Conservation 

Assessments for Five 

Forest Bat Species in the 

Eastern United States

United States 

Department of 

Agriculture

Forest Service

General Technical 

Report NC-260

Technical Guide

2006
Front Cover: Illustrations by Fiona Reid, Ontario, Canada ©. Species from top: 

Pipistrellus subflavus, Myotis leibii, Myotis austroriparius, Myotis septentrionalis, 

Nycticeius humeralis.
Conservation 

Assessments for Five 

Forest Bat Species in the 

Eastern United States

United States 

Department of 

Agriculture

Forest Service

General Technical 

Report NC-260

Technical Guide

2006

Edited by

Frank R. Thompson, III
Thompson, Frank R., III, ed. 2006. Conservation assessments for five forest bat species in the Eastern United States. Gen. 

Tech. Rep. NC-260. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Research Station. 82 p.

Assesses the status, distribution, conservation, and management considerations for five Regional Forester Sensitive 

Species of forest bats on national forests in the Eastern United States: eastern pipistrelle, evening bat, southeastern 

myotis, eastern small-footed myotis, and northern long-eared bat. Includes information on the taxonomy, description, 

life history, habitat distribution, status, and population biology of each species.

KEY WORDS: conservation status, habitat use, life history, Myotis austroriparius (southeastern myotis), Myotis 

leibii (eastern small-footed myotis), Myotis septentrionalis (northern long-eared bat), Pipistrellus subflavus (eastern 

pipistrelle), Nycticeius humeralis (evening bat), Region 9, USDA Forest Service

Disclaimer

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opportunity provider and employer.
Conservation Assessments for Five Forest Bat Species in the Eastern United States

Contents

Conservation Assessments for Five Forest Bat Species in the 

Eastern United States

Frank R. Thompson, III, Editor.....................................1

Status and Conservation of Five Forest Bat Species in the 

Eastern United States: Issues and Concerns

Sybill Amelon ...............................................................3

Conservation Assessment: Pipistrellus subflavus (Eastern 

Pipistrelle) in the Eastern United States

Sybill Amelon .............................................................11

Conservation Assessment: Nycticeius humeralis (Evening 

Bat) in the Eastern United States

Sybill Amelon and Dirk Burhans................................31

Conservation Assessment: Myotis austroriparius

(Southeastern Myotis) in the Eastern United States

Sybill Amelon, Mark Yates, and Craig Pullins ...........43

Conservation Assessment: Myotis leibii (Eastern SmallFooted Myotis) in the Eastern United States

Sybill Amelon and Dirk Burhans................................57

Conservation Assessment: Myotis septentrionalis (Northern 

Long-Eared Bat) in the Eastern United States

Sybill Amelon and Dirk Burhans................................69
ii Conservation Assessments for Five Forest Bat Species in the Eastern United States
Conservation Assessments for Five Forest Bat Species in the Eastern United States 

Conservation Assessments for Five Forest 

Bat Species in the Eastern United States

Frank R. Thompson, III, Editor1

Preface

The primary goals of this assessment are to consolidate and 

synthesize existing information on the status, distribution, 

conservation, and management considerations for five species 

of forest bats on national forests in Region 9: Pipistrellus 

subflavus (eastern pipistrelle), Nycticeius humeralis (evening 

bat), Myotis austroriparius (southeastern myotis), M. leibii

(eastern small-footed myotis), and M. septentrionalis (northern 

long-eared bat). These species are listed as Regional Forester 

Sensitive Species on one or more forests of the Eastern Region. 

The regional forester listing affords protection for a species on 

the national forests for which it is listed. The forest’s goal is to 

protect and improve the species’ habitat where management 

practices warrant consideration of special habitat needs and to 

ensure that it does not become threatened or endangered. 

A review of the status, biology, and management 

of M. leibii was previously completed for the George 

Washington and Jefferson National Forests in Region 8 

(Erdle and Hobson 2001). A 1999 report produced by Bat 

Conservation International (Bat Conservation International 

1999) summarizes information about forest bats, provides an 

overview of knowledge about relationships between forest 

bats and forest management practices, identifies practices for 

enhancing bat habitat, provides information on key limiting 

factors for Indiana bats (M. sodalis), presents information 

on the North American Bat Conservation Plan, and includes 

excerpts from the land management plans of many national 

forests. In the current assessment, authors incorporated recent 

information from research activities that occurred in subsequent 

years and summarized information on biology, natural history, 

and habitat necessary to address conservation issues for the 

five species. This assessment focuses on the national forests 

and States represented in the Eastern Region. It also includes 

1

 Project leader, U.S. Department of Agriculture, Forest Service, North Central Research Station, Columbia, MO.

information on other States within the range of each of the 

five species. Because of recent advances in technology and the 

increased focus on bat conservation, several new studies related 

to the five focal species have been completed or are in progress. 

The assessment is organized into six chapters. The first 

chapter provides some general background information 

on forest bats and summarizes information needs for the 

conservation of the five species addressed in the assessment. 

Because of a lack of demographic information on any of these 

populations to assess viability, research needs and priorities 

are included in the background section from the perspective 

of theoretical constructs and approaches to obtaining the 

additional information needed to assess conservation and 

management for these species. The five subsequent chapters 

cover taxonomy, description, life history, habitat distribution, 

status, and population biology of each species. 

This assessment was prepared at the request of Region 9 

of the U.S. Department of Agriculture (USDA) Forest Service. 

The assessment highlights information needs of national forests 

but should also be of interest to anyone in bat conservation. 

Each chapter generally follows the format of other conservation 

assessments for species in Region 9 of the USDA Forest 

Service. Manuscripts were prepared by the authors, submitted 

to the editor, and reviewed by individuals with bat biology and 

conservation expertise in a blind, peer-review process overseen 

by the editor. 

This conservation assessment consolidates and synthesizes 

existing information for five species of forest bats. It does 

not represent a management decision by the USDA Forest 

Service. Although authors and reviewers used the best scientific 

information available and consulted subject experts to prepare 

this document, it is expected that new information will arise. 

In the spirit of continuous learning and adaptive management, 

readers who have information that may help conserve the 

subject taxon, are encouraged to contact the Eastern Region of 

the USDA Forest Service Threatened, Endangered and Sensitive 

Species Program at 310 Wisconsin Avenue, Milwaukee, WI, 

53203.
 Conservation Assessments for Five Forest Bat Species in the Eastern United States

Acknowledgments

I thank the authors for their contributions; Fiona Reid for 

illustrations of the species; Bat Conservation International 

and Keith Geluso for distribution maps; Susan Loeb, Richard 

Clawson, and Tommy Parker for their review of the assessment; 

the North Central Research Station Communications Group for 

assistance with the production of the publication; and Region 

9 and the Shawnee National Forest for their support of the 

project. 

References

Bat Conservation International. 1999. Bats in eastern 

woodlands. Washington, DC: U.S. Department of Agriculture 

Forest Service; U.S. Department of the Interior, U.S. Fish 

& Wildlife Service; National Council for Air and Stream 

Improvement. 56 p. http://www.batcon.org.

Erdle, S.Y.; Hobson, C.S. 2001. Current status and conservation 

strategy for the eastern small-footed myotis (Myotis leibii). Tech. 

Rep. 00-19. Reston, VA: Virginia Department of Conservation 

and Recreation, Division of Natural Heritage. 17 p.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 

Status and Conservation of Five Forest 

Bat Species in the Eastern United States: 

Issues and Concerns

Sybill Amelon1

Bats have a higher diversity of behavior, diet, and morphology 

than any other mammalian order. Bats are primary predators 

of nocturnal insects, including many agricultural and forest 

pests; bats, therefore, play a key role in many forest ecosystems 

(Tuttle 2001). The insectivorous family Vespertilionidae (to 

which all five of these species belong) occurs throughout 

temperate and tropical areas and is the largest and most widely 

distributed family of bats (Koopman 1993). Despite this 

diversity, a relative void in knowledge exists for many of North 

America’s bat species. This gap can be attributed in part to the 

fact that many of the techniques and methods used to assess 

habitat use or abundance for other mammals are not suitable for 

bats (Kunz and Kurta 1988b). 

This chapter summarizes some of the conservation issues 

and information needs for eastern forest bats as an introduction 

to conservation assessments of five bat species. The concept 

of bat conservation initially emerged in the late 1940s and 

early 1950s through the efforts of several researchers (Griffin 

1940, Mohr 1952). Efforts to study bats, especially those that 

cluster in roosts, continued through the next three decades 

(Fenton 1970, Kunz and Kurta 1988a, Mumford and Cope 

1964, Tuttle 1976, LaVal et al. 1977). Despite these efforts, 

and largely due to bats’ unique characteristics (small body 

size, volancy, nocturnal activity, low reproductive rate, and 

acoustic orientation), bats remain among the least studied 

wildlife species. Information on the ecology and population 

status of most North American bat species is still very limited. 

Technological advances in the past decade have enhanced 

research and conservation efforts (Kunz 2003, Kunz and Racey 

1998, Barclay et al. 1996), but there continues to be a lack of 

methodologies and consistent, repeatable research approaches 

to provide the information needed to address habitat use, 

population status, and trends. 

Twenty species of bats inhabit eastern North America at 

least part of the year. Of these species, four are federally listed 

1

 Wildlife biologist, U.S. Department of Agriculture, Forest Service, North Central Research Station, Columbia, MO.

endangered (Myotis sodalis, M. grisescens, Corynorhinus 

townsendii virginianus, and C. t. ingens); at least another eight 

species are status undetermined in part of their geographic 

ranges. These numbers indicate that 60 percent (at a minimum) 

of eastern North American bat species are experiencing 

population declines in part or all of their geographic ranges.

(NatureServe 2002).

Declining bat populations are a concern for land 

management agencies throughout the Nation and also for 

international agencies (Kunz and Racey 1998). Conservation 

efforts are hampered by insufficient knowledge of factors 

influencing bat populations, habitat requirements, and 

ecosystem roles. This lack of information greatly impedes 

focused and comprehensive conservation management 

strategies. From the perspective of developing guidelines 

for integrating forest bat habitat needs at strategic and 

operational planning levels, information about the patterns of 

community structure and habitat use at multiple spatial and 

temporal scales is basic and vital (Kunz 1996). Development 

of effective conservation strategies for North American bat 

species will involve consideration of both roosting and foraging 

requirements, as well as the spatial distribution of these 

elements, during each critical life history period. 

Most conservation efforts have centered on rare or 

endangered species. While these efforts are extremely 

important, more abundant species with critical ecosystem 

roles have been less studied. From an ecosystem perspective, 

conservation efforts for these species may be the most 

important (Pierson 1998).

Research Needed To Address Conservation 

Status 

An ultimate goal of a conservation assessment is to address 

the long-term population status and viability of the species 

of interest. To accomplish this goal, information and data on 
 Conservation Assessments for Five Forest Bat Species in the Eastern United States

abundance, reproductive rate, survival rate, age structure, 

and mortality rate are necessary. Most of these factors are 

missing for each of the five forest bat species included in 

this conservation assessment. Therefore, a determination 

of whether these species are secure and likely to remain or 

are declining and not likely to remain, given current land 

management practices, can be based only on theoretical 

premises. Given the lack of information on these five species 

within Region 9 of the U.S. Department of Agriculture (USDA) 

Forest Service, adaptive management approaches that consider 

new information as it becomes available will likely be the best 

approaches to conserving these species.

Research and Monitoring Considerations

Methods designed to survey microchiropterans have been 

developed fairly recently and few researchers consider any 

method paramount for all species or situations (Kunz and Kurta 

1988b). Traditionally, capture in mist nets or harp traps has 

been used to determine relative abundance of species within 

particular habitats (Tidemann and Woodside 1978, Tuttle 

1974). Mist-netting commonly results in declines in capture 

rate when used on successive days (Kunz and Brock 1975, 

Kunz and Kurta 1988a, Stevenson and Tuttle 1982a, Humphrey 

et al. 1979). Bats quickly learn to avoid nets or net locations. 

Although capture techniques enable the collection of some 

demographic information (Racey 1988, Anthony et al. 1981), 

these techniques do not equally sample all species. In addition 

to unequal probability of capture, these methods usually focus 

on a location-specific maximum likelihood of bat activity, such 

as a watering site or travel corridor. The use area represented 

by the captures is usually unknown. Differences in foraging 

strategy and location (Kalko and Schnitzler 1993, Swift and 

Racey 1983, Walsh and Mayle 1991), temporal and spatial 

heterogeneity (Thomas and West 1989), observer experience 

(Kunz 1973), and habitat conditions (Hayes 1997, Grindal et al. 

1992) may affect sampling success. Bat activity tends to vary 

with ambient air temperature, humidity, and insect availability; 

therefore, sampling sites need to be visited more than once 

during the sampling season to account for these temporal and 

environmental variations.

Temperate forest bats typically use a variety of habitats 

for roosting and foraging; these habitats frequently are 

distributed over relatively large spatial distances. Bats do not 

uniformly occupy all available habitats within their potential 

range. Habitats differ in their suitability and, therefore, in their 

influence on the reproductive success of animals. The diverse 

spatial and temporal distribution of habitats used by forest 

bats indicates their distribution, abundance, and conservation 

should be assessed at multiple spatial scales. Even with the 

introduction of bat detectors to allow acoustical identification 

of noncaptured species and miniaturized radio transmitters 

to improve the ability to study bat habitat use requirements, 

broadscale studies in North America are lacking (O’Shea and 

Bogen 2003). 

Bats are particularly vulnerable to environmental changes 

affecting longevity or reproductive success (Walsh and Harris 

1996). In comparison to other small mammals, bats have low 

reproductive rates and long life spans, characteristics that 

require high survival rates to ensure persistent populations 

(Kunz 1996). Some species have very specific roost habitat 

requirements; aggregations in colonies make them susceptible 

to elevated mortality. Loss or modification of roosting and 

foraging habitat may strongly affect species with these life 

history characteristics. It has been suggested that land-use 

change is one of several factors contributing to recent bat 

population declines (Crampton 1995, Robinson and Stebbings 

1997). Reduction of large trees and snags within forested stands 

may affect roost availability and may increase the distance 

between roosting, foraging, and drinking sites. The increased 

energy cost of longer distances between roosting and foraging 

sites may be of particular importance to reproductive females 

(Kunz 1987). As land use changes from forested to nonforested, 

certain species that avoid crossing openings when commuting 

or foraging may be restricted from accessing distant resources 

(Limpens and Kapteyn 1991). Forested corridors connecting 

forested patches have been shown to provide valuable foraging 

habitat as well as travel corridors for bats between roosting and 

foraging sites (van Zyll de Jong 1995). No studies were found 

that quantified relationships between forest bat reproductive 

success relative to quantity and quality of roosting and foraging 

habitats.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 

Species distribution and abundance are often functions 

of the distribution of their resources (Brown 1984). Bats, like 

other animals, are closely associated with the resources of the 

habitats in which they live. Given the dependence of temperate 

bats on flying insects, considerable differences exist in their 

seasonal resource needs. It is impossible for insectivorous 

bats to remain year long in temperate climates where insects 

are unavailable for long periods and maintain endothermic 

temperature regulation; they must migrate or hibernate. 

Temperate region bats are subject to selective pressures 

for both roosting and foraging habitats during the summer 

and migratory periods (Kunz 1982). When suitable habitat 

is available, individual species forage and optimize energy 

budgets in their use of habitats. While many species are flexible 

to some extent in their ability to use prey opportunistically 

within a range of habitat conditions, at some point lack of 

optimum habitat conditions may affect fecundity (Whitaker and 

Long 1998). Sympatric species may overlap in habitat or flight 

style, but they are probably not equally effective in catching 

prey compared to the energy they use (Ahlen 1981). Although 

their habitats may overlap, their spatial or temporal niches 

are sufficiently different to allow coexistence of many species 

in the same areas. Bats select roosts that provide suitable 

thermal conditions necessary for metabolic and reproductive 

demands (Barclay 1991, Kunz and Stern 1995), protection from 

predators (Fenton et al. 1983), and proximity to foraging sites 

(Geggie and Fenton 1985, Kunz 1982). Since most temperate 

region bats mate during the fall, encountering mates should not 

affect selection of summer habitats. Few studies have examined 

the relative influences of foraging and roosting requirements on 

bats’ habitat selection. 

Forests vary in structure and composition with age, 

productivity, and disturbance history. Therefore, the habitats 

they offer for bats differ in amount of foraging space and 

suitable roosting sites. There are conflicting indications 

regarding whether sympatric species of insectivorous bats’ use 

of available habitats differs. 

Existing Surveys, Monitoring, and Research

Many of the national forests in Region 9 and the associated 

State Departments of Natural Resources are conducting annual 

or biannual hibernation population counts for cave-dwelling 

species. In some instances, these counts are targeted at the 

federally listed Myotis sodalis (Indiana bat) and M. grisescens

(gray bat). In other instances, hibernacula counts have the intent 

of counting hibernating individuals of any bat species present. 

In addition, many national forests are conducting summer mistnet or acoustic surveys to identify the presence and locations of 

forest bat species. 

Survey Protocol

While mist-net surveys are fairly consistent in design and 

implementation, considerable variation exists in determining 

“on the ground” selection of mist-net locations. In addition, the 

overall quantity of locations recommended in the Indiana Bat 

Draft Recovery Plan (USFWS 1999) (a guide frequently used 

by national forests to design mist-net surveys) was originally 

designed to be used on a relatively small “project location” 

rather than as a tool to examine distributions over landscapescale areas. 

Research Priorities

Based on information obtained from bat researchers, U.S. Fish 

& Wildlife Service, recovery plans, and forest plans, the following research needs are identified with an indication of relative 

priority (from a species viability perspective) (Brack and Tyrell 

1990; Clark 2001; Kunz 1996; Kunz and Kurta 1988b; Kunz 

and Robson 1995; Kurta and Murray 2002; Norberg 1998; 

O’Shea and Bogen 2003; Pierson 1998; Rabot 1999; Racey 

1988; Stevenson and Tuttle 1982b; Taylor 2003; Turchin 1998; 

Tuttle 2000; USFWS 1983; Williams 2001; Barclay et al. 1996, 

1999; Brigham et al. 1997; Carroll et al. 2002; Carter et al. 

1999; Gopukumar et al. 2003; Webb et al. 1996).
 Conservation Assessments for Five Forest Bat Species in the Eastern United States

Monitor Population Trend and Abundance

1. Develop and validate methods to assess abundance of 

forest bat species during nonhibernating periods. (High 

priority.)

2. Develop a long-term population monitoring strategy for 

nonhibernating periods. (High priority but subsequent to 

#1 above.) 

Determine Terrestrial Habitat Relationships

1. Determine summer habitat use relationships (roosting 

and foraging) for forest bats across multiple spatial and 

temporal scales within the range of each species, by 

demographic group. This effort should be coordinated 

across the range of the species to provide for adequate 

sample size to evaluate meaningful relationships. (High 

priority but subsequent to Monitor Population Trend and 

Abundance section.)

2. Evaluate habitat quality by associating habitat parameters 

with reproductive success. (Due to the patchy distribution 

of most forest bat species, design studies using baseline 

or pre-treatment to post-treatment at the same location.) 

(High priority but subsequent #1 above and to Monitor 

Population Trend and Abundance section.)

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based on sounds. Myotis. 18-19: 128-136.

Anthony, E.L.; Stack, M.H.; Kunz, T.H. 1981. Night roosting 

and the nocturnal time budget of the little brown bat Myotis 

lucifugus: effects of reproductive status, prey density, and 

environmental conditions. Oecologia. 51: 151-156.

Barclay, R.M.R. 1991. Population structure of temperate zone 

insectivorous bats in relation to foraging behaviour and energy 

demand. Journal of Animal Ecology. 60: 165-178.

Barclay, R.M.R.; Fullard, J.H.; Jacobs, D.S. 1999. Variation 

in the echolocation calls of the hoary bat (laci): influence of 

body size, habitat structure, and geographic location. Canadian 

Journal of Zoology. 77: 530-534.

Barclay, R.M.R.; Kalcounis, M.C.; Stefan, C.; et al. 1996. Can 

external radiotransmitters be used to assess body temperature 

and torpor in bats? Journal of Mammalogy. 77(4): 1102-1106.

Brack, V.; Tyrell, K. 1990. A model of the habitat used by the 

Indiana bat (Myotis sodalis) during the summer in Indiana: 

1990 field studies. Indianapolis: Indiana Department of 

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Brigham, R.M.; Grindal, S.D.; Firman, M.C.; Morissette, J.L. 

1997. The influence of structural clutter on activity patterns of 

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Brown, J.H. 1984. On the relationship between abundance and 

distribution of species. American Naturalist. 124(2): 255-279.

Carroll, S.K.; Carter, T.C.; Feldhammer, G.A. 2002. Placement 

of nets for bats, perception of perceived fauna. Southeastern 

Naturalist. 1: 193-198.

Carter, T.C.; Menzel, M.A.; Chapman, B.R.; et al. 1999. A new 

method to study bat activity patterns. Wildlife Society Bulletin. 

27(3): 598-602.

Clark, D.R., Jr. 2001. DDT and the decline of free-tailed bats 

(Tadarida brasiliensis) at Carlsbad Caverns, New Mexico. 

Archives of Environmental Contamination and Toxicology. 40: 

537-543.

Crampton, L. 1995. Habitat selection by bats and the potential 

impacts of forest fragmentation on bat populations in aspen 

mixed-wood forests in northern Alberta. Calgary, AB: 

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Fenton, M.B. 1970. Population studies of Myotis lucifugus in 

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Fenton, M.B.; Merriam, H.G.; Holroyd, G.L. 1983. Bats of 

Kootenay, Glacier and Mount Revelstoke National Parks in 

Canada: identification by echolocation calls, distribution and 

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Hayes, J.P. 1997. Temporal variation in activity of bats and 

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 Conservation Assessments for Five Forest Bat Species in the Eastern United States

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Pierson, E.D. 1998. Tall trees, deep holes and scarred 

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Rabot, T. 1999. The Federal role in habitat protection. 

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10 Conservation Assessments for Five Forest Bat Species in the Eastern United States
Conservation Assessments for Five Forest Bat Species in the Eastern United States 11

Conservation Assessment: Pipistrellus 

subflavus (Eastern Pipistrelle) in the 

Eastern United States

Sybill Amelon1

Taxonomy and Nomenclature

The eastern pipistrelle, [Pipistrellus subflavus (F. Cuvier 1832) 

(f. L. sub under; flavus yellow—i.e., somewhat yellow)], 

belongs to the class Mammalia, order Chiroptera, family 

Vespertilionidae, subfamily Vespertilioninae, genus/species 

Pipistrellus subflavus (1959). The genus Pipistrellus (formerly 

Vespertilio) includes 48 species (Hornacki et al. 1982). 

