0.709 1.565 0.297 1.029 

0.0014 

0.749 (0.037) 0.0014 

0.704 (0.061) 0.109 

0.440 (0.049) 0.113

Eutherian 

Mammals (i.e., 

placental) 

3-45 3.35 0.525 (0.057) 0.813 (0.023) 46 0.967 2.196 0.371 1.022 0.015 

rodents 3-48 10.5 1.022 (0.141) 0.507 (0.087) 33 0.524 1.598 0.316 1.030 0.313 

3-37

herbivores 3-46 5.94 0.774 (0.109) 

non-herbivores 3-47 2.58 0.412 (0.058) 

Iguanids 3-52 0.224 -0.650 (0.029) 

0.727 (0.039) 17 0.959 2.566 0.406 1.059 

29 0.977 1.980 0.321 1.035 

25 0.981 1.075 0.161 1.040 

0.041 

0.862 (0.026) 0.027 

0.799 (0.023) 

Source: Nagy, 1987. 

0.088 
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3-42
� �

4. EXPOSURE ESTIMATES 

This section provides equations to estimate oral doses of chemical contaminants 

for wildlife, along with a discussion of dose estimates for other exposure routes. Section 

4.1 provides general dose equations. Equations for drinking water exposures are 

presented in Section 4.1.1, followed by equations for dietary exposures in Section 4.1.2. In 

the dietary exposure section, data on the caloric and water content of various food types 

and diet assimilation efficiencies are also provided. An equation and data to facilitate 

estimating doses received through soil or sediment ingestion are discussed in Section 

4.1.3. Sections 4.1.4 and 4.1.5 provide a qualitative discussion of inhalation and dermal 

dose estimates. Section 4.2 describes considerations for analyses of uncertainty in 

exposure assessments. References are provided in Section 4.3. 

4.1. GENERAL DOSE EQUATIONS 

EPA's (1992a) Framework for Ecological Risk Assessment defines exposure as the 

co-occurrence of or contact between a stressor and an ecological component. When 

assessing risks of exposure to chemical contaminants, potential dose is often the metric 

used to quantify exposure. Potential dose is defined as the amount of chemical present in 

food or water ingested, air inhaled, or material applied to the skin (U.S. EPA, 1992b). 

Potential dose is analogous to the administered dose in a toxicity test. Because exposure 

to chemicals in the environment is generally inadvertent, rather than administered, EPA's 

(1992b) Guidelines for Exposure Assessment use the term potential dose rather than 

administered dose. 

A general equation for estimating dose for intake processes is: 

t2 

Dpot � � C(t) IR(t) dt [4-1] 

t1 

4-1
where Dpot is the total potential dose over time (e.g., total mg contaminant intake between 

t1 and t2), C(t) is the contaminant concentration in the contacted medium at time t (e.g., mg 

contaminant/kg medium), and IR(t) is the intake rate of the contaminated medium at time t 

measured as mass ingested or inhaled by an animal per unit time (e.g., kg medium/day). If 

C and IR are constant over time, then the total potential dose can be estimated as: 

Dpot = C × IR × ED [4-2] 

where ED is the exposure duration and equals t2 - t1. 

Therefore, if C and IR are constant, the potential average daily dose (ADDpot) for the 

duration of the exposure, normalized to the animal's body weight (e.g., mg/kg-day), is 

estimated by dividing total potential dose by ED and by body weight (BW): 

ADDpot = (C × IR × ED) / (BW × ED), or [4-3] 

ADDpot = (C × IR) / BW 

If C or IR vary over time, they may be averaged over ED. However, it is not always 

appropriate to average intake over the entire exposure duration: For example, a given 

quantity of a chemical might acutely poison an animal if ingested in a single event, but if 

that amount is averaged over a longer period, effects might not be expected at all. 

Similarly, developmental effects occur only during specific periods of gestation or 

development. A toxicologist should be consulted to determine which effects may be of 

concern given the exposure pattern and chemicals of interest. For carcinogenic 

compounds, it may be more appropriate to average exposure over the animal's lifetime. 

Again, address any questions to a toxicologist. 

In addition, IR and BW can be combined into a normalized ingestion or inhalation 

rate (NIR) (e.g., kg medium/kg body weight - day): 

NIR = IR / BW [4-4] 

4-2
Therefore, 

ADDpot = C × NIR [4-5] 

It is important to remember that NIR can vary with changes in age, size, and reproductive 

status of an animal. 

Two other variables often are used in calculations of average daily dose. A 

frequency term (FR) is used to denote the fraction of the time that an animal is exposed to 

contaminated media. In ecological exposure assessments, this term often is used when 

a the foraging range of an animal is larger than the area of contamination. An absorption

factor (ABS) is used when an estimate of absorbed dose rather than potential dose is

desired. It is commonly assumed that absorption in the species of concern in the field is

the same as in the test organism, so no absorption factor is needed. However, if

absorption is expected to differ, a ratio of the absorption factors would be used in the

exposure equation.

4.1.1. Drinking Water

Figure 4-1 presents two wildlife oral exposure equations corresponding to two patterns of

contamination of water:

(1) the animal obtains some of its drinking water from a contaminated source 

and the remainder from uncontaminated sources; and 

(2) the animal consumes drinking water from several sources contaminated at 

different levels. 

a

The frequency term should be estimated with care. For example, if a feature attractive to wildlife

is contaminated, an animal may spend a proportionally longer time in the contaminated area. 

Similarly, if only part of an animal's theoretical foraging range has suitable habitat, the animal may 

spend more time feeding in that habitat. Finally, animals may avoid areas or media with 

contamination they can detect. 

