United States

Department

of Agriculture

Forest Service

Rocky Mountain

Research Station

General Technical

Report RMRS-GTR-43

January 2000

Ecology and Conservation

of the Cactus Ferruginous

Pygmy-Owl in Arizona
Cover photo—Clockwise from top: photograph of fledgling in Arizona by Jean-Luc Cartron, photograph of adult ferruginous pygmy-owl in Arizona by Bob Miles, photograph of adult cactus ferruginous

pygmy-owl in Texas by Glenn Proudfoot.

Fort Collins Service Center

Telephone (970) 498-1392

FAX (970) 498-1396

E-mail rschneider/rmrs@fs.fed.us

Web site http://www.fs.fed.us/rm

Mailing Address Publications Distribution

Rocky Mountain Research Station

240 W. Prospect Road

Fort Collins, CO 80526-2098

Abstract ____________________________________

Cartron, Jean-Luc E.; Finch, Deborah M., tech. eds. 2000. Ecology and conservation of the cactus

ferruginous pygmy-owl in Arizona. Gen. Tech. Rep. RMRS-GTR-43. Ogden, UT: U.S. Department

of Agriculture, Forest Service, Rocky Mountain Research Station. 68 p.

This report is the result of a cooperative effort by the Rocky Mountain Research Station and the

USDA Forest Service Region 3, with participation by the Arizona Game and Fish Department and the

Bureau of Land Management. It assesses the state of knowledge related to the conservation status

of the cactus ferruginous pygmy-owl in Arizona. The population decline of this owl has been attributed

to the loss of riparian areas before and after the turn of the 20th century. Currently, the cactus

ferruginous pygmy-owl is chiefly found in southern Arizona in xeroriparian vegetation and wellstructured upland desertscrub. The primary threat to the remaining pygmy-owl population appears to

be continued habitat loss due to residential development. Important information gaps exist and

prevent a full understanding of the current population status of the owl and its conservation needs.
Jean-Luc E. Cartron and Deborah M. Finch

Rocky Mountain Research Station

2205 Columbia SE

Albuquerque, NM 87106

Ecology and Conservation of the Cactus

Ferruginous Pygmy-Owl in Arizona

Technical Editors:

Federal Recycling Program Printed on Recycled Paper
Authors __________________

Sam L. Beasom (1945-1995) was Director of the Caesar

Kleberg Wildlife Research Institute at Texas A&M University,

Kingsville, Texas. He received his Ph.D. in Wildlife and Fisheries Science from Texas A&M University. He served as Editorin-chief of the Journal of Wildlife Management in 1986 and

1987. He was also President of the Texas and New Mexico

Chapters of the Wildlife Society in 1977 and 1979, respectively,

and President of the Southwest Section of the Wildlife Society

in 1983 and 1984. His research interests focused on predatorprey interactions, land use effects on wildlife, and population

ecology of game species.

Jean-Luc E. Cartronis a Research Wildlife Biologist with the

U.S.D.A Forest Service’s Rocky Mountain Research Station in

Albuquerque, New Mexico, and a Research Assistant Professor with the Department of Biology at the University of New

Mexico. He received his Ph.D. in Biology from the University of

New Mexico, examining the influence of phylogenetic history

and current ecological conditions on the reproductive strategies of birds. He is conducting a long-term study of ospreys in

the Gulf of California in Mexico, monitoring population size and

reproductive success. Research interests include life history

theory, evolutionary biology, and raptor conservation biology.

Russell B. Duncan is proprietor of R. B. Duncan & Associates, a biological consulting firm located in Tucson, Arizona,

specializing in endangered species surveys and consultation.

Russell received his B.A. in Ecology with minors in Classical

History and Outdoor Recreation from Prescott College, Prescott,

Arizona, in 1981. He later attended the University of Arizona,

where he completed graduate level courses in Population

Biology and Evolution. Russell has lived in Arizona since 1976

and has traveled and worked extensively throughout the Southwest. The primary focus of his work has been the herpetofauna

and avifauna of the Southwest, including endangered raptors

such as the Mexican spotted owl and cactus ferruginous

pygmy-owl. Russell is a member of the Basin and Range West

Working Group for the U.S. Fish and Wildlife Service’s Mexican

Spotted Owl Recovery Team, and a consultant to the Malpai

Borderlands Group on issues related to land use management

and spotted owls.

Deborah M. Finch is a Research Wildlife Biologist and

Project Leader with the U.S.D.A. Forest Service’s Rocky Mountain Research Station in Albuquerque. She received her B.S. in

Wildlife Management from Humboldt State University, California, her M.S. in Zoology from Arizona State University, and her

Ph.D. in Zoology from the University of Wyoming. Deborah’s

research interests include neotropical migratory bird ecology

and reproduction, bird migration, endangered species, riparian

and grassland ecosystem ecology and conservation, and relationships between commodity use and natural resources.

Deborah has published more than 80 articles and journal

papers and is an active member of several professional societies, including the American Ornithologists’ Union, the Cooper

and Wilson Ornithological Societies, the Society for Conservation Biology, Wildlife Society, Ecological Society of America,

and New Mexico Riparian Council.

Lois T. Haight has conducted research and co-authored

numerous scientific papers with her husband, R. Roy Johnson,

including several on the ferruginous pygmy-owl. She received

her B.F.A. from Ohio State University and conducted postgraduate work at the University of Texas, Arlington, where she

studied ornithology and museum curating. Her interests have

focused mainly on the avifauna and botany of the North

American Southwest (southwestern U.S. and northwestern

Mexico).

R. Roy Johnson began avian studies in the North American

Southwest in 1952. During the 1960s and 1970s, he visited all

sites in Arizona where the ferruginous pygmy-owl had been

recorded historically. He received an M.S. in ornithology from

the University of Arizona in 1960 and a Ph.D. in Botany from the

University of Kansas in 1964. He held positions at several

universities before joining the National Park Service to direct

research on the Colorado River at Grand Canyon in 1973. In

1979, he came to the University of Arizona, Tucson, as National

Park Service Senior Ecologist and Professor of Renewable

Natural Resources, retiring in 1992. He is an Elective Member

of the A.O.U. and has published 200 papers, mostly on riparian

birds and plants.

Kenneth J. Kingsley is a senior ecologist with SWCA, Inc.

Environmental Consultants. He has a B.A. in Biology from

Prescott College, Prescott, Arizona (1972), M.S. in Biological

Sciences from the University of Nevada, Las Vegas (1981), and

Ph.D. in Entomology and Ecology from the University of Arizona (1985). He has worked on a wide variety of issues

involving the effects of human actions and development on

wildlife, including conducting biological surveys, evaluations

and assessments for endangered species and conservation

planning.

David J. Krueper is an Avian Senior Technical Specialist

with the Bureau of Land Management (BLM), Tucson Field

Office, Arizona. He has gathered data on avian use and natural

history dynamics in riparian habitats of the American Southwest for the past 19 years. David is the lead biologist for BLM

in issues regarding the cactus ferruginous pygmy-owl in Arizona. He has been coordinating the BLM habitat assessments

and pygmy-owl surveys for the past two years in southeastern

Arizona, and is a member of the Biological Team for the Cactus

Ferruginous Pygmy-Owl Recovery Plan. He also has a strong

interest in studying avian populations and habitat relationships

in the New World tropics, and has traveled extensively in Latin

America where he has gained experiential knowledge of pygmyowl habitat use.

Jody L. Mays received her M.S. in Range and Wildlife

Management from Texas A&M University. Her thesis, “Population size and distribution of cactus ferruginous pygmy-owls in

Brooks and Kenedy counties, Texas,” examines population

attributes and habitat associations of cactus ferruginous pygmyowls in southeastern Texas. Her research interests include

endangered species, environmental education, avian and bat

biology, animal behavior, and GIS applications to wildlife research. She recently served as a Biological Technician working

on the Kemp’s Ridley Sea Turtle Restoration Project at Padre

Island National Seashore.
Glenn A. Proudfoot is Research Assistant and Ph.D. candidate at Texas A&M University, College Station, Texas and

former Associate Scientist at the Caesar Kleberg Wildlife

Research Institute. He received his B.S. in Biology with a minor

in Wildlife Management from the University of Wisconsin,

Stevens Point, and his M.S. in Range and Wildlife Science from

Texas A&M University, Kingsville. Since January 1994, his

research addressing the natural history of ferruginous pygmyowls in southern Texas has resulted in six journal publications

and 33 research notes. In 1998, he accepted appointment from

the U.S. Department of Interior to the Ferruginous Pygmy-Owl

Recovery Team. His research interests include predator-prey

ecology and habitat assessment and interactions.

W. Scott Richardson is the Urban Wildlife Specialist for

Region V of the Arizona Game and Fish Department. He

received a B.S. degree from Brigham Young University in

Range/Wildlife Management with a minor in Botany. He completed a Master’s degree in Wildlife Ecology, also from Brigham

Young University, where his thesis investigated habitat use and

food habits of black bears in southeastern Utah. He has been

with the Arizona Game and Fish Department and in Tucson for

just over five years. His focus has been on urban wildlife habitat

protection and enhancement. Specifically, he has been looking

at javelinas, bats, and raptors, and how they utilize and interact

with the urban environment. Since 1995, Scott has coordinated

the Department’s cactus ferruginous pygmy-owl survey and

research project which is looking at the distribution and natural

history of the species. In addition to the biological aspects of the

project, the Department is trying to provide pygmy-owl information and education to the general public, local agencies and

governments, and special interest groups. The objective of this

outreach is to provide the most current, scientific information to

the community as they address the issues surrounding the

cactus ferruginous pygmy-owl.

Stephen M. Russell received a degree in Biology from

Virginia Polytechnic Institute and then earned a Ph.D. at

Louisiana State University, where he did dissertation studies in

British Honduras (Belize). He taught at the University of New

Orleans before joining the faculty at the University of Arizona.

Recently, he retired to emeritus status after 32 years at Arizona,

where he taught, did research, and investigated the birds of

Sonora. He has served as President of the Arizona-Sonora

Desert Museum and the Cooper Ornithological Society and

was Secretary of the American Ornithologists’ Union for several

years. He is currently Chair of the North American Banding

Council. Current research interests focus upon the behavior

and ecology of hummingbirds.

Thomas H. Skinner has worked for the U.S.D.A. Forest

Service and BLM in three different states, and is currently the

Wildlife Program Manager for the Coronado National Forest.

He received his B.A. in Biology from Carleton College, Northfield,

Minnesota, and a M.S. in Range Management, Wildlife Option,

from the University of Arizona, Tucson. He is coordinating the

Coronado National Forest’s cactus ferruginous pygmy-owl

program which entails habitat assessment and surveys, biological assessments for all projects and activities that may

affect the owl and its habitat, and consultation with the U.S. Fish

and Wildlife Service. He is coordinating this effort with other

agencies and is currently administering a challenge cost-share

project with the Arizona Game and Fish Department to provide

for more information and better management for the owl.

Scott H. Stoleson is a Research Wildlife Biologist with the

Rocky Mountain Research Station in Albuquerque, New Mexico.

He received his B.A. in Biological Science from Dartmouth

College, and his Ph.D. in Wildlife Ecology from Yale University.

He spent portions of seven years studying birds in the llanos of

Venezuela, where ferruginous pygmy-owls were abundant,

and a year and a half in Ecuador. His research interests include

breeding biology and demography of birds, parrot conservation

and management, population modeling, and riparian conservation. His current research examines the breeding biology and

habitat associations of the southwestern willow flycatcher and

other riparian birds in the Gila Valley of New Mexico.

Lauren Turner has worked for the U.S.D.A. Forest Service

for 19 years, on seven National Forests in four different regions

of the United States. She is currently the Ecosystem Manager

on the Plumas National Forest in California. She received her

B.A. in Biological Sciences from California State University,

Stanislaus. She was a Wildlife Biologist on the Tonto National

Forest from 1995-1999, where she coordinated that Forest’s

cactus ferruginous pygmy-owl program. The program included

habitat assessment and surveys, biological assessments for all

projects and activities possibly affecting the owl and its habitat,

protection and/or enhancement of habitat, and consultation

with the U.S. Fish and Wildlife Service. She coordinated that

effort with the Arizona Game and Fish Department and with

Native American communities on lands adjacent to the National

Forest.

Acknowledgments__________

Many individuals not listed as authors contributed to the

development of this document. The authors benefitted from

discussions with H. Hollis, T. Tibbitts, D. Bieber, M. Richardson,

G. Dahlem, M. Terrio, D. Abbate, and P. Sawyer. Access to

cactus ferruginous pygmy-owl habitat was generously granted:

in Texas by Butch Thompson, King Ranch, Inc; in Arizona, by

several private property owners. P. Siminski kindly provided

information on the ferruginous pygmy-owls held captive at

the Sonoran Desert Museum. J. Van DeWater drew the

illustrations for the entire document. Special thanks are extended to Ellen Paul and The Ornithological Council, who

arranged a blind review process. R. Glinski, T. Corman, D. Holt,

D. Brockway, K. Kingsley, B. Millsap, R. Wilson, J. Kelly,

N. Douglas, and T. Gatz reviewed earlier versions of the

chapters and provided constructive comments and additional information. M. Dillon, M. Willock, and P. Stoleson

edited and proofed the document. Funding and logistic support were provided by the Forest Service Regional Office in

Albuquerque and by the Rocky Mountain Research Station.

Finally, this document could not have been written without all

the individuals who spent many hours in the field conducting

surveys and monitoring nests in Arizona and Texas.
Contents____________________________

Page

Introduction ....................................................................................................................... 1

Jean-Luc E. Cartron

Deborah M. Finch

Chapter 1: The Cactus Ferruginous Pygmy-Owl: Taxonomy,

Distribution, and Natural History.................................................................. 5

Jean-Luc E. Cartron

W. Scott Richardson

Glenn A. Proudfoot

Chapter 2: A Historical Perspective on the Population Decline

of the Cactus Ferruginous Pygmy-Owl in Arizona ................................... 17

R. Roy Johnson

Jean-Luc E. Cartron

Lois T. Haight

Russell B. Duncan

Kenneth J. Kingsley

Chapter 3: The Status of the Cactus Ferruginous Pygmy-Owl in Arizona:

Population Surveys and Habitat Assessment .......................................... 27

W. Scott Richardson

Jean-Luc E. Cartron

David J. Krueper

Lauren Turner

Thomas H. Skinner

Chapter 4: The Ferruginous Pygmy-Owl in the Tropics and at the Northern

End of its Range: Habitat Relations and Requirements........................... 47

Jean-Luc E. Cartron

Scott H. Stoleson

Stephen M. Russell

Glenn A. Proudfoot

W. Scott Richardson

Chapter 5: Research on the Ferruginous Pygmy-Owl in

Southern Texas: Methodology and Applications ..................................... 57

Glenn A. Proudfoot

Jody L. Mays

Sam L. Beasom

Chapter 6: Research Needs for the Conservation of the

Cactus Ferruginous Pygmy-Owl in Arizona .............................................. 65

Jean-Luc E. Cartron

W. Scott Richardson

Deborah M. Finch

David J. Krueper
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 1

Jean-Luc E. Cartron

Deborah M. Finch

Introduction

In March 1997, the U.S. Fish and Wildlife Service

listed the Arizona population of the cactus ferruginous

pygmy-owl (Glaucidium brasilianum cactorum) as

endangered under the Endangered Species Act (U.S.

Fish and Wildlife 1997). Federal listing for the owl in

Arizona resulted from a petition submitted in 1992 to

the U.S. Fish and Wildlife Service (Galvin et al. 1992,

U.S. Fish and Wildlife 1994). It was finalized based on

historical and current evidence suggesting a significant population decline of this subspecies had occurred in Arizona and the owl population in this state

was now nearly extirpated (see Phillips et al. 1964,

Johnson et al. 1979, Monson and Phillips 1981, Rea

1983: 65-66, Hunter 1988, Millsap and Johnson 1988,

U.S. Fish and Wildlife 1997). The loss and alteration

of the owl’s habitat was identified as the primary

threat to the remaining population (e.g., Johnson

et al. 1979, Millsap and Johnson 1988, Hunter

1988, U.S. Fish and Wildlife 1997). In July 1999,

critical habitat for the cactus ferruginous pygmy-owl

was also designated on 296,240 ha (731,712 acres) of

federal, state, and private lands in Pima, Pinal, and

Maricopa counties.

The primary goal of this report is to document and

explore the conservation needs of the cactus ferruginous pygmy-owl in Arizona. Although it is intended

for a broad audience, one specific objective of this

conservation assessment is to provide the U.S. Forest

Service and other agencies and stakeholders with the

information necessary to ensure the conservation of

the owl and its critical habitat. In 1996, the Southwest

Region of the U.S Forest Service requested assistance

from the Rocky Mountain Research Station in developing a conservation assessment for the pygmy-owl.

Because historical owl habitat existed on national

forests of southern and central Arizona, the region

believed an analysis of owl status and habitat would be

of benefit in managing habitats to recover owls on

national forests. Our product is the outcome of this

original request. Experts from state and federal agencies, universities, and other institutions were invited

to participate in writing the report. For more information about individual authors, see the Authors section

of this report.

A recovery team for the cactus ferruginous pygmyowl was appointed by the U.S. Fish and Wildlife

Service in 1998. Its function is to develop a recovery

plan that identifies delisting criteria and recommends

a course of action to restore sufficient, stable, and selfmaintaining population levels of the owl. Thus, another objective of the conservation assessment is to

assist the recovery team by providing information for

use in the development of the recovery plan while also

discussing important issues and suggesting research

needs.

The conservation assessment for the cactus ferruginous pygmy-owl is primarily a literature review, yet

original data are presented in several chapters. It
2 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

relies extensively on information gathered in Arizona

by the Arizona Game and Fish Department since 1995

and in Texas by researchers from the Cesar Kleberg

Wildlife Research Institute since 1992. In Arizona,

efforts focused initially on population surveys but

have also recently included nest monitoring, habitat

sampling, and telemetry (Abbate et al. 1996,

Richardson pers. comm.). In Texas, where a sizeable

population of the owl has been located (Wauer et al.

1993, Mays 1996), research continues to document the

natural history of the owl and determine demographic

parameters and habitat use in this state (Proudfoot

1996, Proudfoot and Beasom 1997, Proudfoot and

Radomski 1997). Unquestionably, the research in

Arizona and Texas has provided some important

information. Yet, at the same time, many questions

remain unanswered.

Chapter 1 focuses on the taxonomy, distribution,

and natural history of the cactus ferruginous pygmyowl. In particular, this chapter consolidates an important amount of published and unpublished data on the

breeding biology and diet of the owl. As indicated,

behavioral observations suggest that much of the

biology of the owl revolves around an opportunistic

hunting strategy and on predator avoidance. Observed

and potential causes of owl mortality are described;

they include predation, parasites, and human-related

factors. Throughout the chapter, the authors outline

areas of uncertainty, such as genetic relatedness of the

Arizona and Texas populations, habitat requirements,

competition for cavities with other species, demographic parameters, and seasonal movements.

The ferruginous pygmy-owl (Glaucidium brasilianum) reaches the northern edge of its distribution in

the southwestern U.S. Early studies establish the

presence of the owl along rivers and streams of central

and south Arizona around the turn of the 20th century

(Bendire 1888, 1892, Breninger 1898). The owl population decline in Arizona, which is the focus of Chapter 2, has been reported to have occurred around 1950

(see Monson and Phillips 1981). Using both the existing literature and museum specimen records, the

authors indicate that a sharp decrease in the number

of owls probably began earlier, at least in central

Arizona. Chapter 2 also examines the possible effects

of biogeography and habitat loss on the population

decline.

Chapter 3 is a review of the current survey effort in

Arizona, with sections on the survey protocol, survey

results, and habitat description in survey areas. Population surveys have become a priority for federal and

state agencies, as well as private development interests. An initial survey protocol was developed by the

Arizona Game and Fish Department. It provided recommendations on the timing of surveys, distance

between call points, and broadcast and listening times

at each call point. Due to changes in management

needs and the results of ongoing research, the initial

survey protocol has been revised and will likely be

revised in the future in order to maximize survey

effectiveness. The present distribution of the cactus

ferruginous pygmy-owl in Arizona is not well understood, but in the last two years, much information has

been obtained. Although more owls have been located

due to the increased survey effort, population size

still appears to be small.

Chapter 4 explores habitat preferences and requirements of the ferruginous pygmy-owl using descriptions of vegetation types that are reportedly associated with higher densities of the owl in various parts

of its range. Because an essential conservation issue is

whether the owl should be managed as a riparian

species or an upland species, the authors also examine

the possible respective roles and importance of these

two vegetation types. As indicated in Chapter 2, the

owl was historically reported chiefly from riparian

woodlands and thickets in Arizona. Recently, however, it has been primarily found in desertscrub (e.g.,

Lesh and Corman 1995, Abbate et al. 1996, Chapter 3).

Despite the persistence of what seems like suitable

riparian habitat, there are few owl records from riparian areas in recent years.

Several attributes of the cactus ferruginous pygmyowl make this bird difficult to detect and study. With

the use of broadcasted conspecific calls, however, population surveys have located a higher number of owls

than previously estimated, both in Texas and Arizona.

In Texas, tools such as radiotransmitters, video cameras, and nest boxes have also proven valuable for

conducting studies on this bird (Proudfoot 1996,

Proudfoot and Beasom 1996, 1997). Chapter 5 is a

description of the equipment selected for research on

the cactus ferruginous pygmy-owl in Texas, along with

a review of the methodology and applications for the

use of that equipment.

Chapter 6 concludes the conservation assessment

and reviews research needs for the conservation of

the cactus ferruginous pygmy-owl in Arizona. The

recent increase in the number of pygmy-owls located

(Chapter 3) indicates surveys are key to a better

understanding of the size, distribution, and structure

of the Arizona owl population. Demographic and habitat use studies are also needed. One management

issue discussed in the chapter and tied to research is

the possible use of nest boxes in some riparian areas.

Nest boxes may be useful to 1) locate more owls, 2)

conduct habitat studies, and 3) improve habitat quality where nest sites may be limited.

The historical range of the owl in Arizona represents

only the northern edge of the species’ wide distribution. In the tropics, the ferruginous pygmy-owl is one

of the most common birds of prey (Chapter 1). In
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 3

contrast to the California condor (Gymnogyps californianus) or the whooping crane (Grus americana), the

fate of the Arizona owl population likely does not

condition the viability of the entire species. Yet, it

should also be noted that in recent times species have

often become extinct or endangered as a result of

human activities leading to incremental range contractions. An important provision of the Endangered

Species Act is to list those disappearing populations

whose loss would lead to a significant gap in the range

of the species. Throughout the conservation assessment, no attempt is made to rank the need to preserve

the Arizona population of the cactus ferruginous pygmyowls among other conservation demands. With the

federal listing comes a legal obligation to develop and

implement a plan for the conservation of this owl.

References ________________

Abbate, D., A. Ditty, S. Richardson, and R. Olding. 1996. Cactus

ferruginous pygmy-owl surveys and nest monitoring in the

Tucson Basin area, Arizona. Final Rep. Internal Enhancement

#U95503. Phoenix, AZ: Arizona Game and Fish Department.

Bendire, C.E. 1888. Notes on the habits, nests and eggs of the genus

Glaucidium Boie. Auk 5:366-372.

Bendire, C.E. 1892. Life histories of North American birds. U.S.

National Museum Spec. Bulletin 1. 446 p.

Breninger, G. F. 1898. The ferruginous pygmy owl. Osprey 2: 128.

Galvin, P., D. C. Carlton, M. Pyott, R. Silver, K. Suckling. 1992.

Petition to list the ferruginous pygmy-owl Glaucidium brasilianum cactorum, as a federally endangered species. Luna, NM.

14 p.

Hunter, W. C. 1988. Status of the cactus ferruginous pygmy-owl

(Glaucidium brasilianum cactorum) in the United States and

northern Mexico. Phoenix, AZ: U.S. Fish and Wildlife Service.

13 p.

Johnson, R. R., L. T. Haight, and J. M. Simpson. 1979. Owl populations and species status in the southwestern United States. Pp.

40-59. In: Schaeffer, P. P., and S. M. Ehlers, eds. Owls of the west:

their ecology and conservation. Proceedings National Audubon

Society. Tiburon, CA: George Whittel Education Center.

Lesh, T. D., and T. E. Corman. 1995. Cactus ferruginous pygmy-owl

surveys in Arizona: 1993-1995. Technical Report 76. Phoenix, AZ:

Nongame and Endangered Wildlife Program, Arizona Game and

Fish Department.

Mays, J. L. 1996. Population size and distribution of cactus ferruginous pygmy-owls in Brooks and Kenedy counties, Texas. Master’s

thesis. Kingsville, TX: Texas A&M University.

Millsap, B. A., and R. R. Johnson. 1988. Ferruginous pygmy-owl.

Pp. 137-139. In: Glinski, R. L., B. G. Pendleton, M. B. Moss,

M. N. LeFranc, Jr., B. A. Millsap, and S. W. Hoffman, eds.

Proceedings of the Southwest raptor management symposium

and workshop. Scientific Technical Series 11. Washington, D.C.:

National Wildlife Federation.

Monson, G., and A. R. Phillips. 1981. Annotated checklist of the

birds of Arizona. Tucson, AZ: University of Arizona Press.

Phillips, A.R., J. Marshall, and G. Monson. 1964. The birds of

Arizona. Tucson, AZ: University of Arizona Press.

Proudfoot, G. A. 1996. Natural history of the cactus ferruginous

pygmy-owl. Master’s thesis. Kingsville, TX: Texas A&M

University.

Proudfoot, G. A., and S. L. Beasom. 1996. Responsiveness of cactus

ferruginous pygmy-owls to broadcasted conspecific calls. Wildlife

Society Bulletin 24:294-297.

Proudfoot, G. A., and S. L. Beasom. 1997. Food habits of nesting

ferruginous pygmy-owls in southern Texas. Wilson Bulletin

109:741-748.

Proudfoot, G. A., and A. A. Radomski. 1997. Absence of hematozoa

from ferruginous pygmy owls (Glaucidium brasilianum) in southern Texas. Journal of the Helminthological Society of Washington 64:154-156.

Rea, A. M. 1983. Once a river: bird life and habitat changes on the

middle Gila. Tucson, AZ: University of Arizona Press. 285 p.

Richardson, W. S., urban wildlife specialist, Arizona Game and Fish

Department, Tucson. [Personal communication]. August 1999.

U.S. Fish and Wildlife Service. 1994. Proposed rule to list the

cactus ferruginous pygmy-owl as endangered with critical habitat in Arizona and threatened in Texas. Federal Register

59(237):63975-63986.

U.S. Fish and Wildlife Service. 1997. Determination of endangered

status for the cactus ferruginous pygmy-owl in Arizona. Federal

Register 62(46):10730-10746.