Four subspecies of P. subflavus are recognized (Davis 

1959):

1. P. s. clarus (Baker 1954: 585). Type locality 2 miles (mi) 

west (W) of Jimenez, 850 feet (ft), Coahuila, Mexico.

2. P. s. floridanus (Davis 1957: 213). Type locality 

Homosassa Springs, head Homosassa River, Citrus 

County, Florida.

3. P. s. subflavus (F. Cuvier 1832: 17). Type locality Eastern 

United States, probably Georgia. Restricted by Davis 

(1959) to Le Conte Plantation, 3 mi southwest (SW) of 

Riceboro, Liberty County, Georgia, (V. erthrodactylus 

temminck, V. monticola audubon and bachman, and

obscurus miller are synonyms).

4. P. s. veraecruscis (Ward 1891: 745). Type locality Las 

Vigas, Canton of Jalapa, Veracruz, Mexico.

P. subflavus subflavus is the most widely distributed race. 

Menu (1984) proposed changing the genus from Pipistrellus

to Perimyotis based on dental morphology. To date, inadequate 

evidence exists to support this change.

Description of Species

Pipistrellus subflavus is the smallest bat found throughout the 

Eastern and Midwestern States. Characteristic measurements 

include wingspan, 200 to 260 millimeters (mm); total length, 

74 to 98 mm; tail length, 30 to 46 mm; hindfoot, 7.3 to 10.5 

mm; ear, 11 to 14.5 mm; forearm, 31.4 to 36 mm; and skull, 

12.3 to 13.3 mm. Weight ranges from 4.6 to 7.9 grams (g). 

Females are consistently heavier than males. Mean female 

spring and fall weights are 5.8 and 7.9 g, respectively; whereas, 

mean male spring and fall weights are 4.6 and 7.5 g, respectively. Pelage color varies from pale yellow-orange to dark 

reddish-brown, to grayish-brown, and sometimes nearly black. 

A characteristic feature is the distinctly tricolored hair. Hairs 

are dark at the base and tip and lighter yellowish or brownish 

in the center. Juvenile pelage is darker than adult pelage. The 

forearm of the wing is distinctly pinkish and lighter than the 

dark, nearly black wing membrane. The anterior third of the 

uropatagium is furred. The ears are longer than they are wide 

and extend slightly past the end of the nose when pressed forward. The tragus is straight, tapers to a rounded tip, and is less 

than half the ear length. The hindfoot is large, more than half as 

long as the tibia. The dorsal surface of the foot and toes is covered with conspicuous hair. The calcar is not keeled; it exceeds 

the tibia in length. The third, fourth, and fifth metacarpals are 

subequal. The skull is short with a broad rostrum. The dental 

formula is i 2/3, c 1/1, p 2/2, m 3/3, total 34. A characteristic 

feature of this species is the presence of one small premolar in 

the upper and lower jaws (Fujita and Kunz 1984, Hamilton and 

Whitaker 1979).

Biology, Life History, and Natural History

Reproductive Biology and Phenology

Eastern pipistrelles are polygamous with breeding activity 

occurring in the fall and potentially into spring. Spermatozoa 

are stored in the uterus of hibernating females until spring 

ovulation (Guthrie 1933). Females begin arriving from 

hibernacula in late April (southern areas) through May 

(northern areas). Maximum numbers are reached from late May 

1

 Wildlife biologist, U.S. Department of Agriculture, Forest Service, North Central Research Station, Columbia, MO.
12 Conservation Assessments for Five Forest Bat Species in the Eastern United States

to late June (south to north, respectively). Female P. subflavus

may enter daily torpor in early weeks of pregnancy but rarely 

in late pregnancy and lactation (Hoying and Kunz 1998). 

Jones and Suttkus (1973) found male to female sex ratios were 

approximately equal. 

The gestation period, measured from implantation to 

parturition, lasts at least 44 days (Wimsatt 1945). Two pups 

are typical, with mean litter size of 1.9 to 1.95 (Cope and 

Humphrey 1972, Hoying and Kunz 1998, Wimsatt 1945). The 

relative mass of each pup at birth (expressed as a percentage 

of the female’s post partum body mass) ranges from 23 to 

27 percent. The litter weight ranges from 44 to 54 percent 

(Hoying and Kunz 1998). These relative weights represent the 

upper extreme of maternal effort among vespertilionid bats. 

Parturition occurs from late May through the first 3 weeks of 

June in Florida (Jennings 1958); from early June to early July 

in Missouri (LaVal and LaVal 1980), Illinois (Feldhammer et 

al. 2001), Pennsylvania (Lane 1946), the city of Terre Haute in 

Indiana (Whitaker 1998), and eastern Massachusetts (Hoying 

and Kunz 1998); and from late June to early July in southern 

Indiana (Cope and Humphrey 1972) and Vermont (Davis 

1963). These data suggest that parturition is more synchronous 

in northern populations. 

Newborn pipistrelles are born hairless and pink with eyes 

closed and pinnae folded (Hoying and Kunz 1998). They are 

capable of making loud clicking sounds that may aid their 

mothers in retrieving them (Hoying and Kunz 1998). Neonates 

become fully furred during their first week (Whitaker 1998). 

Forearm length and body mass increase linearly for the first 

2 weeks after birth; the rate of increase is then reduced. The 

relative length of the forearm reaches approximately 95 percent 

of adult size, and the body mass reaches 70 to 80 percent of 

adult mass by 3 weeks of age, the approximate time of first 

flight (Hoying and Kunz 1998, Whitaker 1998). Ossification 

of the epiphyses is nearly complete by 42 to 48 days (Hoying 

and Kunz 1998). Several factors may influence postnatal 

growth in bats; climate and food availability may be the most 

important (Hoying and Kunz 1998, Orr 1970, Stevenson and 

Tuttle 1982). Low ambient and roost temperatures may result in 

prolonged periods of food shortage and expenditure of energy 

on thermoregulation, which may contribute directly to low 

postnatal growth rates (Hoying and Kunz 1998). Parturition 

synchrony, combined with clustering in maternity colonies, 

should increase metabolic rates and lead to rapid postnatal 

growth rates (Stevenson and Tuttle 1982, Kurta et al. 1989). If 

females require periods of torpor due to low temperatures and 

low food availability, reduced milk output and energy output to 

the pups could contribute to their reduced growth rate (Hoying 

and Kunz 1998). Whitaker (1998) described volant juveniles 

at approximately 4 weeks of age; these juveniles foraged 

with their mothers for at least an additional week. The adult 

females abandoned the maternity roosts soon after weaning; the 

juveniles remained longer.

Histological data suggest that eastern pipistrelle 

males behave in a manner similar to other North American 

vespertilionid bats in displaying testicular gametic function in 

summer followed by a regression of the gonads before mating 

and hibernation (Krutzsch and Crichton 1986). The eastern 

pipistrelle, however, differs in the retention of some testicular 

spermatozoa and the fact that only slight differences occur 

in summer versus winter activity of the accessory glands. 

These data suggest that hibernation is longer and the period 

of sexual quiescence is shorter in the eastern pipistrelle than 

in other temperate vespertilionids. Males may not reach full 

reproductive maturity until their second year (Krutzsch and 

Crichton 1986).

Subadult pipistrelles were observed to first arrive at 

hibernacula in early August in Missouri (LaVal and LaVal 

1980). Data available from the literature suggest that differences 

in maturity rates vary by geographical location of the 

population. Davis (1963) observed that subadults in Vermont, 

Ontario, and Quebec had not undergone first molt and that 

epiphysis had not completely closed at the time of entry to 

hibernacula. No apparent growth occurred during hibernation, 

and subadults were recognized at departure from hibernacula 

in April and May. Conversely, subadults from West Virginia, 

Kentucky, and Florida molted in autumn, and the epiphyses 

were closed at the time of entry to hibernacula. Hoying and 

Kunz (1998) found epiphyses were closed by 48 days of age in 

Massachusetts but determined that climatic factors influenced 

the rate of maturity. Based on physiological conditions, 

estimates indicate that sexual maturity likely occurs between 

3 and 15 months, depending on environmental conditions 

(Krutzsch and Crichton 1986, Hoying and Kunz 1998). 
Conservation Assessments for Five Forest Bat Species in the Eastern United States 13

Ecology and Behavior

Bats require highly advanced morphological adaptations in 

their wing system for efficient flight (Norberg 1981, 1986; 

Norberg and Raynor 1987). Flight mechanics may impose 

significant limits on behavior; bats with different foraging 

behavior require differing wing structures to minimize energy 

costs. Norberg (1981) and Norberg and Raynor (1987) describe 

the wing adaptations that influence flight characteristics. Wing 

size is described by wing loading (WL), which is the weight 

(M) divided by the wing area (S) expressed in newtons per 

square meter (N/m2). Slow-flying bats have large wings and 

low WLs; bats with smaller wings have to compensate with 

faster speeds for their body size. Wing shape is described by the 

aspect ratio (AR), which approximates narrowness of the wing. 

Findley et al. (1972) found the AR index to be the most useful 

variable in predicting flight speed. 

Comparisons of wing morphology with known habitat 

associations suggest that bats with low ARs foraged in highclutter forest areas, while those with high ARs foraged in 

areas that are more open. Forest clutter refers to the amount 

of interference to echolocation sound waves that exist in a 

particular patch of forest. The higher the density of forest 

vegetation, the greater the clutter effect to sound wave 

transmission. Farney and Fleharty (1969) examined 40 P. 

subflavus and calculated an AR of 6.92 + 0.037 and a WL 

of 0.063 + 0.002. These values indicate low WL and higher 

wingtip shape. Pipistrelles frequently alternate echolocation 

signals depending on the level of clutter encountered, indicating 

they are adapted to foraging in canopy gaps, edge habitats, and 

open habitats (Veilleux et al. 2003).

Winter hibernacula and summer maternity sites are 

generally in different locations (Davis 1959a; Griffin 1934, 

1936; Guthrie 1933; McNab 1974a). Disproportionate sex 

ratios have been reported (Brack and Twente 1985, Davis 

1964, Hall 1962, Jones and Pagels 1968) and attributed to 

higher survival rates in males and differences in selection of 

hibernacula between males and females. LaVal and LaVal 

(1980) observed large numbers of these bats captured at 

hibernacula in Missouri in late April and May and again in 

late July and August and suggested that this species may enter 

hibernacula earlier and leave hibernacula later than other 

species. 

In spring, P. subflavus disperse from hibernacula and 

migrate to maternity roosts. Maternity colonies have been 

reported in trees, caves, and rock crevices, as well as in road 

culverts, buildings, and other manmade structures (Hoying and 

Kunz 1998, Humphrey 1975, Jones and Pagels 1968, Jones and 

Suttkus 1973, Lane 1946, Humphrey et al. 1976, Sandel et al. 

2001, Veilleux et al. 2003). During the maternity period, sexes 

are segregated; females remain in small maternity colonies 

and males remain solitary (Findley 1954, Lane 1946). The 

longest migration distance recorded for P. subflavus was 52.8 

kilometers (km). A female was banded at Sheffield, MA, in 

April and recovered at Katonah, NY, during hibernation. Adult 

female eastern pipistrelle bats at a maternity colony in eastern 

Massachusetts spent 77 percent of their time in day roosts at 

rest, 16 percent of their time alert, and 7 percent of their time 

grooming (Winchell and Kunz 1996). The highest activity 

levels occurred immediately after morning return to the roost 

from foraging and immediately before evening departure. 

Obligate associations with other species have not been 

observed. Davis and Mumford (1962) observed red bats as 

the most consistent associate species on its feeding grounds in 

summer, although evening bats (Nycticeius humeralis), Indiana 

bats (Myotis sodalis), big brown bats (Eptesicus fuscus), 

and silver-haired bats (Lasionycteris noctivagans) were also 

collected in shotgun samplings.

Echolocation characteristics in open habitats indicate the 

eastern pipistrelle produces 5 milliseconds (ms) of frequency 

modulated/constant frequency (FM/CF) echolocation calls. Two 

harmonics have been noted: the first with energy between 35 

and 19 kilohertz (kHz) and the second with energy between 70 

and 38 kHz (MacDonald et al. 1994).

Hibernation 

Mammalian hibernation is characterized by periods of torpor 

interrupted cyclically by spontaneous arousal. Individuals 

aroused during hibernation tend to fly or move around between 

periods of torpor. Eastern pipistrelles appear to be obligate 

hibernators (Brack and Twente 1985, McNab 1974a, Sandel et 

al. 2001). Hibernation occurs singly or in very small groups 

in caves, mines, road culverts, and other manmade structures 

and is often associated with other species including Myotis 

lucifugus, M. grisescens, M. septentrionalis, M. austroriparius, 
14 Conservation Assessments for Five Forest Bat Species in the Eastern United States

M. sodalis, and Eptesicus fuscus (Brack and Twente 1985, 

Davis 1964, McNab 1974b, Mumford and Whitaker 1975, 

Myers 1964, Sandel et al. 2001). Eastern pipistrelles frequently 

use portions of hibernacula with constant, lower temperatures 

(Fitch 1966, Hall 1962) and higher humidity (Ploskey and 

Sealer 1979).

The expenditure rate of energy during hibernation is a 

critical factor affecting survival of the eastern pipistrelle bat. 

Ploskey and Sealer (1979) estimated the minimum quantity of 

fat required by eastern pipistrelles at the beginning of hibernation to be 0.91 g fat/g fat-free dry mass. An average-weight 

eastern pipistrelle bat (4.6 to 5.6 g) entering hibernation would 

need to weigh 6 to 8 g. Fat-free dry mass remains relatively 

constant throughout the hibernation period. Fat content varies 

seasonally, with the highest fat index occurring in October 

and the lowest in May (Ploskey and Sealer 1979). Females had 

significantly larger fat deposits, which may be a source of extra 

energy needed for gestation or may simply reflect differences 

in metabolism or hormonal balance between the sexes (Herreid 

1964). During hibernation, male P. subflavus decrease in mass 

from September to April, while females decrease in mass from 

September to March (Fitch 1966). Total loss of mass for males 

is higher (39 percent) than for females (29 percent).

In laboratory experiments with P. subflavus found hibernating, individuals responded to increasing temperatures by 

increasing heart rate (Davis and Reite 1967). When temperatures approached 0 o

C, bats aroused from hibernation. McNab 

(1974a) found P. subflavus to be an obligate hibernator even in 

Florida, where ambient temperatures remain high even in cave 

environments. The inability to avoid hibernation was attributed 

to the species’ reproductive requirements; in particular, the 

long period of torpor required for successful sperm storage in 

the female. Krutzsch and Crichton (1986) suggested that the 

reproductive period is extended in this species as a function of 

increased duration of hibernation, that testicular spermatozoa 

persist longer, and that accessory glands are not differentiated 

between winter and spring/summer. Pipistrelles, more frequently than other temperate hibernating bats, remain in deep torpor 

for longer periods between arousals from hibernation. Some 

have suggested that this length of torpor may be related to the 

pipistrelle’s smaller size and longer total time spent in hibernation (McNab 1974a). Brack and Twente (1985) found a period 

of 111 days was the maximum duration of hibernation between 

arousals for eastern pipistrelle bats. 

The eastern pipistrelle bat is capable of a 30-fold range in 

aerobic metabolism between hypothermia of hibernation and 

foraging flight (Lechner 1985). Examination of bats between 

fall (mean body weight = 6.22 g) and spring (mean body 

weight = 4.58 g) revealed no significant differences for total 

lung volume, alveolar surface area, mean septal thickness, or 

membrane diffusing capacity. Lechner (1985) found, despite 

the loss of 13 percent of fresh weight for both the heart and 

lungs and 25 percent for the liver during hibernation, blood-free 

protein and DNA content were not altered, indicating resistance 

to hibernation-induced proteolysis.

Food Habits

Analysis of stomach contents (Whitaker 1972) and analysis 

of fecal pellets (Brack and Finni 1987, Griffith and Gates 

1985) revealed that the diet of P. subflavus consists of species 

of coleopterans, homopterans, dipterans, hymenopterans, and 

lepidopterans. Prey items primarily consist of small insects 

ranging in size from 4 to 10 mm in length. Lepidopterans 

were found to be consumed more than relative availability and 

coleopterans and homopterans less than relative availability in 

Georgia (Carter et al. 1998). Carter et al. (2003) examined fecal 

pellets from 27 eastern pipistrelle bats in West Virginia and 

found their diet to be highly variable. Lepidoptera, coleoptera, 

hymenoptera, hemiptera, diptera, homoptera, and tricoptera 

were fairly equally represented.

Mortality and Predation Factors

Based on fall hibernacula counts of subadults and juveniles, 

juvenile mortality during the period of early flight may be as 

high as 50 percent (Hoying and Kunz 1998). Failure to store 

sufficient fat reserves may cause significant mortality among 

subadults during the first hibernation period (Davis 1966). 

Mortality from predation, accidents, disturbance, and inclement 

weather has been documented although no consistent predators 

or causes of mortality were noted (Gillette and Kimbrough 

1970). Predators included a vole (Martin 1961), a frog (Creel 

1963), an American swallow-tailed kite (Lee and Clark 1993), 

and a hoary bat (Lasiurus cinereus) (Bishop 1947). Mortality 

from flooding (Baker 1978) and snowstorms (Rysgaard 1941) 

have been recorded. 
Conservation Assessments for Five Forest Bat Species in the Eastern United States 15

Mortality from bands has been reported in several bat 

species. Improved band designs have become available within 

recent years, although even these improved designs may not 

be appropriate for all species. Nationally coordinated banding 

efforts still do not exist in North America. 

Endoparasites include trematodes; when infected, 

helminth load is highest in autumn (Nickel and Hansen 1967). 

Ectoparasites include chiggers, with reported infestation rates 

of 23 to 24 percent, and spinturnicid mites (Whitaker and 

Loomis 1979, Whitaker and Mumford 1973). 

Longevity

The highest longevity record for P. subflavus is for a male 

that was captured in Illinois 14.8 years after its initial capture 

(Walley and Jarvis 1971). Other records include ages of 

approximately 11 years (Paradiso and Greenhall 1966), 10 

years (Mohr 1952), and 6 years (Hitchcock 1965). Davis and 

Hitchcock (1965) reported high mortality of juveniles during 

their second summer. Davis (1966) stated that high mortality 

occurs between the first and second hibernation periods, most 

likely during winter. Jones and Pagels (1968) argued that, 

because survivorship was based on band return at a specific 

location, variation in survivorship observed by Davis (1966) 

could not be distinguished from the dispersal of individuals to 

new areas. 

Banding Data

Banding efforts by Miller and Allen (1928) marked initial 

attempts to study migration in North American bats. Four 

P. subflavus bats were banded and subsequently recovered 

3 years later when they returned to the summer roost where 

they were initially banded. Success of banding studies is 

highly variable, largely based on the species of study and the 

questions being addressed. Some species are less likely to be 

recaptured at summering sites due to trap avoidance, and some 

species are more sensitive to banding injuries. Due largely to 

these limitations, large-scale banding efforts were abandoned 

(Greenhall and Paradiso 1968). 

Site Fidelity

High site fidelity (30 to 60 percent) has been reported for P. 

subflavus for hibernacula (Hahn 1908, Menzel et al. 1999), 

with many individuals remaining in the same location within 

hibernacula for several weeks (Veilleux et al. 2003). 

Fewer studies have examined site fidelity associated with 

maternity colonies. Whitaker (1998) observed six maternity 

colonies in buildings in Indiana and found P. subflavus to 

switch roosts frequently during the maternity period both with 

and without volant young. These observations suggest that even 

in this species, which has a high litter mass to maternal weight 

ratio, the practice of roost switching (and moving young) is a 

common occurrence similar to that documented for this and 

other tree-roosting species. Jones and Suttkus (1973), working 

in Louisiana, found nearly 60 percent of the females observed 

used only one building as a roosting site. Females were 

observed to have higher site fidelity to roosting location than 

males did. Males observed roosting in the same study area were 

found to have lower site fidelity to a single building. Veilleux 

et al. (2001) examined roost site fidelity for 18 pregnant or 

lactating females and found these bats used 2.8 + 1.7 roost 

trees and changed trees 2.3 + 1.9 times, on average. Colony 

sizes were found to be similar before and after roost changes, 

suggesting that colonies may change roosts as groups. 

Distribution

P. subflavus occurs throughout most of eastern North and 

Central America and into parts of the Midwestern United States 

(Fujita and Kunz 1984). The eastern border of the range of the 

subspecies subflavus follows the Atlantic coast from Georgia to 

Nova Scotia. Broders et al. (2001) reported new records from 

southern coastal New Brunswick. The northern border extends 

from central Minnesota eastward through southeastern Ontario 

and Quebec. Minimal records are reported from southeastern 

Michigan (Kurta 1982). The southwestern border extends from 

the Edwards Plateau in Texas south to Tamaulipas, Mexico 

(Davis 1959b). The Gulf of Mexico along Florida’s panhandle 

marks the southern border of the range. P. s. floridanus occurs 

throughout peninsular Florida and southeastern Georgia. P. s. 

clarus extends from northern Coahuila, Mexico, to Texas and 

is separated from the range of P. s. subflavus by the Rio Grande 

Valley (Davis 1959a). P. s. veraecrucis is known from tropical 

lowlands and mountainous sections of eastern Mexico and 

northeastern Honduras (Davis 1959a). Brack and Mumford 

(1984) indicated accordance between the southern limit of 
16 Conservation Assessments for Five Forest Bat Species in the Eastern United States

the Wisconsinan glaciation and the northern range of the 

pipistrelle; they pointed out that captures north of the glacial 

limit were always along riparian habitats. Barbour and Davis 

(1969) stated that the bat was found over watercourses but not 

over forests or fields. Recently, western range expansion has 

been documented (Geluso et al. 2004) (fig. 1). 