4-3 
Figure 4-1. Wildlife Dose Equations for Drinking Water Exposures 

One Source of Contamination 

ADD = C × FR × NIR [4-6] pot 

Different Sources With Varying Levels of Contamination 

n 

ADD = � (C × FR ) x NIR [4-7] pot i i 

i=1 

ADDpot = Potential average daily dose (e.g., in mg/kg-day). 

C = Average contaminant concentration in a single water source (e.g., in mg/L or 

in mg/kg, because 1 liter of water weighs 1 kg). 

FR = Fraction of total water ingestion from the contaminated water source 

(unitless). 

NIR = Normalized water ingestion rate (i.e., fraction of body weight consumed as 

water per unit time; e.g., in g/g-day) 

and 

th Ci = Average contaminant concentration in the i water source (e.g., in mg/L).

 FRi = Fraction of water consumed from the ith water source (unitless). 

n = Number of contaminated water sources. 

In the first case, the distribution and mean value of the contaminant concentration in the 

one source could be determined. In the second case, the different water sources are likely 

to be characterized by different mean levels of contamination, and consumption from these 

sources would be weighted by the fraction (FRi

) of the animal's total daily water ingestion 

obtained from each source. FR (or FRi

) in Figure 4-1 is a function of the degree of overlap 

of the contaminated water source(s) and the animal's home range. If the area of the 

contaminated water source is larger than the typical home range for the species, FR could 

4-4
equal one for many individuals. The number of individuals for which FR equals one could 

be estimated from information on population density, distribution, and social structure. 

For large, mobile animals, the area of contamination may be smaller than the area over 

which a single animal is likely to move. In these cases, FR for an animal with the 

contaminated area entirely within its home range can be estimated using information on 

the home range, attributes of the contaminated area, and drinking behavior of the animal. 

Home range estimates should be used with care because (1) the area in which an animal 

moves varies with several factors, including reproductive status, season, and habitat 

quality; (2) most animals do not drink or feed randomly within their home range; (3) the 

term home range has been used inconsistently in the literature; and (4) estimates of home 

range can vary substantially with the measurement technique used. In this Handbook and 

accompanying Appendix, we have tried to identify clearly which estimates of home range 

correspond to a daily activity and foraging home range. 

When using home range data, we recommend that users consult the Appendix 

tables for the species of interest to become familiar with how estimates of home range size 

vary with geographic area, season, type of habitat, animal reproductive status, and 

measurement technique. The Appendix tables provide both the sample size and a brief 

description of the method used to estimate home range size, which can help indicate the 

robustness of an estimate and whether it is likely to over- or underestimate home range 

size. For mark-and-recapture studies, the number of recaptures per animal is provided 

when possible to assist the user in determining the degree to which the reported values 

may underestimate true home range size. If a study indicated that the home range 

estimate is likely to include areas outside of the animals' usual activity range (e.g., distant 

egg-laying sites used only once per season), this would be noted in the Appendix tables, 

and the value would not be included in Chapter 2. Some animals use a fixed "home base" 

some distance from feeding grounds such as a rookery. For these animals, we have 

reported foraging radius (the distance they will travel to a feeding area). Foraging radius 

can be used to determine whether the animal might feed or drink in a given contaminated 

area. 

4-5
4.1.2. Diet 

Wildlife can be exposed to contaminants in one or more components of their diet, 

and different components can be contaminated at different levels. In this section, we 

outline methods of estimating food ingestion rates that allow total doses to be estimated 

when different components of the diet are contaminated, either at similar or different levels 

(Section 4.1.2.1). We also provide data on caloric content of foods and assimilation 

efficiencies that can be used in the dose equations provided (Section 4.1.2.2). 

4.1.2.1. Dose Equations 

Figure 4-2 presents a generic equation for estimating oral doses of contaminants in 

food for wildlife species. FRk is a function of the degree of overlap of the k type of th 

simplest case, the normalized ingestion rate for each food type, NIRk, is known on a wetFigure 4-2. Wildlife Dose Equations for Dietary Exposures 

m 

ADDpot = � (Ck × FRk × NIRk) [4-8] 

k=1 

ADDpot = Potential average daily dose (e.g., in mg/kg-day). 

Ck = Average contaminant concentration in the kth type of food (e.g., in mg/kg wet 

weight). 

FRk = Fraction of intake of the kth food type that is contaminated (unitless). For 

example, if the kth component of an animal's diet were salmon, FRk for salmon 

would equal the fraction of the salmon consumed that is contaminated at level 

Ck. If all of the salmon consumed were contaminated at level Ck, then FRk 

would equal one. 

NIRk = Normalized ingestion rate of the kth food type on a wet-weight basis (e.g., in 

g/g-day). 

m = Number of contaminated food types. 

4-6
contaminated forage or prey and the animal's home range (see Section 4.1.1). In the 

weight basis, and Equation 4-8 can be used directly. In many cases, however, NIRk is 

unknown or has been determined for laboratory diets that differ significantly from natural 

diets in terms of caloric value per unit wet weight. Ingestion rates based on relatively dry 

laboratory diets might underestimate the amount of food a free-living animal consumes. 

There are several ways to estimate NIRk, depending on the type of information that 

is available. If dietary composition is expressed as the number of each prey type captured 

on a daily basis (Nk), estimating the normalized ingestion rate for each prey type (NIRk) 

requires only one step: 

NIRk = (Nk × Wtk) / BW [4-9] 

where Wtk is the body weight of the kth prey type and BW is the body weight of the 

predator. 

Figure 4-3 presents a flow chart depicting equations that can be used if the 

proportion of the diet for a given food type has been measured or estimated on a wetweight basis. These equations may require estimates of the free-living metabolic rate 

(FMR) of the organism and the metabolizable energy (ME) of the organism's forage or prey. 