Wauer, R.H., P.C. Palmer, and A. Windham. 1993. The ferruginous

pygmy-owl in south Texas. American Birds 47:1071-1076.

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 5

Jean-Luc E. Cartron

W. Scott Richardson

Glenn A. Proudfoot

Chapter 1:

The Cactus Ferruginous Pygmy-Owl:

Taxonomy, Distribution, and Natural

History

The cactus ferruginous pygmy-owl (Glaucidium

brasilianum cactorum) is a small, cryptic owl that is

often difficult to observe. Its natural history and

conservation needs are poorly understood. Despite

ongoing research in Texas and Arizona, the available

information remains limited. In addition, factors influencing demographics (e.g., habitat configuration,

causes of mortality and reproductive failure, and

prey availability) may vary geographically, increasing

the need for information from all parts of the range.

Without a significant commitment to additional research, management and recovery strategies will be

difficult to develop. This chapter first describes the

taxonomy and distribution of the ferruginous pygmyowl (G. brasilianum). It then discusses the known

ecology of cactorum.

1. Taxonomy and distribution _______

The taxonomy of the genus Glaucidium (order

Strigiformes, family Strigidae) is a topic of debate

among authorities, at both the species and subspecies

levels. Both Johnsgard (1988) and Sibley and Monroe

(1990) list 12 species of owlets and pygmy-owls occurring worldwide, including the ferruginous pygmy-owl.

However, recent molecular and vocalization studies

distinguish a number of additional mainland New

World species of pygmy-owls (Vielliard 1989, Robbins

and Howell 1995, Howell and Robbins 1995, D. Holt

pers. comm.). The austral pygmy-owl, sometimes

considered a separate species, G. nanum (e.g., Meyer

de Schauensee 1970), has recently been treated as a

morph of G. brasilianum (Marín et al. 1989, Stoltz

et al. 1996). Conversely, the pygmy-owl of southwest

Ecuador and northwest Peru, once treated as G. brasilianum (Meyer de Schauensee and Phelps 1978), has

been proposed as a distinct species, G. peruanum, by

König (1991) and Stoltz et al. (1996).

The ferruginous pygmy-owl, also called the ferruginous owl, is considered abundant or extremely

abundant throughout most of its range, which is centered on the Neotropics (Fig. 1-1) (Phillips et al. 1964,

Johnsgard 1988, Terres 1991). In Mexico, this species

was the one most often collected between 1840 and

1991 (Enriquez-Rocha et al. 1993). To the south, the

ferruginous pygmy-owl’s distribution extends to central Argentina, even to Tierra del Fuego if nanum is

treated as conspecific (Johnsgard 1988, König and

Wink 1995). At the northern edge of its geographic

range, the ferruginous pygmy-owl reaches central

Arizona and extreme southeast Texas (Fig. 1-2). Since

1937, the form found from central Arizona south to

Michoacan in western Mexico (see Johnsgard 1988)

has been recognized as the subspecies cactorum (van

Rossem 1937, Friedmann et al. 1950, Blake 1953,

Sprunt 1955, Phillips et al. 1964, Monson and Phillips
6 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

1981, Millsap and Johnson 1988, Binford 1989).

Whether the ferruginous pygmy-owl which ranges

from southeastern Texas to Tamaulipas and Nuevo

Leon in northeastern Mexico (see Johnsgard 1988) is

also cactorum has not been resolved. Peters (1940)

refers to the ferruginous pygmy-owl of Texas as

ridgwayi and to the ferruginous pygmy-owl of Arizona

as cactorum. Since Friedmann et al. (1950), however,

both forms have been treated as cactorum. Molecular

analyses are currently in progress to decide whether

the two owls should be taxonomically divided (Proudfoot

et al. unpubl. data). Pending the results of these

Figure 1-1. Geographic range of the ferruginous pygmyowl (adapted from Johnsgard 1988). The distribution includes nanum (Marín et al. 1989, Stoltz et al. 1996) but not

peruanum (Meyer de Schauensee and Phelps 1978). The

distribution of the recently described subspecies stranecki

(König and Wink 1995) is not included.

analyses, we follow the currently accepted taxonomy

(Johnsgard 1988, U.S. Fish and Wildlife 1997, American Ornithologists’ Union 1998) and consider the

ferruginous pygmy-owl of Texas and northeastern

Mexico as cactorum.

In southern Mexico and throughout Central

America cactorum is replaced by G. b. ridgwayi. In

South America, several subspecies have been described. One is the widely distributed G. b. brasilianum (Fisher 1893, van Rossem 1937, Friedmann et

al. 1950, Schaldach 1963, Phillips et al. 1964, Meyer de

Schauensee 1966, Karalus and Eckert 1974, Oberholser

1974, Johnsgard 1988, Sick 1993). Another subspecies

recently described from central Argentina is G. b.

stranecki (König and Wink 1995). The austral pygmyowl of Tierra del Fuego may represent the southernmost subspecies of the ferruginous pygmy-owl.

Two populations of cactorum are generally recognized (e.g., Burton 1973, Johnsgard 1988, but see

comments above) (Fig. 1-2). In the west, the cactus

ferruginous pygmy-owl ranges north to central and

southern Arizona. The historical boundaries of its

distribution in Arizona are New River in the north, the

confluence of the Gila and San Francisco rivers to

the east, and the desert of southern Yuma County to

the west (Fisher 1893, Phillips et al. 1964, Monson and

Phillips 1981, Hunter 1988). This western population

extends south along the Pacific slope of the Mexican

Plateau, where it is common in lowlands and foothills

(Peterson and Chalif 1973). The eastern population

occurs from extreme southeastern Texas south to

Tamaulipas and Nuevo Leon in northeastern Mexico.

In Texas, it occurs in the live oak (Quercus virginiana)-

honey mesquite (Prosopis glandulosa) forest of the

historical Wild Horse Desert in Brooks and Kenedy

counties (Mays 1996). Historically, it was also often

reported along the Rio Grande in Star and Hidalgo

counties (Oberholser 1974, Texas Ornithol. Soc. 1984,

Proudfoot in press).

The eastern and western populations are separated

over most of their ranges by a series of biogeographic

barriers: the United States’ Chihuahuan desert basins and associated mountain ranges and Mexico’s

Sierra Madre Occidental and Oriental and Mexican

Plateau. These barriers may prevent contact between

the two populations. There is no record of the cactus

ferruginous pygmy-owl in any U.S. location between

Arizona and south Texas (Bailey 1928; Phillips et al.

1964, Oberholser 1974, Williams 1997). In Mexico, it is

rarely encountered on the Mexican Plateau above

1200 m on the west side and 300 m on the east side

(Friedman et al. 1950). At the southern tip of the

Mexican Plateau, however, the two ranges may merge

(Johnsgard 1988, but see Burton 1973 for a different

opinion).
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 7

2. Description ____________________

The cactus ferruginous pygmy-owl is a small graybrown or rufous-brown owl, approximately 16.5 to

18 cm long. In comparison with G. b. brasilianum

and G. b. ridgwayi, this subspecies exhibits shorter

wings, a longer tail, and generally lighter coloration

(van Rossem 1937, Phillips et al. 1964, Proudfoot

1996). The head is relatively small and without ear

tufts. The eyes are lemon yellow and the crown is finely

streaked with flecks of buff. On the nape, a pair of

conspicuous black patches outlined in white is suggestive of eyes. The back is not spotted as in the

northern pygmy-owl (G. gnoma), but plain, rusty brown

(Robbins et al. 1966). The white breast shows welldefined streaks of brown. The tail is long compared to

other small owls and is rufous in color with seven or

eight darker brown cross bars. Although no true seasonal changes in plumage coloration are documented,

Breninger (1898) reported that the rufous coloring of

the tail and upper body becomes less noticeable through

the spring months. According to Ridgway (1914), the

Figure 1-2. Geographic range of the cactus ferruginous pygmy-owl (adapted from U.S. Fish and Wildlife 1994). Whether the

eastern and western parts of the range are completely disjunct is unknown. The eastern population is currently treated as the

subspecies cactorum, but its taxonomic status remains uncertain.

Arizona and Texas populations of cactus ferruginous

pygmy-owls exhibit slightly distinct color forms, the

latter occurring with a more rufous plumage. A

gray-brown phase with white tail bands has been

described in other parts of the species’ distribution

(Edwards 1972).

As is typical in owls, the female is larger, weighing

around 75 g while the male averages 64 g (Proudfoot

unpubl. data) (Fig. 1-3). Additionally, subtle differences in plumage exist between the sexes, at least in

the United States (Abbate et al. 1996, Proudfoot 1996).

Compared to males, females display a more pronounced cinnamon-rufous color tone on their coverts,

remiges, occipitals, and scapulars (Proudfoot 1996).

Overall, juveniles are similar to adults but are distinguished for the first few weeks by their shorter tails

and by well-contrasted white, tear-drop-like feather

ends that form a broken line running from shoulder

to rump when the birds are perched. Other characteristics of fledglings include lighter, less distinct

eye patches on the nape, the lack of buff on their

crowns, and more white on their underparts
8 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

(Abbate et al. 1996). Fledglings in Arizona also exhibit a more chocolate brown color, lacking any real

rufous coloration except on their tails.

The vocal repertoire of the cactus ferruginous

pygmy-owl comprises several calls, some of which

appear to be specific to age or sex of the owl. The

advertising call of the adult male is heard primarily at

dawn and dusk but also during daylight and even

moon rise, especially during the courtship period. It is

ventriloquial (Sprunt 1955) and consists of a prolonged and monotonous series of clear, mellow, whistling notes uttered at approximately 1400 Hz (Stillwell

and Stillwell 1954). During the breeding season, females utter a rapid chitter, possibly a contact call with

the male and juveniles and also for food begging

(Abbate et al. 1996, Proudfoot and Johnson in press).

When the female receives food from the male, the same

chitter may be used to signal her position to the

fledglings (Abbate et al. 1996). Two additional female

calls have been recorded; the “chirp,” sometimes repeated with short pauses in between, may be used to

signal distress or for warning (Abbate et al. 1996). The

other call is similar to the territorial vocalization of the

male, only at a higher pitch and slower beat (Phillips

et al. 1964, Abbate et al. 1996). The specific function of

this latter call is not well understood. The fledglings’

primary vocalization is a chitter similar to the female’s

but at a higher pitch. When they are flushed from a

perch, fledglings also produce a high-pitched chirplike call (Proudfoot and Johnson in press, Richardson

unpubl. data).

Like other species in the genus Glaucidium, the

ferruginous pygmy-owl is reported to hunt both day

and night (Oberholser 1974, Sick 1993). Yet, except

during nestling development, cactorum is primarily

diurnal (Proudfoot and Johnson in press). Although

the ferruginous pygmy-owl is generally quite cryptic,

it is sometimes seen during the day perched on exposed branches (Sutton 1951, Oberholser 1974). The

tail, often cocked at an angle with the body, is jerked

from side to side when the owl is agitated (Sprunt

1955, Oberholser 1974). Unlike many owl species, the

ferruginous pygmy-owl flies with audible wingbeats

due to reduced numbers, lengths, and surface area

coverage of the barbs and barbules (D. Holt, pers.

comm.). The ferruginous pygmy-owl’s flight is generally short and consists of quick sallies from one lookout

point to another. It has been compared to that of a

shrike (e.g., Sprunt 1955).

3. Habitat ________________________

Across its range, the ferruginous pygmy-owl occurs

in many distinct environments, such as scrublands,

forests, cerrados (i.e., a neotropical type of open woodlands), and towns (Meyer de Schauensee 1966, Davis

Figure 1-3. Sexual dimorphism in the cactus ferruginous pygmy-owl. Note the difference in color tone

and the larger size of the female, right. Photograph by Glenn Proudfoot.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 9

1972, Meyer de Schauensee and Phelps 1978, Hilty

and Brown 1986). Partly because of this species’ plasticity and partly due to the lack of detailed habitat

studies, the habitat requirements of cactorum remain

poorly understood. The following section profiles habitat occupied by the cactus ferruginous pygmy-owl and

discusses some potentially important habitat characteristics (Fig. 1-4). This topic is addressed in more

detail in Chapter 4.

In the eastern part of the range, plant communities

supporting the cactus ferruginous pygmy-owl are

coastal-plain oak associations, mesquite bosques, and

Tamaulipan thornscrub in south Texas (Tewes 1993,

Wauer et al. 1993, Mays 1996), lowland thickets,

thornscrub associations, riparian woodlands and second-growth forests in northeastern Mexico (van Rossem

1945, Enriquez-Rocha et al. 1993, Tewes 1993).

In western Mexico, the owl may occur in Sonoran

desertscrub, Sinaloan thornscrub, Sinaloan deciduous forest, riverbottom woodlands, cactus forests, and

thornforests (Enriquez-Rocha et al. 1993, U.S. Fish

and Wildlife 1997). In Arizona, the owl is historically

associated with cottonwood (Populus fremontii) and

mesquite (Prosopis velutina) riparian woodlands

(Bendire 1888, Breninger 1898, Phillips et al. 1964),

and Sonoran desertscrub (Johnson and Haight

1985). Recently, cactus ferruginous pygmy-owls

have been chiefly reported from Sonoran desertscrub (see Chapter 3).

The physical settings and vegetation compositions

of southern Texas and Arizona have very little in

common. However, the frequent association between

G. brasilianumand thickets and edges, and its regular

use of densely foliated exotic landscape trees in

Arizona (Chapter 4) suggests that vegetation structure is more important to this owl than vegetation

composition. Similarities between currently occupied

habitat in Arizona and Texas include the presence of

thorny bushes: ironwood (Olneya tesota) in Arizona

and lime prickly ash (Zanthoxylum fagara) in south

Texas. Results from research in Texas (Proudfoot

1996) indicate the importance of moderate (50 to 75%)

to dense (76 to 100%) understory cover and trees large

enough to hold cavities. Understory cover may be

critical for both foraging and fledgling survival

(Fig. 1-4, see also Chapter 4).

Figure 1-4. Known and hypothesized ecological relations of the cactus ferruginous pygmy-owl ( + : ecological

relations benefitting individual cactus ferruginous pygmy-owls; – : ecological relations with a negative impact on

individual cactus ferruginous pygmy-owls). The degree of competition for nesting cavities with other species is

unclear.
10 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

4. Breeding cycle __________________

Until recently, the breeding biology of the cactus

ferruginous pygmy-owl was largely undocumented.

Since 1994, however, critical information has been

obtained, especially in Texas, where nests have been

monitored using radio telemetry and miniature video

cameras with infrared-light-emanating diodes

(Proudfoot 1996, Chapter 5). In Arizona, nest sites

have been located and monitored since 1996 (Abbate et

al. 1996, Richardson unpubl. data). These studies

have provided region-specific information on the

breeding chronology of the owl, habitat use by the

fledglings, and adult-fledgling interactions.

Typically, the nest site is a natural cavity or an

abandoned woodpecker hole in a tree or in a large

columnar cactus. Nest cavities in trees have been

recorded primarily in live-oak and cottonwood but also

in Montezuma baldcypress (Taxodium mucronatum),

willow (Salix sp.), and honey mesquite (Bendire 1892,

Gilman 1909, Rea 1983: 169, Proudfoot 1996, Russell

and Monson 1998). In Arizona, all nest cavities detected between 1995 and 1998 have been in saguaro

cacti (Carnegiea gigantea) (Abbate et al. 1996,

Richardson unpubl. data). Nest height varies from 2 to

12 m above ground (Breninger 1892, Gilman 1909,

Oberholser 1974, Proudfoot in press). No lining material is added inside the cavity (Breninger 1898,

Proudfoot 1996).

Cactus ferruginous pygmy-owl eggs are white and

almost spherical and weigh approximately 8 g. They

are laid at regular intervals of 32-39 hours (Proudfoot

and Johnson in press). Clutch size ranges between

three and seven eggs (Bent 1938, Heintzelman 1979,

Proudfoot and Johnson in press). In Texas, the most

commonly recorded clutch size is five (Proudfoot 1996);

in Arizona, it is four (Hunter 1988); in Sonora, it is

three or four (Russell and Monson 1998). In Texas,

incubation is conducted solely by the female and lasts

about 28 days (Proudfoot in press). However, recent

observations (Richardson unpubl. data) indicate the

male may play a limited role in incubation in Arizona.

If the first clutch fails, a replacement clutch may be

produced within 21 days (Proudfoot unpubl. data).

Hatching is asynchronous, occurring every 20 to 26

hours. During the first week after hatching, the female

remains with the nestlings, leaving the nest only to

obtain food, cast a pellet, and/or defecate (Proudfoot

and Beasom 1997). As the nestlings develop, the female spends more time outside the cavity and both

adults bring food to the nest (Proudfoot unpubl. data).

Intense competition for food occurs among the nestlings, occasionally resulting in siblicide (Proudfoot in

press). Fledging time ranges between 21 and 30 days

(Scherzinger 1977, Terres 1991, Proudfoot 1996). After fledging, both adults hunt but the female delivers

most of the prey items to the juveniles. Initially, the

fledglings remain near the nest, often in proximity to

each other, and utilize dense, thorny shrubs and trees

for cover. Over time, the size of the area the fledglings

use increases while the amount of contact with the

adults decreases. Approximately two months after fledging, the young disperse from the nest site (Proudfoot

1996). Preliminary data indicate that adults maintain

their pair bond following the dispersal of the juveniles

and appear to mate for life (Proudfoot unpubl. data).

5. Ecological relations _____________

Hunting and prey base

Pygmy-owls are known as fierce hunters capable of

killing prey twice their own size (Terres 1991, Sick

1993). Early accounts describe the cactus ferruginous

pygmy-owl attacking young chickens and adult birds

the size of robins (Breninger 1898, Bent 1938,

Johnsgard 1988). Recently, this owl was observed

killing mourning doves (Zenaida macroura) and large

desert spiny lizards (Sceloporus magister) in Arizona

(Richardson unpubl. data). In Texas, it feeds on large

prey such as eastern meadowlarks (Sturnella magna)

and hispid cotton rats (Sigmodon hispidus) (Proudfoot

and Beasom 1997). When hunting, ferruginous pygmyowls typically perch and scan their surroundings

(Breninger 1898, Abbate et al. 1996). Once prey is

detected, they strike it from above or engage in a short

flight pursuit (Abbate et al. 1996). Sick (1993) argues

that the “eye spots” of the ferruginous pygmy-owl’s

nape feathers trick the other birds into flying in front

of it rather than behind it. The owl can then strike the

unsuspecting prey in a sudden, dashing flight.

The cactus ferruginous pygmy-owl is a prey generalist (Table 1-1). Its prey base includes birds, lizards,

insects, small mammals (Bendire 1888, Sutton 1951,

Sprunt 1955, Earhart and Johnson 1970, Oberholser

1974), snakes (Sprunt 1955), and frogs (Proudfoot and

Beasom 1997). In Texas, thirty-six prey species representing five classes have been recorded (Proudfoot and

Beasom 1997). In Arizona, prey items were primarily

reptiles but also included birds, mammals, and insects

(Table 1-2). The cactus ferruginous pygmy-owl is an

opportunistic predator: it takes advantage of seasonal

opportunities such as the emergence of insects or the

presence of nestlings in nearby nests (Abbate et al.

1996). After a meal, the owl may cache prey remains in

a tree, cavity, or ball of mistletoe (Phoradendron sp.)

(Sprunt 1955, Abbate et al. 1996, Proudfoot 1996).

The cactus ferruginous pygmy-owl is referred to as

the “terror of small birdlife” (Sprunt 1955). Thus, it is

not surprising that this owl is commonly mobbed by a

wide variety of other bird species (Gilman 1909, Sutton

1951, Sprunt 1955).
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 11

Table 1-1. List of identified prey species in the diet of cactus ferruginous pygmy-owls in Texas and Arizona. The list of prey species

for Texas is from Proudfoot and Beasom (1997) and for Arizona from Richardson (unpubl. data).

Prey category Texas Arizona

Amphibians narrow-mouth toad (Gastrophryne olivacea) —

Birds Bewick’s wren (Thryomanes bewickii) cactus wren (Campylorhynchus brunneicapillus)

blue grosbeak (Guiraca caerula) Gambel’s quail (Callipepla gambelii)

brown-crested flycatcher (Myiarchus tyrannulus) house finch (Carpodacus mexicanus)

eastern meadowlark (Sturnella magna) mourning dove (Zenaida macroura)

Nashville warbler (Vermivora ruficapilla) verdin (Auriparus flaviceps)

northern cardinal (Cardinalis cardinalis)

northern mockingbird (Mimus polyglottos)

pyrrhuloxia (Cardinalis sinuatus)

Mammals common evening bat (Nycticeius humeralis) Bailey’s pocket mouse (Chaetodipus baileyi)

hispid cotton rat (Sigmodon hispidus) Merriam’s kangaroo rat (Dipodomys merriami)

hispid pocket mouse (Chaetodipus hispidus)

house mouse (Mus musculus)

northern pygmy-mouse (Baiomys taylori)

Texas kangaroo rat (Dipodomys compactus)

Reptiles four-lined skink (Eumeces tetragrammus) desert spiny lizard (Sceloporus magister)

ground skink (Scincella lateralis) western whiptail lizard (Cnemidophorus tigris)

Great Plains skink (Eumeces obsoletus) zebra-tailed lizard (Callisaurus draconoides)

keeled earless lizard (Holbrookia propinqua)

rose-bellied lizard (Sceloporus variabilis)

six-lined racerunner (Cnemidophorus sexlineatus)

Texas horned lizard (Phrynosoma cornutum)

Texas spiny lizard (Sceloporus olivaceus)

Texas spotted whip-tail (Cnemidophorus gularis)

Invertebratesa cicada (Cicadidae) butterfly (Lepidoptera)

click-beetle (Elateridae) cicada (Cicadidae)

cone-nosed blood sucker (Reduviidae) grasshopper (Orthoptera)

dragonfly (Aeshnidae) sphinx moth (Sphingidae)

grasshopper (Acrididae and Tettigoniidae)

lighting bug (Lampyridae)

preying mantis (Mantidae)

round-headed katydids (Phaneropterinae)

true katydids (Pseudophyllinae)

walking stick (Heteronemiidae)

a

 Invertebrates are identified to the order or family level only.

Table 1-2. Diet of cactus ferruginous pygmy-owls in Arizona, 1996-1998. Based on visual observations of

one nesting pair in 1996, one nesting pair in 1997, and three nesting pairs in 1998. Each

percentage of the diet is calculated by dividing the number of individual prey items in a taxonomic

group by the total number of prey items. Data compiled from Abbate et al. (1996) and from

Richardson (unpubl. data).

Prey category 1996 (% of Diet) 1997 (% of Diet) 1998 (% of Diet)

Reptiles 47 (56%) 23 (43%) 36 (35%)

Birds 7 (8.3%) 20 (38%) 28 (27%)

Mammals 4 (4.8%) 1 (2%) 7 (7%)

Insects 4 (4.8%) 1 (2%) 3 (3%)

Undetermined 22 (26.2%) 8 (15%) 28 (27%)

Total 84 (100%) 53 (100 %) 102 (100%)
12 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

Predation avoidance

Cryptic coloration, use of trees with a dense foliage

and spines, a perch-and-wait hunting strategy, and a

low, rapid flight may all represent predator avoidance

adaptations of the cactus ferruginous pygmy-owl. In

Arizona, reactions of nesting cactus ferruginous

pygmy-owls to Harris’s hawks (Parabuteo unicinctus)

approaching or perching in proximity to the nest site

were regularly observed. Typically, the response of

the owls was to cease vocalizations and remain motionless until the hawks had left (Richardson unpubl.

data).

Other ecological relations

Although many aspects of the cactus ferruginous

pygmy-owl’s biology are related to predator avoidance

and food habits, other types of interactions with the

local avifauna have also been documented (Fig. 1-4).

As an obligate cavity nester, this owl is dependent on

medium-sized woodpeckers such as the Gila woodpecker (Melanerpes uropygialis) (Gilman 1909, Rea

1983) and flickers (Colaptes spp.) in Arizona, and the

golden-fronted woodpecker (Melanerpes aurifrons) in

Texas. Use of cactus ferruginous pygmy-owl nest boxes

by brown-crested flycatchers (Myiarchus tyrannulus),

golden-fronted woodpeckers, eastern screech owls (Otus

asio), and European starlings (Sturnus vulgaris) was

documented in Texas. In Arizona, purple martins

(Progne subis), ash-throated flycatchers (Myiarchus

cinerascens), elf owls (Micrathene whitneyi), western

screech owls (Otus kennicottii), Gila woodpeckers,

northern flickers, starlings, house sparrows (Passer

domesticus) and house finches (Carpodacus mexicanus)

all use saguaro cavities and represent potential competitors for nest cavities. Species such as the Gila

woodpecker and the greater roadrunner (Geococcyx

californianus) have been observed raiding pygmy-owl

prey caches, indicating another potential source of

competition with the local avifauna (Richardson

unpubl. data).

6. Mortality _______________________

Natural causes

Little is known about the rate or causes of mortality

of cactus ferruginous pygmy-owls in Arizona or Texas.

Due to its small size, however, the cactus ferruginous

pygmy-owl may be very susceptible to predation. In

Texas, several cases of mortality by a great-horned owl

(Bubo virginianus), Harris’s hawk, and Cooper’s hawk

(Accipiter cooperi) have been documented, and raccoon

and bullsnake depredation of nestlings is common

(Proudfoot and Johnson in press).

While the use of dense, thorny cover may reduce

the threat of predation for fledglings, their initial

inexperience and lack of coordinated flight leads to

other types of mortality. From 1995 through 1998, 18

fledglings were monitored in Arizona. Within 24 hours

of fledging, one juvenile disappeared (Abbate et al.

1996); another was rescued on the ground after being

injured by a curve-billed thrasher (Toxostoma curvirostre) (Abbate et al. 1996); three were impaled on

cholla or other cacti, but worked free or were rescued,

and one was removed from a road and placed in a

nearby tree (Richardson unpubl. data). In Texas, one

fledgling ended up on the ground after colliding with

a tree and was placed back in the tree by the observer.

Mortality among fledglings before and during dispersal averaged 38% (Proudfoot unpubl. data).

Although little is known about the prevalence and

impact of diseases on the survival and recruitment of

the cactus ferruginous pygmy-owl, several pathogens

may affect this bird. In South America, the ferruginous pygmy-owl is sometimes infected with blood

parasites (hematozoa) such as Haemoproteus and

Leucocytozoon (Bennett et al. 1982). One Haemoproteus species can be lethal in quails and one

Leucocytozoon species has been known to kill geese,

ducks, grouse, and turkeys (Clarke 1938, Fallis 1945,

Cook 1971a, 1971b, Harris 1972). In owls, hematozoa are

thought to be pathogenic, causing anemia, bacterial

diarrhea, and septicemia (Hunter et al. 1987). Blood

smears obtained from cactus ferruginous pygmy-owls

did not detect the presence of hematozoa in the Texas

population (Proudfoot and Radomski 1997). Samples

from Arizona are under analysis (Proudfoot et al.

unpubl. data).