Bats remained at roost trees for 6 days, on average, before 

moving to new roosts; they traveled approximately 19 to 139 

m between roost trees. P. subflavus have been noted to roost 

among the foliage of trees (Davis and Mumford 1962, Findley 

1954, Veilleux et al. 2003), in buildings (Whitaker 1998), in 

the twilight zone of caves (Humphrey and Cope 1976), and in 

Spanish moss (Davis and Mumford 1962). Menzel et al. (1999) 

reported an individual female roosting in live oak trees in the 

understory of an oak-pine community type. Other tree species 

used by this individual included Ilex vomitoria, Vaccinnium 

arboreum, Persea borbonia, and Pinus spp. This female also 

roosted in clumps of Spanish moss. Lacki and Hutchinson 

(1999) observed eastern pipistrelles roosting in rock shelters 

and cliffs in Kentucky. The general landscapes used by eastern 

pipistrelles include partly open country with large trees and 

woodland edges. 

Foraging Habitat

P. subflavus seem to prefer watercourses for foraging but are not 

restricted to these sites (Davis and Mumford 1962). P. subflavus 

primarily feed over water and at forest edges (Barley 1923, 

Blair 1935, Bowles 1975, Schmidly et al. 1977). This species 

uses farm ponds and other water sources provided some trees 

are available in the vicinity (Barbour and Davis 1969, Davis 

and Mumford 1962). This species has a relatively slow, erratic 

pattern of flight (Hoying and Kunz 1998, Paradiso 1969). 

Gould (1955) reported pipistrelles to have acquired 1.4 to 1.7 g 

of food during a 30-minute foraging bout. Foraging behavior 

of light-tagged eastern pipistrelles included long sessions of 

foraging activity (84 to 294 seconds per foraging episode) just 

over the top of streamside vegetation and taller streamside 

trees (Harvey 1999, Caire et al. 1984). This species is believed 

to intermittently forage from dusk to midnight and then have 

another period of feeding activity toward dawn. Veilleux et al. 

(2003) found eastern pipistrelle females foraging up to 4.3 km 

from their roost locations. 

Hibernation Period (October to April)

P. subflavus use caves, mines, and rock crevices as hibernation 

sites in winter, roosting in warmer parts of the cave or mine 

(Speakman et al. 1991). This species is believed to rarely fly 

outside the hibernation site in winter (Whitaker and Rissler 

Habitat Requirements

Maternity Period (May to August)

Roosting Habitat

Veilleux et al. (2003) found lactating female pipistrelle bats (2003) found lactating female pipistrelle bats 

in Indiana roosting exclusively in dead clusters of leaves 

(65 percent), live foliage (30 percent), or squirrels nests (5 

percent). Frequently used tree species include several oaks. 

Mean roost tree height was 20.8 m + 7.1 stand density (SD). 

Roost height from the ground was 15.7 + 6.8 m. Roost tree 

diameter at breast height was 33.2 centimeters + 18.8 SD. 

Source: Geluso et al. 2004.

Figure 1. Westward range expansion of the eastern 

pipistrelle (Pipistrellus subflavus) in the United States, 

including new records (open circles) from New Mexico, 

South Dakota, and Texas.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 17

1992) and to accept full gates on the caves or mines used for 

hibernation (Currie 1999). Menzel et al. (1999) found the 

average humidity of female P. subflavus roosting sites to be 

higher than those used by males (64.2 percent and 61.5 percent, 

respectively) during hibernation in Georgia mines. Roost height 

and temperature were not different between sexes; temperatures 

of –6 to14 oC have been documented (Barbour and Davis 1969, 

McNab 1974b, Sandel et al. 2001). This temperature range is 

among the highest documented for eastern forest bat species 

(Rabinowitz 1981). Other factors found to positively correlate 

with higher roosting densities are presence of standing water, 

size of mine entrance, and gradient of mine entrance (Menzel et 

al. 1999). Minimum temperature was found to be a significant 

predictor of pipistrelle abundance at hibernating locations in 

Texas, with occupancy being greatest in December and January 

(Sandel et al. 2001). In Arkansas, eastern pipistrelle bats used 

54 of 93 surveyed caves (Briggler and Prather 2003). The bats 

tended to use larger caves with higher thermal stability and 

east-facing openings. More eastern pipistrelle bats were found 

in caves with a wider range of temperature regimes within a 

season but less variation between seasons. 

Potential Threats

Natural or Human Factors

Factors contributing to bat population declines have been 

attributed to pesticide poisoning (Geluso 1976, Reidinger 1976, 

Tuttle 1979), chemical pollution, siltation of waterways (Hall 

1962, Tuttle 1979), flooding (Hall 1962), and disturbance by 

humans (Clark and Alexander 1983, Clark and Lamont 1976, 

Clark and Rattner 1987, Currie 1999, Fenton 1970, Humphrey 

1978, O’Shea and Clark 2001, Reidinger and Cockrum 1978, 

Sheffield and Chapman 1992, Tuttle 1981, Esher et al. 1980, 

Humphrey et al. 1976). Disturbance during the hibernation 

or maternity periods is a significant factor in the widespread 

decline of cave- and mine-dependent bat species (Clark and 

Alexander 1983, Clark et al. 1983). The foremost factor leading 

to population declines is unwarranted destruction of roost sites, 

particularly hibernacula (Cope et al. 1991). North American 

bat conservation efforts have therefore focused primarily on 

protecting hibernacula from vandalism and physical alterations.

Food chain poisoning by pesticides—in particular 

insecticides such as organochlorines and anticholinesterase—

has been demonstrated to have negative impacts on 

insectivorous bats (Powell 1983). Lipids of brown fat from four 

species of hibernating bats in Maryland (including P. subflavus) 

contained significantly higher concentrations of DDE (FIA 

2003) than those found in white fat. Brown fat facilitates 

arousal from hibernation by producing heat through rapid 

metabolism of triglycerides. In vitro, P. subflavus brain ATPases 

were sensitive to DDT and DDE at concentrations considerably 

below environmental levels (Esher et al. 1980). A single P. 

subflavus collected along Virginia’s Holston River contained 

elevated levels of mercury (Hg), suggesting a possible 

relationship to Hg-contaminated industrial effluents. 

Present or Potential Risks to Habitat 

Although there is still much to learn about this species’ 

maternity and winter habitat requirements, initial information 

concerning summer habitat indicates use of deciduous forest 

trees in landscapes that include interspersed nonforested 

patches. Since this habitat is widespread and abundant in 

Eastern North America, the primary risk to habitat may involve 

availability and suitability of winter habitat or pesticide 

exposure in summer habitats. The widespread recreational 

use of caves and indirect or direct disturbance by humans 

during the hibernation period pose the greatest known threat 

to this species. Because of this species’ consistent use of deep 

torpor during hibernation, response to nontactile disturbance 

in the form of lights and movement near hibernating locations 

may not be detectable until well after the activities occur. 

Bats in deep torpor may take an hour or more to arouse from 

disturbance. In addition, this species hibernates singly, often 

in very accessible locations within hibernacula, which, in 

combination with slow arousal, makes P. subflavus highly 

susceptible to tactile disturbance or persecution.

Inadequacy of Existing Regulatory Mechanisms

Early bat roost protection efforts focused on eliminating or 

reducing disturbances by installing informative signs or “bat 

friendly” gates and fences. The purpose was to control human 

disturbance during critical hibernation and maternity periods. 

In some cases, these efforts were disadvantageous because of 
18 Conservation Assessments for Five Forest Bat Species in the Eastern United States

limited understanding of bat behavior and cave microclimate 

factors. Early gate designs in some instances restricted natural 

air flow patterns, resulting in inappropriate temperatures during 

at least some portion of the hibernation period. 

Protecting natural and manmade winter roosting structures 

would be one of the highest priorities for this species. Funding 

to facilitate these protection measures is often unavailable for 

nonlisted species.

Population Status

Rangewide

Both Global Heritage Status and National Heritage Status 

are “5,” indicating the species is globally and nationally 

demonstrably widespread and common.

State

Individual State Heritage Status is described in State 

Summaries and in table 1.

Table 1. Population status of Pipistrellus subflavus by State1.

State or 

province Status2 Current estimate Summer habitat (reported) Winter habitat (reported)

Alabama S5 Caves

Arkansas S4 Caves

Connecticut S4

Delaware S5

Florida SU

Georgia S5 Common in the mountains and piedmont; 

locally abundant on the coastal plain

At forest edges, over forest canopy, 

and over bodies of water

Caves, rock crevices, 

old mines, hollow 

trees, buildings, and 

clumps of Spanish 

moss

Illinois S5 Caves

Indiana S4 Buildings and trees Caves

Iowa S4

Kansas S4 Rocky areas, buildings, and trees Caves, mines, and 

sinkholes

Kentucky S4, S5 Common across Kentucky in summer 

and during migration; nearly every cave 

across the State harbors at least a few 

hibernating individuals

Hollow trees and buildings; in forest 

understory, along stream corridors, 

and along woodland edges

Caves, mines quarries, 

and sinkholes

Louisiana S4, S5

Maine SU

Massachusetts S4

Michigan S2

Minnesota S3

Mississippi S5

Missouri SU Buildings, trees, and rock crevices Caves and mines
Conservation Assessments for Five Forest Bat Species in the Eastern United States 19

Nebraska S1

New Hampshire S1

New Jersey SU

New York S3

North Carolina S5

Ohio S?

Oklahoma S4 Forests and woodlands Caves, buildings, and 

rocky crevices

Pennsylvania S4, S5 Trees Caves, buildings, and 

rocky crevices

Rhode Island S4

South Carolina S?

Tennessee S5

Texas S5 Forested streams Box culverts

Vermont S3

Virginia S5

West Virginia S5 Caves and mines

Wisconsin S3, S4

New Brunswick S2

Nova Scotia S1

Ontario S3

Table 1. Population status of Pipistrellus subflavus by State1 (continued).

State or 

province Status2 Current estimate Summer habitat (reported) Winter habitat (reported)

1

 Information about population and habitat use is based on literature cited. See text and References section.

2

 Status based on Natural Heritage State Rarity ranks (NatureServe 2002). S1: Extremely rare; usually 5 or fewer occurrences in the State, or, in the case 

of communities, covering less than 50 hectares (ha) in aggregate; or may have a few remaining individuals; often especially vulnerable to extirpation. S2: 

Very rare; usually between 5 and 20 occurrences, or, in the case of communities, covering less than 250 ha in aggregate; or few occurrences with many 

individuals; often susceptible to becoming endangered. S3: Rare to uncommon; usually between 20 and 100 occurrences; may have fewer occurrences, but 

with a large number of individuals in some populations; may be susceptible to large-scale disturbances. S4: Common; usually more than 100 occurrences, 

but may be fewer with many large populations; may be restricted to only a portion of the State; usually not susceptible to immediate threats. S5: Very 

common; secure under present conditions. SU: Status uncertain, often because of low search efforts or cryptic nature of the element.
20 Conservation Assessments for Five Forest Bat Species in the Eastern United States

Habitat Status

Summary of Land Ownership and Existing Habitat 

Protection

National Forests

Estimates of the potential available habitat for P. subflavus

were based on U.S. Department of Agriculture (USDA) Forest 

Service Forest Inventory and Analysis (FIA) data, which 

estimate the amount of upland hardwood and pine-hardwood 

forest land more than 60 years old for all States with national 

forests in Regions 8 and 9 (Southern and Eastern Forest 

Service Regions combined to look at the entire species range) 

and Region 9 (examined alone to look at potential available 

habitat for States in the Eastern Region), excluding rarely 

used deciduous forest types (such as aspen). This coarse-scale 

assessment of habitat availability considers forest type and age 

class based on USDA Forest Service FIA data (FIA 2003); this 

analysis does not consider other aspects of forest structure that 

may influence use by this species. The database used is subject 

to sampling errors associated with coarse-scale inventory. 

Estimates were for the acreage of upland hardwood and pinehardwood forest land for forests of all ownerships, including 

other federally owned, State-owned, county/municipal-owned, 

and privately owned lands within these States. Approximately 

5.9 percent of upland hardwood, bottom-land hardwood, and 

pine-hardwood forest types occur on National Forest System 

(NFS) lands within the eastern range of this species; 2.9 percent 

occur on NFS lands within Region 9 (figs. 2 and 5). Estimates 

indicated that 358,219,772 potential acres of upland hardwood, 

bottom-land hardwood, and pine-hardwood forest land that 

could potentially serve as foraging habitat occur within the 

eastern range of this species. Estimates also indicate that 

stands more than 60 years old in upland hardwood and pinehardwood forest types would provide suitable trees to meet the 

roosting requirements of this species. Within the eastern range 

of this species, estimates indicate that 330,457,331 acres occur 

and 88,687,204 acres, or 27 percent, of the total available are 

more than 60 years old (figs. 3 and 4). On NFS lands within 

Region 9, estimates indicate 9,671,251 acres of potential 

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, Michigan, 

Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, New Jersey, 

New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Rhode Island, 

South Carolina, Tennessee, Texas, Vermont, Virginia, West Virginia, 

Wisconsin.

Figure 2. Ownership of upland hardwood, bottom-land 

hardwood, and pine-hardwood forest types within the eastern 

range of P. subflavus. 

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, 

New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, 

Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West 

Virginia, Wisconsin.

Figure 3. Acreage by ownership of upland hardwood forest 

type and percentage of upland hardwood forest type more 

than 60 years old by ownership within the eastern range of P. 

subflavus.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 21

using 11 of the sites (Kurta 2000). A colony of pipistrelles 

originally located in 1959 in a building was no longer present 

in 1989 (Kurta 2001). During late summer and fall (August 

through October), P. subflavus was the most frequently captured 

bat in abandoned Indiana coal mines (1.7 per visit) (Whitaker 

and Stacy 1996).

Michigan. State status is very rare; usually between 5 and 20 

occurrences (S2, table 1). P. subflavus will likely be listed as 

a “species at risk” for the Ottawa National Forest’s upcoming 

forest plan (Unger and Kurta 1998). Records show pipistrelles 

are associated with abandoned early 20th century copper, iron, 

and silver mines scattered across the forest (Johnson 2001). 

Broders et al. (2001) pointed out that the species’ range extends 

into glaciated New Brunswick and Nova Scotia, likely because 

of the presence of suitable hibernacula.

No pipistrelles were caught with extensive mist-net 

procedures in the Huron-Manistee National Forests during the 

summer of 1998 and 1999 (Tibbels and Kurta 2003). Only two 

captures of pipistrelles were reported from swarming surveys 

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, 

New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, 

Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West 

Virginia, Wisconsin.

Figure 4. Acreage by ownership of pine and pine-hardwood 

forest types and percentage of pine and pine-hardwood forest 

types more than 60 years old by ownership within the eastern 

range of P. subflavus. 

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, 

New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, 

Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West 

Virginia, Wisconsin.

Figure 5. Acreage by ownership of bottom-land hardwood 

forest type and percentage of bottom-land hardwood forest type 

more than 60 years old by ownership within the eastern range 

of P. subflavus.

foraging habitat (upland hardwood, bottom-land hardwood, 

and pine-hardwood forest types) and 3,786,768 acres of upland 

hardwood and pine-hardwood forest types more than 60 years 

old (40.3 percent) are available for roosting (figs. 3 and 4). 

State Summaries

Illinois. State status is very common (S5, table 1). Mist-net 

surveys at 41 sites within the Shawnee National Forest during 

the summers of 1999 and 2000 resulted in the capture of 

417 bats of 10 species. Eastern pipistrelles were caught most 

frequently in edge habitats. 

Indiana. State status is common (S4, table 1). Mumford and 

Cope (1964) noted P. subflavus as a common, permanent 

resident more commonly found in summer than winter. Winter 

activity of bats at Copperhead Cave, an abandoned clay mine, 

was monitored in 1989. Although eastern pipistrelles were 

noted in hibernation, only 13 were found to be active during 

midwinter (Johnson 2001). Surveys at 27 abandoned coal mine 

entrances between 1984 and 1996 found eastern pipistrelles 
22 Conservation Assessments for Five Forest Bat Species in the Eastern United States

in the Huron-Manistee National Forests at a dam during 12 

nights between August 23 and September 24, 1998 and 1999 

(Knowles 1992). One bat was tracked to a healthy white oak 

(Quercus alba) in the middle of a shelterwood cut and later 

to a healthy red oak (Q. rubra), where it apparently roosted 

in leaves near the top (about 20 m high). A second pipistrelle 

roosted in the foliage of a white oak. Other sources also 

indicate that pipistrelles may roost in clusters of dead leaves 

(Williamson 2001).

In a study of bat use of red pine (Pinus resinosa) forests 

in the Huron-Manistee National Forests, acoustic methods 

identified pipistrelles in unthinned open stands and thinned 

stands but not in normal unthinned red pine stands (Trombulak 

et al. 2001). 

Broders et al. (2001) believed that the distribution of 

pipistrelles in Canada was influenced by the availability of 

hibernacula, primarily “solution caves” formed by water dissolving holes in limestone or similar rocks. Pipistrelles in New 

Brunswick, Canada, foraged over water (Broders et al. 2001). 

As safety work is completed on abandoned mine shafts 

on the Ottawa National Forest, provisions will be made to keep 

mines “bat friendly” while keeping people out (Johnson 2001).

Minnesota. State status is rare to uncommon (S3, table 1). 

Although an occurrence is recorded in northern Minnesota 

(Lacki and Bookhout 1983), P. subflavus occurs primarily 

in the southern half of the State. The species is located 

considerably east of the Chippewa National Forest (Dunn and 

Hall 1989), where no occurrences of this species are known. 

Although the range was previously thought not to include 

northern Minnesota, two individual hibernators have been 

collected in northeast Minnesota (Williamson 2001).

Missouri. State status is undetermined (SU, table 1). Extensive 

surveys for forest bats have been conducted on the Mark Twain 

National Forest from 1997 to present (Amelon 2001). Trapping 

sites have included upland ponds and trails, streams and rivers, 

roads, caves, and mines. A geographical area or habitat appears 

to be associated with this species’ distribution pattern. In 1999, 

only nine eastern pipistrelles were captured during summer 

surveys in riparian and upland habitats within the south central 

portion of the State. All individuals captured were males. 

During 2001 and 2003 surveys that also took place in riparian 

and upland habitats within central and southeast portions of 

the State, only 10 to 12 percent of total captures were eastern 

pipistrelles. During 2002 surveys in the southwest portion of the 

State, nearly 20 percent of captures were eastern pipistrelles (20 

percent females, 80 percent males). In the areas with a higher 

percentage of eastern pipistrelles represented, females were 

most frequently captured along streams and males were fairly 

evenly distributed between riparian and upland habitats. Eastern 

pipistrelles were well represented in fall hibernacula surveys.

New Hampshire. State status is extremely rare; usually five or 

fewer occurrences (S1, table1).

Ohio. State status is undetermined (S?, table 1). Distribution 

and activity of bats on the Wayne National Forest were studied 

in the summer and winter of 1979 and 1980. Surveys were 

conducted at abandoned mines and riparian sites. P. subflavus

represented 13 percent of the summer captures and was found 

to use some of the mines for hibernation (Sanders 2000).

Pennsylvania. State status is common to very common (S4, S5; 

table 1). Between 1980 and 1988, 190 abandoned mines and 

caves were surveyed for hibernating bats. Hibernating bats were 

found at 71 percent of the surveyed sites; eastern pipistrelle bats 

were found at 56 percent of the sites, representing the widest distribution of the species found hibernating (Dunn and Hall 1989).

Vermont. State status is rare to uncommon (S3, table 1). 

Trapping records from Dorset Cave and Greely Talc Mine 

indicate low numbers of eastern pipistrelles (two) were captured 

among 4,065 bats captured in September 2000. Surveys 

conducted at Dorset Cave between 1935 and 2001 indicate that 

total numbers of bats observed show no obvious trend over 

time. Cave surveys in Vermont indicate P. subflavus has been 

present in low numbers throughout the entire period (Geluso et 

al. 2004).

Dorset Cave was gated in 1985 but may need modifications 

to improve conditions. This site is an important bat resource in 

Vermont. Sanders (2000) recommended that this site be closed 

to recreation year round. Forest bat surveys conducted in 1999 

found that 126 bats representing five species were found to be 
Conservation Assessments for Five Forest Bat Species in the Eastern United States 23

using areas in or near the Green Mountain National Forest; P. 

subflavus was not found in this survey (Amelon 2001). 

West Virginia. State status is very common (S5, table 1).

Wisconsin. State status is rare to common (S3, S4; table 1).

This bat is not documented on the Chequamegon-Nicolet 

National Forest, but the Wisconsin Natural Resources Natural 

Heritage database indicates that it is documented in Crawford, 

Grant, Iowa, Lafayette, Pierce, Richland, and Vernon Counties.

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30 Conservation Assessments for Five Forest Bat Species in the Eastern United States
Conservation Assessments for Five Forest Bat Species in the Eastern United States 31

Conservation Assessment: Nycticeius 

humeralis (Evening Bat) in the Eastern 

United States

Sybill Amelon1 and Dirk Burhans2

Taxonomy and Nomenclature

The evening bat or evening myotis [Nycticeius humeralis

(Rafinesque 1818) (f. L. nycticeius belonging to the night; 

humeralis pertaining to the humerus)] belongs to the class 

Mammalia, order Chiroptera, family Vespertilionidae, 

subfamily Vespertilioninae, genus/species Nycticeius humeralis

(Rafinesque 1818). Other common names include twilight bat 

and black-shouldered bat. The genus Nycticeius includes 14 

species; but only two of these species are native to the New 

World (Watkins 1972).

Three subspecies of N. humeralis are recognized (Hall and 

Kelson 1959): 

1. N. h. humeralis = Vespertilio humeralis (Rafinesque 1818: 

445). Type location is Kentucky. = Nycticea crepuscularis

(Le Conte in [McMurtrie 1831: 432]). Type location is not 

stated. 

2. N. h. mexicanus (Davis 1944: 380). Type location is Rio 

Ramos, Nuevo Leon, Mexico.

3. N. h. subtropicalis (Schwartz 1951: 233). Type location is 

Monroe Station, Collier County, Florida.

Description of Species

N. humeralis is a medium-sized bat that resembles a small big 

brown bat (Eptesicus fuscus), but its much shorter forearm 

and single upper incisors distinguish it from E. fuscus. 

Characteristic measurements include wingspan, 260 to 280 

millimeters (mm); total length, 88 to 105 mm; tail length, 36 

to 41 mm; hindfoot, 6 to 9 mm; ear, 11 to 15 mm, thick and 

leathery; forearm, 34 to 38 mm; and skull, short and broad 

with a nearly straight dorsal profile. Weight ranges from 5 to 

14 grams (g). Females are consistently heavier than males. 