Estimated FMRs can be found in the species profiles in Chapter 2, and allometric equations 

for estimating FMR on the basis of body weight are provided in Chapter 3 (Section 3.5). ME 

should be averaged over the food types when ME on a wet-weight basis (e.g., cal/g wet 

weight) differs substantially among the different foods. Section 4.1.2.2 describes how to 

estimate ME. 

A common situation facing someone conducting a wildlife exposure assessment for 

predators is that in a key study, dietary composition is expressed as a percentage of the 

total number of prey captured over a period of time instead of as a percentage of the total 

wet weight of food ingested daily. Because some prey can be substantially larger than 

others (e.g., rabbits compared with voles), and because ME of different types of prey may 

4-7

Figure 4-4. Estimating NIRk Based on Different ME Values When Dietary Composition Is 

Expressed as Percentage of Total Prey Captured 

Step 1: Calculate the metabolizable energy (ME) content of each prey or food type 

on a wet-weight basis: 

ME(wet wt)k = GE(wet wt)k × AEk [4-13] 

Step 2: Estimate the average number of prey (or other food items) consumed each 

day: 

Navg = FMR / (weighted average prey ME) 

m 

Navg = FMR / (� PNk × Wtk × ME(wet wt)k) 

k=1 

Step 3: Calculate IRk: 

IRk = Ntot × PNk × Wtk 

Step 4: Normalize to body weight: 

NIRk = IRk / BW 

[4-14] 

[4-15] 

[4-16] 

th ME(wet wt)k = Metabolizable energy in the k prey or food type (e.g., in kcal/g wet weight). th GE(wet wt)k = Gross energy content of the k food type (e.g., in kcal/g wet weight). th AEk = Assimilation efficiency for the species for the k food type (unitless).

Navg = Average number of prey (or other food items) eaten each day.

FMR = Free-living metabolic rate (e.g., in kcal/day).

m = Number of different types of prey or other foods. th PNk = Proportion of the total number of prey that is composed of the k prey type

(unitless). It often is the case that larger numbers of relatively small prey 

and smaller numbers of relatively large prey are captured. (If the total 

number of prey of each type captured each day are reported in the 

literature, calculations of IRk are very simple [i.e., Nk × Wtk] and steps 1 and 

2 are unnecessary.) 

W th tk = Body weight of an individual of the k food type (e.g., in g). th IRk = Ingestion rate of the k food type (e.g., in g/day). 

4-9
and the weighted average ME of the prey. Given Navg , the ingestion rate for each prey type 

(IRk) can be computed on a wet-weight basis and normalized to body weight (NIRk). 

Because Navg is estimated using prey weight, different sizes of the same prey species (e.g., 

smaller and larger fish) should be separated into appropriate size intervals to reduce 

uncertainty in the estimate. 

4.1.2.2. Energy Content and Assimilation Efficiencies 

The total or gross energy (GE) content of a food type is a function only of 

characteristics of the food. On the other hand, metabolizable energy (ME) depends on 

characteristics of both the food and the organism eating it. To clarify the meaning of ME, 

Figure 4-5 presents a flow chart of energy utilization by animals. Digestible energy in a diet 

is GE consumed minus the energy lost as feces; digestible energy efficiency (DE) is 

digestible energy divided by GE. ME is GE consumed minus the energy lost as both feces 

and urine. Assimilation efficiency (AE, also called metabolizable energy efficiency) is ME 

divided by GE. Rearranging this relationship, ME is equal to GE of the diet multiplied by 

the animal's AE for the diet as shown in Figure 4-6, Equation 4-17. General ME values can 

be found in Table 3-1 or more specific ones calculated from GE content of the food and the 

AE of the animal eating that food, as discussed below. 

The GE content of food typically is reported using one (or more) of three measures: 

(1) energy per unit total dry weight, (2) energy per unit ash-free dry weight, or (3) energy 

per unit fresh biomass (i.e., per unit wet weight) (Górecki, 1975). Caloric content per unit 

total dry weight is obtained directly from the combustion of dried material in a calorimeter. 

Ash-free dry weight is the dry weight after subtracting the ash content.

b The ash-free dryweight caloric value exceeds the total dry-weight caloric value by the ratio of the total dry 

weight to the ash-free dry weight. Typically, animal (exclusive of thick shells) and plant 

materials are 1 to 10 percent ash on a wet-weight basis and 5 to 30 percent ash on a dryweight basis (Ashwell-Erickson and Elsner, 1981; Cummins and Wuycheck, 1971; 

b

Ash constituents typically include calcium carbonate (e.g., shell), calcium phosphate (vertebrate 

bone), and hydrated silica salts. 

4-10 

Figure 4-6. Metabolizable Energy (ME) Equation 

ME = GE × AE [4-17] 

where: 

ME = Metabolizable energy (e.g., in kcal/g) 

GE = Gross energy (e.g., in kcal/g) 

AE = Assimilation efficiency (unitless) 

This Handbook assumes ME and GE are estimated on a wet-weight basis. To estimate ME or 

GE of the kth food type on a wet-weight basis from dry-weight measurements, the following 

equations can be used: 

GE(wet wt)k = GE(dry wt)k × (1 - proportion waterk) or [4-18] 

GE(wet wt)k = GE(dry wt)

k × (dry 

weightk/wet weightk) [4-19] 

and 

ME(wet wt)k = ME(dry wt)k × (1 - proportion waterk) or [4-20] 

ME(wet wt)k = ME(dry wt)

k × (dry 

weightk/wet weightk) [4-21] 

Hunt, 1972). The ash content of the diet is not metabolized and thus does not provide 

energy to the animal. Figure 4-6 (Equations 4-18 through 4-21) illustrates how the caloric 

content per unit of fresh biomass can be obtained by adjusting the dry-weight value based 

on the water content of the biomass. A summary of GE contents of many wildlife food 

types are presented in Tables 4-1 a given species on a wet-weight basis tends to be more 

variable than caloric content on a dry-weight basis because plants, and to a lesser degree 

animals, vary in their water content depending on environmental conditions. Ash-free dryweight caloric values are not presented because it is not appropriate to use them with the 

equations and AEs in this chapter. Ash contents are accounted for in the AEs presented in 

Table 4-3. 