The protozoal disease trichomoniasis represents a

potential threat to the cactus ferruginous pygmy-owl

in the Tucson area. The parasite is readily transmitted

from prey to predator (Stabler 1951) and the owl’s

local prey include mourning doves and house finches

(Table 1-1), both of which occur in high concentrations

in urban Tucson and are known carriers of the disease.

In addition, trichomoniasis has been documented in

nearly every raptor in the Tucson area. In particular,

it is found in other small birds of prey, such as the

American kestrel (Falco sparverius), western screech

owl, and burrowing owl (Athene cunicularia). High

nestling mortality due to this disease has been observed in Cooper’s hawks in metropolitan Tucson

(Boal and Mannan 1996).

Nothing is known about the influence of starvation

on the mortality of adults. As in other owl species

(see Miller 1989), death by starvation probably has a

higher incidence in juveniles than in adults. Finally,

one dead cactus ferruginous pygmy-owl with cholla

embedded in both feet was found floating in Dripping
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 13

Springs at Organ Pipe Cactus National Monument in

November 1972 (T. Tibbitts pers. comm.).

Human-related deaths

The incidence and impact of direct and indirect

human-related deaths among wild birds are not well

known. Casualties caused by pest control, pollution,

collisions with cars, TV towers, and glass windows,

electrocution by power lines, and cat predation are

often underestimated, although likely increasing in

occurrence due to human population growth (Banks

1979, Klem 1979, Churcher and Lawton 1987). Even

where human-related deaths are uncommon, they

may still substantially affect populations of rare birds.

Given the propensity for cactus ferruginous pygmyowls to occur in residential areas in Arizona, humanrelated factors may be a significant cause of owl

mortality there. A cactus ferruginous pygmy-owl

nesting near a house was rescued after colliding with

an automobile window. Although it survived, it

showed evidence of cranial hemorrhage (Richardson

unpubl. data). Cats may be another local cause of

mortality. In Texas, one adult owl and one fledgling

were killed by a domestic cat. In Arizona, children

were observed shooting pellet or BB guns near a nest

site (Richardson unpubl. data); hence, shooting should

also be considered a potential cause of owl mortality

within urban areas.

7. Home range and territoriality ____

Estimates of both home range and territory size for

the cactus ferruginous pygmy-owl are based on limited

information. In other owl species, home-range and

territory size may vary as much as tenfold or more

among areas or individuals (Hayward 1983, Cramp

1985, Zabel et al. 1992). Initial results from ongoing

research in Texas suggest that the home range of

cactus ferruginous pygmy-owls may expand substantially during dry years (Proudfoot unpubl. data).

In Texas, cactus ferruginous pygmy-owls defend

their territories year round. Areas used outside the

breeding season varied between 19 and 116 ha

(Proudfoot 1996). During incubation, adult males

used 1.34 to 8.52 ha (average 4.1) (Proudfoot 1996).

In Arizona, one female used an area approximately

0.2 ha in size during the prefledging period. This area

increased to about 14 ha between fledging and juvenile

dispersal and was also used by the fledglings (Abbate

et al. 1996). Estimates of territory size in Arizona have

ranged between .01 and 4 ha (Hunter 1988, Millsap

and Johnson 1988, Felley and Corman 1993). In Organ

Pipe National Monument, owl territories appear linear along washes (Hunter 1988). Recent studies using

telemetry have begun in Arizona to gather additional

information on territory and home range sizes

(Richardson unpubl. data).

In south Texas, the status of the cactus ferruginous

pygmy-owl as a year-round resident is clearly established (Proudfoot in press). In Arizona and western

Mexico, owls are seen throughout the year (Bendire

1888, Rea 1983:169, Russell and Monson 1998). However, Russell and Monson (1998) report a larger number of sightings during the spring and summer compared to the winter in northern but not southern

Sonora. Therefore, small scale migration for some

individuals cannot be completely ruled out. In the

last two years, telemetry has been used to study

pygmy-owl movements in Arizona, but more information is needed before any conclusion regarding this

issue is made.

8. Summary ______________________

Ongoing studies in Arizona and Texas have increased our understanding of the natural history of

the cactus ferruginous pygmy-owl (e.g., breeding

biology, prey base). However, significant gaps in the

knowledge of the pygmy-owl’s status and biology

(i.e., demographics, seasonal movements and fledgling dispersal, habitat requirements and preferences,

competition for cavities with other species, and factors

influencing home-range and territory size) exist in

Arizona, and the taxonomic relationship between the

Arizona and Texas owl populations is uncertain. Hence,

additional research is critical to the conservation of

this species. The importance of research for the management and recovery of the Arizona owl population is

addressed in Chapter 6.

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USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 17

R. Roy Johnson

Jean-Luc E. Cartron

Lois T. Haight

Russell B. Duncan

Kenneth J. Kingsley

Chapter 2:

A Historical Perspective on the

Population Decline of the Cactus

Ferruginous Pygmy-Owl in Arizona

The cactus ferruginous pygmy-owl (Glaucidium

brasilianum cactorum) was discovered in the U.S. by

Bendire in 1872 in the Tucson area (Coues 1872).

During the next five decades, naturalists collected

many specimens of this owl and typically described the

subspecies as common or fairly common along some

streams and rivers of central and southern Arizona. A

common view among regional ornithologists is that

the cactus ferruginous pygmy-owl’s Arizona population sharply declined around 1950 (see Monson and

Phillips 1981). As a result of a petition (Galvin et al.

1992), the cactus ferruginous pygmy-owl became federally listed as Endangered in Arizona in 1997 (U.S.

Fish and Wildlife 1997). In retrospect, however, many

questions remain on the magnitude and timing of the

population decline. In this chapter, we review early

records of cactus ferruginous pygmy-owls from the

published literature, U.S. Forest Service files, and

museum specimen collections. Evidence of a sharp

population decline dating back to the early 20th century exists for the Phoenix area, including the lower

Salt River. Along the lower and middle Gila River

Valley, a severe population decline is also apparent

but its timing is uncertain. In southern Arizona,

changes in the overall status of the owl are more

difficult to detect in part due to the lack of baseline

information. However, along Rillito Creek and the

Santa Cruz River in particular, an early population

decline is also probable. Along these two rivers, and

along the Salt and Gila rivers, the owl’s population

decline could have coincided with intensive woodcutting and the construction of the first dams, causing

deforestation and reduced waterflow early in the 20th

century. The current status of the cactus ferruginous

pygmy-owl population in Arizona is also addressed in

Chapter 3.

1. A species at the edge of its

range ____________________________

The ferruginous pygmy-owl (G. brasilianum) reaches

the northern edge of its distribution in Arizona and

Texas. Using the scissor-tailed flycatcher (Tyrannus

forficatus) and the indigo bunting (Passerina cyanea)

as examples, Brown (1984) notes that the abundance

of a species tends to decline from the center to the edge

of the range. Towards the edge, the distribution of a

species also tends to be more patchy (Brown 1984).

Despite historical accounts describing the cactus ferruginous pygmy-owl as common or fairly common at

various locations in Arizona (see below), it is difficult

to determine what the overall status of the owl was in

the state. It is unknown whether the owl was found

throughout its geographic range in Arizona (Fig. 2-1),

which extended north to New River, just north of

Phoenix; east to Geronimo along the Gila River, and
18 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

possibly even to the confluence of the Gila and San

Francisco rivers; and west to Agua Caliente and the

desert ranges of Yuma County (Fisher 1893, Gilman

1909, Swarth 1914, Aiken 1937, Phillips et al. 1964,

Monson and Phillips 1981, Hunter 1988). Alternatively, this bird may have shown an insular population

structure characterized by the local occurrence of

distinct subpopulations, its absence in other parts of

the range reflecting natural discontinuities in vegetation structure and composition and/or topographic

conditions.

2. The historical importance of

riparian areas _____________________

Judging from historical accounts by early ornithologists, the cactus ferruginous pygmy-owl was once

frequently encountered in cottonwood (Populus

fremontii) forests, mesquite (Prosopis velutina)-cottonwood woodlands, and mesquite bosques along the

Gila and Salt rivers in central Arizona, and along the

Santa Cruz River and Rillito Creek near Tucson

(Bendire 1888, Breninger 1898, Gilman 1909, Swarth

1914). The owl was also recorded in Sonoran desert

scrubland, but in this habitat it was apparently found

in areas supporting pockets of xeroriparian and riparian vegetation (Fisher 1893, Howell 1916, Kimball

1921). At New River, for instance, Fisher (1893) described the cactus ferruginous pygmy-owl as “quite

common” in thickets of intermixed mesquite and

saguaro (Carnegiea gigantea) cacti. Elsewhere in the

desert, the presence of this bird may have been more

infrequent, as Kimball (1921) concluded that, overall,

it was rare in the Santa Catalina foothills. Furthermore, Breninger (1898) differentiated the nesting habits of the elf owl (Micrathene whitneyi) and the cactus

ferruginous pygmy-owl, the former alone, in his opinion, occupying saguaro cavities. At the same time, it

should be noted that most early surveys were probably

conducted along rivers, the harsh climate and limited

water supply reducing coverage of surveys in the

desert. Recent observations of the owl in upland

desertscrub (see Chapter 3) indeed suggest that the

cactus ferruginous pygmy-owl may have been overlooked in this habitat during the late 19th and early

20th centuries. Overall the owl cannot presently be

considered an obligate riparian bird in Arizona, yet it

seems that river valleys and washes probably were

its primary habitat before the population decline

occurred.

3. Population decline and local

extirpations ______________________

It is generally reported that the Arizona population

of cactus ferruginous pygmy-owls started to decline

sharply around 1950 (Monson and Phillips 1981,

Abbate et al. 1996). However, many riparian areas

had already been altered before they were ever surveyed by naturalists (Phillips and Monson 1964, see

also below). Other areas, where the cactus ferruginous

pygmy-owl had been reported around the turn of the

century, were apparently not surveyed again for decades (Johnson et al. unpubl. ms.). The lack of information means that the owl population decline could

have begun earlier. By the early 1950s, the cactus

ferruginous pygmy-owl was already regarded by some

as rare (e.g., Brandt 1951). The apparent population

decline was later also recognized by Phillips et al.

(1964), Johnson et al. (1979), Monson and Phillips

(1981), and Hunter (1988). The cactus ferruginous

pygmy-owl was even described as extirpated “except

possibly in the Organ Pipe Cactus National Monument region” (Monson and Phillips 1981). Between

1971 and 1988, fewer than 20 credible cactus ferruginous pygmy-owl sightings were recorded (Hunter 1988).

Although these records showed that the owl could still

Figure 2-1. Map showing the approximate range of the cactus

ferruginous pygmy-owl in Arizona (based on data from Fisher

1893, Phillips et al. 1964, Monson and Phillips 1981, Hunter

1988). Note the extended distribution to the east along the Gila

River. Whether the range truly extends this far east is based on

two unconfirmed reports in the 1970s and 1980s (Hunter 1988,

T. Corman pers. comm.).
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 19

be found at various locations, no persistent breeding

population was known anywhere in the state.

With the use of broadcast surveys in recent years,

more owls have been recorded in northwestern Tucson

and elsewhere in southern Arizona (see Chapter 3).

Several nesting pairs were identified chiefly in the

Tucson area (Abbate et al. 1996, Wilcox et al. 1999).

Thus, new questions arise concerning the true magnitude and long-term significance of the population

decline reported earlier. However, a sharp population

decline ultimately resulting in the extirpation of the

owl appears certain for two general areas: the Phoenix

area, including the lower Salt River and New River,

and the lower and middle Gila River. Elsewhere, the

magnitude of any population decline is confounded by

the lack of baseline information, especially in

desertscrub, and the recent increase in sampling effort

resulting in more detections (see Chapter 3).

Central Arizona

The cactus ferruginous pygmy-owl was once a common inhabitant of the cottonwood groves in the Salt

River Valley (Breninger 1898). As previously mentioned, it was also “quite common” at New River

(Fisher 1893). On several occasions between 1892 and

1905, Breninger collected skins and eggs in the Phoenix area. Additional specimens were secured during

that period by Fisher, Lusk, Campbell, and Bennett

(Johnson et al. unpubl. ms.).

Only three specimens of cactus ferruginous pygmyowls were collected along the Salt River after 1905.

Initially, the decline in the number of specimens

collected in the Phoenix area may be in part attributed

to the fact that soon after the turn of the century, and

until about 1930, ornithologists shifted their attention

toward Tucson (Johnson et al. unpubl. ms.). However,

the decline becomes especially revealing after 1930,

when several resident ornithologists began to collect

and publish work conducted near Phoenix. Mostly

during the 1930s and 1940s, Lyndon Hargrave studied

the birds of the Salt River Valley, publishing occasional notes and collecting specimens from the region

(Johnson et al. unpubl. ms.). During that same period,

Allan Phillips and Lewis Yaeger collected in the area.

Vic Housholder worked in the area from the 1930s

through the 1950s.

The small number of specimens collected, despite

the presence of increasing ornithological activity after

1930, suggests a sharp, early population decline of the

cactus ferruginous pygmy-owl in the Phoenix area,

including the lower Salt River (Johnson et al. unpubl.

ms.). The specimen of cactus ferruginous pygmy-owl

that Hargrave collected in 1933 below Stewart

Mountain Dam proves that the owl still occurred

locally at this time. Later, when Phillips and Yaeger

worked in the region, they collected owl specimens in

1949 and 1951, which are among the last known

collected in the state. As late as 1964, the owl was

reported as still occurring at the mouth of the Verde

River and eastward along the Salt River (Phillips et al.

1964). However, at that second location it had in fact

not been recorded for more than a decade (Johnson et

al. unpubl. ms.).

Following Phillips, Johnson and Simpson (1971)

started intensive record keeping and specimen collection at one location near the mouth of the Verde River

along the Salt River, known as Blue Point Cottonwoods (BPC). The work of all these ornithologists

along the Salt River was nearly continuous over seven

decades, and it shows the extirpation of the owl from

that location by the early seventies (Millsap and

Johnson 1988). After the last record in 1971, numerous attempts to find another owl even using playback

recordings have been unsuccessful.

The cactus ferruginous pygmy-owl was also “common” along the lower and middle Gila River (Breninger

1898). Breninger encountered enough individuals of

this species to notice its gradual expansion along

irrigation canals. Writing about owl species he recorded along the lower and middle Gila River at Agua

Caliente, Sacaton, and Blackwater, Gilman (1909)

later described the cactus ferruginous pygmy-owl as

“fairly numerous.” Although Agua Caliente alone is

mentioned in his account of this owl, Gilman also

collected specimens at the other two locations (Johnson

et al. unpubl. ms.). At Blackwater, he collected two

females, one in January 1908, the other in March of

that same year. The dates given for those specimens,

together with information contained in two written

accounts by Gilman (Gilman 1909, Rea 1983) indicate

that he encountered the cactus ferruginous pygmyowl in all seasons. In retrospect, his work strongly

suggests that the cactus ferruginous pygmy-owl was

present along an extensive stretch of the lower and

middle Gila River. Besides the three specimens Gilman

collected and the nesting pair he described from Agua

Caliente, one specimen had earlier been secured by

Judson (Johnson et al. unpubl. ms.).

Unfortunately, the population status of the cactus

ferruginous pygmy-owl along the middle and lower

Gila River was not assessed again until 1963, at which

time Rea (1983) began to survey the avifauna of the

Gila River Indian Reservation, including Sacaton and

Blackwater. Rea’s work showed that the owl was now

extirpated on the reservation. Interestingly, none of

his Native American consultants recognized this bird

from specimens, thus suggesting that the extirpation

had occurred long before his study.

Southern Arizona

Records of cactus ferruginous pygmy-owls in southern Arizona exist for the Tucson area and, after 1949,
20 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

for Organ Pipe Cactus National Monument as well

(Hensley 1954). Due to the lack of baseline information, recent owl records from other locations, such as

Sycamore Canyon in Santa Cruz County or the Tohono

O’odham Reservation (Stejskal 1981, Taylor 1995,

Johnson et al. unpubl. ms.), are difficult to interpret.

After Bendire’s discovery of the cactus ferruginous

pygmy-owl in 1872 and his description of this bird as

common at Fort Lowell (now Tucson) along Rillito

Creek, there were specimens collected at that same

location on several occasions between 1872 and 1916

(Brewster 1883, Howell 1916, Johnson et al. unpubl.

ms.). One specimen was also collected along the Santa

Cruz River (Brown 1884). Scott (1886) referred to the

owl as a bird “not uncommon about Tucson.” However,

from the 1920s through the 1940s, with two possible

exceptions - skins collected in 1922 by Kimball and a

reported observation in 1949, both at an unspecified

location in the Tucson area (Johnson et al. unpubl.

ms.)-, the owl was not mentioned from Rillito Creek or

the Santa Cruz River in the literature, nor was any

specimen collected. For example, Brandt (1951) worked

in southeastern Arizona between 1935 and 1948, but

he found no cactus ferruginous pygmy-owl along Rillito

Creek. We are not aware of any record showing the

presence of the owl along Rillito Creek or the Santa

Cruz River since the 1940s.

While an early extirpation seems probable along

Rillito Creek and the Santa Cruz River, the owl continued to be recorded in Sabino Canyon and elsewhere in

the Santa Catalina Mountains at regular intervals

through the 1970s (e.g., Kimball 1921, Brandt 1951,

Davis 1974, Demaree 1976, Johnson et al. unpubl.

ms.). Phillips et al. (1964) reported a population decline near Tucson but this population decline is not

well documented. In recent years, broadcast surveys

have led to the discovery of a breeding population of

owls in the Tucson area (see Chapter 3). The fact that

pygmy-owls are now found in desertscrub rather than

riparian areas further confounds any effort to evaluate the magnitude and timing of a population decline

in the Tucson area.

4. Habitat loss and alteration along

floodplains _______________________

Reasons for the population decline and local extirpations of the cactus ferruginous pygmy-owl have been

called speculative by some (Rea 1983, Hunter et al.

1987). Peripheral populations may be at a higher risk

of sporadic local extinction. In birds, there is evidence

suggesting that after periods of environmental stress,

population density declines proportionally more at the

edge of the range (Mehlman 1997). Furthermore, the

contraction or expansion of the range documented

for several North American birds of prey (e.g., Phillips

et al. 1964, Weidensaul 1989, Williams 1997) underscores the dynamic nature of geographic boundaries.

The relative instability of peripheral populations may

help explain why the largely tropical ferruginous

pygmy-owl seemingly experienced a population decline in Arizona, at the very northern edge of its

distribution.

While biogeography may have played an important

role, it is generally recognized that loss of habitat was

one, if not the, primary causal factor (Johnson et al.

1979, Johnson and Haight 1985, Hunter 1988, Millsap

and Johnson 1988). The coincidental occurrence of

habitat loss and population decline was witnessed

both in Texas and in Arizona (see Oberholser 1974,

Johnson et al. unpubl. ms.). Where the pygmy-owl’s

habitat has been preserved in Texas, a sizeable population still occurs (Mays 1996).

The history of riparian habitats in Arizona has been

called one of “destruction” (Phillips and Monson 1964)

and “desertification” (Johnson and Simpson 1988).

Indeed, it is now estimated that since the end of the

19th century, at least 90% of all the original vegetation

along Arizona’s rivers has disappeared due to human

activities (Johnson and Carothers 1982, Fleishner

1994). Some rivers which once had a perennial flow of

water are now dry over the lower part of their course.

In many areas, their banks are lined with exotic

tamarisk (Tamarix spp.) or are almost devoid of vegetation (Hastings and Turner 1965, Johnson 1979,

Rea 1983, Tellman et al. 1997). The severe population

decline of several bird species, such as the southwestern willow flycatcher (Empidonax traillii extimus)

(Unitt 1987, Taylor and Littlefield 1986, U.S. Fish and

Wildlife 1995, Sogge et al. 1997) and the yellow-billed

cuckoo (Coccyzus americanus) (Laymon and Halterman

1987) over the entire Southwest has been linked to the

disappearance of riparian habitat. In parts of their

range, Lucy’s warblers (Vermivora luciae) have clearly

suffered from the loss of mature bosques caused by

woodcutting and diminishing water tables (Rea 1983,

Johnson et al. 1997).

In modern times, the growth of cities throughout the

Southwest has been placing increasing demands on

regional watersheds (Tellman et al. 1997). Groundwater pumping and water diversion in particular represent important threats to riparian woodlands (e.g.,

Johnson and Carothers 1982, Tellman et al. 1997).

Yet, although some riparian landscapes have been

drastically altered during the last several decades,

many others were lost around the turn of the 20th

century. The history of southwestern rivers is indicative of early human-related changes that caused

severe deforestation and reduced waterflow. An early

population decline of the cactus ferruginous pygmyowl along the Gila, Santa Cruz, and Salt rivers would

have coincided with a severe loss of riparian areas.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 21

Gila River

During the first half of the 19th century, the flow of

water was perennial along most of the Gila River’s

course (Dobyns 1981). Below its confluence with the

Salt River, the river reached 200 yards in width (see

Tellman et al. 1997). The banks were described as

supporting tall cottonwoods and willows (Salix spp.)

as well as abundant wildlife that included “flights of

white brant [snow goose] . . . geese, and ducks, with

many signs of deer and beaver” (Emory 1848). Javelinas, otters, turkeys, and mountain lions were also

described (Tellman et al. 1997). Islands in the middle

of the river sheltered numerous beaver; fish were

abundant (Tellman et al. 1997). Some fish, such as the

Colorado squawfish (Ptychocheilus lucius), weighed

nearly 50 pounds, and, along with the razorback sucker

(Xyrauchen texanus) in the Salt River, supported commercial fishing (Minckley 1973).

While the Pima and Maricopa Indians who lived

along the banks of the Gila must have somewhat

affected this river, drastic changes in the surrounding

vegetation and the flow of water did not occur until the

arrival of the first Anglo-Americans (Dobyns 1981,

Tellman et al. 1997). The activities of the newcomers

included intensive beaver trapping, cattle grazing,

and mining. Beaver trapping caused the many pools

behind their dams to disappear along with the wildlife

they had supported. Overgrazing led to the loss of

vegetation and an increase in soil erosion. Mining

caused water pollution and diversion, as well as deforestation in order to produce fuel and mine timbers. In

1876, for instance, untold miles of mesquite thickets

were harvested to produce charcoal (Tellman et al.

1997). The water table dropped substantially due to

diversion and groundwater pumping. A canal built by

farmers in 1887 at Florence significantly reduced

waterflow downstream. Beginning in 1921, several

dams were built that further reduced waterflow and

ended seasonal flooding, thus preventing the regeneration of native vegetation (Tellman et al. 1997). Rea

(1983) describes riparian areas along the Gila River

during Gilman’s time as already affected by humans

and “rapidly deteriorating.”

The Santa Cruz River and Rillito Creek

Historically, the flow of water in the Santa Cruz

River was mostly perennial from the river headwaters

in the San Rafael Valley to north of the Tucson Mountains (Tellman et al. 1997). Early accounts describe a

river lined with cottonwood trees, willows, and walnuts (Juglans major), and occasional forests of huge

mesquite trees (Froebel 1859, Swarth 1905, Willard

1912). Swamps created by springs occurred at several

locations and supported lush vegetation (Dobyns 1981).

Wildlife was abundant and diverse with the local

occurrence of tortoises, waterfowl, beaver, muskrats,

and large mammals such as grizzly bears and bobcats

(Tellman et al. 1997).

The banks of Rillito Creek, historically a main tributary of the Santa Cruz River, supported large cottonwoods (Surgeon General’s Office 1875). There was a

marsh near Fort Lowell. Evidently, the vegetation

along the Santa Cruz was lush in 1872 when Bendire

(1888) collected his first cactus ferruginous pygmyowl specimens. In his succinct description of the habitat, he refers to the presence of “heavy mesquite

thickets.”

During Bendire’s time, the banks of the Santa Cruz

River and Rillito Creek were already beginning to

change (see Tellman et al. 1997). As trees were cut to

provide domestic and industrial fuelwood for the growing city of Tucson, the banks of the Santa Cruz River

suffered heavy deforestation. Swarth (1905) and

Willard (1912) both describe giant mesquite trees,

many of them sixty feet high, with a thick understory

of hackberry (Celtis spp.) and other thorny bushes,

along the Santa Cruz on the Papago Indian Reservation (now known as the San Xavier District of the

Tohono O’odham Reservation), but Swarth adds that

the location of the mesquite grove on the reservation

“is the only reason for the trees surviving as long as

they have, since elsewhere every mesquite large enough

to be used as firewood has been ruthlessly cut down, to

grow again as a straggly bush.”

Salt River

In the absence of drought, the flow of the Salt River

was once perennial, with pools created by beaver dams

(B. Foltz, pers. comm.). The river banks were lined

with cottonwood, mesquite, and willow trees (Tellman

et al. 1997). Humans first impacted the river system

with woodcutting and water diversion for agricultural

needs. Initially, human-caused changes in the vegetation along the Salt River may have been less dramatic

than on the Gila and Santa Cruz rivers. Yet, during

the first decade of the century, the Salt River Project

was initiated and the construction of the first of four

dams on the Salt River east of its confluence with the

Verde River was completed as early as 1911 (Tellman

et al. 1997). By the end of the 1930s, the other three

dams had been built. Together, those dams turned the

lower Salt River into a string of lakes and prevented

the regeneration of the native vegetation (Tellman et

al. 1997).

5. Blue Point Cottonwoods: a glimpse

of the past ________________________

BPC occurs on the Tonto National Forest between

Stewart Mountain Dam (Saguaro Lake) and Granite
22 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

Reef Dam. Located approximately 50 km upstream

from downtown Phoenix and 3 km upstream from the

confluence of the Verde and Salt rivers, the area

extends for nearly 2 km and supports the most extensive native cottonwood-mesquite habitat remaining along the lower Salt River. In a preliminary report,

Johnson and Simpson (1971) describe a large stand of

mature cottonwoods with mesquite understory and a

marsh of open water located in an abandoned meander

of the Salt River and lined with arrowweed (Pluchea

sericea) and tamarisk. In the marsh, dense stands of

cattail (Typha domingensis) grow along with duckweed (Lemna sp.) and a rare water fern for the region

(Azolla sp.). On the desert hills and flats immediately

adjacent to the riparian and aquatic habitats is semiarid Arizona Upland and Lower Colorado River Valley

vegetation that includes washes lined by xeroriparian

habitat (Brown et al. 1980, Johnson et al. 1984).

Despite the presence of a dam upstream to control

flooding, the area is thought to resemble many riparian habitats of the past (Johnson and Simpson 1971,

Rea 1983).

