Authors ROBIN E. CHRISTY is research assistant and STEPHEN D. WEST is associate 

professor, Wildlife Sciences Group, College of Forest Resources, University of 

Washington, Seattle, Washington 98195. This paper is a result of Supplemental 

Agreement PNW 90-351. 
Biology and Management 

of Old-Growth Forests 

Mark H. Huff, Richard S. Holthausen, and Keith B. 

Aubry, Technical Coordinators 

Biology of Bats in Douglas-Fir 

Forests 

Robin E. Christy and Stephen D. West 

U.S. Department of Agriculture, Forest Service 

Pacific Northwest Research Station Portland, 

Oregon General Technical Report PNW-GTR-308 

February 1993 
Abstract Christy, Robin E.; Stephen D. West. 1993. Biology of bats in Douglas-fir forests. 

Gen. Tech. Rep. PNW-GTR-308. Portland, OR: U.S. Department of Agriculture, 

Forest Service, Pacific Northwest Research Station. 28 p. (Huff, Mark H.; 

Holthausen, Richard M.; Aubry, Keith B., Tech. coords. Biology and management 

of old-growth forests). 

Twelve species of bats occur in Douglas-fir forests of the Pacific Northwest, of which 

nine are known to roost in tree cavities, bark crevices, or foliage, and several are 

closely associated with old-growth forests. Thus bat populations may be detrimentally 

affected by forest management practices involving the removal of large, old trees and 

snags. We review the life history characteristics and habitat relations of bats in the 

Pacific Northwest and provide information useful in managing forests for the 

persistence of native bat populations. 

Keywords: Bats, Pacific Northwest, natural history, old-growth forests. 
Preface Information about old-growth Douglas-fir forests and the wildlife species associated 

with them is critical to forest managers in the Pacific Northwest. Management of these 

forests has become a major public policy issue. Extremely high levels of concern have 

been expressed for a broad variety of values associated with old-growth forests, 

including ecological, social, and religious values as well as commodity values derived 

from timber production. Forest managers are faced with a need to devise balanced 

strategies that retain all these values at levels acceptable to the public and consistent 

with the National Forest Management Act. 

Forest acreage in an "old-growth" stage of development has declined rapidly in the 

Pacific Northwest since the 1950s. This has caused increasing concern about species' 

associations with old forests and maintenance of viable populations for the most 

closely associated species. Decisionmakers need to know which species show strong 

associations with old-growth forests and to understand the ecological requirements of 

those species. Methods and tools are needed to effectively manage and monitor these 

species and their habitat. 

The purpose of this series of publications on the "Biology and Management of 

Old-Growth Forests" is to summarize the life history characteristics and habitat 

relations of species showing strong associations with old-growth forests in Washington, 

Oregon, and northern California, and to suggest options for their management. 

University and Federal scientists who collaborated in the USDA Forest Service, Pacific 

Northwest Research Station, old-growth research program have produced a 

comprehensive list of associated species. Their technical research results were 

presented at a symposium in March 1989 in Portland, OR, and published in a book, 

"Wildlife and Vegetation of Unmanaged Douglas-Fir Forests." We offer this series of 

management publications as a sequel to that research and to address other issues 

related to the management of late seral ecosystems. The series is funded by the 

Wildlife Habitat Relationships Program, Pacific Northwest Region, USDA Forest 

Service. The goal is to provide timely information to managers so they can make 

well-informed decisions about the management of old-growth forests. 

Mark H. Huff 

Richard S. Holthausen 

Keith B. Aubry 
 1 Introduction 

 3 Reproduction and Survival 

 4 Foraging and Water Intake 

 7 Migration, Hibernation, and Movement Patterns 

 9 Roosts and Hibernacula 

13 Research on Bats in Old-Growth Douglas-Fir Forests 

15 Review of Other Bat Studies in the Pacific Northwest 

17 Conclusion and Research Needs 

20 Scientific Names 

20 Acknowledgements 

21 Literature Cited 

28 Glossary 

Contents 
Introduction As a group, bats have unique adaptations and occupy a specialized niche. They are the 

only mammals capable of true flight and have developed echolocation to a remarkable 

degree, capabilities making them the preeminent foragers of nocturnal flying insects. 

Bats belong to the order Chiroptera, meaning "hand wing." Their wings are actually 

hands, each finger functioning as a wing bone with the thumb as a claw at the leading 

edge of the wing. A thin sheet of skin connects the finger bones to form the wing, and in 

most species, an additional flight membrane stretches between the two hindlegs. 