4-12
Table 4-1. Gross Energy and Water Composition of Wildlife Foods: Animal Prey (values n expressed as mean [standard deviation] where n = number of studies)

Type of food 

Aquatic 

invertebrates 

bivalves (without shell) 

crabs (with shell) 

shrimp 

isopods, amphipods 

cladocerans 

insect larvae 

vertebrates 

bony fishes 

Pacific herring 

small fish (e.g., bluegill) 

Terrestrial 

invertebrates 

earthwormsa 

grasshoppers, crickets 

beetles (adult) 

mammals 

mice, voles, rabbits 

birds 

passerines 

with peak fat reservesb 

with typical fat reserves 

mallard (flesh only) 

gulls, terns 

reptiles and amphibians 

snake, lizards 

frogs, toads 

kcal/g kcal/g 

wet wt % H20 dry wt References 

0.80 82 (4.5)

3 4.6 (0.35)4 1,2,3,4,5,6 

1.0 (0.21)5 74 (6.1)

5 2.7 (0.45)4 1,2,3,7 

1.1 (0.24)4 78 (3.3)

7 4.8 (0.31)6 1,3,4,6,7 

1.1 71-80 3.6 (0.78)3 4,6,7 

0.74 79-87 4.8 (0.62)14 2,4 

5.3 (0.37)8 1,4 

1.2 (0.24)18 75 (5.1)

18 4.9 (0.38)18 7 

2.0 (0.43)3 68 (3.9)

3 6.1 (0.50)4 8,9 

4.1 (0.47)3 1,7 

0.78-0.83 84 (1.7)

3 4.6 (0.36)4 1,7 

1.7 (0.26)3 69 (5.6)

11 5.4 (0.16)4 1,10,11 

1.5 61 (9.8)

5 5.7-5.9 1,10,11 

1.7 (0.28)14 68 (1.6)

4 5.0 (1.3)17 12,13,14 

7.8 (0.18)10 15 

1.9 (0.07)3 68 5.6 (0.34)13 10,14,15,16 

2.0 67 5.9 10 

1.9 4.4 1 

1.4 66 4.5 (0.28)5 

1.2 85 (4.7)

3 4.6 (0.45)3 

14,17 

12,14 

Note: For Tables 4-1 and 4-2, a single value represents the results of a single study on one species, 

and should not be interpreted as a mean value or a value indicating no variation in the category. 

Two values separated by a hyphen indicate that values were obtained from only two studies. 

a

Not including soil in gut, which can constitute one-third of the wet weight of an earthworm. b

Peak fat reserves occur just prior to migration. Typical fat reserves are for resident passerines or 

migratory species during nonmigratory seasons. 

References: (1) Cummins and Wuycheck, 1971; (2) Golley, 1961; (3) Tyler, 1973; (4) Jorgensen et 

al., 1991; (5) Pierotti and Annett, 1987; (6) Minnich, 1982; (7) Thayer et al., 1973; (8) Ashwell-Erickson 

and Elsner, 1981; (9) Miller, 1978; (10) Collopy, 1975; (11) Bell, 1990; (12) Górecki, 1975; (13) Golley, 

1960; (14) Koplin et al., 1980; (15) Odum et al., 1965; (16) Duke et al., 1987; (17) Congdon et al., 1982. 

4-13
algae 

aquatic macrophytes 

emergent vegetation 

Terrestrial 

monocots 

young grasses 

mature dry grasses 

dicots 

leaves 

roots 

bulbs, rhizomes 

stems, branches 

seeds 

fruit 

pulp, skin 

pulp, skin, seeds 

kcal/g 

Type of food wet wta % H20 

Aquatic 

0.41-0.61 84 (4.7)3 

87 (3.1)

3 

[45-80]b 

1.3 70-88 

7-10 

85 (3.5)

3 

9.3 (3.1)

12 

1.1 (0.30)3 77 (3.6)

3 

kcal/g 

dry wt 

2.36 (0.64)4 

4.0 (0.31)12 

4.3 (0.13)3 

4.2 

4.3 (0.33)5 

4.2 (0.49)57 

4.7 (0.43)52 

3.6 (0.68)3 

4.3 (0.34)51 

5.1 (1.1)

57 

2.0 (3.4)

28 

2.2 (1.6)

10 

References 

1,2,3

1,2,4

1,2,4

5,6

1,5,7,8

9

9

2,7,10

9

6,9,11,12

10,13 

10 

Note: For Tables 4-1 and 4-2, a single value represents the results of a single study on one species, 

and should not be interpreted as a mean value or a value indicating no variation in the category. 

Two values separated by a hyphen indicate that values were obtained from only two studies. 

a Few determinations of the energy content of plants have been made on a wet-weight basis

because plants fluctuate widely in water content depending on environmental conditions. b Values in brackets represent total range of field measurements, instead of values from only two 

studies, as for the remainder of the table. Buchsbaum and Valiela (1987) found the water content 

of the emergent marsh vegetation Spartina alterniflora, S. patens, and Juncus gerardi to decrease 

over a summer from 80 to 60 percent, 70 to 45 percent, and 78 to 61 percent, respectively, as the 

marsh dried. In contrast, they found a submerged macrophyte to maintain water content within a 

few percent throughout the season. 

References: (1) Cummins and Wuycheck, 1971; (2) Jorgensen et al., 1991; (3) Minnich, 1982; (4) 

Boyd and Goodyear, 1971; (5) Davis and Golley, 1963; (6) Drozdz, 1968; (7) Golley, 1960; (8) 

Kendeigh and West, 1965; (9) Golley, 1961; (10) Karasov, 1990; (11) Dice, 1922; (12) Robel et al., 

1979; (13) Levey and Karasov, 1989. 