To study the local bird community, Johnson and

Simpson delineated a 250 acre (100 ha) plot that

extended 1.6 km along the marsh with a maximum

width of .8 km. The study area consisted of seven basic

habitats (Table 2-1) which together contributed to the

diversity and complexity of the habitat. The study

area was surveyed from 1969 until the early 1980s. Of

208 avian species recorded within the plot’s boundaries, 69 were breeding (Table 2-2). Among them, the

least bittern (Ixobrychus exilis), Cooper’s hawk (Accipiter cooperii), elf owl (Micrathene whitneyi), blackchinned hummingbird (Archilocus alexandri), browncrested flycatcher (Myiarchus tyrannulus), vermilion

flycatcher (Pyrocephalus rubinus), common raven (Corvus corax), and blue grosbeak (Guiraca caerulea) also

once bred along the Gila River on the Gila River Indian

Reservation (Rea 1983). Presumably, the extirpation

of these species on the reservation coincided with the

loss of their habitat (e.g., the tall stands of cottonwood

or willow trees with well developed understory for the

Cooper’s hawk and the brown-crested flycatcher, and

the marshy areas for the least bittern). At BPC, where

these same habitat types have persisted, the birds

mentioned above still occurred when the study ended.

Even so, some species, including the common blackhawk (Buteogallus anthracinus) and the cactus ferruginous pygmy-owl, ceased to occur on the study plot,

arguably as a result of the more general loss of riparian vegetation statewide.

Although total ecological losses due to human activities since the arrival of European settlers will never be

fully known, the long-term study conducted at BPC,

together with historical descriptions of riparian landscapes, offers a glimpse of past riverine conditions.

The history of BPC between 1969 and 1995 also provides insight on the fragile nature of riparian habitats

and the associated impact of human activities. During

that period, grazing by cattle and horses had a sometimes deleterious effect on the native ecosystem. Cattails in the marsh were devoured by cattle during some

years, leaving no cover for several species of aquatic

and marsh birds (e.g. pied-billed grebe [Podilymbus

podiceps], least bittern, common moorhen [Gallinula

chloropus], American coot [Fulica americana], and

common yellowthroat [Geothlypis trichas]). Permittee

grazing was removed from the plot in 1977-1978 (Goldfield allotment permit canceled permanently in 1981)

but trespass grazing continued into the 1990s. During

the 1970s, the area was fenced, but fences to the north

were destroyed by recreationists and fences to the

south were destroyed by floods.

The pulsing action of flooding alternating with periods of non-flooding is an essential process in maintaining natural riparian ecosystems in the Southwest

(e.g., Molles et al. 1998). However, when these natural

processes are interrupted by dams, such as those

along the Salt River, floods may then become destructive to riparian ecosystems (Johnson and Carothers

1982). Such is the case with BPC. During the late

1970s and early 1980s, several years of heavy winter

rains resulted in large spring-water releases by the

Salt River Project from upstream dams. During the

Table 2-1. Habitat types on the Johnson-Simpson study plot.

Type Acres Hectares

Closed canopy mesquite bosque 80 32

Open canopy mesquite bosque 45 18

Mesquite bosque w/ cottonwood overstory 15 6

Old river bed (sand, rocks, scattered mesquites, shrubs, cacti, and other perennials) 50 20

River and banks 25 10

Marsh 7 3

Upland (ridges dissected by washes w/ xeroriparian vegetation) 28 11

Total 250 100
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 23

Table 2-2. Breeding birds on the study plot at Blue Point Cottonwoods (data from Phillips et al. 1964, Johnson and Simpson 1971,

Johnson et al. 1987, Johnson unpubl. data, and L. L. Hargrave & A. R. Phillips unpubl. field notes).

Breeding Local Riparian Number of breeding

Species common namea habitatb statusc dependencyd pairs on plot

Pied-billed grebe M SR OBL 1 (some years)

Least bittern M SR OBL 2

Great blue herone PR OBL 1

Green heron CE SR OBL 3

Ospreye,f WR OBL 1 (extirpated)

Bald eagle C ON OBL 1 (winters 71-72, 88-89)

Cooper’s hawk C PR OBL 1

Common black-hawk C SR OBL 1 (extirpated)

Harris’s hawk C PR PREF 1 (some years)

Red-tailed hawk C PR FAC 1

American kestrel CF PR PREF 2

Gambel’s quail DFW PR PREF Fluctuates, 1-7 coveys

Sora M ON OBL 1 (summer 1951)

Common moorhen M SR OBL Varies, up to 4

American coot M SR OBL Varies, up to 6

Killdeer E ON PREF 2

White-winged dove CWF SR PREF 74±

Mourning dove CWF PR PREF 99±

Yellow-billed cuckoo C SR OBL 3

Greater roadrunner ACDFW PR PREF 3

Barn-owl C PR PREF 1

Western screech-owl CW?g PR PREF 230±

Great-horned owl C, Cliffs PR PREF 2

Ferruginous pygmy-owl CW PR PREF Extirpated

Elf owl F SR NON 7

Lesser nighthawk F SR NON 10+

Common poorwill F SR NON 4+

Black-chinned hummingbird CW SR OBL 11±

Costa’s hummingbird DF SR NON 2+

Gila woodpecker CFDW PR PREF 16

Ladder-backed woodpecker CW PR OBL 16

Gilded flicker CD PR FAC 5

Black phoebe ERM PR OBL 3

Vermilion flycatcher CW SR OBL 1h

Ash-throated flycatcher CFW PR PREF 24

Brown-crested flycatcher C SR OBL 15

Western kingbird C SR OBL 2

Northern rough-winged swallow R SR OBL 7

Cliff swallow R SR OBL Remains of 33 old nests

Common raven R PR PREF 1

Verdin DW PR PREF 109±

Bushtit D Vagrant 1 (nested 1973)

Cactus wren F PR FAC 9

Rock wren F PR NON 2

Bewick’s wren C PR OBL 2

Black-tailed gnatcatcher D PR FAC 5

Curve-billed thrasher CFW PR PREF 4

Crissal thrasher W PR OBL 7

Phainopepla DW WR PREF 19

European starling CF WR PREF 26

Bell’s vireo EW SR OBL 14

Lucy’s warbler CW SR OBL 510±

Yellow warbler C SR OBL 3

Common yellowthroat M SR OBL 6

Yellow-breasted chat E SR OBL 4

(con.)
24 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

Summer tanager C SR OBL 4

Northern cardinal DW PR OBL 11

Blue grosbeak E SR OBL 3

Canyon towhee F PR NON 1+

Abert’s towhee CW PR OBL 25±

Black-throated sparrow F PR NON 2

Song sparrow EM PR OBL 20

Red-winged blackbird E PR OBL 15±

Bronzed cowbird CW SR OBL 2+

Brown-headed cowbird ALL SR PREF 10± females

Hooded oriole CW SR OBL Extirpatedi

Bullock’s oriole CW SR OBL 12±

House finch CDW PR FAC 30±

Lesser goldfinch C SR OBL 18

Totals: 69 species 1,527+ pairs

a

After 7th ed. A.O.U. Checklist (1998). b

Breeding Habitat: A=Abandoned river channel of sand and rock with sparse desertscrub; C=Fremont cottonwood (Populus fremontii)-Goodding

willow (Salix gooddingii); D=desert washes; E=water edge, including mesquite (Prosopis velutina), arrowweed (Pluchea sericea) & seepwillow

(Baccharis salicifolia) [see R]; F=foothills, largely saguaro (Cereus giganteus)-palo verde (Cercidium sp.)-bursage (Ambrosia sp.) and mixed cacti;

M=marsh vegetation, largely cattails (Typha domingensis), bulrushes (Scirpus spp.), common reed (Phragmites), water fern (Azolla sp.), duckweed

(Lemna minor); R=riverbank and cliffs (sand, soil & rocks in contrast to vegetation in E); W=mesquite woodland (bosque), including Acacia spp. c

Status on study plot, may differ from Salt River Valley in general: ON=occasional nester; PR=permanent resident; SR=summer resident;

WR=winter resident. d

After Johnson et al. 1987.

e

Feeding territory only, nesting off of study plot.

f

Last seen nesting in this area by Werner, summer 1951 (not Johnson, as stated by Phillips et al. 1964). Hargrave (pers. comm.) knew it as a

relatively common nester on transmission lines along the Salt River between Roosevelt Dam and Mesa and Robinson (1930) recorded a pair nesting

at Canyon Lake. g

Extrapolation from random censusing of displaying pairs in open and closed-canopy mesquite and cottonwood gallery forest with mesquite

understory (Johnson et al. 1981). h

Vermilion flycatchers (Pyrocephalus rubinus) were here in numbers during the 1940s and 1950s but after 1 pair bred in 1969, they disappeared

from the plot until after a large burn in the late 1980s or early 1990s when at least 2 pairs returned. i

Earlier records showed the hooded oriole (Icterus cucullatus) more common than the Bullock’s oriole (I. bullockii). In 1969, the last pair of hooded

orioles was recorded nesting at BPC (Johnson unpubl. data). Phillips suggests that this may be largely due to an increase in brood parasitism by

the bronzed cowbird on hooded orioles. This would not, however, explain the increase in the Bullock’s oriole population.

Table 2-2. Con.

Breeding Local Riparian Number of breeding

Species common namea habitatb statusc dependencyd pairs on plot

early spring of 1978, 1979, and 1980, flows of 2.5 m to

3.5 m or more in depth flooded most of the HargravePhillips-Johnson study area. Although mesquite trees

were rarely damaged, some mature cottonwoods and

many of the seepwillow (Baccharis salicifolia),

arrowweed, and other riparian shrubs were uprooted.

The marsh was greatly damaged from scouring of

cattails, common reeds (Phragmites australis), bulrushes (Scirpus spp.), and other herbaceous or semiwoody plants. However, the receding water also left

seed beds and many cottonwood and willow seedlings

later grew into medium-sized trees during the 1980s.

In the Southwest, the lack of regular natural flooding also contributes to the accumulation of debris and

an increase in both frequency and intensity of fire in

riparian areas (Crawford et al. 1993, Stuever 1997). At

BPC, fire is presently one of the most damaging

factors. Several fires of 25 acres or more during the

mid to late 1980s burned much of the study area.

Although many of the mesquites recovered, or partially recovered, several small stands of cottonwoods

disappeared. As shown by recent visits, the larger

stands along the marsh escaped damage and continue

to thrive.

Most lowland riparian habitats in Arizona have

suffered a substantial loss in biological diversity and

a reduction in the population density of native plants

and animal species. In the past, many riparian areas

apparently shared the same habitat complexity and

bird species richness of BPC. Even the documented

changes in the local vegetation at BPC due to grazing,

fires, and human-caused flooding serve as a reminder

of the potential magnitude of human impacts on riparian habitats. The population decline of the cactus

ferruginous pygmy-owl and other species associated

with riverine ecosystems in Arizona may be viewed as

symptoms of this broader problem created by human

interruption of natural riparian processes along southwestern lowland river systems.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 25

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USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 27

W. Scott Richardson

Jean-Luc E. Cartron

David J. Krueper

Lauren Turner

Thomas H. Skinner

Chapter 3

The Status of the Cactus Ferruginous

Pygmy-Owl in Arizona: Population

Surveys and Habitat Assessment

In 1993, the Arizona Game and Fish Department

(AGFD) began formal population surveys in an attempt to document the numbers and distribution of

cactus ferruginous pygmy-owls (Glaucidium brasilianum cactorum) in Arizona. Surveys were initiated to

gather information on this little-known subspecies

which was considered for listing at the time. Prior to

1993, birders and avian biologists had conducted

many informal surveys in a sporadic and opportunistic fashion. However, the information derived from

those surveys was limited and often inaccessible, and

contributed little to the overall understanding of the

distribution and abundance of the species. From 1993

to 1997, even the more formal cactus ferruginous

pygmy-owl surveys were limited in number and area

covered and resulted in only a handful of cactus ferruginous pygmy-owl detections. With the listing of the

cactus ferruginous pygmy-owl as an endangered species, significantly more surveys were conducted in

1998 and 1999 by the AGFD, licensed consultants,

land management agencies, and agency contractors.

The increased number of pygmy-owl detections during

those two years resulted from this additional survey

effort.

While there is a considerable amount of potentially

suitable cactus ferruginous pygmy-owl habitat that

remains unsurveyed, we have learned the following

information about the distribution of cactus ferruginous pygmy-owls within Arizona: 1) despite increased

survey efforts and an increased number of cactus

ferruginous pygmy-owl detections, the Arizona population of cactus ferruginous pygmy-owls still appears

small; 2) the currently known population of cactus

ferruginous pygmy-owls occurs chiefly in desertscrub

habitats rather than riparian habitats reported in

historical accounts (see Chapter 2); 3) the population

of cactus ferruginous pygmy-owls appears patchily

distributed across suitable habitat with population

pockets occurring in northwest Tucson, southern

Pinal County, the Altar Valley, Organ Pipe Cactus

National Monument, and the Tohono O’odham

Reservation.

In this chapter, we discuss some of the difficulties

and challenges of developing an effective and practical survey protocol including results and insights

from previous surveys. We then describe important

riparian and desertscrub habitats which represent

occupied cactus ferruginous pygmy-owl habitats or

habitats presumed suitable for cactus ferruginous

pygmy-owls. We then briefly describe initial agency

efforts to better characterize and describe suitable

cactus ferruginous pygmy-owl habitat. Finally, we present our recommendations for future survey efforts.

1. Survey Protocol _________________

In the last two decades, broadcast surveys have

been promoted as a reliable and effective technique
28 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

to study the distribution and size of many small owl

populations (Johnson et al. 1981, Lynch and Smith

1984, McGarigal and Fraser 1985, Smith et al. 1987,

Ganey 1990, Stahlecker and Rawinski 1990, Noon et al.

1992, Wauer et al. 1993). Because of the lack of adequate information regarding the numbers and distribution of cactus ferruginous pygmy-owls in Arizona,

the AGFD developed a broadcast survey protocol as

they initiated formal cactus ferruginous pygmy-owl

population surveys in 1993 (Felley and Corman 1993).

This original protocol was developed based on the little

information known at that time about the biology of

cactus ferruginous pygmy-owls and similar survey

protocols employed for other small owl species. As

surveys progressed and the effectiveness of the protocol was evaluated, a revision of the AGFD protocol

took place in 1996 (Abbate et al. 1996). The 1996

revisions included increasing the distance between

call points and increasing the amount of time spent at

each call point. Other slightly different protocols were

utilized by contractors surveying for special projects in

1998. Adjustments to the original protocol were in

response to changes in research objectives, management needs, and experience gained from previous

survey experience.

Protocol development attempts to maximize cactus

ferruginous pygmy-owl response to tapes by directing

surveys to be performed during the highest known

activity periods (i.e., dawn and dusk), and at the

appropriate time of year (i.e., the courtship and nesting season) (Gilman 1909, Terres 1991, Wauer et al.

1993). There has been considerable discussion about

the effectiveness of surveys outside the peak breeding

season. The original survey protocol defined a survey

season extending from September to April (Felley and

Corman 1993) but, while there appears to be some

calling activity in the early fall, the vast majority of

recent cactus ferruginous pygmy-owl detections have

occurred during the spring courtship and nesting

period, with a decrease in calling and responsiveness

observed through the remainder of the year (Richardson

unpubl. data).

Another debated issue has been the recommended

distance between calling stations for a survey. Results

of initial response distance testing in Texas indicate

that owls will respond to a taped call from a distance

of at least 700 m (Chapter 5). However, current protocols for surveying in Arizona recommend call point

distances ranging from 150 m to 400 m. While shorter

distances between call points decrease survey coverage and thus present some logistical and economic

concerns, they do address reduced responsiveness or

ability to detect owls because of local demographic

and physical factors. Many of the cactus ferruginous

pygmy-owls found in Arizona occur in urbanized

areas with significant background noises from automobiles, humans, dogs, etc. which reduce a surveyor’s

ability to detect an owl. Additionally, it has been

suggested that, at least for the boreal owl (Aegolius

funereus), the physiological state of individual owls,

the amount of competition among males for nest

sites, and mating success can all influence rates of

detection (Hayward et al. 1992). In Arizona, low population densities of cactus ferruginous pygmy-owls, and

perhaps reduced competition for nest sites, may be

associated with lower rates of responsiveness. Thus, if

call points are too far apart and/or the time spent at

each point is too short, some owls may escape detection. The challenge has been to develop a protocol

which balances the significant repercussions of not

detecting an owl, when it could potentially be impacted by some activity, with increased costs and

logistical difficulties resulting from a conservative

survey protocol. Direct costs are associated with

actually conducting surveys; there are also indirect

costs if the protocol results in the delay of project

implementation. Another question considered is the

need for two protocols, one dealing with project clearance and another for population assessment and research activities.

In an effort to address issues regarding survey

protocol and associated management issues, the U.S.

Fish and Wildlife Service (USFWS) and the AGFD

developed a survey protocol that was released for

public comment in late 1998 (Appendix 3-1). This

proposed survey protocol received significant review

by a wide variety of public interests. Public comment

is currently being evaluated and a finalized protocol is

expected sometime in 1999. While economic interests

such as development, grazing, and mining may be best

served by a stable protocol that can be considered in

long-term planning efforts, the cactus ferruginous

pygmy-owl survey protocol must be adaptive enough

to incorporate advances in our understanding of this

species. For example, it is only within the past two

years that radio telemetry has been utilized to help us

understand aspects of cactus ferruginous pygmy-owl

biology such as home range, territoriality, and habitat

use. Telemetry will also allow us to test responsiveness of known owls to tape broadcasts. This new

information must be utilized in order to develop the

most effective survey protocol.

2. Responses of other bird species to

broadcast surveys _________________

The ferruginous pygmy-owl is known as the “terror

of small birdlife” (Sprunt 1955). Judging from the

numerous accounts describing the owl as mobbed by

songbirds and hummingbirds (Gilman 1909, Sprunt

1955, Tyler and Phillips 1978, Abbate et al. 1996,

Russell and Monson 1998), the occurrence of this owl

is likely perceived as a threat by the local avifauna.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 29

Mobbing is a behavior specifically directed against

potential enemies during the reproductive season

(Kruuk 1964, Hoogland and Sherman 1976, Shields

1984) and raids of neighboring songbird nests by

cactus ferruginous pygmy-owls have been documented

in Texas and Arizona (see Chapter 1). Mobbing was

observed at all nest sites monitored in Arizona and

involved a wide variety of species (Abbate et al. 1996,

Richardson unpubl. data).

In addition to mobbing, birds also respond to

pygmy-owls with vocalizations (i.e., alarm calls),

movements, agitation, or some combination of the

three. In the Tucson area, where cactus ferruginous

pygmy-owls have been found, 25 species (14 of which

are year-round residents) responded to broadcast calls

with agitated behavior and/or alarm calls (Table 3-1).

Among those species, the verdin (Auriparus flaviceps),

Gila woodpecker (Melanerpes uropygialis), and blacktailed gnatcatcher (Polioptila melanura) were described

as the birds most often reacting to cactus ferruginous

pygmy-owls (Abbate et al. 1996). In the Coronado National Forest, where no pygmy-owl was found, several

bird species responded with movement, vocalization,

and/or agitation during 1997 surveys (Table 3-2). Of

these, however, only two identified species exhibited

agitated behavior and the bushtit (Psaltriparus

minimus) alone is a local year-round resident.

If bird responses were species specific, they could

indicate whether cactus ferruginous pygmy-owls are

in the surveyed area. However, using these responses

during broadcast surveys as an indicator of recent or

present exposure to cactus ferruginous pygmy-owls in

the area is tenuous. The residency status of responding birds is the first important consideration, as the

owl is abundant in the tropics (see Chapters 1 and 4).

For migratory species, such as most hummingbirds

and warblers, agitated behavior or alarm calls in

response to tape playing may only reflect exposure to

Table 3-1. List of species responding to broadcast calls of cactus ferruginous pygmy-owls with

distress/alarm calls and/or agitated behavior in the Tucson area during surveys from 1994

to 1997 (data compiled from Collins and Corman 1995, Lesh and Corman 1995, Abbate

et al.1996, Proudfoot and Beasom 1997, and Skinner unpubl. data).

Local status Documented predation by

Bird species (<4,000 ft elevation) ferruginous pygmy-owls

Anna’s hummingbird Year-round resident —

Ash-throated flycatcher Summer resident —

Bewick’s wren Winter resident a Yes (Texas)

Bell’s vireo Summer resident —

Black-tailed gnatcatcher Year-round resident —

Bridled titmouse Year-round resident —

Broad-billed hummingbird Summer resident —

Bushtit Year-round resident —

Cactus wren Year-round resident Yes (Arizona)

Cassin’s kingbird Summer resident —

Curve-billed thrasher Year-round resident —

Gila woodpecker Year-round resident —

House finch Year-round resident Yes (Arizona)

House sparrow Year-round resident —

Hooded oriole Summer resident —

Lucy’s warbler Summer resident —

Northern cardinal Year-round resident Yes (Texas)

Northern mockingbird Year-round resident b Yes (Texas)

Phainopepla Year-round resident —

Pyrrhuloxia Year-round resident Yes (Texas)

Ruby-crowned kinglet Winter resident —

Summer tanager Summer resident —

Verdin Year-round resident Yes (Arizona)

Vermilion flycatcher Summer resident c —

Western kingbird Summer resident —

a

 During the summer, the Bewick’s wren occurs at higher elevations.

b As seasonal dispersal occurs, breeding populations may differ from winter populations below 4,000 ft

(1,220 m). Many breeding individuals that breed below 4,000 ft may have wintered south of the Arizona

border. c

 During the winter, the vermilion flycatcher is local and sparse.
30 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

the owl in the tropics during the non-breeding season.

Even when responding birds are year-round residents, however, it is not known whether they are

reacting specifically to the owl’s call based on personal

exposure or if they simply perceive the call as fitting

the characteristics of a potential predator.

Despite the questions surrounding the use of bird

responses during unsuccessful surveys as an indication of owl presence, mobbing in particular is valuable to locate cactus ferruginous pygmy-owls. In fact,

mobbing response is the primary tool used to detect

cactus ferruginous pygmy-owls during research when

the owls are not vocalizing or if a radio transmitter is

not attached. Prior to the use of telemetry, most

cactus ferruginous pygmy-owl locations associated

with nest monitoring were the results of investigating areas where mobbing behavior by songbirds was

observed. While monitoring owls during research, it

is also very rare to go through a session without

recording mobbing behavior. Therefore, mobbing response during broadcast surveys is a good tool to help

locate this very cryptic species.

3. Population Surveys______________

As listed by Hunter (1988), detections of cactus

ferruginous pygmy-owls during the 1970s and 1980s

were scattered in various parts of south and central

Arizona, occurring in both riparian and in desertscrub/

xeroriparian habitats (Table 3-3). However, the survey effort of the last five years suggests a somewhat

different pattern of distribution, with few owls detected in meso-riparian habitat. Cactus ferruginous

pygmy-owls have been found in association with

desertscrub and xeroriparian vegetation in four general areas: Organ Pipe Cactus National Monument,

northwest Tucson/southern Pinal County, the Tohono

O’odham reservation, and the Altar Valley. The only

Table 3-2. List of species responding to broadcast calls of cactus ferruginous pygmy-owls during surveys at various locations

on the Coronado National Forest during the spring of 1997.

Location of survey(s) Type of habitat Species responding Type of responsea

Providencia Canyon Xeroriparian ash-throated flycatcher M, V

Bewick’s wren M, V

broad-billed hummingbird M

house finch M?, V

vermilion flycatcher M

Finger Rock Canyon Xeroriparian with ash-throated flycatcher M, V, A

occasional cottonwoods broad-tailed hummingbird M

Agua Caliente Canyon Xeroriparian flycatcher sp. M, V

gnatcatcher sp. M

hummingbird sp. M?

phainopepla M?

Wilson’s warbler M?

Sabino Canyon Riparian ash-throated flycatcher A

bushtit M, A

northern cardinal M

gnatcatcher sp. A

hummingbird sp. M

Pima Canyon Xeroriparian hummingbird sp. M

Sycamore Canyon Riparian broad-tailed hummingbird M

northern pygmy-owl V

Santa Catalina State Park Riparian black-tailed gnatcatcher M

flycatcher sp. V

verdin M, V

common poorwill V?

a M = response with movement towards the observer, V = response with vocalizations, A = response with agitated behavior, ? = movement or

vocalization recorded, but not in obvious response to tape playing.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 31

owls found in meso-riparian areas occurred in the

Altar Valley. Surveys completed from 1993 through

1996 were conducted primarily by the AGFD. Survey

areas were selected based on historic occurrences

and thus focused primarily on riparian areas. Some

historic locations, however, occurred in desertscrub

and were surveyed. In addition, some desertscrub

areas on Breeding Bird Atlas blocks were also surveyed. A few surveys were conducted by federal

agencies within their jurisdictions including Organ

Pipe Cactus National Monument and Saguaro National Park. These surveys detected very few owls

(Table 3-4).

With the listing of the cactus ferruginous pygmyowl as an endangered species in 1997, agencies and

consultants increased the cactus ferruginous pygmyowl survey effort significantly. Surveys were still

focused on areas where owls had been detected in the

past, but expanded to include areas of potentially

suitable desertscrub where projects were planned to

occur. In conjunction with the increased survey effort,

experience gained by researchers and increased public

awareness have resulted in more owls being found in

recent years (Table 3-4). Even with the increased

survey effort, there are still large areas of potentially suitable habitat that remain unsurveyed and,

although we have detected an increasing number of

birds, information on the natural history, distribution

and habitat requirements of cactus ferruginous pygmyowls still remains limited. The results of population

surveys do not yet allow for an estimate of population

size. For these reasons, surveys should remain a high

priority in the next few years.

4. Description of Important Habitat

Areas and Survey Effort ____________

The cactus ferruginous pygmy-owl in Arizona has

been documented in a variety of riparian and

desertscrub habitats (Bendire 1888, Breninger 1898,

Gilman 1909, Phillips et al. 1964, Hunter et al. 1987,

Hunter 1988, Abbate et al. 1996). Some of the historic

locations, particularly those in riparian habitat, have

undergone considerable alteration since the time of

Table 3-3. General location of detections from 1971 to 1988 (adapted from Hunter 1988).

Time of Status of

Location documented presence individuals located

Northwest Tucson and 1976 individual

 Marana/Red Rock 1980-1987 pair with young

Tanque Verde Ranch 1975 individual

Sabino Canyon Visitor Center 1971, 1976 pair with young

OPCNM 1977-1985 2+ pairs

early 1980s individual

early 1980s individual

lower San Pedro watershed 1985-1987 pair

1987 individual

Salt River 1971 individual?