Pelage color dorsally varies from dull, medium brown to dark 

brown; ventrally, the fur is lighter. Hairs are short and very dark 

near the base. Juvenile pelage is darker than adult pelage. The 

tragus is short and rounded. The dental formula is i 1/3, c 1/1, 

p 1/2, m 3/3, total 30. A characteristic feature of this species is 

the presence of a single upper incisor (Hamilton and Whitaker 

1979, Watkins 1972).

Biology, Life History, and Natural History

Reproductive Biology and Phenology

The reproductive cycle of N. humeralis is not well known. 

Evening bats are polygamous, with breeding activity occurring 

in the fall and potentially into spring (Bain and Humphrey 

1986). In Florida, mating apparently begins in October and 

occurs throughout the winter (Bain and Humphrey 1986). 

Sperm are stored in the uterus of hibernating females until 

spring ovulation (Guthrie 1933). 

In northwest Missouri, the earliest reported captures in the 

year were in late April and early May (Easterla and Watkins 

1970, Watkins 1970). At a colony in Montgomery County, 

IN, Humphrey and Cope (1968) observed 2, 42, 106, and 159 

N. humeralis on May 1, 7, 14, and 21, respectively. Adult males 

and females segregate at least in spring and summer (Jones 

1967).

In Florida, young were born synchronously in late May 

(Bain and Humphrey 1986). In northern Missouri, females gave 

birth by mid-June (Watkins and Shump 1981). All palpitated 

females had twins, although one gave birth to triplets after 

capture (Bain and Humphrey 1986). Watkins (1970) found an 

average of 1.9 embryos out of 87 bats collected from April 19 

to July 8. Additional information collected by Watkins (1970) 

1

 Wildlife biologist, U.S. Department of Agriculture, Forest Service, North Central Research Station, Columbia, MO.

2

 Postdoctoral associate, Department of Fisheries and Wildlife Science, University of Missouri, Columbia, MO.
32 Conservation Assessments for Five Forest Bat Species in the Eastern United States

indicates a high percentage of females with three embryos. 

In Alabama and Louisiana, births occur from mid-May to 

mid-June. Young are born hairless and pink with eyes closed; 

eyes open 12 to 30 hours later. Short fur can be detected at 5 

days of age (Jones 1967). Newborn N. humeralis are capable 

of making loud clicking sounds that may aid their mothers in 

retrieving them (Jones and Genoways 1967). Growth rates vary 

by type of roost and geographic location (Jones and Pagels 

1968). Young become volant in approximately 3 weeks (Bain 

and Humphrey 1986, Watkins 1970, Wilkinson 1992). Sex 

ratios have been reported as equal among offspring, skewed to 

females as juveniles, and nearly equal for adults (Humphrey 

and Cope 1970). Juvenile males were reproductively mature 

at less than 1 month old (Bain and Humphrey 1986). Males 

generally disperse from natal roosts, whereas females remain 

until southern migration (Bain and Humphrey 1986, Watkins 

and Shump 1981).

Ecology and Behavior

In northern Missouri, southern migration of N. humeralis began 

in mid-September (Watkins and Shump 1981). October 11 and 

20 were the last dates bats were found at colonies in Missouri 

and Iowa, respectively (Easterla and Watkins 1970). Humphrey 

and Cope (1968) noted reductions from 275 to 30 individuals 

from August 15 to September 21, respectively, at a colony in 

Montgomery County, IN.

The absence of N. humeralis in the northern extent of 

its range during winter strongly suggests that it migrates. 

Humphrey and Cope (1970) found several individuals 176 

to 547 kilometers (km) south of their summer locations. 

Autumn fat deposition indicates this species prepares for long 

migrations and/or hibernation (Baker 1968). Evening bats are 

rarely known to use caves. They have been found to use tree 

hollows during winter (Duchamp 2000).

Maternity colonies have been reported in trees, buildings, 

and other human-made structures (Clem 1992, Cope and Humphrey 1967, Humphrey and Cope 1970). Sexes are segregated 

during the maternity period; females remain in small maternity 

colonies and males remain solitary (Clem 1992). 

Of 19 N. humeralis monitored in Indiana, only three made 

more than one foraging trip per night; all three were lactating 

females (Clem 1993). Post-lactating females foraged for the 

longest bouts (mean = 127.4 minutes [min]), followed by 

lactating females (mean = 107.2 min) and pregnant females 

(mean = 78.3 min) (Clem 1993). N. humeralis does not appear 

to have exclusive feeding territories; in 38 percent of 80 

monitored flights, two or more bats fed in the same area at 

the same time (Clem 1993). Obligate associations with other 

species have not been observed. N. humeralis has been observed 

roosting with big brown bats.

Of nursing bouts monitored by Wilkinson (1992), 18 

percent involved females nursing nondescendant offspring that 

tended to be females. He proposed that adult females benefited 

by dumping excess milk and that favoring female young helps 

increase colony size because male offspring tend to disperse. 

In open habitats, N. humeralis produce 7 millisecond, 

frequency modulated/constant frequency (FM/CF) echolocation 

calls. Minimum frequency is typically 34 to 36 kilohertz (kHz), 

and maximum frequency is typically 47 to 50 kHz.

Hibernation

Little is known about the hibernation behavior of N. humeralis. 

The species has only occasionally been observed at mine or 

cave entrances during swarming activities in the fall. Anecdotal 

information suggests this species spends the winter in tree cavities or buildings in the southern regions of its range. N. humeralis is believed to be active during warm periods in the winter.

Food Habits

N. humeralis has been reported feeding on coleopterans and 

hemipterans (Whitaker 1972). In a study of guano pellets 

in Indiana (Whitaker and Clem 1992), beetles, moths, 

and leaf hoppers were reported to be the main foods that 

evening bats ate; the spotted cucumber beetle (Diabrotica 

undecimpunctata), an agricultural pest, was the species the bats 

took most frequently (14.2 percent of total volume). Carter et 

al. (1998) found that N. humeralis feed on coleopterans and 

hymenopterans in Georgia.

Mortality and Predation Factors 

Whitaker et al. (1991) stated that two mites (Steatonyssus 

ceratognathus and Acanthophthirius nycticeius) and the bat 

bug (Cimex adjunctus) were the only ectoparasites infesting 

N. humeralis throughout its range. Endoparasites include 
Conservation Assessments for Five Forest Bat Species in the Eastern United States 33

nematodes (Watkins 1970, 1972). Predators of N. humeralis

include humans, cats, raccoons, snakes, and birds of prey.

Longevity

The greatest observed longevity for N. humeralis is 5 years 

(Watkins 1972). 

Banding Data and Site Fidelity

Based on early banding records, the maximum distance 

N. humeralis travels is 547 km in the fall (Cope and Humphrey 

1967). Homing studies found that individuals would return 

to their original capture sites from distances of up to 153 km 

(Cope and Humphrey 1967).

Distribution

In summer, N. humeralis occurs in at least small numbers as 

far north as New Jersey, Pennsylvania, southern Michigan, and 

Illinois, but reaches its maximum numbers in the South, where 

it is found as far west as Kansas and eastern Texas and as far 

south as northern Veracruz, Mexico; it is thought to be absent 

from the Appalachians (Hamilton and Whitaker 1979) (fig. 1).

Habitat Requirements 

Maternity Period (May to August)

Roosting Habitat

Menzel et al. (1999) found (1999) found N. humeralis roosting in slash pine, 

loblolly pine, and live oak. The preferred tree species was oak. 

Before 1993, all the N. humeralis maternity colonies known 

from Indiana were located in buildings; between 1960 and 

1993, 11 colonies in buildings were abandoned (Whitaker et al. 

2002). In 1994, researchers studied a maternity colony in Vigo 

County, IN, where evening bats were using hollows in silver 

maples as roosting sites. These silver maples were located in a 

650-hectare (ha) bottom-land hardwood forest. Females were 

found to switch roosts frequently, even when pups were present. 

The number of females fluctuated greatly at specific trees on a 

given night. When young become volant, movement between 

trees increases. In South Carolina, Menzel et al. (2001) found 

13 of 14 roosts used by three adult female N. humeralis in 

cavities of upland longleaf pine sawtimber stands characterized 

by open canopies. The mean number of days between roost 

changes was 2.3. The remaining roost was under the exfoliating 

bark of a live longleaf pine. Roosts have been located in 

Spanish moss (Jennings 1958) and under exfoliating bark 

(Chapman and Chapman 1990, Menzel et al. 2000).

Foraging Habitat

Female N. humeralis bats in Indiana were found to forage in 

association with their roosts in bottom-land forests (Whitaker 

and Gummer 2003). N. humeralis in South Carolina foraged 

over riparian zones, over beaver ponds, and in gaps in bottomland hardwood and swamp forests (Menzel et al. 2001). Attic 

temperatures below 13 °C decreased foraging activity of bats in 

an Indiana bell tower, and colonies emerged later after sunset as 

the breeding season progressed (Clem 1993).

N. humeralis is believed to intermittently forage from dusk 

to midnight and then have another period of feeding activity 

toward dawn. 

* = Isolated or questionable records.

Source: Bat Conservation International 2003, http://www.batcon.org.

Figure 1. The distribution of Nycticeius humeralis. 
34 Conservation Assessments for Five Forest Bat Species in the Eastern United States

Hibernation Period (October to April)

Whitaker and Gummer (1993) suggested that N. humeralis

moves south during winter and hibernates in tree holes near 

major rivers. They based their findings on recaptures of 

individuals that were banded in Indiana and later found in 

Kentucky. In southern portions of their range, N. humeralis has 

been found in buildings and hollow trees during winter. 

Potential Threats

Natural or Human Factors

Bat population declines have been attributed to pesticide 

poisoning (Geluso 1976, Reidinger 1976), chemical pollution 

(Tuttle 1979), siltation of waterways (Tuttle 1979), flooding 

(Hall 1962), and disturbance by humans (Fenton 1970, 

Humphrey 1978, Tuttle 1979, Speakman et al. 1991). Food 

chain poisoning by pesticides—in particular insecticides 

such as organochlorines and anticholinesterase—has been 

demonstrated to negatively affect insectivorous bats (Clark 

2001, Cockrum 1970, Reidinger and Cockrum 1978, Clark et 

al. 1983). 

Because N. humeralis bats often use buildings, Whitaker 

and Gummer (1993) considered them highly sensitive to 

disturbances by humans and less tolerant of human disturbance 

than were big brown bats (E. fuscus), a species that will 

relocate to a new roost after evictions. Bain (1981) indicated 

that excessive disturbance to a nursing colony caused 

abandonment. A colony in a church bell tower declined by 

49 percent in 1990 after 1989 banding and radiotelemetry 

studies (Clem 1992). Watkins (1970) stated that evening bats 

abandoned six northwestern Missouri colonies in reaction 

to his survey and netting operations, although other colonies 

persisted despite disturbance.

Present or Potential Risks to Habitat

The evening bat is a species whose range coincides with the 

historic extent of large river valleys, lowland swamps, and the 

wetlands characteristic of the Southeastern United States and 

the Mississippi and Ohio River Valleys. Although minimal 

data are available on historic habitat use, current studies and 

anecdotal reports strongly suggest this species may have been 

associated with bottom-land forests, swamps, and wetlands. 

Realistic estimates of the original extent of lowland forest 

and wetlands are not available because accurate records of these 

types were not maintained until the early 20th century, and 

many accounts of wetland size were little more than speculation 

(Hefner and Brown 1985). Hayes and Klopatek (1979) 

estimated that the precolonial forested wetland area of the 

United States was about 27.2 million ha (67.2 million acres). 

Although current estimates of lowland forest and wetlands 

area vary, it has been estimated that as of the mid-1950s the 

United States had about 19.1 million ha (47.2 million acres) of 

forested wetlands. The estimated area of southern bottom-land 

hardwoods declined to 12.5 to 13.1 million ha (30.9 to 32.4 

million acres) by the mid-1970s (Hefner and Brown 1985). By 

the mid-1980s, an additional 1.4 million ha (3.5 million acres) 

of lowland forest and wetlands were lost, mostly from the 

Southeastern United States.

The most dramatic bottom-land hardwood loss in the entire 

Nation has occurred in the Lower Mississippi River region. 

This vast area extends nearly 1,000 km (621 miles) from the 

confluence of the Mississippi and Ohio Rivers to the Gulf of 

Mexico; it originally covered more than 10.1 million ha (25.0 

million acres) (Hefner and Brown 1985). Recent estimates 

reveal that fewer than 2 million ha (4.9 million acres) of 

lowland forest and wetlands remain in the lower Mississippi 

River region, and the remaining portions of the original area are 

extremely fragmented. 

Inadequacy of Existing Regulatory Mechanisms 

Protection of natural and human-made roosting structures is 

one of the highest priorities for conservation of N. humeralis. 

Funding to facilitate protection measures is often unavailable.

Population Status

Rangewide

Both Global Heritage Status and National Heritage Status 

are very common—G5, N5 (NatureServe 2002)—indicating 

the N. humeralis is globally and nationally demonstrably 

widespread and common.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 35

State

Individual State Heritage Status is described in the State 

Summaries and in table 1. N. humeralis is believed to be 

most common in the southern parts of its range. Systematic, 

uniform population surveys have not been routinely conducted; 

population data are fairly scarce; and concerns of accuracy exist 

among areas and sampling methods. Demographic information 

on reproductive rates, sex ratios, movement between roosting 

sites, movement between maternity roosts and winter roosts, 

recruitment, and reproduction is necessary to provide a 

quantitative estimate of population viability. 

Habitat Status

Summary of Land Ownership and Existing Habitat 

Protection

National Forests

Estimates of the potential available habitat for N. humeralis 

were based on U.S. Department of Agriculture (USDA) Forest 

Service Forest Inventory and Analysis (FIA) data, which 

estimates the amount of upland hardwood and pine-hardwood 

forest land more than 60 years old for all States with national 

forests in Regions 8 and 9 (Southern and Eastern Forest 

Service Regions combined to look at the entire species range) 

and Region 9 (examined alone to look at potential available 

habitat for States in Region 9), excluding rarely used deciduous 

forest types such as aspen. This coarse-scale assessment of 

habitat availability considers forest type and age class based 

on FIA data (USDA 2003). This analysis does not consider 

other aspects of forest structure that may influence use by 

this species. The database used is subject to sampling errors 

associated with coarse-scale inventory. Estimates were for 

the acreage of upland hardwood and pine-hardwood forest 

land for forests of all ownerships, including other federally 

owned, State-owned, county/municipal-owned, and privately 

owned lands within these States. Approximately 5.9 percent of 

upland hardwood, bottom-land hardwood, and pine-hardwood 

forest types occur on National Forest System (NFS) lands 

within the range of this species; 2.9 percent occur on NFS 

lands within Region 9 (figs. 2 and 5). Estimates indicate that 

Figure 2. Ownership of upland hardwood, bottom-land 

hardwood, and pine-hardwood forest types within States 

overlapping the range of N. humeralis. 

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, 

New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, 

Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West 

Virginia, Wisconsin.

358,219,772 potential acres of upland hardwood, bottomland hardwood, and pine-hardwood forest land that could 

potentially serve as foraging habitat occur within the range of 

this species. Estimates also indicate that stands more than 60 

years old in upland hardwood and pine-hardwood forest types 

would provide suitable trees to meet this species’ roosting 

requirements. Within the range of this species, estimates 

indicate that 304,486,806 acres occur and 94,453,427 acres, 

or 31 percent of the total available, are more than 60 years 

old (figs. 3 and 4). On NFS lands within Region 9, estimates 

indicate 9,671,251 acres of potential foraging habitat (upland 

hardwood, bottom-land hardwood, and pine-hardwood forest 

types) and 3,786,768 acres of upland hardwood, bottom-land 

hardwood, and pine-hardwood forest types more than 60 years 

old (39.3 percent) available for roosting (figs. 3 and 4). 

State Summaries

Illinois. State status is rare to uncommon (S3, table 1). Mist-net 

surveys at 41 sites within the Shawnee National Forest during 

the summers of 1999 and 2000 resulted in the capture of 417 
36 Conservation Assessments for Five Forest Bat Species in the Eastern United States

bats of 10 species. N. humeralis were caught most frequently in 

forested habitats. 

Indiana. State status is extremely rare; usually five or fewer 

occurrences in the State (S1, table1). N. humeralis is Statelisted Endangered. All 12 N. humeralis colonies visited in 

1959 were no longer active in the 1980s (Cope et al. 1991, 

Whittaker and Gummer 1993); six of the buildings containing 

colonies were demolished, two colonies were evicted, and 

three colonies left after buildings were remodeled. A single 

remaining colony of 358 bats was discovered in a church bell 

tower in 1987 during an extensive statewide survey (Whitaker 

and Gummer 1988).

Whitaker and Gummer believe that Indiana populations 

had declined based on declining numbers of historic colonies, 

lack of new colonies, and decreases in reported cases of rabies 

in N. humeralis (Whitaker and Gummer 1993). They also 

speculated that N. humeralis does not compete successfully 

with big brown bats for roosts in buildings (Whitaker and 

Weeks 2001). Previously unknown populations were recently 

Figure 4. Acreage by ownership of pine and pine-hardwood 

forest types and percentage of pine and pine-hardwood 

forest types more than 60 years old by ownership within 

States overlapping the range of N. humeralis. 

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, 

New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, 

Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West 

Virginia, Wisconsin.

Figure 5. Acreage by ownership of bottom-land hardwood 

forest type and percentage of bottom-land hardwood forest 

type more than 60 years old by ownership within States 

overlapping the range of N. humeralis. 

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, 

New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, 

Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West 

Virginia, Wisconsin.

Figure 3. Acreage by ownership of upland hardwood forest 

type and percentage of upland hardwood forest type more 

than 60 years old by ownership within States overlapping 

the range of N. humeralis. 

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Hampshire, 

New Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, 

Rhode Island, South Carolina, Tennessee, Texas, Vermont, Virginia, West 

Virginia, Wisconsin.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 37

State Status2 Summer habitat (reported) Winter habitat (reported)

Alabama S5 Buildings

Arkansas S3 Buildings and trees

Delaware SNR/SU

Florida SNR/SU

Georgia S5 At forest edges, over forest canopy, and over bodies of water Buildings, trees, and clumps 

of Spanish moss

Illinois S3 Buildings and trees

Indiana S1 Buildings and trees Buildings and trees

Iowa S3

Kansas S3, S4 Rocky areas, in buildings, and trees Buildings and trees

Kentucky S2, S3 Hollow trees and buildings; in forest understory, along stream 

corridors, and along woodland edges

Buildings and trees

Louisiana S5

Mississippi S5

Missouri SNR/SU Buildings, trees, and rock crevices Buildings and trees

Nebraska S3

New Hampshire NA

New Jersey SNR/SU

North Carolina S5B

Ohio SNR/SU

Oklahoma S4 Forests and woodlands Buildings and trees

Pennsylvania SNR/SU Trees Buildings and trees

South Carolina SNR/SU

Tennessee S5

Texas S5 Forested streams Buildings and trees

Virginia S4

West Virginia S1 Buildings and trees

Table 1. Population status of Nycticeius humeralis by State.1

1

 Information about population and habitat use is based on literature cited. See text and References section.

2

 Status based on Natural Heritage State Rarity ranks (NatureServe 2002). S1: Extremely rare; usually 5 or fewer occurrences in the State, or, in the case of 

communities, covering less than 50 hectares (ha) in aggregate; or may have a few remaining individuals; often especially vulnerable to extirpation. S2: Very 

rare; usually between 5 and 20 occurrences, or, in the case of communities, covering less than 250 ha in aggregate; or few occurrences with many individuals; often susceptible to becoming endangered. S3: Rare to uncommon; usually between 20 and 100 occurrences; may have fewer occurrences, but with 

a large number of individuals in some populations; may be susceptible to large-scale disturbances. S4: Common; usually more than 100 occurrences, but 

may be fewer with many large populations; may be restricted to only a portion of the State; usually not susceptible to immediate threats. S5: Very common; 

secure under present conditions. SNR/SU: Status not ranked/Status uncertain, often because of low search effort or cryptic nature of the element.
38 Conservation Assessments for Five Forest Bat Species in the Eastern United States

discovered during netting surveys in the Prairie Creek area of 

Vigo County, IN (Whitaker and Gummer 2001). The authors 

believe the species is relatively common on the floodplain 

of the lower Wabash River, a large undeveloped floodplain 

(Sparks et al. 1998, Whitaker and Gummer 2001). 

Michigan. State status: NA. The range of N. humeralis is 

believed not to include Michigan.

Minnesota. State status: NA. The range of N. humeralis is 

believed not to include Minnesota.

Missouri. State status is undetermined (SNR/SU, table 1). 

Watkins (1970) found 28 colonies in northwest Missouri and 

adjacent Iowa and estimated that 12 colonies had fewer than 

100 individuals and 5 had more than 200; he estimated that 

1 of the latter contained 950 bats. N. humeralis was the most 

common of eight bat species surveyed in northwest Missouri 

and adjacent Iowa in the late 1960s (Watkins 1970).

New Hampshire. State status: NA. The range of N. humeralis

is believed not to include New Hampshire.

Ohio. State status is undetermined (SNR/SU, table 1). 

Distribution and activity of bats on the Wayne National Forest 

were studied in the summer and winter of 1979 and 1980. 

Surveys were conducted at abandoned mines and riparian 

sites; N. humeralis was not recorded in the surveys (Lacki and 

Bookhout 1983).

Pennsylvania. State status is undetermined (SNR/SU, table 1). 

Vermont. State status: NA. The range of N. humeralis is 

believed not to include Vermont.

West Virginia. State status is extremely rare; usually five or 

fewer occurrences in the State (S1, table1).

Wisconsin. State status: NA. The range of N. humeralis is 

believed not to include Wisconsin.

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Whitaker, J.O.; Gummer, S.L. 1993. The status of the evening 

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42 Conservation Assessments for Five Forest Bat Species in the Eastern United States
Conservation Assessments for Five Forest Bat Species in the Eastern United States 43

Conservation Assessment: Myotis 

austroriparius (Southeastern Myotis) in 

the Eastern United States

Sybill Amelon1, Mark Yates2, and Craig Pullins2

Taxonomy and Nomenclature

The southeastern myotis [Myotis austroriparius (Rhoads 1897) 

(f. G. mys mouse; otis ear; and L. austro southern; riparius

edges of streams—i.e., southern mouse-eared bat using edges 

of streams)] belongs to the class Mammalia, order Chiroptera, 

family Vespertilionidae, subfamily Vespertilioninae, genus/

species Myotis austroriparius (LaVal 1970). Type location is 

Tarpon Springs, Pinellas County, Florida. M. austroriparius

is considered monotypic (LaVal 1970). M. a. gatesi (Lowery 

1943) and M. a. mumfordi (Rice 1957) are synonyms. 