4-14
Table 4-3. General Assimilation Efficiency (AE) Values (values expressed as mean [standard n deviation] where n = number of studies)

Group Prey/Forage 

Birds 

animals 

birds of prey birds, small mammals 

eagles, seabirds fish 

waterfowl aquatic invertebrates 

birds terrestrial insects 

plants 

passerines wild seeds 

non-passerines wild seeds 

birds cultivated seeds 

birds fruit pulp, skin 

birds fruit pulp, skin, seeds 

birds grasses, leaves 

grouse, ptarmigans stems, twigs, pine needles 

geese emergents (e.g., spartina) 

ducks aquatic vegetation 

geese, grouse bulbs, rhizomes 

Mammals 

animals 

pinnipeds fish 

mammals small birds, mammals 

mammals fish 

small mammals insects 

voles, mice 

lemmings, voles 

rabbits, voles, mice 

rabbits, voles, rats 

plants 

seeds, nuts 

mature grasses 

green forbs 

"herbivory" 

AE % Reference 

78 (5.2)

16 1,2,3,4 

79 (4.5)

9 1,2,4,5 

77 (8.4)

3 1 

72 (5.1)

16 1,5,6 

75 ( 9)11 1 

59 (13)25 1 

80 ( 8)17 1 

64 (15)31 1 

51 (15)22 1 

47 ( 9.6)3 1* 

34 ( 5.3)8 1,1 

39 ( 9.1)4 1* 

23 ( 5.3)5 1* 

56 (18)4 1 

88 (1.1)

5 7,8 

84 (6.5)

4 9,10,11 

91 12 

87 (4.9)

6 11,13 

85 (7.3)

8 

41 (9.1)

5 

73 (7.6)

8 

76 (7.6)

5 

11,14 

15 

11,14,15 

11,14,16 

References: (1) Karasov, 1990; (1*) calculated from data presented in Appendix I of Karasov, 1990; 

(2) Stalmaster and Gessaman, 1982; (3) Koplin et al., 1980; (4) Castro et al., 1989; (5) Ricklefs, 1974; 

(6) Bryant and Bryant, 1988; (7) Ashwell-Erickson and Elsner, 1981; (8) Miller, 1978; (9) Litvaitis and 

Mautz, 1976; (10) Vogtsberger and Barrett, 1973; (11) Grodzinski and Wunder, 1975; (12) estimated 

by dividing 4.9 kcal/g gross energy for bony fishes (Table 4-1) by metabolizable energy of 4.47 

reported for fish consumed by mammals (Nagy, 1987); (13) Barrett and Stueck, 1976; (14) Drozdz, 

1968; (15) Batzli and Cole, 1979; (16) Drozdz et al., 1971. 

4-15
Table 4-3 summarizes AEs for several different types of foods and species. Assimilation 

efficiency is a function of both the consumer species' physiology and the type of diet. 

Factors that reduce many species' ability to assimilate the energy contained in food 

include the ash content of the diet and the percentage of relatively indigestible organic 

materials such as chitin (arthropods) or cellulose (plants). The higher the ash content, the 

lower the AE, all else being equal. 

Fat content also influences GE. For example, carbohydrates (approximately 4.3 

kcal/g) and proteins (approximately 5.7 kcal/g) typically provide about half as many 

calories per gram as fat (approximately 9.5 kcal/g) (Peters, 1983). Thus, small changes in 

fat content of animal tissues or plant seeds cause significant changes in their caloric value. 

For example, just prior to fall migration, passerine birds have achieved peak fat deposition 

and average 7.8 kcal/g dry weight. Non-migrating passerines (i.e., permanent residents or 

migratory species during nonmigrating seasons) average only 5.6 kcal/g dry weight. Two 

references with substantial compilation of data on caloric content of biological materials 

are Jorgensen et al. (1991) and Cummins and Wuycheck (1971). The latter includes 

extensive data on invertebrates. 

Figure 4-7 provides a sample calculation of food ingestion rates using the 

methodology outlined above. 

4.1.3. Soil and Sediment Ingestion 

In this section, we review information on the ingestion of soil and sediment for the 

species included in this Handbook (and similar species). Despite the potential importance 

of soil and sediment ingestion as a route of exposure of wildlife to environmental 

contaminants, data to quantify these ingestion rates are limited at this time. 

4-16
Figure 4-7. Example of Estimating Food Ingestion Rates for Wildlife Species From Free-Living 

Metabolic Rate and Dietary Composition: Male Mink 

1. Estimate Field Metabolic FMR (kcal/day) = 0.6167 (g Wt)0.862 

Rate (FMR) [Equation 3-47] = 0.6167 (1,040)0.862 

= 246 (kcal/day) 

2. Normalize to Body Weight NFMR (kcal/g-day) = 246 (kcal/day)/1,040 (g Wt) a 

(Wt) [Equation 3-40] = 0.24 (kcal/g-day) 

3. Estimate Average Metabolizable Energy (ME ) of Diet [Equation 4-12] avg 

Dietary 

Item 

(k=5) 

Proportion 

of Diet 

(P )k 

b 

Gross 

Energy 

(GE )k 

c 

(kcal/g wet 

wt) 

Assimilation 

Efficiency 

(AE )k 

d 

Metabolizable 

Energy (ME )k 

(kcal/g wet wt) 