Gila River watershed 1978 a individual

1985 a individual

Upper Santa Cruz watershed mid-1970s b individual

1975 c individual

Lower Sycamore Canyon 1986 d individual

aSightings of cactus ferruginous pygmy-owls at the Bonita Creek-Gila River confluence and Gila River-San

Francisco River confluence may be questionable (T. Corman, pers. comm.). There are no historical (pre1970) records even close to this area. One owl sighted is only described as a “small, tuftless owl at the entrance

to a tree cavity.” In retrospect, this bird could have been an elf owl (Micrathene whitneyi). b, c These two records are from elevations reaching approximately 4,000 ft. d The owl reported may have been a northern pygmy-owl (Glaucidium gnoma) (T. Corman, pers. comm.).
32 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

noted pygmy-owl occurrence (see Chapter 2). Other

areas, though, have developed or maintain potentially

suitable habitat characteristics, such as vegetation

structural diversity and nesting substrates. The following is a description of some of the important habitat areas that remain in Arizona and an indication of

survey efforts in those areas. Due to limited manpower

or inaccessibility, some of these areas have not yet

been surveyed adequately, while others -not all of

these are described here- have not yet been surveyed

at all.

A map (Fig. 3-1) is included with the location of all

survey areas. For several of these, information is

provided in the text on recent vegetation changes and

outstanding threats to the habitat. When determined

by surveyors, qualitative estimates of cavity availability and woodpecker abundance are also reported.

Lower San Pedro

Lands considered to be suitable for cactus ferruginous pygmy-owl occupancy in the lower San Pedro

River drainage (Fig. 3-1) primarily consist of a mixture

of cottonwood (Populus fremontii), Goodding willow

(Salix gooddingii), velvet mesquite (Prosopis velutina)

and exotic tamarisk (Tamarix spp.)-dominated riparian vegetation.

The riparian habitat along the lower San Pedro

River varies from vast expanses of gallery cottonwood/

willow forest with a dense understory of tamarisk to

decadent stands of cottonwood interspersed with monotypic stands of tamarisk. Extensive mesquite bosques

are found in several areas near Cascabel and Mammoth and to the north around Cook’s Lake. Located

near the confluence of Aravaipa Creek and the San

Pedro River, Cook’s Lake is a 270-acre wetland surrounded by dense stands of cottonwoods, Goodding

willow, netleaf hackberry (Celtis laevigata var.

reticulata), buttonbush (Cephalanthus occidentalis),

velvet mesquite, and velvet ash (Fraxinus velutina)

and bordered on its eastern side by upland Sonoran

desertscrub (Lesh and Corman 1995). The local occurrence of one of the largest breeding populations of the

Southwestern willow flycatcher (Empidonax traillii

extimus) for the state of Arizona (Sferra et al. 1997) is

notable, since this endangered bird may be viewed as

an indicator of riparian habitat health (S. Stoleson,

pers. comm.). Bingham Cienega, another wetland near

the town of Redington, is bordered by large cottonwoods, Goodding willows, Mexican elderberry (Sambucus mexicana), netleaf hackberry, and velvet ash. It

is adjacent to a mesquite bosque and surrounded by

hills supporting Sonoran desertscrub vegetation (Lesh

and Corman 1995). Historic records of pygmy-owl

occurrence (Hunter 1988, Table 3-3) have come from

the lower San Pedro River in the vicinity of Dudleyville

and from the mesquite bosques near the mouth of

Aravaipa Canyon. The former location had a dense

understory of tamarisk with a dispersed canopy of

cottonwood trees. The latter habitat was dominated

by large mesquite bosques. Elevation ranges from

1,920 ft (585 m) at Winkelman to 3,040 ft (927 m) at

Cascabel.

Most of the area along the lower San Pedro River is

privately owned with significant portions of Arizona

State Trust Land in adjacent Sonoran Desert uplands.

The Bureau of Reclamation and the Arizona Chapter

of The Nature Conservancy currently administer large

blocks of dense riparian habitat within the lower San

Pedro near Dudleyville. Public lands administered by

the Bureau of Land Management (BLM) along the

river total approximately 2000 acres, including several hundred acres under conservation easements. In

1993, surveys were conducted near Winkelman, Mammoth, San Manuel, and Redington (Felley and Corman

1993). Area coverage totaled 59.1 km2

. Additional

surveys were conducted in 1994 from Winkelman

south to Aravaipa Creek, near Mammoth, and along

Table 3-4. Number of cactus ferruginous pygmy-owls detected (including young of the year) resulting from surveys conducted

from 1993 to 1999 (data compiled from Felley and Corman 1993, Collins and Corman 1995, Lesh and Corman 1995,

Abbate et al. 1996, Richardson unpubl. data, and T. Tibbitts pers. comm.).

Year

Location 1993 1994 1995 1996 1997 1998 1999

Northwest Tucson/southern Pinal County 1 2 6 12 10 20 39

Organ Pipe Cactus National Monument 1 0 1 3-6 2 9 8

Silverbell and Tucson mountains ND ND 0 0 0 1 0

Buenos Aires National Wildlife Refugeb NDa ND 0 ND ND 3 10

Altar Valley (except Buenos Aires National ND ND ND ND ND 0 21

 Wildlife Refuge)

Total 2 2 7 15-18 12 33 78

a

 No data.

b

 The Buenos Aires National Wildlife Refuge and the rest of the Altar Valley are distinguished.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 33

Figure 3-1. Location of survey areas. 1: lower San Pedro River, 2: middle Gila River, 3: Santa Cruz and tributaries, 4: Salt and Verde

rivers, 5: Sycamore Canyon, 6: northwest Tucson and southern Pinal County, 7: Silverbell and Tucson mountains, 8: Organ Pipe

Cactus National Monument, 9: Tohono O’odham Reservation, and 10: Altar Valley, including Buenos Aires National Wildlife Refuge.

The shaded area corresponds to the distribution of the cactus ferruginous pygmy-owl in Arizona (Chapter 2).
34 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

Bingham Cienega (Collins and Corman 1995). In 1995,

only Bingham Cienega and Cook’s Lake were surveyed (Lesh and Corman 1995). On the public lands

near Cascabel managed by the BLM, no surveys were

conducted prior to 1999. One survey conducted in

April 1999 resulted in no detections. Despite the

survey effort, much of the habitat along the lower San

Pedro, especially on private lands, has not yet been

surveyed.

Habitat restoration is occurring on both public and

private lands within the lower San Pedro River Basin

through adjustments in livestock management practices, revegetation of the floodplain with native riparian trees, and construction of erosion control structures in the uplands. The BLM is actively pursuing a

land acquisition process using Land and Water Conservation funds. Land acquisition, land exchange, and

conservation easements continue to be the best habitat conservation programs along the lower San Pedro

River. Despite substantial recharge from side drainages north of Cascabel, however, the growth of Sierra

Vista and increasing groundwater pumping (Tellman

et al. 1997) represent a threat to the riparian vegetation along the San Pedro River.

Middle Gila River

Upstream from Ashhurst-Haydn Dam to near Kelvin,

the banks of the middle Gila River support regenerating cottonwoods and willows intermixed with extensive mesquite bosques. In several areas, extensive

stands of tamarisk line both sides of the river, forming

nearly impenetrable thickets. The middle Gila River is

completely dependent on water releases from Coolidge

Dam which withholds water from the San Carlos

Reservoir. Land ownership patterns along this reach

of the river consist primarily of private, AZ State Trust

Lands and Bureau of Reclamation (BoR) lands. The

BLM manages the BoR lands due to a cooperative

agreement with this agency. On July 12, 1999, the

entire length of the middle Gila River was designated

as critical habitat for the cactus ferruginous pygmyowl. This riparian corridor, however, has not been

surveyed for cactus ferruginous pygmy-owls due to

funding and personnel constraints.

Santa Cruz Watershed

The cactus ferruginous pygmy-owl was once described as a resident of the riparian habitat along

Rillito Creek (Bendire 1888). However, changes in the

vegetation along the Santa Cruz watershed since the

turn of the century have been pronounced (see Chapter 2). The perennial reaches of the Santa Cruz once

found at San Xavier and Tucson are now dry and

deeply entrenched (Tellman et al. 1997). In Tucson,

the banks of both the Santa Cruz and Rillito Creek are

soil cemented. Perennial surface water is now found

only in the upper Santa Cruz River where it receives

wastewater from the Nogales treatment plant and in

some of the river’s tributaries (Tellman et al. 1997).

The remaining floodplain riparian habitat is mostly

confined to narrow, linear areas along major washes

such as Cañada del Oro and Sutherland Washes near

the western foothills of the Santa Catalina Mountains,

and along Sabino Canyon Wash, Tanque Verde, and

Rincon Creek east of Tucson (Fig. 3-1).

The Cañada del Oro Wash and connecting Sutherland

Wash are large, sandy washes that flow only during

heavy rainfalls. They are found in part in Santa

Catalina State Park (Coronado National Forest), where

they were surveyed in 1994, 1995, 1997, and 1999 at

an elevation ranging from 2,640 ft (805 m) to 3,200 ft

(976 m). The banks of both washes support mature

riparian vegetation consisting primarily of velvet

mesquite trees and desert willows (Chilopsis linearis).

The vegetation also includes some walnut (Juglans

major), and a few small cottonwoods. The shrub layer

is composed of catclaw acacia (Acacia greggii),

graythorn (Ziziphus obtusifolia) and desert broom

(Baccharis sarothroides). In the uplands, the vegetation is dominated by saguaros (Carnegiea gigantea)

and foothill palo verde (Cercidium microphyllum) but

also includes ocotillo (Fouquieria splendens), prickly

pear and cholla (Opuntia spp.), white bur sage (Ambrosia dumosa) and fairy duster (Calliandra

eriophylla).

Sabino Creek is a perennial stream which originates

on the Santa Catalina District of the Coronado National Forest. Owls were detected at the Sabino Canyon Visitor Center in the 1970s (Hunter 1988). Within

the Forest’s boundaries, riparian habitat along the

creek is thin, yet continuous, and typically consists of

ash, willow, mesquite, and cottonwood. Understory

plants include hackberry. Cavities are numerous and

woodpeckers are common. The area is open to the

public and receives approximately one million visitors

every year. Near its confluence with Tanque Verde in

northeast Tucson, some of the vegetation has been

cleared due to urban development. Original,

unimpacted habitat along Sabino Creek and Tanque

Verde consists of dense mesquite bosques with patches

of large Fremont cottonwoods (Lesh and Corman 1995).

Lower Sabino Creek and Tanque Verde were surveyed

in 1993 and 1995. Sabino Creek was also surveyed on

the Coronado National Forest in 1997.

Agua Caliente originates on the Santa Catalina

District of the Coronado National Forest and runs

southwest beyond the limits of the forest to its

confluence with Tanque Verde in northeast Tucson. It

consists of a rocky and sandy wash flanked with

xeroriparian vegetation and occasional, thin patches

of riparian habitat. The riparian vegetation along
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 35

Agua Caliente on the Coronado National Forest includes ash, walnut, Arizona sycamore (Platanus

wrightii), and willow. Along the wash’s lower segment,

the riparian vegetation is comprised of Arizona sycamore, desert willow, eucalyptus (Eucalyptus spp.),

and Fremont cottonwood, with mesquite bosques in

some areas. Agua Caliente was surveyed in 1997.

Rincon Creek was surveyed in 1993 and 1998. Along

the banks of Rincon Creek is a fairly narrow strip of

riparian vegetation that consists typically of cottonwood, sycamore, velvet ash, and velvet mesquite. Downstream, these trees are replaced by mesquite groves.

Land use varies from light grazing to large residential

subdivisions.

Cienega Creek has perennial surface waters along a

segment located in the Cienega Creek Preserve at an

approximate elevation of 1,000 m (Abbate et al. 1996).

Dense mesquite bosques occur locally, intermixed with

Fremont cottonwood, desert willow, and other broadleaf riparian species. The creek also supports grasses,

sedges, and other strictly water-dependent species.

On the upper slope, the vegetation includes grasses,

shrubs, and large cacti. While livestock grazing has

been excluded from the preserve, trespass cattle can

still be found regularly in the riparian area. Development outside is sparse. Cienega Creek was surveyed in

1996, 1997, 1998, and 1999. Cactus ferruginous pygmyowl nest boxes were placed in this drainage in 1998,

but were unused by cactus ferruginous pygmy-owls.

Arivaca Creek and its tributaries are located in the

Buenos Aires National Wildlife Refuge in the Altar

Valley (see Altar Valley section).

Lower Salt and Verde Rivers on Tonto

National Forest

The cactus ferruginous pygmy-owl was once a common resident of the Salt River Valley (Breninger

1898). Its occurrence along the Salt River was noted

until 1971 (see Chapter 2). The local decline of the owl

coincided with the disappearance of the original riparian vegetation due to woodcutting and the construction of dams (see Chapter 2). Along the Verde River,

there is no known record of cactus ferruginous pygmyowls, yet their historical occurrence here is certainly

possible in light of records from New River (Fisher

1893), Cave Creek (Johnson et al. unpubl. ms.), and

Blue Point Cottonwoods (Johnson and Simpson 1971).

In May 1997, approximately 13,000 acres on the

Tonto National Forest were surveyed for cactus ferruginous pygmy-owls, chiefly along the Salt and Verde

rivers (Fig. 3-1). In 1998, 12,412 acres were surveyed

by a contractor. In 1997, the survey area along the

Verde River was from Horseshoe Dam to three miles

below the dam, along a portion of the west bank of

Bartlett Reservoir, and between Bartlett Dam and the

Fort McDowell Indian Reservation. Along the Salt

River, surveys were conducted between Stewart Mountain Dam and Granite Reef Dam. The confluence of the

two rivers, which lies at an elevation of 1,500 ft (457

m), was also surveyed in 1993 and in 1994 (Felley and

Corman 1993, Collins and Corman 1995). In 1998,

riparian areas and adjacent uplands were surveyed

along the Verde and Salt rivers, Sycamore Canyon just

upstream from Horseshoe Dam, Cave Creek, and New

River. However, the topography of the latter two areas

surveyed (i.e., steep canyons) suggests that the historical records from Cave Creek and New River (Fisher

1893, Johnson et al. unpubl. ms.) did not originate

from within the Forest boundaries. Additional areas

surveyed in 1998 included the Bulldog Canyon-Usery

Pass area and Hog Canyon.

Along the Salt and Verde rivers, the vegetation is in

places characterized by mesquite bosques and small

patches of cottonwood-willow and sycamore. The banks

of the Verde River have several marshes with cattails

(Typha domingensis). Tamarisk dominates an area

near Granite Reef Dam. The mesquite bosques lack an

understory and are largely degraded by off-highway

vehicle use. Riparian vegetation is flanked by Sonoran

desertscrub consisting predominantly of scattered

mesquite and palo verde, with associations of triangleleaf bur sage (Ambrosia deltoidea), cholla cactus, prickly

pear, saguaro, creosote bush (Larrea tridentata), and

occasional ironwood (Olneya tesota). This habitat is

mostly open, with scattered patches of dense vegetation, and little vertical structural diversity. Near the

confluence of the Salt and Verde rivers, the Salt River

Recreation Area includes a picnic area, nature trails,

and a large parking lot. Livestock grazing has been

banned from the Tonto National Forest but still occurs

on the Fort McDowell Indian Reservation along the

Verde River and a section of the northern bank of the

Salt River. According to Johnson and Haight (1998),

habitat suitability in survey areas along the Verde

River seems comparable to that along the Salt River.

Blue Point Cottonwoods (see Chapter 2) was described between 1969 and the early 1980s as one of the

last remnants of the original floodplain landscapes in

the Salt River Valley. The area was last surveyed in

1998. It consists of a marsh of open water lined with

large stands of cottonwoods and a mesquite understory. The marsh is typically dry during the winter

when water is held upstream. Trespass grazing represents the primary threat to the habitat.

Sycamore Canyon in the Atascosa/Pajarito

Mountains

Sycamore Canyon, located in the Nogales District of

the Coronado National Forest, was surveyed in

1994 and 1997. With intermittent surface waters,
36 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

it supports lowland riparian vegetation consisting

primarily of Arizona sycamore, velvet ash, willow,

walnut, and seepwillow (Baccharis salicifolia).

Saguaros, junipers (Juniperus spp.), and oaks (Quercus

spp.) occur on the slope of the canyon. Mesquite grows

at the edges of the main drainage at the mouth of the

canyon. The habitat supports a substantial number of

woodpeckers while sycamores and saguaros provide

many cavities.

Northwest Tucson and Southern Pinal

County

This area is bounded on the south by Cortaro Farms

Road, on the east by the Catalina Mountains and State

Highway 79, on the west by I-10 and on the north by

Florence and Coolidge (Fig. 3-1). It is a region of

diverse desert scrub of varying quality. This area has

been the most intensively surveyed area for cactus

ferruginous pygmy-owl in the state. Surveys have

been conducted formally since 1993 and have continued through 1999 (Table 3-4). The area contains most

of the cactus ferruginous pygmy-owls detected since

1993. It contains a mixture of private, state, and BLM

lands. Residential occupancy ranges from scattered

ranches on hundreds of acres to densities as high as six

residences per acre. Livestock grazing and recreational

use occur throughout the area. There are large areas

of natural desert characterized as Sonoran desertscrub.

Density and diversity of vegetation are highest to the

south. To the north, the vegetation becomes progressively more open and less diverse. Mesquite and foothill palo verde are dominant species. Saguaros and

ironwoods are common and can become dominant in

some localities, but are completely absent in others.

The understory consists of a variety of cholla, prickly

pear, hedgehog (Echinocereus spp.) and fishhook barrel cacti (Ferocactus spp.). Triangle-leaf bursage is the

dominant understory shrub, but creosote and

burroweed (Isocoma tenuisecta) are common. Desert

hackberry (Celtis pallida), acacia species and desert

willow increase along the numerous dry washes found

in the region. Much of the survey work and most of the

cactus ferruginous pygmy-owl detections have occurred

in the bajadas of the Tortolita Mountains. Elevation

ranges from 2,100 ft (640 m) to near 3,000 ft (915 m) in

the areas surveyed. This site occurs in one of the

fastest developing areas of the state with continued

fragmentation and loss of habitat likely.

Silverbell and Tucson Mountains

The Silverbell and Tucson Mountains are located on

the western edge of the Tucson Basin (Fig. 3-1). The

area is characterized by the occurrence of potentially

suitable desertscrub that has been surveyed for cactus

ferruginous pygmy-owls in a relatively intense manner by both agency personnel and private consultants.

Surveys have been conducted from 1995 through 1999.

One owl was located in 1998 in the Tucson Mountains.

Recreational, residential, mineral and agricultural

uses all occur in the area. The density and diversity of

the desertscrub vegetation vary across this region but

are typical of the upper Sonoran desertscrub vegetation classification. Saguaros are common with velvet

mesquite, foothill paloverde and ironwood making up

the dominant tree species. A shrub species which is

common in this area, but not as common in northwest

Tucson, is jojoba (Simmondsia chinensis). The most

common shrubs and cacti are the triangle-leaf bursage, creosote, acacia, prickly pear, cholla, and barrel

cactus. Desert hackberry is common along the washes.

Elevation ranges from 610 m to 915 m in areas

surveyed. Because both county and national parks

occur in this area, there is some level of habitat

protection for a rather large area. However, much of

the area is still subject to development and other

potential impacts.

Organ Pipe Cactus National Monument

Cactus ferruginous pygmy-owls have been documented here since the late 1940s (Hensley 1954).

Periodic surveys for cactus ferruginous pygmy-owls

have likely occurred on the Monument since that time.

More recently, annual surveys have been conducted

since 1993 (Table 3-4). Owls have been detected every

year since then, except 1994, and nesting was documented in 1998 and 1999. The surveyed areas are

typical desertscrub in the drainages and bajadas of

nearby mountain ranges. While overall precipitation

is less than that of northwest Tucson and the Tucson/

Silverbell Mountain areas, it is still characterized by

many of the same species such as saguaro, ironwood,

foothill paloverde, velvet mesquite, triangle-leaf

bursage, creosote, prickly pear, and cholla. Livestock

grazing no longer occurs on the Monument and recreation is the primary human activity for the area.

Tohono O’odham Reservation

Agencies and contractors have not generally been

allowed on the Reservation to conduct surveys. However, some surveys have been conducted since 1997 to

clear various planned and occurring projects on the

Reservation. Breeding Bird Atlas surveyors have been

conducting Atlas activities on the Reservation and

have detected a number of cactus ferruginous pygmyowls. The Reservation is a large block of relatively

undisturbed desertscrub which is located between the

two major areas where cactus ferruginous pygmy-owls

have been found recently, Organ Pipe Cactus National
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 37

Monument and the Tucson Basin. Based on its proximity and the fact that cactus ferruginous pygmy-owls

were detected in 1997 and 1998 (Johnson et al. unpubl.

ms.), the Reservation represents a key habitat area

that must be considered in the status of the cactus

ferruginous pygmy-owl population in Arizona.

Altar Valley

The Altar Valley runs south from State Highway 86

to the Mexican border. It is bounded on the west by the

Baboquivari Mountains and on the east by the Sierrita,

Cerro Colorado and Las Guijas mountains (Fig. 3-1).

The Buenos Aires National Wildlife Refuge is included

in the Altar Valley and extends south to the Mexican

border. It was surveyed in 1995, 1998, and 1999 (Table

3-4). The rest of the Altar Valley area was primarily

surveyed only during 1998 and 1999. Owls have been

detected throughout the area, the majority of which

are occurring in desertscrub or desertscrub/desert

grassland transition areas. Owls have also been detected in riparian habitat along Arivaca Creek and its

tributaries.

The desertscrub habitat in the Altar Valley is less

dense and less diverse than those previously described.

There are far fewer saguaros and the tree species are

primarily velvet mesquite and foothill paloverde. Existing desert grassland is characterized by scattered

mesquites and Lehmann’s lovegrass (Eragrostis

lehmanniana). Most owls detected to date were found

along washes lined with well-structured xeroriparian

vegetation. In comparison with the uplands, vegetation diversity and density along washes with pygmyowls are enhanced. Elevations are higher here, with

owls being found right at 4,000 ft (1,220 m).

Arivaca Creek and Brown Canyon on Buenos Aires

National Wildlife Refuge were surveyed in 1995 and at

an elevation of 3,080 ft (939 m) to 3,980 ft (1,213 m)

(Lesh and Corman 1995). Arivaca Creek and San Luis

Wash were surveyed in 1998 and 1999. Along Arivaca

Creek, the riparian vegetation is dominated by cottonwoods, netleaf hackberry, Arizona ash, and velvet

mesquite. Vegetation in the San Luis tributary is

similar, but less dense. In a few areas, mesquite form

large bosques. Brown Canyon, to the north of Arivaca

Creek, is lined with large Arizona sycamores, velvet

mesquite, Emory oaks (Quercus emoryi), netleaf hackberry, and catclaw acacia. Owls were detected during

surveys along Arivaca Creek in 1998, and along San

Luis Wash in 1998 and 1999 (Table 3-4).

Livestock grazing and recreation are the primary

human impacts, although residential development is

increasing. Based on the number of owls found here in

1998 and 1999, additional survey work should be

focused in this area.

5. Habitat Assessment _____________

While we can describe, in general terms, the habitat

in areas where cactus ferruginous pygmy-owls have

been found in Arizona, we lack the numbers of owls

and the research necessary to determine specific habitat needs. In addition, the range of vegetation types

and diversity of areas where cactus ferruginous pygmyowls are found in Arizona have made it difficult to

identify what specific habitat characteristics these

owls are selecting. In an effort to identify and prioritize areas for survey and management, the BLM and

U.S. Forest Service, with input from the AGFD and

USFWS, have developed habitat assessment protocols

(see Appendix 3-2). These protocols were developed to

rapidly assess habitat areas without having to conduct time-consuming, detailed habitat sampling. This

type of assessment is an iterative process. Adjustments are being made based on new information

gathered during ongoing research and also to address

local differences in vegetative communities. Habitat

assessment protocols will likely change in the future

based on location and purpose, but are useful for agencies and others who need some type of quantitative

assessment of cactus ferruginous pygmy-owl habitat.

5. Recommendations ______________

Given the endangered status of the cactus ferruginous pygmy-owl and the associated regulatory requirements, as well as the urgent need to gain a better

understanding of this owl’s biology, survey efforts will

likely continue to intensify. As a result, we will, hopefully, gain a better idea of the numbers and distribution of cactus ferruginous pygmy-owls in Arizona.

Below are recommendations for future cactus ferruginous pygmy-owl survey efforts and habitat assessments:

• Ensure that all surveyors utilize the most recent

approved protocol to maintain consistency and

comparability of survey results. As mentioned

above, a revised protocol is now being considered

for release by the USFWS.

• Continue to update the survey protocol periodically with improved information on the ecology of

cactus ferruginous pygmy-owls as it becomes

available.

• Centralize all completed survey information from

all sources, i.e., agencies, consultants, researchers, etc. Because the information is not centralized and difficult to find, it is currently not easy

to assess survey coverage or intensity statewide.

• Survey potentially suitable habitat in areas

around and between sites recently occupied by

cactus ferruginous pygmy-owls. Some high
38 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

priority areas are northern Pima County and

southern Pinal County in the Tucson Basin,

the Tucson, Silverbell and Roskruge Mountain areas, the middle Gila River, the Altar

Valley, BLM lands north of Organ Pipe Cactus National Monument, and the Tohono

O’odham reservation.

• Conduct surveys in all suitable remaining riparian habitats in southern and central Arizona.

Areas of specific potential include the Lower San

Pedro River, the Gila River, the Salt River, the

Verde River, Arivaca Creek, and the Santa Cruz

River between Rio Rico and Amado.

• Conduct surveys (if proper vegetative components are present) within the range of potential

housing development patterns (i.e., from very

low density development up to high density development, in cluster and sprawl developments).

Survey sites with other types and levels of human activities (recreation, livestock grazing,

mining, etc.) to help clarify the levels and design

of human activities tolerated by cactus ferruginous pygmy-owls.

• Continue to refine existing rapid habitat assessment protocols based on results of ongoing

research.

• Conduct studies on habitat selection and use on

a variety of scales.

• Investigate additional funding sources (agency,

grants, foundations, etc.) to increase survey and

habitat research efforts.

• Utilize telemetry to help document habitat use,

dispersal parameters, broadcast responsiveness,

home range size, etc. These contribute directly to

developing better survey protocols and habitat

assessment methodologies.

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Proudfoot, G. A., and S. L. Beasom. 1997. Food habits of nesting

ferruginous pygmy-owls in southern Texas. Wilson Bulletin

109(4):741-748.

Russell, S. M., and G. Monson. 1998. The birds of Sonora. Tucson,

AZ: University of Arizona Press.

Sferra, S. J., T. E. Corman, C. E. Paradzick, J. W. Rourke, J. A.