Mississippi myotis is an alternative common name.

Description of Species

M. austroriparius (southeastern myotis) is a medium-size 

member of the genus Myotis. Characteristic measurements 

of the M. austroriparius include forearm length, 31 to 41 

millimeters (mm) (Jones and Manning 1989, Choate et al. 

1994); total length, 77 to 97 mm; tail length, 26 to 44 mm; 

hindfoot length, 7 to 11 mm (M. austroriparius’ mean foot 

length of 10.7 is usually larger than that of similar-sized Myotis

species); ear length, 11 to 16 mm; skull, usually less than 

15 mm. Weight ranges from 5.1 to 8.1 grams (g) (Jones and 

Manning 1989, Choate et al. 1994). On average, females are 

slightly larger than males. This species has short, thick, woolly 

fur that dorsally ranges from russet or bright orange-brown 

to dark gray, and ventrally ranges from tan to white. Hairs at 

the venter often have whitish tips (Humphrey and Gore 1992, 

LaVal 1970, Gardner et al. 1992). The southeastern myotis 

molts in late summer, shedding a lighter, rusty coat to acquire 

one of dark gray. Fur may be bi-colored, russet, dark gray, or 

black at the base, and whitish at the tips. Newly molted pelage 

has little contrast between the base and tips of hair (Barbour 

and Davis 1969, Hall 1981). The hairs on the toes extend past 

the ends of the claws. The calcar is not keeled. The tragus of 

the M. austroriparius is relatively short and blunt compared to 

other Myotis. The skull is high and domed with a sagital crest 

and has an abruptly rising forehead. The dental formula is i 2/3, 

c 1/1, p 3/3, m 3/3, total 38 (Jones and Manning 1989).

M. austroriparius is similar to the Indiana bat (M. sodalis), 

gray bat (M. grisescens), and little brown bat (M. lucifugus). 

The Indiana bat lacks long hairs on the toes and has a slightly 

to moderately keeled calcar. The gray bat is larger than the 

southeastern myotis; it has uni-colored fur and lacks contrasting 

whitish tips on its venter, and its wing membrane attaches at 

the ankle instead of the base of the toes. The little brown bat 

also lacks contrasting whitish tips on its venter and is slightly 

smaller then the southeastern myotis. 

Biology, Life History, and Natural History

Reproductive Biology and Phenology

The few details available on M. austroriparius reproduction 

were gathered mostly from studies in Florida. A prominent 

characteristic of reproduction among northern cave-dwelling 

species is delayed fertilization—an adaptation for minimizing 

energetically expensive mating activities when energy reserves 

are lowest after hibernation. Copulation occurs in autumn; the 

female stores sperm during the winter and ovulates when she 

emerges from hibernation (Humphrey 1982). In contrast to the 

norm for most eastern bats, M. austroriparius is polygamous, 

breeding in the spring in southern populations and possibly 

in the fall or spring in northern populations. In Florida, 

M. austroriparius begins forming maternity colonies in late 

March (Rice 1957). Female M. austroriparius bats gather in 

large maternity colonies with mean densities of 150 bats per 

square foot. Males and nonbreeding females generally roost 

in locations other than the maternity colony. Rice (1957) 

1

 Wildlife biologist, U.S. Department of Agriculture, Forest Service, North Central Research Station, Columbia, MO.

2

 Graduate assistants, Department of Fisheries and Wildlife Science, University of Missouri, Columbia, MO.
44 Conservation Assessments for Five Forest Bat Species in the Eastern United States

found maternity colonies were associated with standing water 

in caves. Roosting over water is thought to reduce predation 

during roosting and to provide increased humidity at roosting 

sites (Jones and Manning 1989, Foster et al. 1978). In more 

recent surveys, however, Gore and Hovis (1998) did not find 

a significant association between roosting and the presence of 

water in a cave. 

Parturition occurs in mid-April to early May in Florida 

(Rice 1957) and in May in Illinois (Gardner et al. 1992). In 

contrast to other species of Myotis species, which have one 

offspring per litter, southeastern myotis commonly have two 

offspring per litter (mean = litter size is 1.9) (Hermanson 

and Wilkins 1986, Rice 1957, Foster et al. 1978). This higher 

fecundity rate has been hypothesized to be an adaptation to 

increased exposure to in-flight predation because of longer 

periods of annual activity (Foster et al. 1978). Sherman (1930) 

reported the birth weights of two M. austroriparius bats at 1.10 

and 1.15 g from a female weighing 7.25 g. These fetal weights 

represent approximately 31 percent of the maternal weight, 

which is similar to single fetal weights reported for other 

Myotis species. Foster et al. (1978) found that all deciduous 

teeth were present at birth. Young are born hairless and pink 

with eyes closed and pinnae folded (Sherman 1930). The habit 

of roosting over water may increase the fatality of nonvolant 

juveniles that fall to the roost floor (Rice 1957). Parturition 

synchrony, combined with clustering in maternity colonies, 

should increase metabolic rates and lead to rapid postnatal 

growth rates (Stevenson and Tuttle 1982). At birth, the sex ratio 

is at parity (Hermanson and Wilkins 1986, Rice 1957), but Rice 

(1957) found a shift in this ratio among adults. A decrease in 

the number of adult males found in hibernacula was attributed 

to males using less-protected roosting sites during spring and 

summer while females were in maternity colonies. 

Young are left in clusters in the maternity colony while 

the adults leave to forage. Young become volant at 5 to 6 weeks 

after birth. Rice (1957) captured flying juveniles as early as 

June 9 in Florida. In Texas, Horner et al. (1998) found that 

parturition occurs in late April to early May and that the young 

become volant by the end of May, several weeks earlier than 

young in Florida. Juveniles are sexually mature and able to 

breed the following spring (Rice 1957).

In Florida, male M. austroriparius were found to have 

enlarged epididymides from mid-February to mid-April (Rice 

1957). Gardner et al. (1992) found that males captured in 

Illinois followed trends similar to those of Florida populations; 

scrotal testes were found only in May. 

Ecology and Behavior

Winter hibernacula and summer maternity sites are generally in 

different locations (Mumford and Whitaker 1982, Rice 1957). 

Migration routes are not documented, but Rice (1957) recorded 

movement distances of 28.9 to 72.4 kilometers (km) for banded 

individuals. Dispersal from maternity colonies begins in 

October, with males leaving earlier than females. Rice (1957) 

found the number of individuals at Florida maternity colonies 

declined markedly by the end of October; all individuals 

were gone by the second week of December. The number of 

individuals found in hibernating sites increases following 

departure from maternity roots. There does not seem to be any 

migration of individuals. There is, however, a shift in roost 

locations between spring and summer sites and overwintering 

sites (Gardner et al. 1992). 

In Florida, maternity colonies form during March and 

April (Rice 1957). During the maternity period, few males are 

found in maternity colonies. After the young mature, however, 

males may join the females in maternity colonies (Rice 1957). 

Lowery (1974) observed M. austroriparius roosting in 

buildings and hollow trees. In Arkansas, this species has been 

found using old mines, buildings, hollow trees (Sealander 

1979), and bridges. In Illinois, Kentucky, Tennessee, Indiana, 

and Mississippi, caves are the most frequently used roosting 

sites (Barbour and Davis 1969, Mumford and Whitaker 1982). 

In Arkansas, Heath et al. (1986) reported hibernating colonies 

in abandoned mines. Graves and Harvey (1974) reported 

M. austroriparius as the second most commonly captured bat 

over ponds and streams in western Tennessee.

Obligate associations with other species have not been 

observed. M. austroriparius has been found in maternity 

colonies in Florida with gray bats (Wenner 1984) and freetailed bats (Hermanson and Wilkins 1986, Sherman 1930). 

M. austroriparius also shares bachelor roosts and winter 

roosts with other species, including free-tailed bats (Tadarida 

brasilensis), eastern pipistrelles (Pipistrellus subflavus), big 
Conservation Assessments for Five Forest Bat Species in the Eastern United States 45

brown bats (Eptesicus fuscus), and evening bats (Nycticeius 

humeralis) (Bain 1981, Gore and Hovis 1994, Rice 1957). 

Hibernation 

Mammalian hibernation is characterized by periods of torpor 

interrupted cyclically by spontaneous arousal. Individuals 

aroused during hibernation tend to fly or move around between 

periods of torpor. Unlike many species of Myotis, M. austroriparius has a variable hibernation strategy. This strategy 

is possibly an adaptation to survival in a warmer climate. In 

the northern parts of its range, M. austroriparius may hibernate from September or October until February or March. In 

southern areas, this species remains active throughout much 

of the winter (Jones and Manning 1989). Males and females 

roost together in hibernacula (Humphrey and Gore 1992). 

During hibernation, southeastern myotis bats usually roost in 

clusters of up to 50 individuals in caves or buildings (Jones and 

Pagels 1968, Lowery 1974, Mumford and Whitaker 1982). The 

species may also use mines or bridges (Wilhide 2001, Saugey 

et al. 1989). In some portions of its range, M. austroriparius

may hibernate in association with M. lucifugus (Mumford and 

Whitaker 1982), T. brasiliensis (Sherman 1930, 1939), P. subflavus and Corynorhinus rafinesquii (Jones and Suttkus 1973, 

1975; Mirowsky and Horner 1997), and E. fuscus (Best et al. 

1992, Saugey et al. 1993, Walker et al. 1996). 

Food Habits 

M. austroriparius is associated with water. It forages low over 

the water’s surface, feeding on a variety of insect taxa (Rice 

1955, Zinn and Humphrey 1981). This species leaves the 

roost after dusk to forage (Gardner et al. 1992). On warmer 

nights in early spring and summer, Zinn and Humphrey (1981) 

studied M. austroriparius in Florida and found it to be a 

generalist that shows a preference for dipterans, coleopterans, 

and lepidopterans later in the season. Some have suggested 

that selectivity for dipterans was an adaptation to the longer 

period of activity and reproduction. Schmidly et al. (1977) 

reported southeastern myotis foraging over slow-moving 

streams adjacent to upland areas with loblolly (Pinus taeda) 

and shortleaf (P. echinata) pine with mixed hardwoods. Other 

reported foraging types include mature, forested wetlands in 

Illinois (Gardner et al. 1992) and Texas (Horner 1995); forested 

streams in Tennessee (Graves and Harvey 1974); live oaks 

and shrubby old fields in Florida (Zinn and Humphrey 1981), 

and bottom-land hardwood and in baldcypress (Taxodium 

distichum)–tupelo gum (Nyssa aquatica) swamp in Arkansas 

and South Carolina (Clark et al. 1998, Hoffman et al. 1998).

Mortality and Predation Factors

Limited research has been conducted to determine the mortality 

and survivorship of M. austroriparius. Again, the available 

information is related to Florida populations. Rice (1957) 

estimated the annual survival rate is 46 percent for a stable 

population. He determined this estimate by calculating the rate 

of mortality for the population at a stable level when the birth 

rate is 116 percent. Therefore, this estimate may not hold true 

for declining populations. Because of the species’ colonial 

behavior in caves and other structures associated with water, 

flooding or other disturbances pose a relatively high potential 

for catastrophic losses. Foster et al. (1978) reported preweaning 

mortality to be fairly high—about 12 percent for colonies 

roosting over water. Rice (1957) hypothesized that the presence 

of water beneath maternity colonies increased preweaning 

mortality rates due to dislodged juveniles drowning. 

Predation by rat snakes (Elaphe spp.), raccoons (Procyon 

lotor), and owls (Bubo spp. and Strix spp.) has been observed 

but not in large enough numbers to cause decline concerns. 

Various helminthes inhabit the digestive tracts of M. austroriparius, but its parasite community is small compared to other 

Myotis species from the Midwest (Lotz and Font 1991). Rice 

(1957) and Mumford and Whitaker (1982) reported that mites, 

parasitic flies, chiggers, and intestinal trematodes use M. austroriparius as a host species.

Longevity 

There were no estimates on longevity. 

Banding Data 

Banding efforts by Allen (1921) marked initial attempts 

to study migration in North American bats. Rice (1957) 

documented a single banded individual recovered 43.2 km 

from the roost site. The mean distance traveled by 14 banded 

individuals was 17 km estimated by recaptures. 
46 Conservation Assessments for Five Forest Bat Species in the Eastern United States

Site Fidelity

Fidelity to maternity roost sites is thought to be relatively high 

among M. austroriparius (Gore and Hovis 1998, Rice 1957) 

based on very few records. Mumford and Whitaker (1975) 

recaptured several bats banded in the previous year, which may 

indicate roost-site fidelity from year to year.

Distribution 

M. austroriparius has a disjunct distribution (Hamilton and 

Whitaker 1979) (fig. 1). Miller and Allen (1928) described 

three subspecies based on geographic locations and pelage 

color. LaVal (1970) examined the morphological and pelage 

characteristics and determined no distinct character would 

allow differentiation. Life history characteristics may differ, 

however, among the three distinct geographic populations, 

primarily due to climatic characteristics that allow the 

southernmost populations to remain active all year while the 

northern populations hibernate. M. austroriparius is most 

common in Florida where it is well adapted to the climate. 

Surveys have not been conducted to estimate the total 

population of M. austroriparius. 

M. austroriparius lives in the Southeastern United States 

from coastal southeastern Virginia and eastern North Carolina, 

south into peninsular Florida, west through Louisiana and 

into eastern Texas, northward through southeastern Arkansas, 

and into the Mississippi River Valley to southern Illinois and 

Indiana. The species also is believed to live in certain areas 

along the lower Ohio River Valley in Kentucky, Indiana, and 

Illinois. Barbour and Davis (1969) suggested declining numbers 

in Illinois, Indiana, and Kentucky and concluded the species 

was nearing extinction in the Ohio River Valley. Gardner et al.

(1992) found M. austroriparius in only one of nine previously 

reported winter roosts in Illinois and concluded, based on 

consensus of more than 40 authorities from States within this 

bat’s range, that the population is in serious decline and should 

receive at least a federally threatened status.

Habitat Requirements

Maternity Period (May to August)

Roosting Habitat

Maternity roosts are thought to be the most important 

component of summer habitat because young are born and 

reared on these sites (Gore and Hovis 1994, Humphrey and 

Gore 1992, Rice 1957). Southern populations (specifically 

those in peninsular Florida) typically form maternity colonies 

in warm caves. Rice (1957) believed that maternity caves in 

Florida required permanent water with a large area of horizontal 

ceiling above the water. These conditions are believed to 

maintain high humidity and stable temperatures at the roost and 

provide protection from predators (Rice 1955, Tuttle 1975, Zinn 

1977). More recently, however, surveys of Florida maternity 

caves found only two of eight caves with pools under the roosts; 

four caves were completely dry under the roosts (Gore and 

Hovis 1994).

The physical characteristics that make a cave suitable 

as a maternity roost are not well understood. Zinn (1977) 

suggested that caves with domed ceilings trapped metabolic 

heat and provided a stable temperature regime while outside 

temperatures fluctuated during the nursery period. Recent 

studies have suggested that human disturbance rather than cave 

structure may be the factor determining maternity cave use.

Figure 1. The distribution of Myotis austroriparius.

* = Isolated or questionable records.

Source: Bat Conservation International 2003, http://www.batcon.org.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 47

In other regions of the species’ range, maternity colonies 

use alternative structures. In east Texas, maternity colonies 

were located in hollow trees of bottom-land hardwood forests 

(Horner and Mirowski 1996, Mirowsky 1997). Schmidly et 

al. (1977) found M. austroriparius in oak- and longleaf pine 

(Pinus palustris) forest types. M. austroriparius has been 

captured in baldcypress–tupelo gum swamps in North Carolina 

(Clark et al. 1985) and Illinois (Gardner et al. 1992). Roost 

trees were typically in large, live black and tupelo gum trees 

with triangular entrances near their bases. The cavities extended 

3 to 8 meters (m) up the tree and the colony was located 

near the top; these trees were typically surrounded by water. 

M. austroriparius in Tennessee (Graves and Harvey 1974) 

and Kentucky (Gardner et al. 1992) were captured in mature 

floodplain forests.

Maternity colonies of M. austroriparius have been 

reported in chimneys (Foster et al. 1978), concrete culverts 

(Bain 1981), buildings (Lowery 1974, Kern et al. 1996), mine 

shafts (Sealander 1979), and bridges (Wilhide 2001). Typically, 

few males are found in maternity colonies. Males are believed 

to roost alone or in small bachelor colonies during the summer. 

The specific roost types are not well documented (Hamilton 

and Whitaker 1979).

Movement between summer and winter habitats is usually 

local, barely qualifying as migration. Most individuals leave 

maternity sites in late September or October and gather in 

protected roost sites, frequently over water, to spend the winter. 

Foraging Habitat

There is a dearth of published information on foraging habitat 

for this species. As mentioned earlier, Rice (1957) documented 

a single banded individual recovered 43.2 km from the roost 

site. The mean distance traveled by 14 banded, recaptured 

individuals was 17 km. Gardner et al. (1992) tracked radiotagged individuals foraging up to 2 km from roosting sites. 

These differences in distance traveled seem to indicate that, as 

with many aspects of this species, the southern and northern 

populations may behave differently. 

M. austroriparius bats leave their roosts somewhat later 

than other bats and fly to ponds, swamps, rivers, or lakes 

(Barbour and Davis 1969). They fly low over the water, 

capturing small moths, beetles, midges, and mosquitoes (Zinn 

and Humphrey 1981). Foraging activities center around habitats 

associated with water, including streams, rivers, lakes, ponds, 

swamps, forested wetlands, and bottom-land hardwoods. 

Hibernation Period (October to April) 

Throughout most of its range, M. austroriparius is 

predominantly a cave bat (Gore and Hovis 1998, Rice 1957). 

In Louisiana, however, it is thought to use hollow trees and 

buildings exclusively because of the lack of caves (Lowery 

1974, Rice 1957). In Arkansas, this species has been found 

hibernating in mines and hand-dug wells (Davis et al. 1955, 

Heath et al. 1986, Saugey et al. 1993). It has also been found 

using human-made structures, bridges, culverts (Gardner et al. 

1992, Gore 2002), and barns (Bain 1981) for winter roosts. 

In winter, this species hibernates in caves for shorter 

periods than many other species do. In contrast to other Myotis

species, M. austroriparius do not appear to be obligatory 

hibernators. It puts on little or no fat, uses torpor only during 

short cold spells, and remains active during the winter, which 

may be an adaptation to the more continuous food supply 

available in warmer climates (McNab 1974). Peninsular Florida 

populations were found to be active throughout the year, 

foraging during warm periods. These populations may become 

dormant during periods of colder weather, but they do not 

truly hibernate as do more northern populations (Rice 1957). 

Peninsular Florida populations do, however, move from summer 

roosts to winter roosts. In the panhandle of Florida and adjacent 

areas, bats were found to enter torpor for short periods, leaving 

to forage during warmer periods. Humphrey and Gore (1992) 

reported activity of thousands of M. austroriparius at two 

maternity caves from December through March, indicating 

these bats are active all winter in more southerly locations. 

In more northerly geographic locations, southeastern 

myotis do hibernate, often in caves or mines. Gardner et al.

(1992) found that in the upper Mississippi and Ohio River 

regions, this species is in hibernacula from late September to 

March. Often, even in the colder areas of this species’ range, 

bats were found to be awake or easily disturbed during the 

hibernation period, suggesting an adaptation toward shallow 

torpor rather than true hibernation. Where average winter 

temperatures are warmer, this type of behavior may allow 

for more opportunistic feeding during warmer periods or 
48 Conservation Assessments for Five Forest Bat Species in the Eastern United States

mild winters. A colony of M. austroriparius was discovered 

in an abandoned cotton mill north of Raleigh, NC (Webster 

et al. 1984). The number of bats in this colony fluctuated, 

with highest numbers present from April to December; few 

individuals remained from January to March. These bats were 

observed going into torpor when ambient temperatures dropped 

to 5 oC. Harvey et al. (1991) reported colonies of up to 3,000 

bats in western Kentucky caves. 

Potential Threats

Natural or Human Factors

Disturbance during hibernation or maternity periods is a 

significant factor in the widespread decline of cave- and minedependent bat species (Clark et al. 1998, Currie 1999). The 

foremost factor leading to population declines is destruction of 

roost sites, particularly hibernacula (Humphrey 1975, Sheffield 

and Chapman 1992). Rice (1955) found 11,000 M. austroriparius bats in Mud Cave, which has since become a dumping site 

(Humphrey and Gore 1992). The entrances of two additional 

Florida caves have been blocked (Gore and Hovis 1994), one 

with wire fencing to reduce trespassing and the other with rock 

removed from a nearby agricultural site. Guano piles set on 

fire resulted in the abandonment of another maternity cave in 

Florida (Gore and Hovis 1994). In Alabama, a large maternity 

colony was reported extirpated because of vandals and careless 

cave explorers (Mount 1986). 

Human disturbance also includes indirect habitat 

disturbance. Noise and lights from cave exploration occurring 

during hibernation may awaken or disturb roosting bats and 

cause them to abandon the caves and result in depleting their 

fat supplies. In maternity colonies, disturbance may induce 

adults to fly, resulting in young being knocked from the roost 

leading to juvenile mortality (Foster et al. 1978, Hermanson 

and Wilkins 1986). 

Natural environmental events, such as flooding of caves 

or roost trees, exacerbated by land use changes, may seriously 

impact M. austroriparius populations. About 57,000 bats 

were killed in a flood at Snead’s Cave in Florida in 1990 

(Gore and Hovis 1994). Increased frequency of flooding by 

impoundments or channelization in areas used by bats may 

increase mortality rates. 

Blocking or plugging cave entrances changes airflow 

patterns and may change temperature and humidity regimes and 

subsequently reduce suitable maternity or hibernating habitat 

(Tuttle 1981). The collapse or destruction of natural or artificial 

roosting structures such as caves, mines, buildings, or culverts 

may trap bats or close a roost to future use (Gore and Hovis 

1994). 

Pesticides used to control insects or chemicals from 

agricultural runoff may harm bat populations either directly 

by killing the bats or indirectly by impairing reproductive 

capability or foraging success. Food chain poisoning by 

pesticides—in particular, insecticides such as organochlorines 

and anticholinesterase—has been demonstrated to negatively 

impact insectivorous bats (Clark 1988a, 1988b, 2001; Clark and 

Krynitsky 1983; Cockrum 1970; Reidinger and Cockrum 1978; 

Clark et al. 1983). 