(ME = GE × AE ) k k 

(P × ME ) k 

Fish 0.85 1.2 0.91 1.1 0.93 

Crustacea 0.04 1.1 0.87 0.96 0.038 

Amphibia 0.03 1.2 0.91 1.1 0.033 

Birds/ 

Mammals 

0.06 1.8 0.84 1.5 0.090 

Vegetation 0.02 1.3 0.73 0.95 0.019 

MEavg (kcal/g wet wt) = �(Pk × ME ) 1.1e 

4. Estimate Total NIR (g/g-day) = 0.24 (kcal/g-day) total 

Normalized Ingestion Rate 1.1 (kcal/g wet wt) (i.e., ME ) avg 

(NIR ) [Equation 4-11] = 0.22 (g/g-day) total 

5. Estimate Prey-specific NIR (g/g-day) = 0.85 (P ) × 0.22 (g/g-day) fish fish 

Normalized Ingestion Rates = 0.19 (g/g-day) 

(e.g., NIR ) [Equation 4-10] fish 

Body weight for Montana population in the summer (Mitchell, 1961). a 

Dietary composition based on Alexander (1977). b 

Values from Tables 4-1 and 4-2 (for vegetation, assuming value for young grasses). c 

Values from Table 4-3 (for vegetation, assuming green forbs; for crustacea, assuming equivalent AE d 

for insects; for amphibia, assuming equivalent to mammals consuming fish). 

In this example, ME is the same as the ME value for fish, which comprises 85 percent of the diet. e 

avg 

k 

k 

k =

4-17
4.1.3.1. Background 

Soil is ingested both intentionally and incidentally by many species of wildlife and 

can be a significant exposure pathway for some contaminants (Arthur and Alldredge, 1979; 

Garten, 1980). Many ungulates deliberately eat soil to obtain nutrients; some may travel a 

considerable distance to reach certain areas (salt licks) that are used by many animals. 

Some birds gather mud in their beaks for nest-building, and others consume it for calcium 

(Kreulen and Jager, 1984). Many animals can incidentally ingest soil while grooming, 

digging, grazing close to the soil, or feeding on items that are covered with soil (such as 

roots and tubers) or contain sediment (such as molluscs). Earthworms ingest soil directly; 

the soil in their guts may be an important exposure medium for animals that eat these 

organisms (Beyer et al., 1993).c 

Soil ingestion rates have been estimated for only a few wildlife species and were not 

available in the published literature for most of the animals in this Handbook. The 

percentage of soil ingested is often estimated from the acid-insoluble ash content of 

wildlife scats or digestive tract contents. Scat analysis on small animals is often difficult 

because scat are small. Soil ingestion by large mammals also has been estimated using 

insoluble chemical tracers (Mayland et al., 1977) and using standard x-ray diffraction 

analysis (Garten, 1980). 

4.1.3.2. Methods 

Garten (1980) estimated the amount of soil in the gastrointestinal (GI) tract of a 

small mammal (the hispid cotton rat) using the following equation: 

I = (S - F)W [4-22] 

c

Seed-eating birds often consume "grit" to aid in digestion, which makes them vulnerable to

poisoning by granular formulations of pesticides and fertilizers. In this section, however, we 

restrict our discussion to soils and sediments, which are composed of much smaller particle sizes. 

4-18 
where I equals the amount of soil in the GI tract, S equals the ratio of insoluble ash to dry 

contents in the GI tract, F equals the ratio of insoluble ash to dry contents in fescue (the 

dominant vegetation in the rat's habitat), and W equals the dry weight of GI-tract contents. 

It is also possible to estimate soil ingestion rates from the acid-insoluble ash 

content of the animal's scat because the percentage of acid-insoluble ash in mineral soil is 

much higher (usually at least 90 percent) than in plant or animal tissue (usually no more 

than a few percent). Beyer et al. (in press) used scat samples to estimate the fraction of 

soil in the diet for several species. The equation for this estimation approach is slightly 

more complicated than Equation 4-22, because it accounts for digestibility and the mineral 

content of the soil. They found a significant correlation between the measured and 

predicted relationships of the ratio of acid-insoluble ash to dry weight of scat and the 

percentage of soil in the diet. 

4.1.3.3. Results 

Percent soil in the diet for some of the selected and similar species included in 

Chapter 2 are included in Tables 4-4 and 4-5. Of the species studied, the sandpiper group, 

which feeds on mud-dwelling invertebrates, was found to have the highest rates of 

soil/sediment ingestion (30, 18, 17, and 7.3 percent of diet, respectively, for semipalmated, 

western, stilt, and least sandpipers, although only a single sample was analyzed for each 

species). Wood ducks also can ingest a high proportion of sediment (24 percent) with their 

food. Relatively high soil intakes were estimated for the raccoon (9.4 percent), an 

omnivore, and the woodcock (10.4 percent), which feeds extensively on earthworms. 

Other species that eat earthworms might be expected to exhibit similarly high soil intakes. 

The Canada goose, which browses on grasses, also exhibited a high percentage of soil in 

its diet (8.2 percent). Soil ingestion was lowest for the white-footed mouse, meadow vole, 

fox, and box turtle (<2, 2.4, 2.8, and 4.5 percent, respectively). Box turtles, tortoises, and 

other reptiles, however, have been known to intentionally ingest soil, perhaps for its 

nutrient content (Kramer, 1973; Sokal, 1971). Beyer et al.'s (in press) data should be used 

with caution, because error was introduced by estimating variables in 

4-19
Table 4-4. Percent Soil or Sediment in Diet Estimated From Acid-Insoluble Ash of Scat 

Species 

Birds 

Canada goose 

Mallard 

Wood duck 

Blue-winged teal 

Ring-necked duck 

American woodcock 

Semipalmated 

sandpiper 

Western sandpiper 

Stilt sandpiper 

Least sandpiper 

Mammals 

Red fox 

Raccoon 

White-footed mouse 

Meadow vole 

Reptiles and Amphibians 

Scat 

Samplesa 

% Insoluble 

Ash 

Mean (SE) Range 

Estimated 

% 

Digestibility 

of Diet 

Estimated 

Percent Soil 

in Diet 

(dry weight) 