Spencer, and M. W. Sumner. 1997. Arizona Partners in Southwestern willow flycatcher survey: 1993-1996 summary report.

Tech. Rep. 113. Phoenix, AZ: Nongame and Endangered Wildlife

Program, Arizona Game and Fish Department.

Shields, W. M. 1984. Barn swallow mobbing: self defense, collateral

kin defence, group defence, or parental care? Animal Behavior

32:132-148.

Smith, D. G., A. Devine, and D. Walsh. 1987. Censusing screechowls in southern Connecticut. Pp. 255-267. In: Nero, R. W., R. J.

Clark, R. J. Kerapton, and R. H. Hamre, eds. Biology and

conservation of northern forest owls. Gen. Tech. Rep. RM-142.

Fort Collins, CO: U.S. Department of Agriculture, Forest Service,

Rocky Mountain Forest and Range Experiment Station.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 39

Sprunt, A. 1955. North American birds of prey. National Audubon

Society. New York, NY: Harper and Brothers. 227 p.

Stahlecker, D. W., and J. J. Rawinski. 1990. First records for the

boreal owl in New Mexico. Condor 92:517-519.

Stoleson, S. H., wildlife biologist, Rocky Mountain Research Station, U.S.D.A. Forest Service, Albuquerque. [Personnal communication]. May 1999.

Tellman, B., R. Yarde, and M. G. Wallace. 1997. Arizona’s changing

rivers: how people have affected the rivers. Tucson, AZ: Water

Resources Research Center, College of Agriculture, University of

Arizona.

Terres, J. K. 1991. The Audubon Society Encyclopedia of North

American Birds. Avenue, NJ: Wings Books.

Tibbitts,T., wildlife biologist, Organ Pipe Cactus National Monument, National Park Service, Ajo, AZ. [Personal communication].

May 1999.

Tyler, H. A., and D. Phillips. 1978. Owls by day and night. Happy

Camp, CA: Naturegraph Publishing Inc.

Wauer, R. H., P. C. Palmer, and A. Windham. 1993. The ferruginous pygmy-owl in south Texas. American Birds 47:1071-76.
40 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

3-1-1 Introduction and purpose of the

protocols

Any survey protocol for this species must address

two distinct needs. The first is the need to determine

if cactus ferruginous pygmy-owls are present on those

sites where an activity is proposed that would result in

loss, modification, or disturbance of pygmy-owls or

their habitat. The second is the need to survey the vast

acreage of potential pygmy-owl habitat to gather information on distribution, occurrence, and numbers of

pygmy-owls in Arizona.

A single protocol cannot address these two needs

because of funding and personnel constraints, the

potential ramifications if pygmy-owls are missed on

project sites, and the area that can be covered by a

surveyor. Therefore, we have included a separate

protocol to address each need. The first is a conservative protocol developed to answer, with some degree of

confidence, whether cactus ferruginous pygmy-owls

occupy a project site where an impacting activity has

been proposed. In Arizona, we know of so few individual pygmy-owls, that it is essential to locate and

address potential impacts to any pygmy-owls that

may occur on project sites.

The second protocol is to be used by researchers,

land managers, and others to survey large areas of

unsurveyed habitat. It is designed to allow a greater

area to be surveyed with more effective use of limited

manpower and funds. This will help us increase the

area surveyed in order to answer key questions regarding distribution and occurrence of known and

unknown cactus ferruginous pygmy-owl population

centers in Arizona.

Issuance of permits by USFWS to survey for cactus

ferruginous pygmy-owls is tied to appropriate use of

these two protocols. Permits will be used only after

attendance at a training session approved by AGFD

and USFWS where the circumstances under which

these protocols can be applied will be discussed.

3-1-2 Project clearance protocol

1. Permission to access a property for surveying

must be obtained from all private property owners or those having management authority (public lands) prior to conducting surveys.

2. Surveys must be conducted in potential habitat

from 1 hour before sunrise to 2 hours after sunrise, or from 2 hours before sunset to 1 hour after

sunset, during the period of January through

June. Recent data suggest peak calling activity

occurs from February through April.

3. Sites must be surveyed for two consecutive years

during the above protocol period. Each year,

survey routes must be surveyed a minimum of 3

times, with no less than 15 days between surveys. One survey must be conducted between

February 15 and April 15. These time frames are

necessary to account for variations in annual

weather patterns and the responsiveness of individual pygmy-owls. Surveys should not be conducted if wind or other factors reduce the detectability of calls.

4. Any acreage subjected to surface disturbance

(including vegetation removal or disturbance)

must have been surveyed for presence of pygmyowls within the calendar year in which surface

disturbance occurs. These surveys must have

been conducted in suitable pygmy-owl habitat

within 1500 ft of the acreage being disturbed.

5. Call points along a survey route in urban areas,

sites with high noise disturbance (such as along

roads or highways), or in riparian areas (due to

tree density and noise) must be no more than 150

meters apart. In more remote areas that do not

have the above types of disturbance, the distance

between call points may be extended up to 400

meters, so long as complete coverage is maintained. Distance between survey transects must

be no more than twice the distance between call

points.

6. Conduct a 1-minute listening period at each call

point prior to broadcasting any calls. This will

allow the surveyor to detect any spontaneous

calling and also to become familiar with features

at the call point, such as large trees or saguaros,

residences, water sources, etc., that may affect

pygmy-owl presence or observation.

7. Following the initial listening period, broadcast

calls for 30 seconds and follow this with a 90

second listening and observation period. Broadcast the call in all directions. Set the volume at an

adequate level to get complete coverage along a

survey route without causing distortion of the

Appendix 3-1: Proposed revised cactus ferruginous pygmy-owl survey protocols,

with introduction and summary of changes since 1993. Please note that a survey

protocol has been proposed for project clearance, another for large area search.

The proposed protocols were developed by the Arizona Game and Fish Department

(AGFD) and the U.S. Fish and Wildlife Service (USFWS)._____________________
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 41

call. Equipment used must be able to produce a

minimum of 100 dB at 1 m from the speaker

without distortion.

8. Repeat the calling/listening sequence for at least

10 minutes. Extend this sequence if disturbances

such as dogs, air traffic or vehicles disrupt your

call point.

9. Observe and listen for an additional 2-3 minutes

before proceeding to the next call point.

10. If a cactus ferruginous pygmy-owl is heard or

seen:

a) End broadcasts unless additional responses

are needed to pinpoint the location.

b) Observe the pygmy-owl as long as possible

without disturbing it (i.e. do not chase the

bird or harass it with calls). Record all observations, use of cavities and prey observations are especially important. Listen for

female or fledgling vocalizations or other

evidence that there may be other pygmyowls in the area.

c) Flag the location of the bird, or your best

estimate of where the bird was, with

surveyor’s tape and record the location on a

map (tape will be removed when follow-up

visits are completed).

d) Record the date, time, type and duration of

response (aural or visual), habitat characteristics of the site, and detailed directions

to the site.

11. Complete the attached survey data forms for

each route each time it is surveyed. Be sure to

record survey date, time, weather conditions,

moon phase, and responses of other birds. If a

cactus ferruginous pygmy-owl is located, please

fill out a detection form.

12. If an owl is located, fax a copy of your detection

form and map to AGFD and USFWS within 24

hours of the detection. No later than 10 days after

the completion of the 3rd survey, return all survey

forms and detection forms to AGFD and USFWS:

Arizona Game and Fish Department

Nongame Branch

2221 West Greenway Road

Phoenix, Arizona 85023-4399

(602) 789-3500 Fax (602) 789-3926

United States Fish and Wildlife Service

Arizona Ecological Services Field Office

2321 W. Royal Palm Road, Suite 103

Phoenix, Arizona 85021-4951

(602) 640-2720 Fax (602) 640-2730

It is important that we receive all completed data

forms, whether a pygmy-owl is detected or not. AGFD

and USFWS will respect the rights of private property

owners throughout implementation of this protocol.

3-1-3 Large area search survey protocol

1. Permission to access a property for surveying

must be obtained from all private property owners or those having management authority (public lands) prior to conducting surveys.

2. Surveys must be conducted in potential habitat

from 1 hour before sunrise to 2 hours after sunrise, or from 2 hours before sunset to 1 hour after

sunset, during the period of January through

June. Recent data suggest peak calling activity

occurs from February through April; therefore,

surveys should be conducted during this period if

possible.

3. Sites should be surveyed for two consecutive

years during the above protocol period. Each

year, survey routes must be surveyed a minimum of 3 times, with no less than 15 days

between surveys. One survey must be conducted

between February 15 and April 15. These time

frames are necessary to account for variations in

annual weather patterns and the responsiveness

of individual pygmy-owls. Surveys should not be

conducted if wind or other weather factors reduce detectability of calls.

4. Call points along the survey transect must be

spaced at no more than 480 meters (0.3 miles),

unless a bionic ear or other listening-enhancement device is used, in which case distance between call points may be extended to 800 meters

(0.5 mile). Call points in riparian areas must be

no more than 150 m apart due to tree density and

noise. Distance between survey transects should

be no more than twice the distance between call

points.

5. Conduct a one minute listening period at each

call point prior to broadcasting any calls. This

will allow the surveyor to detect any spontaneous

calling and also to become familiar with features

at the call point such as large trees or saguaros,

residences, water sources, etc., that may affect

pygmy-owl presence or observation.

6. Following the initial listening period, broadcast

calls for 30 seconds and follow this with a 90

second listening and observation period. Broadcast the call in all directions. Set the volume at an

adequate level to get complete coverage along a

survey route without causing distortion of the

call. Equipment must be able to produce a minimum of 100 dB at 1 m from the speaker without

distortion.
42 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

7. Repeat the calling/listening sequence for at least

6 minutes. Extend this sequence if disturbances

such as animals, air traffic, or other noises disrupt your ability to hear responses.

8. Observe and listen for an additional 2-3 minutes

before proceeding to the next call point.

9. If a cactus ferruginous pygmy-owl is heard or

seen:

a) End broadcast unless additional responses

are needed to pinpoint the location.

b) Observe the pygmy-owl as long as possible

without disturbing it (i.e. do not chase the

bird or harass it with calls). Record all observations, use of cavities and prey are especially important. Listen for female or fledgling vocalizations or other evidence that

there may be other pygmy-owls in the area.

c) Flag the location of the bird, or your best

estimate of where the bird was, with surveyors tape and record the location on a map

(tape will be removed when follow-up visits

are completed).

d) Record the date, time, type and duration of

response (aural or visual), habitat characteristics of the site and detailed directions to

the site.

10. Complete the attached survey data forms for

each route each time it is surveyed. Be sure to

record survey date, time, weather conditions,

moon phase, and responses of other birds. If a

cactus ferruginous pygmy-owl is located, please

also fill out a detection form.

11. If an owl is located, fax a copy of your detection

form and map to AGFD and USFWS within 24

hours of detection. No later than 10 days after

completion of the 3d survey, return all survey

forms and detection forms to AGFD and USFWS:

Arizona Game and Fish Department

Nongame Branch

2221 West Greenway Road

Phoenix, Arizona 85023-4399

(602) 789-3500 Fax (602) 789-3926

United States Fish and Wildlife Service

Arizona Ecological Services Field Office

2321 W. Royal Palm Road, Suite 103

Phoenix, Arizona 85021-4951

(602) 640-2720 Fax (602) 640-2730

It is important that we receive all completed data

forms, whether a pygmy-owl is detected or not. AGFD

and USFWS will respect the rights of private property

owners throughout implementation of this protocol.

3-1-4 Summary of changes from 1993 cactus ferruginous pygmy-owl survey protocol.

1993 Protocol Proposed protocol Reasons for proposed changes

Call point intervals of Call point intervals for clearance Closer call points to increase chance of detection

100-150 yards. protocol 150-400 meters. Call in areas with noise disturbance. Greater call

point interval for large area point intervals to cover larger areas in a timely

search protocol 480-800 meters. fashion. Distances based on surveyor’s ability to

detect a pygmy-owl, not on a pygmy-owl’s ability

to hear call.

Calling and listening Calling and listening period 11- Field observations on this and other owls

period of 6-8 minutes 12 minutes at each call point. indicate longer calling and listening periods

at each calling point. can increase detections.

Survey period September Survey period January through Seasonal monitoring and survey efforts show

to April. June, with peak from February regular, consistent calling during this time

through April. period. Fall calling is inconsistent and

generally not in response to survey tapes.

Survey frequency is one Survey frequency is three surveys Field observation of seasonal and individual

survey, one year. separated by at least 15 days with variation in responsiveness.

one survey between February 15

and April 15.

No requirement for Acreage to be disturbed must be Our data indicate increased use area postresurvey if certain surveyed within the same calendar dispersal, and dispersing juveniles, as well

time period lapses. year as the disturbance; surveys as adults, can cause an area to be occupied

must be conducted in suitable one year that wasn’t the previous year.

habitat within 1500 ft of the site

being disturbed.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 43

VEGETATION CHARACTERISTICS

1) Is non-native woody vegetation present within the 1

⁄

4 section? Y (yes) or N (no).

2) Are saguaros or trees >6" dbh with cavities present within the 1

⁄

4 section? Enter the score based upon total estimated

number of suitable nesting trees PER ACRE within the 1

⁄

4 section:

Score # per acre

0 0 (Not suitable)

1 1-5 (Poor)

2 6+ (Moderate to Good)

3) Is there a moderate to high level of woody or perennial vegetation <18" tall present within the 1

⁄

4 section? (see

PHOTO GUIDE for reference only)

Score

0 (No)

1 (Yes)

4) Estimate the total number of woody SPECIES 18" - 6' tall within the 1

⁄

4 section (diversity index) (See back of data

collection form—list of vegetative species below)

Score # spp. w/i 1⁄

4 section

0 <5 spp.

1 5-10 spp.

2 11-15 spp.

3 >15 spp.

5) Estimate the total number of canopy SPECIES >6' tall within the 1

⁄

4 section (see back of data collection form) Note:

do not include saguaros:

Score # species w/i 1⁄

4 section

0 0 (no species)

1 1-4 spp.

2 >4 spp.

6) Does the vegetation structure appear to be relatively equally distributed between the understory (<18"), shrub

(18"-6'), and canopy (>6')layers? (i.e., is there a significant proportion of vegetative biomass in each of these 3

categories, and how are they distributed relative to each other?):

Score Description

1 Midstory shrubs are present in low density, with understory and canopy layers

lacking in proportion to the others

2 Midstory shrub layer well developed but lacking in either an overstory or understory

components in proportion to the others

3 All three layers well represented

7) Utilizing the HABITAT PHOTO GUIDE, identify the photo set that best represents the appearance of the

vegetated landscape in the 1

⁄

4 section.

Score Vegetative Density

1 Low vegetative density

3 Moderate vegetative density

5 High vegetative density

Appendix 3-2: Cactus ferruginous pygmy-owl habitat assessment protocol (key

and data collection forms) used by the Bureau of Land Management in desertscrub.

A similar protocol is used by the Coronado National Forest. The habitat photo

guide is not included. Text in italics is added for clarity. _____________________

3-2-1 Key
44 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

These first 7 habitat questions have been identified as the most critical factors for CFPO occupancy. Therefore,

the RAW SCORES of these 7 habitat components on the data form will be totalled and then multiplied by two to

achieve the FACTORED SCORE. A factored score of 15+ indicates that these habitats have some characteristics

of potential CFPO habitat that MAY warrant further investigation, while a habitat score below 15 indicates low

quality habitat which exhibits few characteristics of potential CFPO habitat.

OTHER HABITAT FEATURES

8) Is there any development or surface disturbance (not including livestock grazing) present within the 1⁄

4

section? (Y/N)

9) Roads within and bordering the 1⁄

4 section are:

Score Type of Road

0 Paved

1 Graded and improved

2 No roads or dirt two-track

10) If development is present within the 1⁄

4 section, which of the following categories best describes the

dominant type of land use?

Score Description

0 Commercial/Industrial and/or >1 residence per acre

1 One residence per acre

2 One residence per 3 or more acres and/or undisturbed or essentially

undisturbed open space

11) Estimate the total % of the 1⁄

4 section that is developed, altered, or has some degree of ground

disturbance.

Score % “disturbed”

0 >50% disturbed

1 25-50% disturbance

2 0-25% disturbance

12) Is there a source of free-standing perennial water present and available?

Score

0 Not present

1 Present and available
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 45

3-2-2 Data collection form

Personnel:___________________________ Survey Dates: ________________

______________

Quad Name (7.5 min): ________________________ ________________

______________

Legal Description: T ____ R ______Section ______ UTM ______________

Allotment Name: __________________________________________________

FOR EACH 1⁄

4 SECTION, PLEASE ANSWER THE FOLLOWING USING THE HABITAT ASSESSMENT FORM KEY PROVIDED:

 VEGETATION CHARACTERISTICS NE/4 NW/4 SE/4 SW/4

1) Non-native woody vegetation?(Y/N)

2) Suitable nesting structure

3) Vegetation <18" present

4) # woody species present

5) # canopy spp. >6' tall

6) Vegetative structure/distribution

7) Photo guide score

TOTALS (raw score/factored score) / // /

 HABITAT FRAGMENTATION/WATER NE/4 NW/4 SE/4 SW/4

8) Development? (Y/N) (see below)

9) Presence of roads

10) Dominant type of land use

11) % of 1⁄4 section developed

12) Presence of water

TOTALS

GRAND TOTALS

8) If development is present w/i this 1

⁄4 section, describe: __________________________________________

___________________________________________________________________________________________

13) Describe any impacts that livestock grazing may have within this section: _______________________

___________________________________________________________________________________________
46 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

CHECK (√) IF VEGETATIVE SPECIES IS PRESENT ON 1⁄4 SECTION

SHRUB SPECIES PRESENT (<6') NE/4 NW/4 SE/4 SW/4

Agave (Agave spp.) ............................. ___ ___ ___ ___

Barrel cactus (Ferocactus) ................. ___ ___ ___ ___

Brittle bush (Encelia farinosa) ......... ___ ___ ___ ___

Buckwheat (Eriogonum spp.) ............ ___ ___ ___ ___

Burro bush/Cheeseweed (Hymenoclea spp.) ___ ___ ___ ___

Canyon ragweed (Ambrosia) ............. ___ ___ ___ ___

Catclaw acacia (Acacia greggii) ........ ___ ___ ___ ___

Cholla (Opuntia spp.) ........................ ___ ___ ___ ___

Chuparosa (Anisacanthus thurberi) . ___ ___ ___ ___

Creosote (Larrea tridentata) ............. ___ ___ ___ ___

Desert broom (Baccharis sarothroides) ___ ___ ___ ___

Desert lavendar (Hyptis emoryii)...... ___ ___ ___ ___

Greythorn (Condalia spp.) ................ ___ ___ ___ ___

Hackberry (Celtis reticulata)............. ___ ___ ___ ___

Hopbush (Dodonaea viscosa)............. ___ ___ ___ ___

Jojoba (Simmondsia chinensis)......... ___ ___ ___ ___

Jumping bean (Sapium biuncifera) .. ___ ___ ___ ___

Mesquite (Prosopis spp.) ................... ___ ___ ___ ___

Mormon tea (Ephedra spp.) .............. ___ ___ ___ ___

Ocotillo (Fouquieria splendens) ........ ___ ___ ___ ___

Palo verde (Cercidium spp.) .............. ___ ___ ___ ___

Prickly pear (Opuntia spp.) ............... ___ ___ ___ ___

Range ratany (Krameria spp.) .......... ___ ___ ___ ___

Saguaro (Carnegiea gigantea) ........... ___ ___ ___ ___

Saltbush (Atriplex spp.) ..................... ___ ___ ___ ___

Triangle-leaf bursage (A.tridentata) . ___ ___ ___ ___

White bursage (Ambrosia dumosa) .. ___ ___ ___ ___

Whitethorn acacia (Acacia constricta) ___ ___ ___ ___

Wolfberry (Lycium spp.) .................... ___ ___ ___ ___

Yucca (Yucca spp.) ............................. ___ ___ ___ ___

____________ .................................. ___ ___ ___ ___

____________ .................................. ___ ___ ___ ___

____________ .................................. ___ ___ ___ ___

CANOPY SPECIES PRESENT (>6')

Catclaw acacia (Acacia greggii) ........ ___ ___ ___ ___

Cholla (Opuntia spp.) ........................ ___ ___ ___ ___

Creosote (Larrea tridentata) ............. ___ ___ ___ ___

Cruxifixion thorn (Canotia holocantha) ___ ___ ___ ___

Desert willow (Chilopsis linearis) ..... ___ ___ ___ ___

Graythorn (Condalia spp.) ................ ___ ___ ___ ___

Hackberry (Celtis spp.) ...................... ___ ___ ___ ___

Ironwood (Olneya tesota) ................... ___ ___ ___ ___

Mesquite (Prosopis spp.) ................... ___ ___ ___ ___

Ocotillo (Fouquieria splendens) ........ ___ ___ ___ ___

Palo verde (Cercidium spp.) .............. ___ ___ ___ ___

Saguaro (Carnegiea gigantea) ........... ___ ___ ___ ___

Salt cedar (Tamarix spp.) .................. ___ ___ ___ ___

Whitethorn acacia (Acacia constricta) ___ ___ ___ ___

____________ .................................. ___ ___ ___ ___

____________ .................................. ___ ___ ___ ___

____________ .................................. ___ ___ ___ ___
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 47

Jean-Luc E. Cartron

Scott H. Stoleson

Stephen M. Russell

Glenn A. Proudfoot

W. Scott Richardson

Chapter 4:

The Ferruginous Pygmy-Owl in the Tropics

and at the Northern End of its Range:

Habitat Relations and Requirements

The habitat needs of the ferruginous pygmy-owl

(Glaucidium brasilianum) are poorly understood. In

the tropics, this common bird of prey inhabits many

distinct vegetation communities or environments (e.g.,

Monroe 1968, Meyer de Schauensee 1970, Stiles and

Skutch 1989, Sick 1993). A resident of woodlands and

open forests, it is also found in the open, perched on

telephone lines or fence posts (Ridgely 1976). At the

northern edge of its range, the ferruginous pygmy-owl

has been recorded in riparian woodlands and thickets

(Bendire 1888, Breninger 1898, Oberholser 1974), live

oak (Quercus virginiana)-mesquite (Prosopis glandulosa) forest (Wauer et al. 1993, Mays 1996, Proudfoot

1996), and Sonoran desertscrub (Monson and Phillips

1981, Millsap and Johnson 1988, Abbate et al. 1996).

In this chapter, we describe some of the vegetation

types associated with the ferruginous pygmy-owl, with

an emphasis on those found to support the highest

densities of the owl. We then explore key pygmy-owl

habitat components suggested by descriptions of

those plant communities.

1. Habitat associations and patterns

of abundance _____________________

South America

Throughout the tropics, the ferruginous pygmy-owl

occupies only lowlands (Meyer de Schauensee 1970,

Davis 1972, Meyer de Schauensee and Phelps 1978,

Hilty and Brown 1986). At higher elevations, it is

replaced by congeneric species, such as least pygmyowls (G. minutissimum complex), the northern

pygmy-owl (G. gnoma), and the Andean pygmy-owl

(G. jardinii). In South America, the ferruginous

pygmy-owl occurs in a broad range of vegetation types

(Table 4-1). As listed by Stotz et al. (1996: 170),

vegetation types with the highest densities of pygmyowls are arid and second-growth scrub. The ferruginous pygmy-owl is less common in forested areas, and

in these areas chiefly occupies open deciduous forest,

second growth, and edges (Hilty and Brown 1986,

Stotz et al. 1996). Two representative examples of

areas with high pygmy-owl population densities are

the central llanos of Venezuela and the xeric coastal

lowlands of western Ecuador.

Although they are found throughout much of Venezuela, ferruginous pygmy-owls are especially abundant in the central llanos (Fig. 4-1), an ecotonal area

between the tropical deciduous forests to the north

and the vast open savannas to the south (Troth 1979).

This region consists of a mosaic of open marshes, wet

meadows, and closed-canopy, partially deciduous forests along major watercourses. Much of the area is

covered by an open woodland of scattered large trees,

primarily of the genera Enterolobium and Pithecellobium, with a dense understory of mostly spiny shrubs

including Acacia, Anona, Mimosa, Randia, and
48 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

Table 4-1. Habitat types occupied by the ferruginous pygmy-owl in some parts of its geographic range.

Geographic region Types of habitat occupied References

South America “forest, scrub, arid woodland”...“towns, cerrado” Meyer de Schauensee 1970

Brazil “forest edges, cerrado, tree plantings” Sick 1993

Columbia “from dry forest and scrubby semiopen areas with Hilty and Brown 1986

trees and thickets to humid terra firme and

várzea forest borders”

Panama “scrubby and light woodland” and “open areas with Ridgely 1976

scattered thickets and trees in lowlands”

Costa Rica “deciduous and evergreen woodland, savanna trees, Stiles and Skutch 1989

semi-open, second growth, coffee plantations,

suburban areas with large trees for nesting”

Honduras “arid woodlands,” “arid interior highlands,” and Monroe 1968

semiopen habitats

Mexico and northern “semiopen areas with hedges and scattered forest patches, Howell and Webb 1995

Central America open forest and edge, semiopen thorn forest, plantations...”

Mexico “mesquite thickets, river woods, scrubby second growth, Peterson and Chalif 1973

forest edges”

Figure 4-1. Vegetation type in Venezuela associated with high densities of ferruginous pygmy-owls. Note the open canopy

and spiny thickets. Photograph by Scott Stoleson.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 49

Zanthoxylum. These woodlands support dense populations of pygmy-owls nesting in cavities of the

Enterolobium and Pithecellobium trees. Owls are also

found, at lower densities, in more open areas that

form seasonal marshes with emergent spiny-leafed

palms (Copernicia), shrubby cactus (Pereskia) and

spiny shrubs (Anona, Randia). Permanent water

sources and major rivers are lined with closed-canopy

forest, which tends to have a poorly-developed understory and very few pygmy-owls (Thomas 1979).

In western Ecuador, the local pygmy-owl, generally considered a morph of the ferruginous pygmyowl (e.g., Meyer de Schauensee and Phelps 1978, but

see König [1991] who treats it as a distinct species

G. peruanum), is found most frequently in xeric coastal

lowlands in riparian and arid thickets (Stotz et al.

1996). Riparian thickets in Ecuador are composed of

dense stands of Baccharis, Salix, and Tessaria adjacent to watercourses. Arid thickets are dominated by

spiny shrubs (Acacia, Capparis, Cercidium, Parkinsonia, Prosopis) and columnar cacti (Armatocereus,

Neoraimondea) (Stotz et al. 1996). In both general

aspect and genus-level floristics, these two habitats

are very similar to riparian and xeroriparian areas

historically or currently associated with ferruginous

pygmy-owls in Arizona. Elsewhere in Ecuador, the

pygmy-owl is chiefly associated with forest edges and

shrubby second growth, but as these habitats are

increasing with deforestation, the owl may be expanding its range within the country.