Present or Potential Risks to Habitat 

Converting or harvesting mature wetland and bottom-land 

forests may impact M. austroriparius in areas where the species 

roosts in hollow trees or forages in mature wetland and bottom-land forests. Gardner et al. (1992) found M. austroriparius

foraging in mature forested wetland, much of which has been 

converted to agriculture within the range of this species. Direct 

habitat loss of bottom-land hardwood, tupelo gum swamps, cypress swamps, and other forested wetlands has also contributed 

to the decline of the southeastern myotis (Mirowsky and Horner 

1997). Reservoir construction and floodplain protection may 

impact suitable habitat and roosting sites for this species. 

Inadequacy of Existing Regulatory Mechanisms

Early bat roost protection efforts focused on eliminating or 

reducing disturbances by installing informative signs or “bat 

friendly” gates and fences to control human disturbance during 

critical hibernation and maternity periods. In some cases, these 

efforts were unfavorable because of limited understanding of 

bat behavior and cave microclimate factors. Some early gate 

designs altered the air flow patterns of the cave environment, 

resulting in increased temperatures that were less desirable for 

hibernation (Currie 1999, Tuttle and Taylor 1995).
Conservation Assessments for Five Forest Bat Species in the Eastern United States 49

Protecting natural and human-made roosting structures is 

one of the highest priorities in all the recovery plans for listed 

species (Harvey 1976, USFWS 1983). Funding and access to 

facilitate these protection measures are often unavailable.

Population Status

Rangewide

Global Heritage Status is G3, G4 and National Heritage 

Status is N3, N4—indicating M. austroriparius may be rare to 

common. The wide range of status ranking is likely the result 

of lack of information on this species globally and nationally 

(NatureServe 2002). Individual State Heritage Status is 

described in State Summaries and in table 1.

Federal

M. austroriparius was a candidate species (C2) to be listed by 

the U.S. Fish & Wildlife Service (USFWS) as either threatened 

or endangered (USFWS 1989). The USFWS, however, 

discontinued the designation of C2 species as candidates 

for listing (USFWS 1996). M. austroriparius is currently 

considered a species of concern until more biological research 

can resolve its conservation status (NatureServe 2002).

State

M. austroriparius is listed as endangered in Illinois, Indiana, 

Kentucky, and Oklahoma. It is a species of concern in Alabama, 

Arkansas, Missouri, South Carolina, Texas, and Virginia (table 1).

M. austroriparius is most common in Florida, where it is 

well adapted to the climate. Surveys have not been conducted 

to estimate the total population of M. austroriparius. Population data are fairly scarce and concerns about accuracy of 

count methods among areas and sampling methods are cited. 

Systematic, uniform population surveys have not been routinely 

conducted in portions of the species’ range outside of Florida. 

Even in Florida, where the best data are available, the population appears to have declined by 16 to 45 percent between 

1957 (Rice 1957) and 1994 (Gore and Hovis 1994). Gore and 

Hovis (1994) compared historical counts from maternity caves 

from various sources ranging from 1936 to 1982 with counts 

made in 1991 and 1992. Nine caves with a historical combined 

maximum use of 140,000 M. austroriparius had no individuals in the recent surveys. But recent surveys show that 85,000 

individuals occupied four caves lacking historical data. 

Demographic information on reproductive rates, 

recruitment rates, sex ratios, and movements between roosting 

sites and between maternity roosts and hibernacula in noncave 

maternity sites would be necessary to quantitatively estimate 

population viability. 

Table 1. Population status of Myotis austroriparius by State.1

State Status2 Historic 

estimate

Current 

estimate

Summer habitat 

(reported)

Winter habitat 

(reported) Threats

Alabama S2 Unknown 3,240a Caves, mines, 

buildings, and 

trees

Caves Human disturbance, loss of suitable 

roosting sites, loss of habitat

Arkansas S2 Unknown Trees and bridges Caves and 

mines

Human disturbance, loss of suitable 

roosting sites, loss of habitat

Florida S3 400,000b 320,000c Caves and 

buildings

Caves Human disturbance, loss of suitable 

roosting sites, loss of habitat

Georgia S3 Unknown Few thousand Human disturbance, loss of suitable 

roosting sites, loss of habitat
50 Conservation Assessments for Five Forest Bat Species in the Eastern United States

Table 1. Population status of Myotis austroriparius by State1 (continued).

a

 Hudson, 1999.

b

 Rice, 1957.

c

 Gore and Hovis, 1998.

1

 Information about population and habitat use is based on literature cited. See text and References section. 

2

 Status based on Natural Heritage State Rarity ranks (NatureServe 2002). S1: Extremely rare; usually five or fewer occurrences in the State, or, in the case 

of communities, covering less than 50 hectares (ha) in aggregate; or may have a few remaining individuals; often especially vulnerable to extirpation. S2: 

Very rare; usually between 5 and 20 occurrences, or, in the case of communities, covering less than 250 ha in aggregate; or few occurrences with many 

individuals; often susceptible to becoming endangered. S3: Rare to uncommon; usually between 20 and 100 occurrences; may have fewer occurrences, but 

with a large number of individuals in some populations; may be susceptible to large-scale disturbances. S4: Common; usually more than 100 occurrences, 

but may be fewer with many large populations; may be restricted to only a portion of the State; usually not susceptible to immediate threats. SNR/SU: Status 

not ranked/Status uncertain, often because of low search effort or cryptic nature of the element. States in BOLD occur in Region 9.

State Status2 Historic 

estimate

Current 

estimate

Summer habitat 

(reported)

Winter 

habitat 

(reported)

Threats

Illinois S1 Unknown Unknown Trees Caves and 

mines

Human disturbance, loss of 

suitable roosting sites, loss of 

habitat

Indiana S1 Unknown Presumed 

extirpated

NA NA Human disturbance, loss of 

suitable roosting sites, loss of 

habitat

Kentucky S1 Unknown Unknown Trees, caves, 

mines, and 

bridges

Human disturbance, loss of suitable 

roosting sites, loss of habitat

Louisiana S4 Unknown Trees Trees Human disturbance, loss of suitable 

roosting sites, loss of habitat

Mississippi S1 Unknown Human disturbance, loss of suitable 

roosting sites, loss of habitat

Missouri SU Unknown Unknown Unknown Human disturbance, loss of 

suitable roosting sites, loss of 

habitat

North 

Carolina

Unknown Trees Human disturbance, loss of suitable 

roosting sites, loss of habitat

Oklahoma S1 Unknown Trees Human disturbance, loss of suitable 

roosting sites, loss of habitat

South 

Carolina

S2, S3 Unknown Trees Human disturbance, loss of suitable 

roosting sites, loss of habitat

Tennessee S3 Unknown Human disturbance, loss of suitable 

roosting sites, loss of habitat

Texas S3 Unknown Trees Buildings, 

bridges, and 

caves

Human disturbance, loss of suitable 

roosting sites, loss of habitat

Virginia S1, S2 Unknown Human disturbance, loss of suitable 

roosting sites, loss of habitat
Conservation Assessments for Five Forest Bat Species in the Eastern United States 51

Habitat Status

Summary of Land Ownership and Existing Habitat 

Protection

National Forests 

Estimates of the potential available habitat for M. austroriparius were based on U.S. Department of Agriculture (USDA) 

Forest Service Forest Inventory and Analysis (FIA) data, which 

estimate the amount of upland hardwood and pine-hardwood 

forest land more than 60 years old for all States with national 

forests in Regions 8 and 9 (Southern and Eastern Forest Service 

Regions combined to look at the entire species range) and 

Region 9 (examined alone to look at potential available habitat 

for States in the Eastern Region), excluding rarely used deciduous forest types such as aspen. This coarse-scale assessment 

of habitat availability considers forest type and age class based 

on USDA Forest Service FIA data (USDA Forest Service 

2003). This analysis does not consider other aspects of forest 

structure that may influence use by this species. The database 

used is subject to sampling errors associated with coarse-scale 

inventory. Estimates were for the acreage of upland hardwood 

and pine-hardwood forest land for forests of all ownerships, 

including other federally owned, State-owned, county/municipal-owned, and privately owned lands within these States. Approximately 3.8 percent of upland hardwood, bottom-land hardwood, and pine-hardwood forest types occur on National Forest 

System (NFS) lands within the range of this species; less than 1 

percent occur on NFS lands within Region 9. Ninety percent of 

the potential habitat for this species occurs on privately owned 

lands (figs. 2 and 5). Estimates indicate that 347,529,086 acres 

of upland hardwood, bottom-land hardwood, and pine-hardwood forest land that could potentially serve as foraging habitat 

occur within the range of this species. Estimates also indicate 

that stands more than 60 years old in upland hardwood, bottomland hardwood, and pine-hardwood forest types would provide 

suitable trees to meet the roosting requirements of this species. 

Within the range of M. austroriparius, estimates indicate that 

93,673,155 acres, or 27 percent of the total available, are more 

than 60 years old (figs. 3 and 4). On NFS lands within Region 9, 

estimates indicate that 11,359,361 acres of potential habitat 

(upland hardwood, bottom-land hardwood, and pine-hardwood 

forest types) and 3,925,418 acres of upland hardwood and pinehardwood forest types more than 60 years old (34.5 percent) are 

available for roosting and foraging (figs. 3 and 4). 

Figure 2. Ownership of upland hardwood, bottom-land 

hardwood, and pine-hardwood forest types within States 

overlapping the range of M. austroriparius. 

Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, 

Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South 

Carolina, Tennessee, Texas, Virginia.

Figure 3. Acreage by ownership of upland hardwood forest 

type and percentage of upland hardwood forest type more 

than 60 years old by ownership within States overlapping 

the range of M. austroriparius. 

Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, 

Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South 

Carolina, Tennessee, Texas, Virginia.
52 Conservation Assessments for Five Forest Bat Species in the Eastern United States

captures in the Bootheel Region in 2000 to 2002; none have 

been captured on the Mark Twain National Forest during fairly 

extensive surveys (Aars and Ims 2000, Amelon 2001). Mist-net 

surveys have been conducted in areas of potential habitat in several States. In South Carolina, Texas, and Illinois, surveys of old 

growth, bottomland, and swamp forests have been conducted 

(Clark et al. 1985, Gardner et al. 1991, Horner 1995, Horner 

and Mirowski 1996, Mirowsky et al. 2004). The primary objective of these surveys was to determine presence and distribution of the species rather than population size. This species is 

believed extirpated from Indiana (Whitaker et al. 2002). 

References

Aars, J.; Ims, R.A. 2000. Population dynamic and genetic 

consequences of spatial density-dependent dispersal in patchy 

populations. The American Naturalist. 155(2): 252-265.

Allen, A.A. 1921. Banding bats. Journal of Mammalogy. 2: 

53-57.

Amelon, S.K. 2001. Unpublished data. Columbia, MO: U.S. 

Department of Agriculture, Forest Service, North Central 

Research Station.

Bain, J.R. 1981. Roosting ecology of three Florida bats:

Nycticeius humeralis, Myotis austroriparius, Tadarida 

brasiliensis. Gainesville, FL: University of Florida. 88 p. M.S. 

thesis.

Barbour, R.W.; Davis, W.H. 1969. Bats of America. Lexington, 

KY: University of Kentucky Press. 286 p.

Best, T.L.; Carey, S.D.; Henry, T.H.; Caesar, K.G. 1992. 

Distribution and abundance of bats (Mammalia: Chiroptera) in 

coastal plain caves of southern Alabama. NSS Bulletin. 225: 

61-65.

Choate, J.R.; Jones, J.K.; Jones, J.C. 1994. Handbook of 

mammals of the South-Central States. Baton Rouge, LA: 

Louisiana State University Press. 336 p.

Figure 4. Acreage by ownership of pine and pine-hardwood 

forest types and percentage of pine and pine-hardwood 

forest types more than 60 years old by ownership within 

States overlapping the range of M. austroriparius.

Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, 

Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South 

Carolina, Tennessee, Texas, Virginia.

Figure 5. Acreage by ownership of bottom-land hardwood 

forest type and percentage of bottom-land hardwood forest 

type more than 60 years old by ownership within States 

overlapping the range of M. austroriparius. 

Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, 

Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South 

Carolina, Tennessee, Texas, Virginia.

State Summaries

Only three States in Region 9 are within the range of M. austroriparius. Missouri has a few individuals, as evidenced by 
Conservation Assessments for Five Forest Bat Species in the Eastern United States 53

Clark, D.R.; Bunck, C.M.; Cromartie, E.; LaVal, R.K. 1983. 

Year and age effects on residues of dieldrin and heptachlor in 

dead gray bats, Franklin County, Missouri—1976, 1977, and 

1978. Environmental Toxicology and Chemistry. 2: 387-393.

Clark, D.R., Jr. 1988a. Environmental contaminants and 

the management of bat populations in the United States. In: 

Proceedings, symposium on management of amphibians, 

reptiles, and small mammals in North America. Laurel, MD: 

U.S. Fish & Wildlife Service: 409-413.

Clark, D.R., Jr. 1988b. How sensitive are bats to insecticides? 

Wildlife Society Bulletin. 16: 399-403.

Clark, D.R., Jr. 2001. DDT and the decline of free-tailed bats 

(Tadarida brasiliensis) at Carlsbad Caverns, New Mexico. 

Archives of Environmental Contamination and Toxicology. 40: 

537-543.

Clark, D.R., Jr.; Cantu, R.; Cowman, D.F.; Maxson, D.J. 1998. 

Uptake of arsenic and metals by tadpoles at an historically 

contaminated Texas site. Ecotoxicology. 7: 61-67.

Clark, D.R., Jr.; Krynitsky, A.J. 1983. DDE in brown and 

white fat of hibernating bats. Environmental Toxicology and 

Chemistry. 31: 287-299.

Clark, M.K.; David, S.L.; Funderburg, J.B., Jr. 1985. The 

mammal fauna of Carolina bays, pocosins and associated 

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Conservation Assessments for Five Forest Bat Species in the Eastern United States 57

Conservation Assessment: Myotis leibii

(Eastern Small-Footed Myotis) in the 

Eastern United States

Sybill Amelon1 and Dirk Burhans2

Taxonomy and Nomenclature

The eastern small-footed myotis [Myotis leibii (Audubon and 

Bachman 1842) (f. G. mys mouse; and otis ear, and leibii in 

honor of G.C. Leib who collected the type specimen; i.e., 

Leib’s mouse-eared bat)] belongs to the class Mammalia, order 

Chiroptera, family Vespertilionidae, subfamily Vespertilioninae, 

genus/species Myotis leibii (Miller and Allen 1928). M. leibii is 

considered monotypic (Best and Jennings 1997). This species 

also has been identified by different common names: Leib’s bat 

(Audubon and Bachman 1842), least brown bat (Mohr 1934), 

and Leib’s masked bat or least bat (Hitchcock 1949).

Type location for the Vespertilio leibii (Audubon and 

Bachman 1842: 284) is Erie County, Michigan (=Ohio—Miller 

and Allen 1928: 172). Type location for the M. winnemana

(Nelson 1913: 183) is Plummers Island (=Montgomery County, 

Maryland—Hall 1981: 188).

Notes on Taxonomy

The M. leibii taxonomy has been confusing (Best and Jennings 

1997; Glass and Baker 1965, 1968). The epithet “subulatus” was 

used as M. subulatus leibii (Miller and Allen 1928); M. subulatus

was also used for M. ciliolabrum, a western species considered 

a subspecies of M. leibii. Based on morphometric measurements of the cranium (Audubon and Bachman 1842; van Zyll 

de Jong 1984, 1985), the western population is recognized as 

M. ciliolabrum and the eastern population as M. leibii. Additional biochemical evidence (Herd 1987) supported the conclusion that they are distinct species. Jones et al. (1992) listed 

these species as distinct; however, Wilson and Reeder (1993) 

did not. Best and Jennings (1997) followed Jones et al. (1992) 

and considered M. leibii monotypic. 

Description of Species 

Myotis leibii is the smallest Myotis in the Eastern United 

States. Characteristic measurements include wingspan, 212 to 

248 millimeters (mm); total length, 72 to 84 mm; tail length, 

30 to 39 mm; hindfoot, 6 to 8 mm and less than one-half as 

long as the tibia; ear, less than 15 mm and exceeds the length 

of the nose when laid forward; forearm, 30 to 36 mm; and 

skull, 12.3 to 13.3 mm. The braincase is somewhat flattened; 

the forehead slopes gradually from the rostrum, in contrast 

to that in other members of the genus. Weight ranges from 3 

to 8 grams (g) (mean summer weight 3.8 g) (Banfield 1974, 

Hamilton and Whitaker 1979, Schwartz and Schwartz 1981). 

The sexes of M. leibii are similar. Females have two mammae. 

The face, ears, wings, and interfemoral membranes are very 

dark brown to black. The dark face and ears appear as a mask. 

Pelage color varies dorsally from pale yellowish brown to 

golden brown; ventrally, pelage is paler. The hairs of the back 

are bi-colored—very dark at the roots and pale at the ends—

giving the back a yellowish-brown appearance. The base of the 

interfemoral membrane and the undersurface of the wings are 

sparsely furred. The tragus is long and pointed; the calcar has 

a prominent keel. The skull is short with a broad rostrum. The 

dental formula is i 2/3, c 1/1, p 3/3, m 3/3, total 38 (Best and 

Jennings 1997, Hamilton and Whitaker 1979). 

1

 Wildlife biologist, U.S. Department of Agriculture, Forest Service, North Central Research Station, Columbia, MO.

2

 Postdoctoral associate, Department of Fisheries and Wildlife Science, University of Missouri, Columbia, MO.
58 Conservation Assessments for Five Forest Bat Species in the Eastern United States

Biology, Life History, and Natural History

Reproductive Biology and Phenology

Little information about reproduction of M. leibii has been 

published. M. leibii is thought to be similar to sympatric Myotis 

that breed in the fall; spermatozoa are stored in the uterus 

of hibernating females until spring ovulation and a single 

pup is born in May or June (Barbour and Davis 1969, Godin 

1977, Hamilton and Whitaker 1979, Merritt 1987). Little is 

known about the development and survival of M. leibii young. 

Anecdotal evidence suggests females fly with newborns as 

early as June (Hobson 1998). Small maternity and nursery 

colonies of M. leibii have been reported in vacant or little-used 

buildings (Barbour and Davis 1969, Merritt 1987, Harvey et al. 

1999b), behind loose bark in trees, and in crevasses on bridges, 

all of which were significantly exposed to sunlight (MacGregor 

2002, Tuttle 1964). Maternity colonies were also located under 

exposed rocks on open ridges and in the expansion joint of a 

concrete bridge (MacGregor et al. 1999).

In Arkansas, a reproductively active male was observed 

on September 14 (Saugey et al. 1993), which is consistent with 

sympatric Myotis species that breed in the fall. Males may 

roost singly or in small groups (Barbour and Davis 1969) and 

may roost in sandstone rock shelters, on cliffs, in caves, and 

even in trees (MacGregor 2002). In Kentucky, males have been 

captured at the entrances of abandoned mines, railroad tunnels, 

and caves during the breeding season (MacGregor 2002). 

Hitchcock (1965) and Mohr (1952) reported sex ratios of 

1:1 at birth. Survival is reported to be greater for males (0.75) 

than for females (0.42); the additional burden of pregnancy 

to thermoregulation is a potential cause of lower survival in 

females (Hitchcock 1965, Hitchcock et al. 1984). 

Ecology and Behavior

M. leibii is one of the rarest bats in North America (Barbour 

and Davis 1969; Griffin 1940; Mohr 1934, 1952; Davis et al. 

1965; Gates et al. 1984). The species has been encountered 

most frequently during fall swarming activities and hibernation 

(Barbour and Davis 1969, Hitchcock 1949, Krutzsch 1966, 

McDaniel et al. 1982). Very little is known about the ecology 

and life history of this species. Concerning the Mammoth 

Cave region of Kentucky, Barbour and Davis (1969) reported, 

“M. leibii is fairly common in late summer flocks of migrating 

bats. The whereabouts of these individuals at other seasons is 

unknown.” 

In open habitats, M. leibii emits frequency-modulated 

(FM) echolocation calls that range from approximately 45 

to 80 kilohertz (kHz) and each has a duration of just under 

3 milliseconds (ms). Based on echolocation design and 

morphological characteristics of wingtip shape and aspect ratio, 

characteristics of foraging locations indicate high levels of 

vegetative clutter (Norberg and Raynor 1987).

M. leibii is reported to be among the hardiest of bats with 

respect to winter temperatures and hibernation (Harvey et 

al. 1981). This species is one of the last to enter hibernacula, 

seldom entering before mid-November (Godin 1977, Gunier 

and Elder 1973) and often departing by early March (Hicks 

2002, Mohr 1936). M. leibii inhabit hilly or mountainous areas 

and has been found at elevations of 300 to 780 meters (m) in 

Pennsylvania (Mohr 1932), 750 m in Virginia (Johnson 1950), 

1,125 m in Kentucky (Barbour 1951), and 675 m in Georgia 

(Baker 1967, Baker and Patton 1967). This species often is 

found in drafty locations near the openings of hibernacula 

where the temperature may drop below freezing and humidity is 

relatively low (Fenton 1972). 

Obligate associations with other species have not been 

observed. M. leibii has been observed roosting in the same 

hibernacula with Eptesicus fuscus, Pipistrellus subflavus, 

M. lucifugus, M. septentrionalis, M. sodalis, and Corynorhinus 

rafinesquii (Butchkowski 2001, Harvey 1989, Schwartz 1954, 

Sealander 1979, Tuttle 1964, Saugey et al. 1993).

Hibernation 

M. leibii appears to be an obligate hibernator, usually roosting 

singly or in small clusters (Fenton 1972, Schwartz 1954, Stihler 

and Brack 1977, Harvey et al. 1991). The largest hibernating 

cluster was reported from Ontario, where 142 individuals were 

clustered on 26 February (Hitchcock 1949). Periods of activity 

observed during hibernation suggest this species may not 

spend as much time in deep torpor as do other cave-hibernating 

species (Hitchcock 1946, Mohr 1936, Tuttle 1964). 
Conservation Assessments for Five Forest Bat Species in the Eastern United States 59

Food Habits

M. leibii is insectivorous and feeds on flying insects. This 

species forages mainly over water, emerging shortly after 

sunset. These bats can fill their stomachs within an hour of 

emerging. They reportedly fly slowly and distinctly at all levels 

of the understory and canopy but usually stay within 1 to 3 m of 

the ground (Barbour and Davis 1969, Harvey 1999, Harvey et 

al. 1999b, Linzey 1998, Merritt 1987).