23 12 (1.5) 3.9 - 38 25 8.2 

88 6.9 (1.1) 0.36 - 47 30 <2 

7 24 (13) 0 - 75 60 11 

12 2.3 (0.36) 0.72 - 5.1 60 <2 

6 0.72 (5.5) 0.50 - 1.2 60 <2 

7 22 (5.5) 6.3 - 40 55 10.4 

1 56 70 30 

1 42 70 18 

1 40 70 17 

1 24 70 7.3 

7 14 (2.6) 4.8 - 25 70 2.8 

4 28 (8.9) 13 - 50 70 9.4 

9 8.5 (0.71) 5.7 - 11 65 <2 

7 8.9 (1.2) 4.2 - 14 55 2.4 

Eastern painted 

turtle 

9 21 (2.9) 11 - 41 70 5.9 

Box turtle 8 18 (6.5) 3.6 - 49 70 4.5 

a

For the sandpipers, the white-footed mouse, and the meadow vole, scat samples from more than one

animal had to be combined into one sample to provide sufficient quantity for chemical analysis. 

Source: Adapted from Beyer et al. (in press). 

4-20
Table 4-5. Other Estimates of Percent Soil or Sediment in Diet 

Species 

Estimated % soil in diet 

(dry weight) Reference 

Jackrabbit 6.3 Arthur and Gates 1988 

Hispid cotton rats 2.8 Garten 1980 

Shorebirds 10-60 Reeder 1951 

the equation (e.g., digestibility) and by the small samples they obtained from some of the 

smaller animals. 

Other studies of soil ingestion by species similar to those presented in this 

Handbook are summarized in Table 4-5. Sediment has been found in the stomachs of 

white-footed mice (Garten, 1980) and ruddy ducks and shovelers (Goodman and Fisher, 

1962). Sediment in the gut of tadpoles inhabiting highway drainages may be responsible 

for high concentrations of lead detected in these organisms (Birdsall et al., 1986). 

4.1.3.4. Dose Equations 

To estimate exposures to contaminants in soils or sediments from the data 

provided in Tables 4-4 and 4-5, Equation 4-23 (Figure 4-8) can be used. If the percent soil 

in the diet is measured on a dry-weight basis, as it usually is, total dietary intake should 

also be expressed on a dry-weight basis. 

4.1.4. Air 

Inhalation toxicity values and exposure estimates are usually expressed in units of 

concentration in air (e.g., mg/m3) rather than as average daily doses. Assessment of the 

inhalation pathway becomes complicated if the toxicity values must be extrapolated from a 

test species (e.g., rat) to a different species (e.g., shrew). Inhalation toxicologists 

extrapolate toxicity values from species to species on the basis of the dose deposited and 

retained in the respiratory tract (the dose that is available for absorption, distribution, 

4-21
Figure 4-8. Wildlife Oral Dose Equation for Soil or Sediment Ingestion Exposures 

m 

ADDpot = (� (Ck × FS × IRtotal(dry weight) × FRk))/BW [4-23] 

k=1 

ADDpot = Potential average daily dose (e.g., in mg/kg-day). 

th Ck = Average contaminant concentration in soils in the k foraging area (e.g., in

mg/kg dry weight). 

FS = Fraction of soil in diet (as percentage of diet on a dry-weight basis divided 

by 100; unitless). 

IRtotal = Food ingestion rate on a dry-weight basis (e.g., in kg/day). Nagy's (1987) 

equations for estimating FI rates on a dry-weight basis (presented in Section 

3.1) can be used to estimate a value for this factor. If the equations for 

estimating FI rates on a wet-weight basis presented in Section 4.2 are used, 

conversion to ingestion rates on a dry-weight basis would be necessary. 

FRk = Fraction of total food intake from the kth foraging area (unitless). 

BW = Body weight (e.g., in kg). 

m = Total number of foraging areas. 

metabolism, and elimination). Once the appropriate toxicity benchmark (in terms of dose) 

has been estimated for the species of concern (e.g., shrew), the corresponding air 

concentration is estimated based on the respiratory physiology of that species. EPA uses 

this approach because it can account for nonlinear relationships between exposure 

concentrations, inhaled dose, and dose to the target organ(s). Because of the complexities 

associated with the extrapolations, an inhalation toxicologist should be consulted when 

assessing this pathway. 

The dose deposited, retained, and absorbed in the respiratory tract is a function of 

species anatomy and physiology as well as physicochemical properties of the 

contaminant. The assessor will need to consider factors such as the target species' airway 

4-22
size, branching pattern, breathing rate (volume and frequency), and clearance 

mechanisms, as well as whether the contaminant is a gas or aerosol and whether its 

effects are systemic or confined to the respiratory tract. Key information on the 

contaminant includes particle size distribution (for aerosols), temperature and vapor 

pressure (for gaseous agents), and pharmacokinetic data (e.g., air/blood partition 

coefficients, metabolic parameters). While physiologically based pharmacokinetic models 

have been useful for these calculations, they are available for only a few laboratory 

species. These issues are discussed in detail in Interim Methods for Development of 

Inhalation Reference Concentrations (U.S. EPA, 1990). Although the document specifically 

describes how to calculate inhalation reference concentrations for humans, the principles 

are useful for any air-breathing species. 

4.1.5. Dermal Exposure 

Dermal toxicity values and exposure estimates are usually expressed as an 

absorbed dose resulting from skin contact with a contaminated medium. This exposure 

pathway can be of great importance to wildlife, particularly when an animal is directly 

sprayed (Driver et al., 1991). Dermal exposures may also be a concern for wildlife that 

swim or burrow. Dermal absorption of contaminants is a function of chemical properties of 

the contaminated medium, the permeability of the animals' integument, the area of 

integument in contact with the contaminated medium, and the duration and pattern of 

contact. A full discussion of quantifying absorbed dose through the skin is beyond the 

scope of this document, and many of the required parameters have not been measured for 

wildlife species. Readers interested in pursuing this exposure pathway may find useful 

information in Dermal Exposure Assessment: Principles and Applications (U.S. EPA, 

1992c). 