Western Mexico

In Sonora, the ferruginous pygmy-owl (subspecies

cactorum) occurs in at least 50 localities, from the

extreme southeastern border with Sinaloa northwest

to the vicinity of Sonoita close to Organ Pipe Cactus

National Monument in Arizona. The owl’s altitudinal

range is from near sea level to about 1,200 m; it has not

been found in the extreme northeastern portion of

Sonora, a region mostly above 1,200 m; nor has it been

found in northwestern coastal areas or in the Gran

Desierto west of Sonoita.

The ferruginous pygmy-owl is common locally in

southern Sonora. Most of the records are from the

tropical deciduous forest and its edges. The tropical

deciduous forest extends from Costa Rica northward

into Sonora in a narrow corridor predominantly at low

elevations on the Pacific slope. In Sonora, this forest is

characterized by deciduous trees that begin to lose

their leaves in October following the summer rains.

Until June of each year, the vegetation is leafless

and temperatures are high. Characteristic plants

include hecho (Pachycereus pecten-aboriginum),

Lysiloma spp., Pithecellobium spp., Tabebuia spp.,

Randia echinocarpa, and guácima (Guazuma ulmifolia). Of 351 bird species recorded in the Alamos

area, only 43 species have been found in more localities than the ferruginous pygmy-owl (Russell in press).

At the southwestern edge of the deciduous forest,

pygmy-owls occupy tropical thornscrub, but more

sparsely. At higher elevations (1,000 m to 1,200 m),

where oaks may coexist with tropical deciduous forest

plants, they reach their upper limits in Sonora. Cactus

ferruginous pygmy-owls may also be found in riparian areas of tropical deciduous forest and in tall

second growth. They are uncommon and local in

desertscrub, which dominates the western half of

Sonora, and in this vegetation type often occur many

kilometers from water sources. Typical vegetation

where the owl has been found in desertscrub includes

columnar cacti, palo verde (Cercidium), and ironwood

(Olneya). It is through this plant community that the

ferruginous pygmy-owl ranges into Arizona.

Outside the tropical deciduous forest, the association between the ferruginous pygmy-owl and lowland

riparian habitats in Sonora is somewhat uncertain. In

the northern part of the state, much of the riparian

habitat has disappeared but there is no historical

evidence that it supported a large number of pygmyowls. Stephens (1885) collected one owl from an organ

pipe cactus near Caborca and another, presumably in

desertscrub, 20 miles south of Caborca. He referred to

the riparian community near Caborca as “timber,” and

so implied a community that no longer exists, but he

did not mention Glaucidium in this area. Neff (1947)

spent time in June and July of 1942 in the AltarCaborca region. Although he described a “wilderness

forest of giant mesquite”, he did not mention the

ferruginous pygmy-owl in his list of notable species

seen. Throughout the rest of Sonora and at low elevations, riparian communities do not appear to support

higher densities of ferruginous pygmy-owls than other

vegetation types.

In Colima and Jalisco, the ferruginous pygmy-owl

(subspecies cactorum) is described by Schaldach (1963)

as abundant in low elevation thornscrub and thorn

forest. Schaldach (1963) also mentions that it does

not occur in the tropical deciduous forest of the region

and is replaced at higher elevations by the northern

pygmy-owl.

In Oaxaca, the ferruginous pygmy-owl (subspecies

ridgwayi) is common in openings in tropical evergreen

and tropical deciduous forests (Binford 1989). It is

fairly common in arid tropical scrub and tropical

semideciduous forests.

Texas

In southern Texas, ferruginous pygmy-owls (treated

as subspecies cactorum, see Chapter 1) were once

common along the lower Rio Grande in Tamaulipan

thornscrub community with Texas ebony (Pithecellobium ebano), honey mesquite, and hackberry
50 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

(Celtis spp.) (Oberholser 1974, U.S. Fish and Wildlife

1994). However, urban and agricultural expansion

from 1920 to 1970 resulted in the loss of more than 90%

of this vegetation type (Oberholser 1974) and only

small, possibly disjunct, populations may now exist.

The largest known population is in the coastal sand

plain of the historical Wild Horse Desert about 80 km

south of Kingsville, with eolian sand as geologic

substrate (Diamond and Fulbright 1990). The climate is “subhumid to semiarid east-coast subtropical,” with rainfall peaking in May, June, September,

and October and overall high humidity (Fulbright

et al. 1990). The human history of the region included

the establishment of large ranches under private

ownership.

The coastal sand plain supports a mosaic of vegetation communities including dune fields and a prairie

dotted with live oak woodlands and groves of honey

mesquite trees (Fulbright et al. 1990). In Kenedy

County, the once distinct live oak woodlands have

merged with mesquite to form a nearly continuous

patch of mixed live oak and honey mesquite forest

(Wauer et al. 1993, Fig. 4-2). Within the forest boundaries, the vegetation is heterogeneous and varies

from live oak with minimal ground cover to mixed live

oak-honey mesquite woodland and mesquite savanna.

An understory vegetation that includes thorny woody

shrubs such as desert hackberry (Celtis pallida),

catclaw acacia (Acacia greggii), and lime prickly-ash

(Zanthoxylum fagara), occurs chiefly in association

with mesquites (Archer 1989, 1990) and, in some areas,

forms “nearly impenetrable thickets” (Wauer et al.

1993).

Wauer et al. (1993) and Mays (1996) recorded the

highest numbers of ferruginous pygmy-owls in the

mixed live oak-mesquite woodlands in Kenedy County.

The owl also occurs, but at lower densities, in monotypic live oak forest and in the mesquite savanna. No

pygmy-owl was detected on the prairie or in the pastures outside the forest (Wauer et al. 1993). Outside

the continuous live oak-mesquite forest, the ferruginous pygmy-owl was recorded either in contiguous

patches of forest or in mesquite bosque associated with

large trees (Mays 1996).

Figure 4-2. Live oak (Quercus virginiana)-honey mesquite (Prosopis glandulosa) habitat in southeast Texas. Note the high density

of understory plants and the semi-open canopy. Photograph by Jean-Luc Cartron.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 51

Figure 4-3. Cactus ferruginous pygmy-owl habitat in Arizona: xeroriparian vegetation along a wash. On the upland, saguaros provide

cavities for nesting. Photograph by Jean-Luc Cartron.

Arizona

The ferruginous pygmy-owl (subspecies cactorum)

ranges into south and central Arizona at elevations up

to 1,200 m. Below 1,000 m, the dominant vegetational

zone is lower Sonoran, with large cacti, velvet mesquite (Prosopis velutina), palo verde, and creosote

bush (Larrea tridentata). Along rivers and creeks,

floodplain riparian corridors typically consisted of

cottonwood (Populus fremontii)-Goodding willow

(Salix gooddingii) forests intermixed with mesquite

bosques. Nearer the owl’s upper elevational boundary, dominant or common riparian tree species also

included walnut (Juglans major), sycamore (Platanus

wrightii), and ash (Fraxinus velutina). Since the late

18th century, most of the original riparian vegetation

has been cleared or altered by human activities

(Chapter 2). At some locations, however, current

vegetation structure and composition likely represent past conditions (Chapter 3).

Historical accounts suggest that the cactus ferruginous pygmy-owl was originally fairly common or

common in riparian woodlands and thickets in Arizona (Bendire 1888, Fisher 1893:199, Breninger 1898,

Swarth 1914:31). At present, however, this bird seems

chiefly associated with Sonoran desertscrub, where it

often gravitates along washes lined with dense

xeroriparian vegetation composed of mesquite, palo

verde, desert ironwood (Olneya tesota), desert hackberry, and catclaw acacia (Fig. 4-3) (Millsap and

Johnson 1988, Lesh and Corman 1995). In the Altar

Valley, pygmy-owls have been located in xeroriparian

vegetation along washes within low-density

desertscrub or mesquite grasslands (Chapter 3). In

the Tucson area, which supports many of the known

owls (Felley and Corman 1993, Lesh and Corman

1995), documented habitat occupancy is higher in lowdensity (one house per 3.3 acres or more) residential

areas. While the vegetation near residences remains

dominated by the native saguaro (Carnegiea gigantea),

foothill palo verde (Cercidium microphyllum), ironwood, and velvet mesquite, it is often denser and more

complex than on adjacent, undisturbed patches of

Sonoran desertscrub due to supplemental irrigation.
52 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

Non-native plants, such as California pepper trees,

Allepo pines, citrus, eucalyptus, and mulberry trees

also enhance vegetation density and diversity. Under

bushes or trees, drip irrigation may create small pools

of water which are used by local wildlife. The presence

of some sort of free-standing water was recorded at or

near all known nest sites in residential areas (Abbate

et al. 1996, Richardson unpubl. data).

Recent survey efforts have resulted in an increased

number of owl detection in areas with little or no

residential development. Statewide, there are now

more known nests in non-residential areas than in

residential areas (Richardson unpubl. data). However, the vegetation of these non-residential areas

(i.e., well-structured upland desertscrub and

xeroriparian vegetation) resembles in structure the

vegetation of low-density residential areas. The influence of residential development on the quality of

cactus ferruginous pygmy-owl habitat may only be

determined through additional surveys and research.

2. Habitat preferences and

requirements _____________________

Because fitness is a more accurate indicator of habitat quality than population density, one must exercise

caution when examining patterns of owl population

density. Higher population density in an area may

indicate habitat preferences and requirements, but

the relationship between habitat suitability and population density can be affected by habitat connectivity

at a geographic scale, site fidelity regardless of quality, and the exclusion of a large proportion of the

population from high-quality sites by a few dominant

individuals (Willis 1974, Lidicker 1975, Wiens and

Rotenberry 1981, 1985).

Foraging, protection, and the importance of

the understory

Although different observers may characterize vegetation differently or determine vegetation types at

different scales, habitat descriptions above (see also

Table 4-1 for more descriptions of ferruginous pygmyowl habitat in the tropics) are typically congruent.

Habitat descriptions in the tropics and in Texas suggest the importance of thickets and woodlands with a

dense understory that often consists of spiny shrubs.

This pattern is consistent with Proudfoot’s (1996)

habitat use versus availability study: ferruginous

pygmy-owls nested disproportionately in areas with

moderate to dense understory. Although more work

is needed to better understand the significance of the

association, a dense understory may benefit the ferruginous pygmy-owl by providing a shelter from

climatic stresses and potential predators for the juveniles (Abbate et al. 1996, Proudfoot 1996). Greater

habitat complexity may also result in more foraging

opportunities for the ferruginous pygmy-owl. Where

vegetation diversity and structure are reduced, the

presence of water may increase habitat quality by

attracting more prey to the area. In 1997, an owl pair

in Texas nested on the edge of a pasture near a water

tank that attracted wildlife, including song birds

(Proudfoot unpubl. data). In the Tucson area, drip

irrigation or water dishes close to monitored nests

attracted a variety of potential prey (Abbate et al.

1996, Richardson unpubl. data).

Cavity nesting and the importance of trees

or saguaros

Because the ferruginous pygmy-owl is an obligate

cavity nester, it requires trees or cacti large enough to

contain a cavity, as well as cavity excavators. Thus,

nest location may strongly reflect nest cavity availability. Historical records suggest that in riparian

areas, mesquite, a hard wood less readily excavated by

Gila woodpeckers and northern flickers, was less frequently used than softwood trees (Hunter 1988). With

the loss and alteration of riparian areas in Arizona,

saguaros may now provide the most available source of

cavities for nesting; most recent nest sites have, in

fact, been located in saguaro cavities (Abbate et al.

1996, Richardson unpubl. data). However, two nests

monitored in 1999 were located in a eucalyptus and an

Arizona ash (Richardson unpubl. data). The eucalyptus was an integral component of an exotic landscape,

but the ash was in an ephemeral wash surrounded by

uplands of mesquite/grassland vegetation with no

available saguaros. The only cavities in the area were

in the large trees along the wash. Within certain

portions of the cactus ferruginous pygmy-owl’s range

in Arizona, riparian and xeroriparian vegetation communities may still contain the only available pygmyowl nest sites.

The density of trees and amount of canopy cover

preferred by ferruginous pygmy-owls remains unclear. Most of the above habitat descriptions suggest

that the highest owl densities are found in semi-open

or open woodlands, often in proximity to forests or

patches of forest. Where the owl occurs in forested

areas, it is more readily observed along the edge or in

openings rather than deep in the forest itself (Binford

1989, Sick 1993). Hence, at a landscape level, this

bird may prefer semi-open, transitional zones between dense stands of trees and open savannas or

scrublands, and semi-open habitats dotted with thickets. Additional research is needed to examine this

association.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 53

4. The importance of riparian and

desertscrub habitats in Arizona _____

Assessing the importance of riparian areas and

desertscrub for maintaining or recovering the ferruginous pygmy-owl in Arizona is essential. As indicated,

the ferruginous pygmy-owl is not consistently dependent on riverine ecosystems throughout its range. In

fact, where the riparian vegetation forms a closedcanopy gallery forest, owl density may be low. In

Sonora, Mexico, where riparian areas closely resemble

those of Arizona, the association between riparian

plant communities and the owl appears weak. One

potential explanation is that in Sonora, as in other

parts of the pygmy-owl’s range, a significant portion of

the land outside of floodplains is wooded, presenting

the owl with a larger choice of suitable habitats. In the

southwestern United States, however, riparian floodplains support most of the low-elevation woodland

vegetation. These areas attract a disproportionate

amount of wildlife (Carothers and Johnson 1975,

Hubbard 1977, Pase and Layser 1977). Migrating

passerines, for instance, exhibit a strong preference

for riparian corridors over the adjacent uplands

(Stevens et al. 1977).

In general, early accounts of the original riparian

vegetation and descriptions of Blue Point Cottonwoods (Chapter 2) are congruent with descriptions of

habitats where ferruginous pygmy-owls are most commonly found. Riparian areas where the owl was detected often included thickets (e.g., Bendire 1888),

while cottonwoods and resident woodpeckers must

have provided many cavities for nesting (see Breninger

1898, Gilman 1909). Riparian areas are linear and

thus tend to have a high proportion of edge. Unless

they have been completely invaded by tamarisk, these

areas support a higher density of breeding birds than

any other low to mid elevation vegetation community

in the Southwest (Carothers et al. 1974, Johnson et al.

1977, Franzreb 1987). Riparian areas of the Southwest generally support a higher average number of

reptile and amphibian species than nonriparian areas

(Brode and Bury 1984, Jones 1988). They may also

support higher diversity and densities of mammalian

species than adjacent uplands (Stamp and Ohmart

1979, Frey and Yates 1996). Such an abundance and

diversity of prey may be essential for a perch-and-wait

predator like the ferruginous pygmy-owl. The continuous corridors of floodplain riparian vegetation once

covering hundreds of miles in the Southwest may have

supported the sizable pygmy-owl population suggested

by Bendire (1888) and Breninger (1898)’s accounts.

The very low number of owls found in riparian vegetation in recent years may reflect loss of habitat connectivity rather than lack of suitability.

Although the majority of recent cactus ferruginous

pygmy-owl detections in Arizona have occurred in

desertscrub, the literature suggests that this vegetation type has always been associated with low densities of this bird, even when it was considered common

in riparian areas (Breninger 1898, Kimball 1921). In

large, fairly pristine, desertscrub areas (e.g., Organ

Pipe Cactus National Monument), records of the owl’s

occurrence are infrequent (Groschupf et al. 1988). In

Sonora, Mexico, limited evidence indicates that cactus

ferruginous pygmy-owls are uncommon in this vegetation type (Russell and Monson 1998). One possible

explanation for the seemingly rare occurrence of the

owl in desertscrub is that this habitat is of marginal

quality (Johnson and Haight 1985, Taylor 1986). Alternatively, the low number of historical records in

desertscrub may chiefly reflect the lack of early studies in desert areas. As mentioned, xeroriparian vegetation in Arizona resembles arid thickets in Ecuador

where ferruginous pygmy-owls are common, and the

tall columnar saguaros of the Sonoran Desert provide

cactus ferruginous pygmy-owls with nesting cavities

(Abbate et al. 1996).

Desertscrub may also play an important role at

another level. Habitat connectivity is greater for

desertscrub than for riparian vegetation. As stated,

this habitat type represents the substrate through

which the owl ranges from Sonora into Arizona, perhaps at times allowing the Arizona population to be

replenished. Dispersing juvenile pygmy-owls traveled

more than 15 miles through desertscrub of varying

quality during radio tracking in 1998 (Richardson

unpubl. data). Research is needed in Arizona to better

understand the size and distribution of the remaining

owl population and to further explore the relative

importance of desertscrub and riparian areas.

Recently, cactus ferruginous pygmy-owls have been

found in areas (i.e., desert grassland communities) of

Arizona where the potential to detect them was

perhaps initially considered to be low (see Chapter 3).

These detections were chiefly the result of an increased survey effort. They indicate that intensified

survey efforts in “marginal” habitats can result in

increased owl detections and change our perception

of the relative importance of vegetation communities

utilized by pygmy-owls. For example, the recent identified nesting of cactus ferruginous pygmy-owls in

xeroriparian vegetation along washes within mesquite grasslands raises questions regarding the

value of these types of areas and their contribution

toward the persistence of the owl in Arizona. As

with nearly all aspects of the owl’s ecology, more

information is needed before we have a complete

understanding of cactus ferruginous pygmy-owl

habitat preferences.
54 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

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importance of riparian habitat to migrating birds. Pp. 156-164. In:
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Johnson, R. R., and D. A. Jones, tech. coords. Importance, preservation and management of riparian habitat: a symposium. Gen.

Tech. Rep. RM-43. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station.

Stiles, F. G., and A. F. Skutch. 1989. A guide to the birds of Costa

Rica. Ithaca, NY: Comstock Publishing Associates.

Stotz, D. F., J. W. Fitzpatrick, T. A. Parker III, and D. K. Moskovits.

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University of Chicago Press.

Swarth, H. S. 1914. A distributional list of the birds of Arizona.

Pacific Coast Avifauna 10:1-133.

Taylor, R. C. 1986. Checklist to the birds of Sonora and the Sea of

Cortez, including Barranca del Cobre. Portal, AZ: Borderland

Productions. 23 p.

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Pp. 213-232. In: Eisenberg, J. F., ed. Vertebrate ecology in the

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ecology in the northern Neotropics. Washington, D.C.: Smithsonian

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U.S. Fish and Wildlife Service. 1994. Endangered and threatened

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pygmy-owl as endangered with critical habitat in Arizona and

threatened in Texas. Federal Register 59:63975-63986.

Wauer, R. H., P. C. Palmer, and A. Windham. 1993. The ferruginous

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44:153-69.

USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 57

Glenn A. Proudfoot

Jody L. Mays

Sam L. Beasom

Chapter 5:

Research on the Ferruginous Pygmy-Owl

in Southern Texas: Methodology and

Applications

Using broadcasted conspecific calls, nest boxes, miniature-video cameras, a fiberoptic stratascope, and

radio-telemetry, researchers from Caesar Kleberg

Wildlife Research Institute conducted studies to assess the viability and profile the natural history of

ferruginous pygmy-owls in Texas (Mays 1996,

Proudfoot 1996a, Proudfoot and Beasom 1996,

Proudfoot and Beasom 1997, Proudfoot and Radomski

1997). Techniques used were specifically designed or

adapted to address the concerns of this species (e.g.,

minimizing risks of nest abandonment resulting from

nest inspection). In this chapter, we summarize research methods used to study ferruginous pygmy-owls

in Texas and provide current information regarding

its status there.

1. Status of ferruginous pygmy-owls

in Texas __________________________

Prior to 1920, the ferruginous pygmy-owl was considered a common resident of riparian areas in the

lower Rio Grande Valley of Texas (Figs. 5-1 and 5-2)

(Oberholser 1974). However, by the early 1970s, over

90% of this habitat was cleared for urban and agricultural expansion, reducing the size of the ferruginous

pygmy-owl population (Oberholser 1974). During the

Texas Breeding Bird Atlas Project, 1987-1992, two

confirmed nest sites were recorded below Falcon Dam

in Starr County, Texas, and six probable sites were

recorded between the Rio Grande River and the 27th

parallel (Proudfoot in press). Wauer et al. (1993)

expressed concern that repeated disturbance by

bird-watchers (e.g., broadcast of conspecific calls during the breeding season) may negatively affect the

Falcon Dam population. In 1993, no ferruginous pygmyowls were detected from broadcast surveys conducted

along the Lower Rio Grande River and, although the

absence of detection may have been influenced by birdwatchers, Tewes (1993) concluded that the cause is

more likely a lack of suitable habitat. Although this

information suggests ferruginous pygmy-owls are rare

in Texas, recent studies have located and monitored 99

ferruginous pygmy-owl nests in Kenedy County from

January 1994-June 1999 (Proudfoot unpubl. data). In

addition, Mays (1996) estimated from 745 to 1,823

individuals may occur in Kenedy County, Texas and

Wauer et al. (1993) estimated 1,308 ferruginous pygmyowls may occur in the live oak (Quercus virginiana)-

mesquite (Prosopis glandulosa) habitat in Brooks,

Kenedy, and Willacy counties, Texas (Fig. 5-2). Hence,

although the ferruginous pygmy-owl is listed as endangered in Arizona (U.S. Fish and Wildlife 1997) and

was proposed for listing as threatened in Texas (U.S.

Fish and Wildlife 1994), a viable population may still

exist in Texas. In Texas, the ferruginous pygmy-owl

has no protection under the Endangered Species Act

(U.S. Fish and Wildlife 1997).
58 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

Figure 5-2. Southern tip of Texas, locations of the Norias Division and Falcon Dam.

Figure 5-1. Known distribution of ferruginous pygmy-owls in Texas.
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 59

2. Study area ______________________

The Norias Division of the King Ranch encompasses

97,877 ha of rangeland in the historical Wild Horse

Desert (Fig. 5-2). The climate is subtropical with mean

annual temperature of 24° C and mean annual

precipitation of 68 cm. Macro-vegetation types on

Norias include coastal grassland, live oak-mesquite

woodland, and honey mesquite savanna. The introduction of sheep and cattle in the 18th century may

have affected natural succession on Norias and contributed to an increase in the dispersal of live oak

seeds, resulting in the fusion of scattered oak groves

into a continuous block of live oak-mesquite forest

encompassing about 30,000 ha (Johnston 1963). However, the distribution of major vegetation types on

Norias has remained essentially the same for the past

century (Wauer et al. 1993).

3. Materials for locating and studying

ferruginous pygmy-owls ___________

Broadcast equipment and use of parabolic

microphone

Broadcasted conspecific calls are commonly used to

locate and survey forest-dwelling raptors (Allaire and

Landrum 1975, Johnson et al. 1981, Marion et al.

1981, Forsman 1983, Hayward and Garton 1983, Lynch

and Smith 1984, McGarigal and Fraser 1985, Smith et

al. 1987, Ganey 1990, Stahlecker and Rawinski 1990).

To assess the effectiveness of this technique for ferruginous pygmy-owls, Proudfoot and Beasom (1996)

compared elicited versus non-elicited (stop-and-listen) call-counts and recorded a >3-fold increase in

detection using elicited call-counts. This study suggests the use of broadcasted conspecific calls may be a

viable tool for locating and surveying ferruginous

pygmy-owls in Texas. Broadcast equipment used

(MS512MR Johnny Stewart Wildlife Caller, Waco,

TX) for this and coexistent ferruginous pygmy-owl

research (Mays 1996) is capable of producing 95-100

dB at a distance of 1 m from the speaker, which meets

minimum output criteria recommended for broadcast

surveys (Fuller and Mosher 1987). To maximize the

effectiveness of broadcast surveys and detection of

responding ferruginous pygmy-owls, recent studies

(Proudfoot unpubl. data) incorporate use of a Bionic

Ear (Silver Creek Industries, Manitowoc, WI) parabolic microphone. Using this system, responding ferruginous pygmy-owls were detected at distances >600

m. In addition, heretofore unreported calls of females

and juveniles (e.g., alarm and distress) were recorded

(Proudfoot et al. unpubl. data).

Mist nets and bow nets

Ferruginous pygmy-owls were captured using a combination of techniques, most of which are commonly

used for numerous raptors (Tordoff 1954, Kenward

and Marcstrom 1983, Bloom 1987). Two or three

mist nets (Item No. CTX, Avinet, Inc. Dryden, NY)

were placed in various configurations (e.g., V shape,

triangular, or open-ended box) in proximity (e.g.,

<75 m) to known ferruginous pygmy-owl locations. In

the center of the mist net configuration a portable

tape-recorder was used to broadcast conspecific-calls.

It was assumed the territorial defensive behavior of

the owl would draw them into the net responding to

the call. To capture responding owls that did not

display enough aggressive behavior (e.g., females) to

become caught in mist nets, self-triggering baited bow

nets (Bird Traps, Czechoslovakia) were placed on the

interior and exterior (<5 m) of the mist net configuration. Caged laboratory mice were used for bait

(Proudfoot 1996a). Using these techniques, 149 adult

ferruginous pygmy-owls were captured from March

1994-June 1999 (Proudfoot et al. unpubl. data).

Radiotransmitters

Radio-telemetry is considered a valuable tool for the

study of elusive species (Neudorf and Pitcher 1997).

From spring 1994-fall 1997, radio-transmitters were

established on 28 adult and 26 juvenile ferruginous

pygmy-owls. To diminish the possibility of nest abandonment, transmitters were not established on adult

females prior to two-weeks posthatch. A backpack

harness was used to attach the transmitters. Transmitter frequencies were from 150.00-150.40 MHz,

mass was from 1.5-2.0 g, and antennae were 16 mm

long. Although the use of radio-transmitters has fostered some concern (e.g., affecting behavior and foraging and reproductive success) (Ramakka 1972, Perry

1981, Kenward 1987, Massey et al. 1988, Croll et al.

1996), no difference in behavior was observed between

radio-tagged and non-radio-tagged owls nor in productivity of breeding pairs (Proudfoot unpubl. data). Similar studies report comparable results (Gilmer et al.

1974, Brigham 1989, Hill and Talent 1990, Morris and

Burness 1992, Neudorf and Pitcher 1997).

Nest boxes

Recent studies using artificial nest structures include economic and ethological research (Korpimaki

1985, Brawn and Balda 1988, Hayward et al. 1992).

Alleviating many logistical problems (e.g., knowledge

of potential nests, access to eggs, nestlings, and adults),

nest boxes may aid study of nesting requirements,

limiting factors, and productivity (Lack 1966, Enemar
60 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

and Sjostrand 1972, Hogstad 1975, Waters et al.

1990). In addition, because artificial nest structures

are mobile and associated with reduced predation

(Miller 1989, Sonerud 1985, 1989), they may be established to augment recovering populations.