Mortality and Predation Factors 

Available information indicates that in most areas of its range, 

M. leibii spends at least the coldest portions of the year in 

hibernacula, primarily in caves and mines. Mortality from 

vandalism, alteration of hibernation sites, disturbance, and 

natural events such as floods is likely to occur as has been 

documented for other Myotis species. Predators would be 

expected to be similar to those documented for similar species, 

including snakes, owls, hawks, raccoons, foxes, and domestic 

cats. Endoparasites and ectoparasites are expected to be similar 

to those found on similar bat species (Mumford and Whitaker 

1975, Whitaker and Loomis 1979, Whitaker and Mumford 

1973); they include mites and chiggers. 

Longevity 

A single longevity record for M. leibii exists. An individual bat 

is reported to have lived 12 years (Hitchcock 1965). 

Banding Data and Site Fidelity

Mohr (1936) found marked bats in the same cave in different 

seasons. Attempts to relocate these bats to alternative roosts 

resulted in their return to the original locations of their capture, 

suggesting some degree of site fidelity. 

Distribution

The current range of M. leibii is from Ontario and Quebec 

through New England then southward to Georgia and Alabama 

and west to Oklahoma, Arkansas, and Missouri, generally 

following the eastern mountain ranges (fig. 1). M. leibii has 

been documented in 125 hibernacula across southeastern 

Canada and the Eastern United States. Most of the occurrences 

have been documented in New York, Pennsylvania, West 

Virginia, and Virginia. Historically, this species has always been 

considered fairly rare with patchy distribution where it is found 

(Barbour and Davis 1969). 

Habitat Requirements

Maternity Period (May to August)

Roosting Habitat

The habitat for M. leibii is mostly in hilly or mountainous 

terrain where the geology provides fractures and cracks in 

exposed rock or in karst areas. Summer roost sites include 

caves, mines (Fenton 1972), buildings (Hitchcock 1955), rocks 

on exposed ridges, cracks in rock faces, outcrops (Harvey et 

al. 1991, Kiser 2001), and bridges (MacGregor 2002). Tuttle 

(1964) reported two individuals under a rock near a rock 

quarry in April in Tennessee. Barbour and Davis (1969), while 

hunting for snakes, discovered an individual under a stone on 

a hillside in Missouri. M. leibii has been observed resting in 

limestone caves in spring and summer in Virginia (Krutzsch 

1966). Several accounts have found this species roosting in 

Figure 1. The distribution of Myotis leibii. 

* = Isolated or questionable records.

Source: Bat Conservation International 2003, http://www.batcon.org.
60 Conservation Assessments for Five Forest Bat Species in the Eastern United States

human-made structures, including houses, barns, and bridges 

(MacGregor and Kiser 1998, Harvey et al. 1999a). Proximity to 

water may be a factor in maternity roost locations (MacGregor 

and Kiser 1998). 

Foraging Habitat

M. leibii has been observed foraging over ponds and streams 

(MacGregor and Kiser 1998).

Hibernation Period (October to April)

M. leibii uses caves, mines, and rock crevices as hibernation 

sites in winter where they can be found in narrow crevices, under rocks on the floor, in human-made tunnels, or in cracks in 

the wall or ceiling (McDaniel et al. 1982). This species usually 

hibernates singly but may be found in small groups with other 

members of its species or other species (Fenton 1972). The 

small size of these bats enables them to push into very small 

crevices and in breakdown areas of mines or caves, where it 

may be difficult to observe or count (Saugey et al. 1989). This 

species is believed to fly outside the hibernation site in winter (Hitchcock 1965, Schwartz 1954) and to accept full gates 

on the caves or mines it uses for hibernation (Currie 1999). 

M. leibii frequently hibernate horizontally instead of vertically 

(Butchkowski 2001, Godin 1977, Martin 1966, Stihler 2001). 

The eastern small-footed myotis seems to be more tolerant 

of temperature extremes and is commonly seen very close to 

cave or mine entrances where air temperatures can vary greatly 

and humidity is relatively low (Barbour and Davis 1969, Merritt 1987, Harvey et al. 1991). Fenton (1972) found M. leibii

to arouse from torpor below –9 oC compared to –4 oC for M. 

lucifugus. Loss of mass during hibernation from December to 

April was approximately 16 percent of body weight.

Potential Threats 

Natural or Human Factors

Disturbance during the hibernation or maternity periods is a 

significant factor in the widespread decline of cave- and minedependent bat species (Clark 1988b, Currie 1999). The main 

factor leading to population declines is destruction of roost 

sites, particularly hibernacula (Humphrey 1978, Sheffield and 

Chapman 1992). North American bat conservation efforts have, 

therefore, focused primarily on protecting hibernacula from 

vandalism and physical alterations.

Food chain poisoning by pesticides—in particular 

insecticides such as organochlorines and anticholinesterase—

has been demonstrated to negatively impact insectivorous 

bats (Clark 1988a, 2001; Cockrum 1952, 1970; Reidinger and 

Cockrum 1978; Clark et al. 1986; Fleming et al. 1983). Bat 

population declines have been attributed to pesticide poisoning 

(Brady et al. 1982, Geluso 1976, Reidinger 1976, Tuttle 1979), 

chemical pollution (Tuttle 1979), siltation of waterways (Tuttle 

1979), flooding (Hall 1962), and disturbance by humans 

(Fenton 1972, Humphrey 1978, Tuttle 1977, Brady et al. 1982, 

Fenton et al. 1980, Speakman et al. 1991). 

Present or Potential Risks to Habitat 

One major threat to M. leibii is the lack of knowledge about 

its life history needs and population status. Because of its 

propensity for mines and loose rock materials, this species 

may be threatened by activities related to mining and surface 

rock disturbance. Mines in several States are subject to 

closure, collapse, natural events such as flooding, or human 

disturbances. Widespread recreational use of caves, causing 

indirect and direct disturbances by humans during the 

hibernation period, poses the greatest known threat to this 

species. Altering cave and mine microclimates by modifying 

airflow patterns may pose a threat to this species. Because of 

its very small size and its association with mining activities, 

this species may be particularly vulnerable to pesticides, heavy 

metal accumulations, and environmental contaminants. 

Inadequacy of Existing Regulatory Mechanisms

A lack of information about the population status of M. leibii

may preclude it from necessary protection. Early bat roost 

protection efforts focused on eliminating or reducing human 

disturbances during critical hibernation and maternity periods 

by installing informative signs or “bat friendly” gates and 

fences. In some cases, these efforts were unfavorable because 

of limited understanding of bat behavior and cave microclimate 

factors. Protecting natural and human-made roosting structures 

is one of the highest priorities in all recovery plans for listed 

species. Funding and access to facilitate these protection 

measures are often unavailable.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 61

Population Status

Rangewide

Both Global Heritage Status and National Heritage Status are 

“3,” indicating this species is rare to uncommon (NatureServe 

2002). Individual State Heritage Status is described in State 

Summaries and in table 1. M. leibii is considered rare or 

uncommon throughout its range (Choate et al. 1994). This 

species was a former C2 candidate. 

Habitat Status 

Summary of Land Ownership and Existing Habitat 

Protection

National Forests

Estimates of the potential available habitat for M. leibii were 

based on U.S. Department of Agriculture (USDA) Forest 

Service Forest Inventory and Analysis (FIA) data, which 

estimate the amount of upland hardwood and pine-hardwood 

forest land more than 60 years old for all States with national 

forests in Regions 8 and 9 (Southern and Eastern Forest 

Service Regions combined to look at the entire species range) 

and Region 9 (examined alone to look at potential available 

habitat for States in the Eastern Region), excluding rarely 

used deciduous forest types such as aspen. This coarse-scale 

assessment of habitat availability considers forest type and age 

class based on USDA Forest Service FIA data (USDA Forest 

Service 2003); this analysis does not consider other aspects 

of forest structure that may influence use by this species. The 

database used is subject to sampling errors associated with 

coarse-scale inventory. Estimates were for the acreage of 

upland hardwood and pine-hardwood forest land for forests of 

all ownerships, including other federally owned, State-owned, 

county/municipal-owned, and privately owned lands within 

these States. Approximately 3.8 percent of upland hardwood, 

bottom-land hardwood, and pine-hardwood forest types occurs 

on National Forest System (NFS) lands within the range of this 

species; less than 1 percent occurs on NFS lands within Region 9. 

Of the potential habitat for this species, 90 percent occurs on 

privately owned lands (figs. 2 and 5). Estimates indicate that 

347,529,086 acres of upland hardwood, bottom-land hardwood, 

and pine-hardwood forest land that could potentially serve as 

roosting and foraging habitat occur within the range of this 

species. Estimates also indicate that stands more than 60 years 

old in upland hardwood, bottom-land hardwood, and pinehardwood forest types would provide suitable trees to meet 

the roosting requirements of this species. Within the range of 

M. leibii, estimates indicate that 93,673,155 acres, or 27 percent 

of the total available, are more than 60 years old (figs. 3 and 4). 

On NFS lands within Region 9, estimates show that 11,359,361 

acres of habitat (upland hardwood, bottom-land hardwood, and 

pine-hardwood forest types) and 3,925,418 acres of upland 

hardwood and pine-hardwood forest types more than 60 years 

old (34.5 percent) are available for roosting and foraging (figs. 3 

and 4). 

To date, reports from hibernacula counts indicate this species 

uses at least 125 caves or mines; M. leibii are usually present 

in these caves or mines in very low numbers. Of the available 

hibernacula count data, the highest numbers of hibernating 

individuals were reported from two sites in New York.

Figure 2. Ownership of upland hardwood, bottom-land 

hardwood, and pine-hardwood forest types within States 

overlapping the range of M. leibii.

Alabama, Arkansas, Connecticut, Delaware, Georgia, Indiana, Kentucky, 

Maine, Maryland, Massachusetts, Missouri, New Hampshire, New 

Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South 

Carolina, Tennessee, Vermont, Virginia, West Virginia.
62 Conservation Assessments for Five Forest Bat Species in the Eastern United States

State Summaries

Missouri. State status is undetermined (SU, table 1). The 

distribution and activity of bats on the Mark Twain National 

Forest were studied in the summer and fall between 1997 and 

2003. Surveys sampled upland flyways and ponds and riparian 

areas; M. leibii accounted for less than 1 percent of bats 

captured each year (Amelon 2001).

New Hampshire. State status is extremely rare (S1, table 1). 

New York. State status is very rare (S2, table 1). M. leibii are 

found near entrances of mines and caves during hibernation and 

associated with talus areas in summer surveys.

Ohio. State status is undetermined (SH, table 1).

Pennsylvania. State status is extremely rare (S1, table 1). An 

analysis of mammals in Pennsylvania based on population 

status, habitat, and threats ranked M. leibii as rare (Kirkland 

and Krim 1990). Dunn and Hall (1989) noted that 52 percent of 

Figure 3. Acreage by ownership of upland hardwood forest 

type and percentage of upland hardwood forest type more 

than 60 years old by ownership within States overlapping 

the range of M. leibii.

Alabama, Arkansas, Connecticut, Delaware, Georgia, Indiana, Kentucky, 

Maine, Maryland, Massachusetts, Missouri, New Hampshire, New 

Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South 

Carolina, Tennessee, Vermont, Virginia, West Virginia.

Figure 4. Acreage by ownership of pine and pine-hardwood 

forest types and percentage of pine and pine-hardwood 

forest types more than 60 years old by ownership within 

States overlapping the range of M. leibii.

Alabama, Arkansas, Connecticut, Delaware, Georgia, Indiana, Kentucky, 

Maine, Maryland, Massachusetts, Missouri, New Hampshire, New 

Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South 

Carolina, Tennessee, Vermont, Virginia, West Virginia.

Figure 5. Acreage by ownership of bottom-land hardwood 

forest type and percentage of bottom-land hardwood forest 

type more than 60 years old by ownership within States 

overlapping the range of M. leibii.

Alabama, Arkansas, Connecticut, Delaware, Georgia, Indiana, Kentucky, 

Maine, Maryland, Massachusetts, Missouri, New Hampshire, New 

Jersey, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South 

Carolina, Tennessee, Vermont, Virginia, West Virginia.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 63

Table 1. Population status of Myotis leibii by State1.

State Status2 Summer habitat (reported) Winter habitat (reported)

Alabama S1

Arkansas S1 Caves and mines

Delaware SU

Georgia S2

Indiana NAa Caves and mines

Kentucky S2 Buildings, bridges, caves, mines, rock outcrops, and trees Caves and mines

Maine S1

Maryland S1

Massachusetts S1a

Missouri SU Glades and rock outcrops Caves and mines 

New Hampshire S1b Caves and mines

New Jersey S1

New York S2a Bridges Caves and mines

North Carolina SU Rocky structures, cliffs, and bridges Caves, mines, and rock shelters

Ohio SHa

Oklahoma S1

Pennsylvania S1b Deciduous mixed forest, talus slopes, and hemlock forest Caves, mines, and rock outcrops

South Carolina S1

Tennessee S2 Under rocks, trees, and buildings

Vermont S1c Caves and mines

Virginia S1

West Virginia S1 Caves, rock outcrops, talus slopes, and rock shelters Caves and mines

a

 State Listed Species of Concern. 

b

 State Listed Endangered. 

c

 State Listed Threatened.

1

 Information about population and habitat use is based on literature cited. See text and References section.

2

 Status based on Natural Heritage State Rarity ranks (NatureServe 2002). S1: Extremely rare; usually five or fewer occurrences in the State, or, in the case 

of communities, covering less than 50 hectares (ha) in aggregate; or may have a few remaining individuals; often especially vulnerable to extirpation. S2: 

Very rare; usually between 5 and 20 occurrences, or, in the case of communities, covering less than 250 ha in aggregate; or few occurrences with many 

individuals; often susceptible to becoming endangered. SH: Historically known from the State but not verified for an extended period (usually more than 

15 years); this rank is used primarily when inventory has been attempted recently. SNR/SU: Status not ranked/Status uncertain, often because of low search 

effort or cryptic nature of the element. 
64 Conservation Assessments for Five Forest Bat Species in the Eastern United States

Pennsylvania hibernacula were small caves of less than 150 m 

(500 feet) in length. Habitat is mostly in hilly or mountainous 

areas, in or near deciduous or evergreen forest, and sometimes 

in mostly open farmland. In Pennsylvania, Mohr (1932) found 

this species mostly in heavy hemlock forests in the foothills of 

mountains that rise to 2,000 feet (600 m).

Vermont. State status is extremely rare (S1, table 1). Reported 

only in Bennington, Orange, Rutland, and Windsor Counties.

West Virginia. State status is extremely rare (S1, table 1). 

M. leibii has been seen resting in limestone caves in West 

Virginia in spring and summer (Krutzsch 1966). Existence of 

M. leibii has been reported in Fayette, Grant, Greenbrier, Hardy, 

Mercer, Monongalia, Monroe, Morgan, Nicholas, Pendleton, 

Pocahontas, Preston, Randolph, Tucker, and Webster Counties.

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Conservation Assessments for Five Forest Bat Species in the Eastern United States 69

Conservation Assessment: Myotis 

septentrionalis (Northern Long-Eared Bat) 

in the Eastern United States

Sybill Amelon1 and Dirk Burhans2

Taxonomy and Nomenclature

The northern long-eared bat [Myotis septentrionalis (Trouessart 

1897) (f. G. mys mouse; otis ear; and L. septentrionalis

northern; i.e., northern mouse-eared bat )] belongs to the 

class Mammalia, order Chiroptera, family Vespertilionidae, 

subfamily Vespertilioninae, genus/species M. septentrionalis

(van Zyll de Jong 1979). Alternative common names include 

eastern long-eared bat and northern long-eared myotis. This 

species was previously identified as a subspecies of M. keenii

(Miller and Allen 1928). M. keenii and M. septentrionalis

occupy nonoverlapping ranges; thus, any reference to M. keenii

outside the Pacific Northwest refers to M. septentrionalis

(Caceres and Barclay 2000). No subspecies are recognized. 

Alternative historic nomenclature includes the following:

• Vespertilio gryphus var. septentrionalis: Type location is 

Halifax, Nova Scotia (Trouessart 1897).

• M. keenii septentrionalis (Miller and Allen 1928: 105). 

Type location not stated.

Van Zyll de Jong (1979) proposed dividing M. keenii into 

two distinct species. Manning (1993) suggested that M. keenii 

and M. septentrionalis are sister species, whereas Nagorsen and 

Brigham (1993) argued that M. evotis and M. septentrionalis

are sister species, based on external and cranial characteristics.

Description of Species

Myotis septentrionalis is a medium-sized bat of the Eastern 

United States and Canada. Characteristic measurements include 

wingspan, 228 to 258 millimeters (mm); total length, 77 to 

100 mm; tail length, 35 to 48 mm; hindfoot, 8 to 10 mm (the 

hindfoot generally is less than 60 percent of the length of the 

tibia); ear, 14 to 19 mm; forearm, 34 to 39 mm; and skull, 14.6 

to 15.6 mm. Weight ranges from 5 to 10 grams (g). Females 

are consistently heavier than males (Caire et al. 1979, Williams 

and Findley 1979). Pelage color dorsally is light brown or 

gray-brown; ventrally, pelage is sometimes a paler gray-brown 

to light gray. The wing membranes are of similar color to the 

dorsal pelage. A characteristic feature is the long ears that 

extend past the nose when laid forward. Juvenile pelage is 

duller than adult pelage. The tragus is straight, very long (10 

to 12 mm), and distinctly pointed at the end. The calcar is 

not keeled in eastern areas of the species’ range but may be 

slightly keeled in northeastern areas. The third, fourth, and fifth 

metacarpals are nearly equal. The skull is narrow with a long 

rostrum. The dental formula is i 2/3, c 1/1, p 3/3, m 3/3, total 38. 

Biology, Life History, and Natural History

Reproductive Biology and Phenology

M. septentrionalis is polygamous. Breeding activity occurs 

in the fall and potentially extends into the spring. Initiation 

of swarming and breeding activities varies by geographic 

location, but, in general, these activities occur from late 

July in the northern part of the species’ range to late August 

in the southern end of the range. Breeding activity extends 

into September and October. Histological data suggest that 

M. septentrionalis males behave in a manner similar to other 

North American vespertilionid bats in displaying testicular 

gametic function in summer followed by a regression of 

the gonads before mating and hibernation. Hibernating 

females store sperm in their uteruses until spring ovulation 

(Racey 1982). Females begin leaving hibernacula in March 

(southern areas) through May (northern areas), with maximum 

numbers leaving from late May to late June (south to north, 

respectively). 

1

 Wildlife biologist, U.S. Department of Agriculture, Forest Service, North Central Research Station, Columbia, MO.

2

 Postdoctoral associate, Department of Fisheries and Wildlife Science, University of Missouri, Columbia, MO.
70 Conservation Assessments for Five Forest Bat Species in the Eastern United States

The gestation period, measured from implantation to 

parturition, is estimated at 50 to 60 days (Baker 1983). One 

pup born in late May (south) to July (north) is typical (Amelon 

2001; Kunz 1971; Kurta 1980, 1982; Caire et al. 1979).Volant 

young have been observed as early as 3 weeks following 

parturition (Amelon 2001; Kunz 1971, 1973; Feldhammer et al. 

2001). In Iowa and New Hampshire, subadults were captured as 

early as July (Clark and Rattner 1987, Sasse and Pekins 1996). 

Data available from the literature suggest that differences in 

maturity rates vary by geographical location of the population. 

Subadult M. septentrionalis have been observed at hibernacula 

in early August in Missouri (LaVal and LaVal 1980). 

Ecology and Behavior

Comparisons of wing morphology with known habitat 

associations suggest that bats with low aspect ratios forage in 

the high clutter of forests while those with high aspect ratios 

forage in more open areas. The wings have an aspect ratio of 

5.8 and wing loading of 6.8 (Norberg and Raynor 1987). The 

wingtip is very rounded. Each of these structural characteristics 

is consistent with bats that use a “gleaning” foraging strategy, 

which indicates they have adapted to foraging in canopy gaps 

and forested areas characterized by open understories and 

low density where the bats can capture prey items moving on 

foliage (Amelon 2001). Faure et al. (1993) found this species 

produces 1 millisecond frequency-modulated echolocation 

calls with a frequency range of 60 to 126 kilohertz and an 

intensity of 78 decibels at 10 centimeters, which is consistent 

with a bat using a gleaning foraging strategy (Fenton et al. 

1983, Neuweiler 1989). 

M. septentrionalis’ winter and summer ranges were 

reported to be the same (Barbour and Davis 1969); however, 

the lack of hibernacula or reproductively active individuals 

suggests that portions of the population may move seasonally. 

Kurta (1982) suggested populations in areas of southern 

Michigan that have no caves or mines may move to southern 

areas of the range during the winter. An individual male 

captured in Missouri traveled 56 kilometers (km) in a month 

from a cave to an apparent summer location where it was 

recaptured behind a shutter on a house (Caire et al. 1979). 

Griffin (1940) reported an individual that moved at least 97 km 

between two caves between February and April. 

Disproportionate sex ratios have been reported, suggesting 

geographic or habitat segregation. Kunz (1971) in Iowa and 

Grindal (1999) in Newfoundland found a 2:1 ratio of females 

to males in summer riparian habitat. Most of the males were 

captured in May and August, when they moved between winter 

and summer locations. In Arkansas, Wilhide et al. (1998) found 

a 1.2:1 ratio of females to males during trapping activities 

at upland ponds. Whitaker and Rissler (1992a) found a ratio 

of 1:1.2 females to males between November and March at 

a hibernacula in Indiana. Griffin (1945), Hitchcock (1949), 

Pearson and Barr (1962), and Stones (1981) found distribution 

of sexes at hibernacula to range from 60 to 78 percent males in 

hibernacula surveys. These authors suggested that females may 

have a higher mortality rate than males, but it seems equally 

feasible, based on high female ratios in summer habitat surveys 

that females may use less observable portions of hibernacula or 

different hibernacula from males.

In spring, M. septentrionalis disperses from hibernacula 

and migrates to maternity roosts. During the maternity period, 

sexes are segregated; females roost in small maternity colonies 

and males roost singly. Maternity colonies of 2 to 99 females 

have been reported (Burke 1999, Lacki and Ladeur 2001, 

Owen 2001, Menzel et al. 2000). Lactating females switch 

roost trees every 2 to 5 days (Foster and Kurta 1999, Lacki 

and Schwierjohann 2001, Owen 2001, Menzel et al. 2002). 