4.2. ANALYSIS OF UNCERTAINTY 

In the risk assessment process, several sources of uncertainty should be evaluated, 

including the uncertainties associated with the exposure assessment and the toxicity 

4-23
assessment. The following sections discuss three sources of uncertainty related to the 

exposure assessment: (1) natural variability in the population in question, (2) uncertainty 

about population parameters as a consequence of limits on sampling the population (i.e., 

sampling uncertainty), and (3) uncertainty about models used to estimate values. There 

are other categories of uncertainties associated with site-specific risk assessments that 

also need to be considered (e.g., selection of substances of concern, data gaps, toxicity 

assessments). Additional discussion of sources and treatment of uncertainty is available 

in Framework for Ecological Risk Assessment (U.S. EPA, 1992a) and Guidelines for 

Exposure Assessment (U.S. EPA, 1992b). For treatment of site-specific uncertainties in 

particular, see the Risk Assessment Guidance for Superfund, Volume I; Human Health 

Evaluation Manual (Part A) Interim Final (U.S. EPA, 1989). 

4.2.1. Natural Variation 

As a review of the data provided in this Handbook makes clear, there is natural 

variation in the values exhibited by populations for all exposure factors. Population values 

for some parameters (e.g., body weight) can assume a normal distribution that can be 

characterized by a mean and variance. We have provided the standard deviation (SD) as 

the measure of population variance whenever possible. If a risk assessor is concerned 

with exposures that might be experienced by animals exhibiting characteristics near the 

extremes of the population's distribution, the SD can be used with the mean value for a 

normally distributed population to estimate the parameter value for animals with 

characteristics at specified points in the distribution (e.g., 95th percentile). We also have 

provided the total range of values reported for each of the exposure factors whenever 

possible. The ranges can be particularly helpful for parameters that are not normally 

distributed, such as home-range size. 

Another aspect of natural variation, however, is that different populations or the 

same population at different times or locations can exhibit different mean values for any 

parameter (e.g., body weight) and even different variances. We have tried to present 

enough data to give users of the Handbook a feel for the range of values that different 

populations can assume depending on geographic location, season, and other factors 

4-24
�

(e.g., habitat quality). We recommend that risk assessors review the data presented in the 

Appendix to appreciate the potential for variation in the parameters of interest. 

Dietary composition, in particular, can vary markedly with season, location, and 

availability of prey or forage. The latter factor varies with local conditions and usually is 

not available for risk assessments. Thus, it can be one of the larger sources of uncertainty 

in wildlife exposure assessments. State and local wildlife experts might be able to help 

specify the local dietary habits of a species of concern and should be consulted if 

screening analyses suggest that exposure at levels of concern is a possibility. 

4.2.2. Sampling Uncertainty 

Another source of uncertainty in exposure estimates results from limited sampling 

of populations. Estimates of a population mean and variance become more accurate as 

the number of samples taken from the population increases. With only a few samples from 

a population, our confidence that the true population mean is near the estimated mean is 

low; as the number of samples increases, our confidence increases. The standard error 

(SE) of the mean is equal to the variance of the population (�) divided by the square root of 

the sample size (n). SE can be estimated from the standard deviation of the population 

divided by the square root of n. SE can be used to calculate confidence limits on an 

estimate of the mean value for a population. For a normally distributed population, the 95-

percent confidence limit of the mean is the estimated mean plus or minus approximately 2 

SEs for reasonable sample sizes (e.g., n = at least 20). 

Sampling uncertainty occurs in many areas of exposure assessment. Contaminant 

concentration is one key parameter subject to sampling error. For site-specific risk 

assessments, as the number of environmental samples increases, the uncertainty about 

the true distribution of values decreases. Even with large sample sizes, however, this 

uncertainty can dominate the total uncertainty in the exposure assessment. Other 

parameters subject to sampling error are the exposure factors presented in this Handbook. 

One of our criteria for selecting values from the Appendix to include in Chapter 2 was a 

sample size large enough to ensure that SE was only a few percent of the mean value. 

4-25
4.2.3. Model Uncertainty 

Two main types of models are likely to be used in wildlife exposure assessments: 

(1) allometric models to predict contact-rate parameters (e.g., food ingestion rates) and (2) 

fate and transport models to predict contaminant concentrations to which wildlife are 

exposed. 

In this Handbook, we have tried to present statistical confidence limits associated 

with allometric equations whenever possible. To reduce the confidence limits associated 

with allometric models, it is important to use a model derived from the smallest and most 

similar taxonomic/dietary group appropriate for the extrapolation. For example, to estimate 

a metabolic rate for a red-winged blackbird, it is preferable to use a metabolic rate model 

derived from data on passerines rather than a model derived from data on many different 

groups of birds (e.g., raptors, seabirds, geese), and best to use a model for Icterids (the 

subfamily to which the red-winged blackbird belongs) rather than a model derived from 

data on passerines. 

Uncertainties in exposure models can include how well the exposure model or its 

mathematical expression approximates the true relationships in the field as well as how 

realistic the exposure model assumptions are for the situation at hand. Judicious field 

sampling (e.g., of contaminant concentrations in certain prey species) can help calibrate or 

confirm estimates in the exposure model (e.g., food-chain exposures). Often a sensitivity 

analysis can help a risk assessor identify which model parameters and assumptions are 

most important in determining risk so that attention can be focused on reducing 

uncertainty in these elements. 

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