In October 1992, to ascertain selectivity of ferruginous pygmy-owls for specific nest-box configurations,

36 nest boxes were constructed from 14.7 x 1.9 cm

rough cut cedar. Box depth varied from 31-46 cm and

entrance size varied from 4.5-6.4 cm in diameter. To

encourage their use, nest boxes were established in

areas known to be occupied by ferruginous pygmyowls. Four nest boxes designed for black-bellied whistling-ducks (Dendrocygna autumnalis) provided another variation in box depth (44 cm), floor surface area

(294 cm2), and entrance hole diameter (9.8 cm). Nest

boxes were established in eight groups of five boxes,

each box varying in depth and entrance size (Proudfoot

1996a).

In April 1993, three nest boxes from different groups

were used by ferruginous pygmy-owls. Nest boxes

used were 31, 44, and 46 cm in depth, with 4.5, 5.1,

and 5.8 cm entrance diameters, respectively

(Proudfoot 1996a). Expanding ferruginous pygmyowl nest box studies to include habitat selection, nest

box placement criteria, nestling development, predation, and productivity, 40 nest boxes were constructed

in the mean configuration used by ferruginous pygmyowls in 1993 and established throughout the study

area (Fig. 5-3).

From 1993-1997, 15 nest boxes were used by ferruginous pygmy-owls and 21 nests were located in natural

cavities. Number of young fledged/nest attempt was

3.47 and 1.96 for nest boxes and natural nest cavities,

respectively. Nest depredation noticeably affected productivity of natural cavities and, at artificial nest

structures, increased in association to nest box age

(Proudfoot et al. unpubl. data).

Optic equipment

To minimize observer stress and disturbance to

nest-cavity occupants, a miniature video-camera system was used to inspect natural and artificial nest

cavities (Proudfoot 1996b). Containing a light source

and powered by one 9 V DC battery, the camera system

transferred a black-and-white image via video patch

cable to a hand held monitor (Sony Watch-Cam, Sony

Electronics, Inc., Itasca, IL). Mounted at the end of a

10 m telescoping aluminum pole, this system allowed

observers to inspect nest cavities from the ground (see

Proudfoot 1996b for detailed description). Although

efficient, limitations of this system (i.e., 49 cm depth of

field and 60° field of view) restricted use to cavities of

cylindrical configuration <49 cm in depth. Therefore,

in summer 1994, a flexible fiber optic stratascope (FS490X108 Schott Fiber Optics Inc., Southbridge, MA)

Figure 5-3. Ferruginous pygmy-owl nest box on live-oak

tree in Texas. Photograph by Jean-Luc Cartron.

was used to complement the miniature video-camera

system. The stratascope lens and light source are

contained in a flexible stainless steel housing 1.3 cm in

diameter x 246 cm in length. This system was used to

inspect cavities that exceeded the limits of the aforementioned monitoring system and occasionally to

qualify occupancy determinations made using the

camera system.

To obtain information on ferruginous pygmy-owl

food habits and nestling behavior, two miniature color

video-cameras (XC-42 Computar, Chugai Boyeki Corp.,

New York, NY) were established in the top of occupied

nest boxes to record nestling activity. The image was

relayed via video patch cable to a cam-corder (Canon

A1, Canon Inc., Japan) placed in proximity to the nest

site. This system obtained about 105 hours of video

footage and did not seem to affect nestling development, age of fledging, or productivity (Proudfoot and

Beasom 1997).

In spring 1997, five miniature video-cameras

equipped with infrared light-emanating diodes and

time lapse recording units (Model AG-1070DC,
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 61

Panasonic Inc., Japan) were established to obtain

information on ferruginous pygmy-owl nesting activity. Cameras were established <1.5 m from cavity

entrances. Time lapse recording systems operated 24

hours/day seven days/week from incubation-fledging,

obtaining >4,500 hours of information (Proudfoot

unpubl. data).

4. Applications and

methodology _____________________

Use of radio-telemetry for developing

survey protocols

The effectiveness of broadcast surveys may be influenced by weather conditions, time of broadcast (AM,

PM), physiological state of individuals being surveyed,

degree of competition among males for nest sites, and

mating success (Hayward et al. 1992). Other factors

may include sensitivity to broadcasted or imitated

calls (Tewes 1993), environmental characteristics, and

effective broadcast radius (i.e., maximum distance

between broadcast station and targeted individual

that will invoke a response without affecting responsiveness). Therefore, it is essential to appropriately

address regulatory empirical factors (i.e., time of broadcast, distance between broadcast stations, and acceptable weather conditions) before conducting surveys.

To determine the effective broadcast radius for ferruginous pygmy-owls in Texas, nine adult males (four

in 1995 and five in 1996) were fitted with radiotransmitters (L. L. Electronics, Mahomet, IL) and

their response distance to broadcasted conspecific

calls was tested. Because spontaneous calling bouts of

ferruginous pygmy-owls are usually crepuscular

(Gilman 1909), testing was restricted to 30 min before

and after sunset, as determined by the U.S. Naval

Observatory, Washington, D.C. No testing was conducted when winds exceeded 19-24 kph (12-15 mph) or

when precipitation occurred (Proudfoot 1996a).

Using a three-element Yagi antenna and portable

radio-receiver (L. L. Electronics, Mahomet, IL) one

observer tracked a radio-tagged pygmy-owl until obtaining visual contact and relayed its location in relation to its distance from established points (e.g., wind

mills, nest trees, fences, gates, etc..) to a second observer via two-way radio. The second observer calculated distance to the owl and used compass bearings

and pacing to obtain the distance desired for testing. A

portable tape recorder was used by the second observer to broadcast conspecific calls toward the targeted individual. Broadcasting continued for three

minutes, during which any movement toward the

broadcast station or vocalization was recorded. Because the characteristic call of pygmy-owls is a simple

series of interrupted single notes, continued broadcast

should not hamper detectability (Proudfoot and Beasom

1996). Radio-telemetry was used to substantiate movement or vocal response of the targeted individual

(Proudfoot 1996a).

In 1995, all ferruginous pygmy-owls tested at 400

and 500 m (n = 4) responded by moving toward the

broadcast station and vocalizing. At 600 m, three

individuals responded with movement and vocal

defense; the fourth only responded vocally. Due to

time constraints, only one ferruginous pygmy-owl was

tested at 700 m in 1995, and it responded by moving

toward the broadcast station and vocalizing (Proudfoot

1996a).

In 1996, two of five birds tested at 700 m moved

toward the broadcast station and vocalized. A third

bird responded vocally at 700 m with limited movement toward the broadcast station and vocalization at

600 m. The fourth bird responded vocally at 600 m and

moved toward the broadcast station and vocalized at

550 m. The fifth bird responded vocally at 550 m and

moved toward the broadcast station and vocalized at

250 m.

Habitat preferences

Tracking 54 radio-tagged ferruginous pygmy-owls

in Texas showed preferential habitat use and seasonal

variation in areal use (Proudfoot unpubl. data). To

compare habitat use to habitat availability, 37 ferruginous pygmy-owls were tracked almost daily for the life

of the transmitters (90+ days) and at each visual

sighting, a 0.04-ha circular plot was established to

determine habitat composition of areas used (Stoddard

and Stoddard 1987). Trees >2 m in height and >2.5 cm

in diameter at breast height (dbh) that occurred within

the 0.04-ha plot were counted, identified according to

species, and measured for dbh. Density board values

were estimated to determine understory cover. A

single board measuring 205 x 8.9 x 1.9 cm, with eight

equal-sized panels of alternating white and orange

color was placed at the center of each plot and observed

from the outer edge from four cardinal directions.

Each panel was rated between zero and six for percentage of the panel covered by vegetation (0 = 0%,

1 = >0-5%, 2 = 6-25%, 3 = 26-50%, 4 = 51-75%, 5 = 76-

95%, 6 = 96-100%). Mean cover values, number of

trees/ha, and dbh of trees within circular plots were

compared to study area composition data obtained in

a systematic-random sample of 219 0.04-ha plots to

determine ferruginous pygmy-owl habitat selection

(Stoddard and Stoddard 1987, Proudfoot 1996a). Habitat use was disproportionate to its availability. Ferruginous pygmy-owls used areas containing significantly (P < 0.05) fewer small trees (<25 cm dbh) and

more large trees (>26 cm dbh), with moderate-dense

understory (50-100% cover) (Proudfoot 1996a). Results from this study were used to gauge habitat
62 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

potential for detecting ferruginous pygmy-owls during broadcast surveys and for establishment of nest

boxes (Proudfoot et al. upubl. ms.).

Home range

To calculate areal use, Universal Transverse Mercator (UTM) coordinates of radio-tagged ferruginous

pygmy-owls were analyzed for 95 and 100% minimum

convex polygons. A TELEM88 home-range analysis

program (Dept. of Fish and Wildlife, Virginia Polytechnic Institute and University, Blacksburg, VA.)

was used to conduct the analysis. Starting from known

UTM locations, observers tracked radio-tagged ferruginous pygmy-owls using compass bearings and

pacing (Stoddard and Stoddard 1987) to calculate the

geographic location of each individual detected. Owls

were tracked almost daily during the lives of the

transmitters (90+ days) (Proudfoot 1996a). The results of this study are in Chapter 1.

Assessment of cavity availability

Because studies on cavity nesting species may be

influenced by the availability of cavities (Waters et al.

1990), observers surveyed the study area to estimate

the number of natural cavities/ha. Transects (400 x

6 m) (n = 104) to locate natural cavities were established at 400-m intervals perpendicular to roads that

intersect the study area. Compasses were used to

orient transects and lines were laid with a topometric

hip-chain (Forestry Suppliers, Inc., Jackson, MS) to

establish boundaries. Trees were temporarily marked

with a chalk tree marker (Forestry Suppliers, Inc.,

Jackson, MS) (Proudfoot 1996a, Proudfoot unpubl.

data). To obtain information on possible interspecific

competition, cavities with entrances >3.8 cm in diameter were inspected for occupancy with the nest box

monitoring system (Proudfoot 1996b). Cavity entrance

diameters were estimated by comparing the size of

the entrance to the size of the camera housing (3.6 x

2.2 cm). The above ground height of cavity entrances

was estimated (+ or – 15 cm) from markings placed on

the telescoping pole that supported the camera. Trees

containing cavities were identified to species and dbh

measured. The number of cavities/ha in the study area

was estimated by multiplying the mean number of

cavities/ha in the area sampled by the size (ha) of the

study area (Proudfoot 1996a).

Transects encompassed 24.96 ha (an estimated 13,995

trees) and contained 261 natural cavities (10.5/ha).

One hundred and twenty cavities (46%) (4.8/ha) were

of the entrance hole diameters used by ferruginous

pygmy-owls, suggesting that the study area supports

a large number of cavities. Although none of the

cavities inspected contained avian occupants

(Proudfoot 1996a), possibly because surveying

preceded nesting for many species in the area, the

potential for competition is indicated by the fact that

several species were found occupying nest boxes (see

Chapter 1).

Nest monitoring

Using the miniature video-camera and stratascope, nest boxes and natural cavities occupied by

ferruginous pygmy-owls were periodically inspected

to obtain information on laying sequence, clutch size,

incubation period, and hatching sequence (Proudfoot

1996ab). In addition, food habits and nestling activities were monitored by establishing miniature videocameras in the top of nest boxes (Proudfoot 1996a,

Proudfoot and Beasom 1997). To document nestling

development, nestlings from seven nest boxes were

photographed on alternating days from one day

posthatch to fledging (Proudfoot 1996a, Proudfoot

unpubl. data). Development information may aid conservation of this species by providing investigators an

estimation of time available to conduct needed research (e.g., banding and marking [essential tools in

avian management]).

Demographic study

The empiric determination of demographic parameters can be used to calculate minimum recruitment

standards for a population (Gehlbach 1994). However,

to obtain information for such an analysis requires

long-term study, and although ongoing ferruginous

pygmy-owl research is addressing the required parameters, insufficient information exists for sound

analysis.

Food habit study

Analysis of prey remains, visual observation, and

analysis of video footage recorded inside active nest

boxes were used to obtain information on ferruginous

pygmy-owl food habits. Prey remains were identified

using dichotomous keys (Jones and Manning 1992,

Chaney 1993) and university reference collections.

Visual observations were conducted from blinds established <5 m from four nest sites; observation time was

about 105 hours. Video footage, obtained from miniature

video-cameras established in the top of two active nest

boxes, provided images of prey items brought to the

nest by adults. About 104 hours of video footage was

analyzed (Proudfoot 1996a, Proudfoot and Beasom

1997).

Thirty-six prey species from five classes (i.e. Insecta, Reptilia, Mammalia, Aves, and Amphibia) were

identified in the diet of ferruginous pygmy-owls from

Texas. Analysis of prey remains (eight nest sites)

identified more individual prey items (184) and prey
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 63

species (28) than visual observations (40 individuals

and 11 species), or analysis of video footage (103

individuals and 12 species). Comparison of prey

items identified/prey item brought to the nest site

showed analysis of video footage exceeded visual

observation in prey identification by 28%.

Hematozoa study

Hematozoa may cause septicemia, marginal anemia, and neonatal bacterial diarrhea (Hunter et al.

1987), reducing survivability and recruitment. To determine presence of hematozoa from ferruginous

pygmy-owls in Texas, blood smears were obtained

from 63 (14 females, 45 males, four nestlings) individuals and analyzed. Results revealed no hematozoa

(Proudfoot and Radomski 1997).

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USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 65

Jean-Luc E. Cartron

W. Scott Richardson

Deborah M. Finch

David J. Krueper

Chapter 6:

Research Needs for the Conservation of

the Cactus Ferruginous Pygmy-Owl in

Arizona

In this chapter, we describe research needs for the

conservation of the cactus ferruginous pygmy-owl

(Glaucidium brasilianum cactorum) in Arizona. Estimates of population size, structure, and dynamics, as

well as demographic data, are needed for the recovery

team to formulate sound population objectives. Habitat loss due to residential development may represent

the primary threat to the pygmy-owl, yet the impacts

of other human activities and of disease or predation

have not been evaluated. Studies of the cactus ferruginous pygmy-owl’s habitat requirements are essential

to determine the importance of various vegetation

types to the owl, protect critical habitat on federal

lands, and develop guidelines for residential development. Using annual population surveys in conjunction

with continued nest monitoring, habitat sampling,

and telemetry will best address Arizona’s owl research

needs. Habitat studies and population surveys in

Sonora, Mexico may be necessary as well. The use of

nest boxes in riparian areas, while presenting potential benefits for the management of the owl, may also

address habitat research needs.

1. Current state of knowledge and

management situation _____________

Historical accounts and specimen records suggest

that the cactus ferruginous pygmy-owl was common or

fairly common in some riparian areas in the late 19th

and early 20th centuries (Chapter 2). A substantial

population decline may have occurred during the first

few decades of the 20th century which eventually led to

the extirpation of the owl along the lower and middle

Gila River, the Santa Cruz River and Rillito Creek,

and the Salt River in the Phoenix area (Chapter 2).

The population decline along those rivers coincided

with the loss and alteration of riparian areas due to

human activities (Chapter 2). Although some riparian

areas appear to remain suitable for pygmy-owl occupancy, very few owls have been detected in this

habitat in the last decade (Chapter 3).

The recent survey effort suggests that population

size of the pygmy-owl is now small (Chapter 3) and

that the owl is chiefly associated with xeroriparian

vegetation and dense, well-structured desertscrub

(Chapters 3 and 4). In at least some areas, the remaining owl population is threatened by urban development (Chapter 3). Added to the threat of habitat loss

is the risk of extinction inherent to small population

size due to stochastic variation in demographic parameters, sex ratio, genetic diversity, environmental

conditions, and disease (Shaffer 1981, Petterson 1985,

Simberloff 1988, Clark et al. 1990).

2. Research needs _________________

In the last two years, the need to rapidly accumulate more information on the population status and
66 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

habitat needs of the cactus ferruginous pygmy-owl

has led to an increased survey effort and to the use of

telemetry (Chapter 3). Habitat sampling and nest

monitoring have also been continued.

Additional research is needed to develop a recovery

plan for the owl, to guide habitat protection and

enhancement efforts on federal lands, and formulate

guidelines for future residential development compatible with the persistence of the cactus ferruginous

pygmy-owl. Delisting criteria typically include population objectives for ensuring the long-term viability of

a species. Examples of population objectives used for

other federally listed species are:

1) Minimum average number of individuals over a

specified number of years (U.S. Fish and Wildlife

Service 1986).

2) Maximum rate of annual population decline over

a specified number of years (U.S. Fish and Wildlife Service 1986).

3) Minimum productivity per active nest (U.S. Fish

and Wildlife Service 1990).

4) Minimum number of self-sustaining populations

(U.S. Fish and Wildlife Service 1996).

The choice of a particular population parameter and

objective requires knowledge about current population size and structure, demographics, and the cause(s)

of the population decline responsible for the listing of

the species. Recovery plans also list recommendations

for reaching the population objective(s). Such recommendations require a good understanding of past,

current, and future threats to the listed species and its

habitat.

Under Section 7 of the Endangered Species Act,

federal agencies are required to protect and enhance

critical habitat located on federal lands. However, efforts by federal agencies regarding critical habitat may

be less effective if the owl’s habitat needs and preferences are not fully understood. Further, due to the lack

of biological information, land managers are having

difficulty developing management guidelines to reduce

impacts of various activities on cactus ferruginous

pygmy-owls. Developers also need development guidelines which outline appropriate development locations,

densities, and patterns. The livestock industry is searching for suitable grazing systems while the recreationists

ponder whether some areas may be restricted due to

pygmy-owls. To answer the need for sound management guidelines, defensible, biological information has

to be gathered through research.

Estimates of population size, distribution,

structure, and movement

In the spring and summer of 1999, 78 owls were

reported from Organ Pipe Cactus National Monument, northwest Tucson, southern Pinal County, and

the Altar Valley (Chapter 3). Despite the increased

number of owls located, many questions remain concerning the exact size and attributes of the Arizona

population. It is only through annual population surveys that an accurate estimate of population size and

population trend will become possible. In particular,

the Tohono O’odham Reservation represents a key

area not yet formally surveyed. In addition to its large

size and the fact that pygmy-owls have been documented within its boundaries, its geographic position

between the Tucson area, the Altar Valley, and Organ

Pipe Cactus National Monument suggests that it

could be occupied by a substantial number of pygmyowls. Other inadequately surveyed locations where

cactus ferruginous pygmy-owls may persist include

the lower San Pedro River and the middle Gila River.

Although some sections of the lower San Pedro River

have been surveyed since 1993 (Chapter 3), the absence of detections is not reliable because most of the

habitat occurs on private lands, and these have not

yet been surveyed. The lower San Pedro still supports

a cottonwood-willow gallery forest and mesquite

bosques. A pair of cactus ferruginous pygmy-owls

was detected at the Dudleyville crossing in the late

1980s (Hunter 1988). Access to private properties

along the lower San Pedro was recently granted to

conduct Southwestern willow flycatcher (Empidonax

traillii extimus) surveys.

For 15 miles, the banks of the Gila River from

Ashhurst-Haydn Dam upstream to near Kearny (elevation 390 m to 540 m) support thickets of exotic

tamarisk (Tamarix spp.), but also regenerating cottonwood and willow intermixed with extensive mesquite bosques (Chapter 3).

In the last five years, cactus ferruginous pygmy-owl

nest sites have been found (Chapters 1 and 4). Yet,

whether the Arizona owl population is self propagating or receives a flow of recruits from Mexico is

uncertain. Long-distance dispersal capabilities of individuals are unknown. In particular, northward

movements of at least some cactus ferruginous

pygmy-owls from across the Mexican border remain

a possibility (Chapter 1). Because the recruitment of

dispersing individuals can lead to the recolonization

of historical habitat and thus population recovery,

determining the presence or absence of long-distance

dispersal is crucial. As noted in Chapter 4, the cactus

ferruginous pygmy-owl seems common locally in

southern Sonora, Mexico. Yet, its population status

over the entire state of Sonora has not been evaluated

using population surveys.

Demographic study

To maximize the chances of success of a recovery or

management plan, conservation biologists have learned

to rely heavily on demographic studies (Dobson and
USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000 67

Lyles 1989, Noon and Biles 1990, Wyllie and Newton

1991, Sjögren 1991, Noon et al. 1992, Powell and

Zielinski 1994, Koehler and Aubry 1994, Donovan et

al. 1995, Olmsted and Alvarez-Buylla 1995). Life history tables and demographic modeling form the basis

on which population growth rates and characteristics

are projected (Ricklefs 1973, 1983). Population growth

rates reflect the influence of age at first breeding, the

proportion of the adult population that breeds, productivity, and juvenile and adult mortality. Based on the

normal ranges of these demographic parameters, it is

also possible to infer optimal rates of population recovery and run sensitivity analyses, the results of which

can point to the factors most responsible for limitations on population growth.

At present, it is unknown whether population size of

the cactus ferruginous pygmy-owl in Arizona is chiefly

limited by high adult mortality, low recruitment (i.e.,

low productivity or high juvenile mortality), a low

proportion of breeding adults, or a combination of the

three. High adult mortality and low recruitment may

be caused by predation, disease, lack of food, or human-related factors. A high proportion of adults that

do not breed is perhaps due to habitat fragmentation,

lack of nest sites, or low owl densities. The use of

banding and radiotelemetry is needed to complement

nest monitoring and provide estimates of survivorship,

and breeding and productivity rates. Initially, these

data could be compared with the demographic data on

the Texas population of ferruginous pygmy-owls.

Besides residential development, potential threats

to the cactus ferruginous pygmy-owl and its current

and historical habitat exist in Arizona. Among them is

the possible incidence of trichomoniasis in cactus

ferruginous pygmy-owls. While it has not yet been

reported, owls found in the Tucson area may be at risk

for contracting the disease (Chapter 1). Other potential causes of mortality, such as window strikes, fence

strikes, cats, and shooting need to be evaluated. In the

last five decades, wildfire frequency has increased in

upland Sonoran Desert communities (Schmid and

Rogers 1988, Narog et al. 1995). With their mortality

reaching 80%, saguaros (Carnegiea gigantea) are especially vulnerable to wildfires (Wilson et al. 1996).

Their numbers have been shown to decrease drastically in burned areas (Cave and Patten 1984).

Habitat study

As shown in Chapter 4, while the ferruginous pygmyowl occurs in various low-elevation plant communities, it may exhibit a preference for semi-open habitats

with large trees (or cacti) and a moderate to dense

understory. Other structural attributes of preferred

habitat, such as amount of edge, stand insularity, and

spatial connectivity, are not well known and require

additional research. Together with vegetation gap

analyses and a knowledge of the population’s distribution and movements, data on habitat characteristics

can be used to create a map of occupied, suitable (i.e.,

suitable for occupancy but currently unoccupied), and

potential (i.e., currently unsuitable for occupancy but

with the potential to develop to a suitable condition)

habitat and to assess habitat connectivity. Ultimately,

such a map can provide critical insight for conservation planning (Murphy and Noon 1992).

A critical, unresolved issue, is whether the ferruginous pygmy-owl in Arizona should be managed as an

upland species, a riparian species, or both. In desertscrub, pygmy-owls have been found in dense upland

desertscrub or along washes lined with xeroriparian

vegetation. They have also been found in low-density

residential areas, often in association with artificially

enhanced native or exotic vegetation (Chapter 4). Why

some pairs would choose to nest near houses in this

type of vegetation may be an indication of habitat

preferences. Alternatively, the association may suggest human encroachment into an area historically

occupied by pygmy-owls.

An essential finding of recent surveys is the observed near-absence of pygmy-owls in presumably

suitable riparian areas. Possible reasons for this finding include loss of connectivity particularly in the

Phoenix area where the owl was once reportedly common or fairly common. Another possible contributing

factor is the lack of large trees or saguaros. In areas

with dense understory, but few trees or saguaros, the

use of nest boxes may help with the recovery of the owl.

It may also identity nest site availability as a key

habitat component currently missing, preventing

recolonization of riparian areas. If nest boxes are used,

they should be closely monitored for occupancy.

Human-related impacts (e.g., development, grazing, recreation) on cactus ferruginous pygmy-owl habitat represent another research priority. In semiurban and semi-rural areas, factors such as densities

of development and size of road may affect cactus

ferruginous pygmy-owl movements and demographics and may best be evaluated by demographic and

habitat use studies. While low-density residential

areas are sometimes compatible with cactus ferruginous pygmy-owl occupancy (Chapter 4), further habitat evaluation is needed. Local extirpation can result

from a reduction in total habitat area and habitat

fragmentation which leads to the insularization of

populations (Wilcove et al. 1986). Habitat fragmentation is often responsible for the disruption of ecological relations such as prey-predator interactions

(Gilbert 1980). In populations with little or no dispersal ability, the loss of connectivity between patches

of suitable habitat becomes an additional problem: as

already mentioned in this chapter, small isolated

populations may become extinct due to stochastic

processes.
68 USDA Forest Service Gen. Tech. Rep. RMRS-GTR-43. 2000

List of priorities

• Increase survey effort. Extend surveys to the

Tohono O’odham Indian Reservation and the

middle Gila River. Through the continued use of

public education and outreach programs, enlist

the cooperation of the public for reporting pygmyowls. Where appropriate, obtain authorization of

private land owners to conduct surveys on their

properties.

• Conduct habitat suitability studies. Compare

survivorship and productivity between nest sites

in undisturbed desertscrub and low-density residential areas.

• Evaluate the impact of human-related activities

(e.g., development, livestock grazing, and recreation) through demographic and habitat use

studies.

• Continue to monitor all nesting pairs located.

• Continue to capture and band individual owls

located. Continue using telemetry to study movements and mortality.

• In riparian areas and other habitat types, evaluate the benefits and costs of nest box use where

the understory is dense but nest site availability

appears limited. Give priority to areas near occupied sites.

• Conduct research in western Mexico to study

population status and habitat associations and

evaluate pygmy-owl population exchanges between Sonora and Arizona.

• Conduct and annually update vegetation gap

analyses to assess habitat connectivity.

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ROCKY MOUNTAIN RESEARCH STATION

RMRS

The Rocky Mountain Research Station develops scientific information and technology to improve management, protection, and use of

the forests and rangelands. Research is designed to meet the needs

of National Forest managers, Federal and State agencies, public and

private organizations, academic institutions, industry, and individuals.

Studies accelerate solutions to problems involving ecosystems,

range, forests, water, recreation, fire, resource inventory, land reclamation, community sustainability, forest engineering technology,

multiple use economics, wildlife and fish habitat, and forest insects

and diseases. Studies are conducted cooperatively, and applications

may be found worldwide.

Research Locations

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*Station Headquarters, 240 West Prospect Road, Fort Collins, CO 80526