Individuals of some species are capable of flying long distances; migratory species of 

the Pacific Northwest may fly from British Columbia to Mexico each year. Of the three 

families of bats found in North America, only one family, the Vespertilionidae (evening 

bats), occurs in the Pacific Northwest. 

The objectives of this paper are to describe the basic biology of bats inhabiting Douglasfir forests in the Pacific Northwest and to discuss their ecological relations with 

old-growth forests1

. Relatively little is known about many aspects of the ecology or 

population dynamics of bats in this region. To the extent possible, we will describe their 

natural history characteristics and habitat requirements. The best sources of information 

on Pacific Northwest bat populations are Cross (1976a) and Maser and others (1981). 

Fortunately, several bat species have distributions extending beyond the Pacific 

Northwest where they have been studied in greater detail; much of the available 

information pertains to populations in the Eastern United States and Canada. As 

appropriate, we have integrated this information into our discussion. Much of the general 

life history information we report comes from three sources: Barbour and Davis (1969), 

van Zyll de Jong (1985), and the Mammalian Species Series of the American Society of 

Mammalogists (Fenton and Barclay 1980, Kunz 1982a, Kunz and Martin 1982, Kurta and 

Baker 1990, Manning and Jones 1989, O'Farrell and Studier 1980, Shump and Shump 

1982, Warner and Czaplewski 1984). 

The USDA Forest Service's Old-Growth Forest Wildlife Habitat Research Program 

(Ruggiero and others 1991) was designed to evaluate the degree to which terrestrial 

vertebrates, including bats, are associated with old-growth Douglas-fir forests in the 

Pacific Northwest. This study is of particular importance because bats generally have 

been overlooked in vertebrate surveys, and very few studies have focused on the 

association of bats with different seral stages. According to echolocation and capture 

studies performed during this study, 12 species of bats inhabit Douglas-fir forests in the 

Washington Cascade and Oregon Coast Ranges (Thomas and West 1991). Certain 

species, such as the western small-footed myotis, generally are not regarded as 

forest-dwelling. Because they were captured during the old-growth study, however, they 

are included here. We caution that this list is based on limited data and should be 

considered interim until additional information on distribution and habitat requirements of 

forest-dwelling bats becomes available. 

Eight of the 12 species occurring in Douglas-fir forests of the Pacific Northwest are in the 

genus Myotis, the mouse-eared bats. These bats are small, weighing 4 to 9 grams with 

wingspans of 22 to 26 centimeters (see "Glossary"). Individual species of Myotis are 

similar to one another and can be difficult to identify (table 1). In addition to the Myotis 

bats, four other species belonging to separate genera occur in Douglas-fir forests: the 

big brown, silver-haired, Townsend's big-eared, and hoary bats. These species generally 

are larger than the Myotis bats, weighing 9 to 27 grams, and are identified easily: 

silver-haired and hoary bats are very distinctively colored, big brown bats are the largest 

brown species (much larger than the Myotis species), and Townsend's big-eared bats 

have relatively large ears and prominent glandular lumps on the nose (table 1). 

1 Scientific names for all species are given at the end of the text. 1
Diagnostic Western Little Long- Silver- 

Characteristicsa,b° California small-footed Keenís Yuma Long-eared brown Fringed legged haired 

Relative size:  Weight (grams) small small small small small-medium small-medium small-medium small-medium medium 

4-5 3-6 5 4-5.5 5-8 6.5-9.5 5-7 6.5-8.5 9-13 

Wings:  Membrane color almost black black almost black brown black dark brown black almost black black 

 Wingspan (centimeters) 22-23 21-25 21-26 22-27 25-29 22-27 27-30 25-27 27-31  Membrane hair hairless hairless hairless sparse hair hairless sparse hair hairless dense hair hairless 

 

Fur characteristics:  Sheen nonglossy nonglossy glossy nonglossy glossy glossy variable nonglossy glossy  Dorsal color dark brown- yellow dark brown black, red, light brown- black and light brown red brown- black with 

red brown brown-blond light brown yellow brown brown-yellow black white tips 

 Ventral color paler buff-white tan-buff paler dorsal colors paler paler dorsal colors paler  Relative length long long average average long long average average average Ear:  Color almost black black dark brown brown black dark brown black almost black black  Relative sizec 

 (millimeters) long (2-4) long (2-4) long (2-4) short (m1) very long (>5) short (t1) long (3-5) short (t1) short (t1) vFoot:  Size ratio to tibiad very small small medium large medium large medium very small medium 

0.37-0.46 0.48 0.50 0.53-0.56 0.50 0.53-0.56 0.50 0.41 0.50 

Calcar: keeled keeled small keel unkeeled unkeeled unkeeled unkeeled keeled unkeeled 