Individuals within the colony frequently may alternate their 

roost trees and association with other females of the group 

(Owen 2001, Sasse and Pekins 1996).

Obligate associations with other species have not been 

observed. M. septentrionalis has been observed in hibernacula 

with M. lucifugus, M. sodalis, M. grisescens, M. leibii, Eptesicus fuscus, and Pipistrellus subflavus, and they generally make 

up a small percentage of bats within a hibernacula (Graves and 

Harvey 1974, Hall 1981, Mumford and Cope 1964, Pearson and 

Barr 1962, Whitaker and Rissler 1992b, Caire et al. 1979).

Hibernation

Mammalian hibernation is characterized by periods of torpor 

interrupted cyclically by spontaneous arousal. Individuals 

aroused during hibernation tend to fly or move around between 

periods of torpor. M. septentrionalis appears to be an obligate 

hibernator. Caire et al. (1979) found prehibernation fat 
Conservation Assessments for Five Forest Bat Species in the Eastern United States 71

deposition of 41 to 45 percent with normal weights observed in 

the spring, which is consistent with fat deposition requirements 

of obligate hibernators. Hibernation occurs singly or in very 

small groups in caves and mines and potentially in crevices in 

hillsides or rock outcrops. Hibernating M. septentrionalis is 

usually found in crevices in the walls or ceilings of hibernacula 

(Caire et al. 1979, Whitaker and Gummer 2001). 

Food Habits

This species is likely an opportunistic insectivore (Kunz 1973). 

Analysis of stomach contents and fecal pellets (Brack and 

Whitaker 2001) revealed that the diet of M. septentrionalis

consists of species of lepidopterans, coleopterans, 

trichopterans, and dipterans. Prey items such as spiders and 

lepidopteran larvae made up 12.7 percent of the food found in 

the bats’ stomachs, further supporting the gleaning foraging 

strategy of this species. In West Virginia, Carter et al. (2003) 

found diets of M. septentrionalis consisted of coleopterans 

and lepidopterans. In the Central Appalachians, Griffith and 

Gates (1985) found the species’ diet consisted of lepidopterans, 

coleopterans, neuropterans, and dipterans.

Mortality and Predation Factors

Failure to store sufficient fat reserves may cause significant 

mortality among subadults during the first hibernation period 

(Davis and Reite 1967). No consistent predators were noted. 

Human disturbance and persecution at hibernacula may be 

significant in some locations. Ectoparasites include batbugs 

(Cimex adjunctus), chiggers (Euschoengastia pipistrelli), 

and mites (Spinturax americanus) (Sasse and Pekins 2000, 

Whitaker and Mumford 1973). 

Longevity

Age structure is unknown. The highest longevity record for 

M. septentrionalis is an individual found dead in a cave 

19 years after initial capture (Hall et al. 1957). 

Banding Data

Banding information has been associated primarily with 

activities at the hibernacula. Hall and Brenner (1968) reported 

a 5.8-percent recapture rate for individuals that were banded 

during swarming activities and were subsequently found 

hibernating. 

Site Fidelity 

In homing experiments, Griffin (1945) found high return rates 

for bats released away from their capture site. One individual 

returned 51.5 km to its home cave in 2.5 hours after being held 

3 days in captivity. Caire et al. (1979) banded 945 individuals at 

hibernacula in Missouri; 47 individuals (4.9 percent) were subsequently recaptured at the same hibernacula the following fall. 

Similarly, in Ohio, Mills (1971) recaptured 4.8 percent of 358 

individuals at their cave of origin the year after initial capture. 

Distribution

M. septentrionalis occurs throughout most of the Eastern 

United States and southern Canada (Hamilton and Whitaker 

1979). The northern border of the range is Newfoundland, 

Quebec, and the Northwest Territories of Canada. The range 

extends southward along the East Coast to Florida and then 

westward through Alabama, Arkansas, and the eastern Great 

Plains (Hamilton and Whitaker 1979, van Zyll de Jong 1985, 

Harvey et al. 1991) (fig. 1). Although M. septentrionalis is 

widespread, its distribution may be irregular or patchy. It is 

more common in the northern part of its range than in the 

southern and western areas. This species is reported to be very 

Figure 1. The distribution of Myotis septentrionalis.

* = Isolated or questionable records.

Source: Bat Conservation International 2003, http://www.batcon.org.
72 Conservation Assessments for Five Forest Bat Species in the Eastern United States

rare in Alabama (Best 2001) and uncommon in Kentucky, 

Tennessee, and Wisconsin (Mumford and Cope 1964, Hamilton 

and Whitaker 1979). 

Habitat Requirements

Maternity Period (May to August)

Roosting Habitat

Maternity roosting sites vary by geographic location. Roost 

sites selected, regardless of geographic location, are warm 

sites that maximize growth rate of the young. Male roost sites 

and nonreproductive female summer roost sites may be found 

in cooler locations including caves and mines. Maternity 

colonies have been reported in tree cavities and crevices, under 

exfoliating bark, in live trees, and in expansion joints of bridges 

(Foster and Kurta 1999, Lacki and Ladeur 2001, Owen 2001, 

Feldhammer et al. 2003, Menzel et al. 2002). A colony of 99 

females was reported using a “rocket box” type bat house. The 

preference of tree species depends on the geographic location. 

In Michigan, M. septentrionalis roosted in crevices, in hollows, 

or under the bark of maple (Acer saccharinum) and ash 

(Fraxinus pennsylvanica) (Foster and Kurta 1999). 

In West Virginia, Owen (2001) found maternity roosts 

in cavities or under exfoliating bark in 11 tree species. Black 

locust (Robinia pseudoacacia) and black cherry (Prunus 

serotina) were used in higher proportions than availability of 

these species. The largest maternity colony (88 individuals) 

recorded in this study was observed exiting a cavity in a 

live black cherry tree. Additional tree species reported as 

M. septentrionalis maternity roost sites include elm (Ulmus 

spp.) (Clark et al. 1987), American beech (Fagus grandifolia) 

(Sasse and Pekins 1996), and sourwood (Oxydendrum

arboreum) and shortleaf pine (Pinus echinata) (Lacki and 

Schwierjohann 2001). Lacki and Schwierjohann (2001) also 

found roosts to be associated with upper slopes and midslopes.

Foraging Habitat

M. septentrionalis typically occurs in forested habitats, in small 

openings, and occasionally over water. LaVal and Clawson 

(1977) observed 11 individuals foraging among trees along 

hillsides and ridges instead of riparian areas. In Iowa, Kunz 

(1971, 1973) found females that foraged in mature deciduous 

uplands and occasionally in adjacent floodplains and agricultural lands. Peak foraging occurs the first 2 hours after dusk and 

the last 2 hours before dawn. 

Hibernation Period (October to April)

The use of different types of hibernacula varies geographically. 

Suitable conditions for hibernacula include high humidity, consistently low temperature, and lack of disturbance. Mines with 

temperatures of 7 to 9 oC in Michigan accounted for approximately 50 percent of the observed hibernating population (Andersen and Robert 1971). The species used caves, mines, and 

rock crevices as winter hibernation sites (Harvey et al. 1999a, 

1999b). Whitaker and Rissler (1992b) observed M. septentrionalis using tiny cracks in the wall of an abandoned mine in 

Indiana. The difficulty in observing these bats in small crevices 

may in part explain the disparity between relatively high numbers of this species recorded in summer surveys and the low 

numbers recorded in hibernacula counts. Hibernation counts for 

this species rarely exceed 100 individuals.

Potential Threats

Natural or Human Factors

Factors contributing to population declines include flooding 

(Hall 1962); disturbance by humans and vandalism of 

hibernacula (Fenton 1970, Humphrey 1978, Speakman et al. 

1991, Thomas 1993, Tuttle 1979); mine closures (Whitaker 

and Gummer 1992); and nursery roost removal. Disturbance 

during the hibernation or maternity periods is a significant 

factor in the widespread decline of cave- and mine- dependent 

bat species (Clark 1987, Currie 1999). Destruction of roost 

sites, particularly hibernacula, is the foremost factor leading 

to population declines (Humphrey 1978, Sheffield and 

Chapman 1992). North American bat conservation efforts have 

therefore focused primarily on protecting hibernacula from 

vandalism and physical alterations. Food chain poisoning by 

pesticides—in particular insecticides such as organochlorines 

and anticholinesterase—has been demonstrated to negatively 

impact insectivorous bats; these impacts may not result in death 
Conservation Assessments for Five Forest Bat Species in the Eastern United States 73

but in impairment of productivity (Clark 1988, 2001; Clark 

and Krynitsky 1983; Cockrum 1970; Reidinger and Cockrum 

1978). Colonies could be slow to recover because of low 

reproductive rates. 

Present or Potential Risks to Habitat

Although much still has to be learned about the maternity and 

winter habitat requirements of this species, initial information 

on summer habitat indicate M. septentrionalis uses dead or 

damaged trees in landscapes that include upland hardwoods or 

pine-hardwood forest types. Because this habitat is widespread 

and abundant in eastern North America, the primary risk to 

habitat may be for wintering habitat or may involve pesticide 

exposure in summer habitats. The widespread recreational use 

of caves and indirect or direct disturbance by humans during 

the hibernation period pose the greatest known threat to this 

species. One major threat is the lack of knowledge about the 

species’ life history needs and population status. Altering cave 

and mine microclimates by modifying air flow patterns may 

pose a threat to this species. 

Table 1. Population status of Myotis septentrionalis by State 1.

State Status2 Summer habitat Winter habitat

Alabama S2

Arkansas S2 Tree cavities, crevices, and under bark Caves and mines

Connecticut SNR/SU

Delaware SNR/SU

Florida SH

Georgia S3

Illinois S4 Caves and mines

Indiana S3 Trees and buildings

Iowa S4 Trees Caves and mines

Kansas S2 Trees Caves and mines

Kentucky S4 Trees Trees, caves, mines, and bridges

Maine S4

Maryland S4

Inadequacy of Existing Regulatory Mechanisms

Early bat roost protection efforts focused on eliminating or 

reducing human disturbance during critical hibernation and 

maternity periods by installing informative signs or “bat 

friendly” gates and fences. In some cases, these efforts were 

unfavorable to bat populations because of changes in bat 

behavior and/or changes in cave microclimate factors due to 

construction activities. Protecting natural and human-made 

roosting structures is one of the highest priorities including 

maintaining water features associated with roosts. Funding 

to facilitate these protection measures is often unavailable. 

Hibernation counts to assess trends have not been consistent for 

this species.

Population Status 

Rangewide

Both Global Heritage Status and National Heritage Status 

is “4,” indicating the species is common (NatureServe 

2002). Individual State Heritage Status is described in State 

Summaries and in table 1.
74 Conservation Assessments for Five Forest Bat Species in the Eastern United States

Table 1. Population status of Myotis septentrionalis by State 1 (continued).

Massachusetts S3

Michigan SNR/SU Trees Mines

Minnesota S3

Mississippi S3

Missouri S3 Tree cavities, crevices, and under bark Caves and mines

Montana S2

Nebraska S3

New Hampshire S3

New Jersey SNR/SU 

New York S3

North Carolina S3 Trees Caves

North Dakota SNR/SU

Ohio SNR/SU

Oklahoma S2 Trees

Pennsylvania S3 Caves

Rhode Island S2

South Carolina S4 Trees

South Dakota S3

Tennessee S4

Vermont S4

Virginia S3

West Virginia S3

Wisconsin S4

1

 Information about population and habitat use is based on literature cited. See text and References section.

2

 Status based on Natural Heritage State Rarity ranks (NatureServe 2002). S2: Very rare; usually between 5 and 20 occurrences, or, in the case of 

communities, covering less than 250 hectares in aggregate; or few occurrences with many individuals; often susceptible to becoming endangered. S3: Rare 

to uncommon; usually between 20 and 100 occurrences; may have fewer occurrences, but with a large number of individuals in some populations; may be 

susceptible to large-scale disturbances. S4: Common; usually more than 100 occurrences, but may be fewer with many large populations; may be restricted 

to only a portion of the State; usually not susceptible to immediate threats. SH: Historically known from the State, but not verified for an extended period 

(usually more than 15 years); this rank is used primarily when inventory has been attempted recently. SNR/SU: Status not ranked/Status uncertain, often 

because of low search effort or cryptic nature of the element. 

State Status2 Summer habitat Winter habitat
Conservation Assessments for Five Forest Bat Species in the Eastern United States 75

Habitat Status

Summary of Land Ownership and Existing Habitat 

Protection

National Forests

Estimates of the potential available habitat for M. 

septentrionalis, were based on U.S. Department of Agriculture 

(USDA) Forest Service, Forest Inventory and Analysis (FIA) 

data, which estimates the amount of upland hardwood and 

pine-hardwood forest land more than 60 years old for all 

States with national forests in Regions 8 and 9 (Southern 

and Eastern Forest Service Regions combined to look at the 

entire species range) and Region 9 (examined alone to look at 

potential available habitat for States in the Eastern Region), 

excluding rarely used deciduous forest types such as aspen. 

This coarse-scale assessment of habitat availability considers 

forest type and age class based on USDA Forest Service FIA 

data (USDA Forest Service 2003); this analysis does not 

consider other aspects of forest structure that may influence 

use by this species. The database used is subject to sampling 

Figure 2. Ownership of upland hardwood, bottom-land 

hardwood, and pine-hardwood forest types within States 

overlapping the range of M. septentrionalis.

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New 

Hampshire, New Jersey, New York, North Carolina, North Dakota, Ohio, 

Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, 

Tennessee, Vermont, Virginia, West Virginia, Wisconsin.

Figure 3. Acreage by ownership of upland hardwood forest 

type and percentage of upland hardwood forest type more 

than 60 years old by ownership within States overlapping 

the range of M. septentrionalis.

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New 

Hampshire, New Jersey, New York, North Carolina, North Dakota, Ohio, 

Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, 

Tennessee, Vermont, Virginia, West Virginia, Wisconsin.

errors associated with coarse-scale inventory. Estimates were 

for the acreage of upland hardwood and pine-hardwood forest 

land for forests of all ownerships, including other federally 

owned, State-owned, county/municipal-owned, and privately 

owned lands within these States. Approximately 5.9 percent of 

upland hardwood, bottom-land hardwood, and pine-hardwood 

forest types occur on National Forest System (NFS) lands 

within the eastern range of this species; 2.9 percent occur on 

NFS lands within Region 9 (figs. 2 and 5). Estimates indicate 

that 358,219,772 acres of upland hardwood, bottom-land 

hardwood, and pine-hardwood forest land could potentially 

serve as foraging habitat occur within the eastern range of 

this species. Estimates also indicate that stands more than 60 

years old in upland hardwood and pine-hardwood forest types 

would provide suitable trees to meet the roosting requirements 

of this species. Within the eastern range of M. septentrionalis, 

estimates indicate that 330,457,331 acres occur, and 88,687,204 

acres, or 27 percent of the total available, is more than 60 years 

old (figs. 3 and 4). On NFS lands within Region 9, estimates 

indicate 9,671,251 acres of potential foraging habitat (upland 

hardwood, bottom-land hardwood, and pine-hardwood forest 
76 Conservation Assessments for Five Forest Bat Species in the Eastern United States

types) and 3,786,768 acres of upland hardwood and pinehardwood forest types more than 60 years old (40.3 percent) 

are available for roosting (figs. 3 and 4). 

State Summaries

Illinois. State status is common (S4, table 1). In a study on the 

Shawnee National Forest that looked at 71 potential hibernation 

sites at caves and mines, mines were found to be the only 

sites used by M. septentrionalis (Whitaker and Winter 1977). 

Pearson and Barr (1962) found that 72 percent of individuals 

hibernating at silica mines were male. 

Indiana. State status is rare to uncommon (S3, table 1). 

Whitaker et al. (2002) assessed population levels over time 

of 10 species of bats in Indiana and found populations of 

M. septentrionalis to be relatively low but stable between 1980 

and 2000. Whitaker and Stacy (1996) found M. septentrionalis

at 5 of 13 abandoned coal mines that contained bats; this 

species accounted for 39 percent of the bats captured.

Michigan. State status is undetermined (SNR/SU, table 1). 

Up to 60 female M. septentrionalis in Michigan roosted in 

large-diameter, live or dead maple and ash trees (Foster and 

Kurta 1999). Individuals switched roosts frequently, and roost 

trees were clustered in a 20-hectare (ha) site. No significant 

differences were found between occupied and unoccupied 

roosts. Stones (1981) found more than 100 individuals in 5 of 

21 mines surveyed. This species accounted for approximately 

60 percent of winter population counts.

Minnesota. State status is rare to uncommon (S3, table 1). 

Goehring (1954) reported several M. septentrionalis bats 

hibernating in shallow crevices of a storm sewer with high 

relative humidity and temperatures ranging from 1.7 to 6.7 oC.

Missouri. State status is rare to uncommon (S3, table 1). The 

distribution and activity of bats on the Mark Twain National 

Forest were studied in the summer and fall between 1997 and 

2003. Surveys sampled upland flyways and ponds and riparian 

areas; M. septentrionalis accounted for 28 to 36 percent of 

Figure 5. Acreage by ownership of bottom-land hardwood 

forest type and percentage of bottom-land hardwood forest 

type more than 60 years old by ownership within States 

overlapping the range of M. septentrionalis.

Alabama, Arkansas, Florida, Georgia, Illinois, Indiana, Kentucky, 

Louisiana, Mississippi, Missouri, North Carolina, Oklahoma, South 

Carolina, Tennessee, Texas, Virginia.

Figure 4. Acreage by ownership of pine and pine-hardwood 

forest types and percentage of pine and pine-hardwood 

forest types more than 60 years old by ownership within 

States overlapping the range of M. septentrionalis.

Alabama, Arkansas, Connecticut, Delaware, Florida, Georgia, Illinois, 

Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Massachusetts, 

Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, New 

Hampshire, New Jersey, New York, North Carolina, North Dakota, Ohio, 

Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, 

Tennessee, Vermont, Virginia, West Virginia, Wisconsin.
Conservation Assessments for Five Forest Bat Species in the Eastern United States 77

bats captured each year. Both males (71 percent of captures) 

and females (59 percent of captures) were captured most 

frequently at upland ponds in summer. Streams accounted for 

17 percent of male captures and 22 percent of female captures; 

flyways and trails accounted for 12 percent of male captures 

and 13 percent of female captures. Fall captures in uplands 

and riparian areas represented only 5 percent of total captures 

(Amelon 2001).

New Hampshire. State status is rare to uncommon (S3, table 1). 

The summer roosting ecology of female M. septentrionalis

was studied on the White Mountain National Forest (Sasse 

and Pekins 1996). Of 281 bats captured during the study, 

M. septentrionalis represented 27 percent of the captures and 

M. lucifugus represented 71 percent. Of the M. septentrionalis 

bats, 26 were tracked to 47 roost trees; 66 percent of the roosts 

were beech and maple snags. Bats in this study switched roosts 

frequently. Roosts were occupied by a mean colony size of 

11 bats during pregnancy. There was no difference in colony 

sizes using live versus dead trees; however, 5 of 7 roosts with 

more than 24 bats were in snags. Snags used as roosts had 

larger diameters, more bark, and lower stand canopy closure 

than did random snags. Sasse and Pekins (1996) suggested that 

snag characteristics alone may not adequately describe roost 

characteristics because this species roosted in locations with 

higher mean live-tree diameters. 

Krusic et al. (1996) used ultrasonic detectors to survey the 

bat species’ flight activity in forests of varying age structure 

within the White Mountain National Forest. In this study, 

calls of Myotis species were grouped, and it would therefore 

be difficult to draw any inferences relative to the use of these 

habitats by M. septentrionalis. In addition, it has been shown 

that bat echolocation calls are strongly affected by the amount 

of clutter in the vicinity of the recorder. Bat echolocation calls 

are also affected by relatively small differences in temperature 

and relative humidity (Hayes 2000, Hayes and Gruver 2000, 

Livengood 2001). These limitations make it difficult to draw 

inferences about relative activity between habitat types or age 

classes without simultaneously accounting for differences in 

the size of sampled areas and differences in sound intensity 

between echolocation calls of different species.

Ohio. State status is undetermined (SNR/SU, table 1). The 

distribution and activity of bats on the Wayne National Forest 

were studied in the summer and winter of 1979 and 1980. 

Surveys were conducted at abandoned mines and riparian sites; 

M. septentrionalis was found hibernating in 23 of 65 coal mine 

shafts. M. septentrionalis accounted for less than 4 percent of 

the bats captured in summer surveys of riparian areas (Lacki 

and Bookhout 1983).

Pennsylvania. State status is rare to uncommon (S3, table 1). 

An analysis of mammals in Pennsylvania based on population 

status, habitat, and threats ranked M. septentrionalis as rare 

(Kirkland and Krim 1990). Between 1980 and 1988, 190 caves 

and abandoned mines were surveyed for bats. Hibernating 

bats were found at 135 sites, or 71 percent of the sites; 

M. septentrionalis was found at 34 of these locations (Kirkland 

and Krim 1990). 

Hall and Brenner (1968) found peak swarming activity 

occurred in mid-August. Males accounted for approximately 81 

percent of the captures.

Vermont. State status is common (S4, table 1). In surveys 

conducted in 1999 and 2000 on the Green Mountain National 

Forest, M. septentrionalis was the most commonly captured 

species (Reynolds 2000, Amelon et al. 2000). This species 

was captured at three of five locations along trails and roads 

in 2000. In 1999, M. septentrionalis was captured at 9 of 10 

locations. Of the 40 individuals caught in August, 26 were 

caught near hibernacula, 8 were caught over streams, and 1 was 

caught along a logging trail. Griffin (1940) found 78 percent 

individuals noted in hibernacula counts were male.

West Virginia. State status is rare to common (S3, table 1). 

Of 159 bats captured by Carter et al. (2003) in the Allegheny 

Plateau and the Ridge and Valley physiographic province, 40 

were members of M. septentrionalis (25 percent). The foraging 

area of 7 females averaged 61.1 ha (Menzel 1999). 

Wisconsin. State status is common (S4, table 1). An abandoned 

mine in southeastern Wisconsin contained approximately 1,000 

M. septentrionalis among 77,000 bats that included three other 
78 Conservation Assessments for Five Forest Bat Species in the Eastern United States

species. Males began arriving at the mine in July, and females 

began arriving in mid-August. Females were no longer detected 

after mid-October. Overall, males accounted for 60 percent of 

the captures at all sampling times. Spring departure began in 

late April; females left before males did.

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