Tail membrane:  Edge hair hairless hairless sparse sparse small-fine sparse large-stiff hairless moderate  Dorsal hair hairless hairless hairless light furring hairless light furring hairless hairless moderate 

Echolocation call:  Frequency (kHz) 67-37 55-41 110-38e 80-40f 97-54 80-40 (25)g 49-31 89-40 30-25 

 Duration (milliseconds) 6 5 3e 5f 5 5 8 10 10 

Other diagnostic  characteristics: striking dark shoulder difficult to dark shoulder notch on ear ear shape 

black face spots distinguish spots; keel broad and lu

from little not reliable short 

 brown myotis character; 

longest ears of  any Myotis 

a The smaller species of Myotis are difficult to identify and a specialist should be consulted whenever possible. b Bats sometimes bite when handled and some individuals do have rabies. If they must be handled to identify, it is wise to wear gloves, especially when dealing with larger species. c Distance ears extend beyond tip of nose when pulled forward. d Foot-to-tibia ratio is a relative measure of the size of the foot. Useful in identification of Myotis bats.e Echolocation frequency and duration assumed to be similar to the northern myotis. f Echolocation frequency and duration assumed to be similar to the little brown myotis. g Echolocation drops to 25 kHz-"honk"-to avoid intraspecies collisions. 

Sources: van Zyll de Jong 1985, Barbour and Davis 1969, Fenton and Bell 1981. 

Table 1-Diagnostic characteristics of bats found in Douglas-fir forests in Washington and Oregon 

Myotis bats
Bats are an extremely diverse vertebrate group with worldwide distribution. Species 

range from 2 to 1500 grams and feed on many foods including fruit, insects, other 

vertebrates, blood, pollen, and nectar (Nowak 1991). In northern temperate regions, due 

to the seasonality of available resources, bats are insectivorous and nocturnal and either 

migrate south or hibernate during the winter. Pacific Northwest species comprise a 

relatively homogeneous group of bats with similar body sizes and diets. Because of this 

similarity and the limited nature of information available on the ecological relations of 

many species, we have organized the following discussion by major life history 

characteristics rather than individual species. 

Reproduction and 

Survival 

Pacific Northwest bats all have similar reproductive patterns. They mate in autumn or 

winter (September-February), and females store the sperm until spring (March-May), 

when ovulation and fertilization occur. Time of parturition differs with latitude (earlier in the 

south and later in the north) but occurs from late May through mid-July in the Pacific 

Northwest (Barbour and Davis 1969, Maser and others 1981). Myotis species and 

Townsend's big-eared bats give birth to one offspring per season; big brown, silver-haired, 

and hoary bats generally have two offspring but may have from one to four (Barbour and 

Davis 1969). 

Most Myotis species, big brown bats, and Townsend's big-eared bats are colonial 

breeders. They form large maternity colonies in the spring, which can range from 12 to 

500 individuals but generally contain less than 100. Colonies consist of the females and 

their young; males and nonbreeding females roost alone or in small groups separate from 

the maternity roosts. Colonialism reduces the energy costs of thermoregulation because 

clustering helps pregnant female bats maintain -high body temperatures, which promotes 

rapid fetal growth (McNab 1982; Racey 1973, 1982; Racey and Swift 1981). This energy 

savings shortens the gestation period, thereby allowing the young to develop sufficiently to 

survive hibernation or migration. Female bats also may benefit from increased rates of 

juvenile growth during the gestation and lactation periods: early weaning provides the 

female with more time to prepare for hibernation or migration, which increases her 

chances of survival. 

Silver-haired and hoary bats are generally considered solitary breeders, although a few 

nursery colonies of silver-haired bats are reported (Doutt and others 1966, Merriam 1884, 

Parsons and others 1986, Seton 1907). The young are born and raised in individual day 

roosts; females and young do not cluster in large colonies. Hoary bats are foliage 

roosters, and males, nonbreeding females, and breeding females with young generally 

roost in different levels of the canopy. Roosts of solitary adults often are located in the 

lower canopy. Clusters of females and their young are located high in the canopy, which 

reduces the risk of predation when the young are incapable of flight, and allows young 

bats the space they need while learning to fly (Constantine 1966). 

Reproductive activity is influenced by environmental conditions and availability of 

resources. Females who cannot forage daily because of cold and wet weather will go into 

torpor if they cannot generate the energy necessary to maintain a high body temperature. 

Pregnant females who enter torpor during gestation have delayed parturition (Racey 

1973, 1982; Racey and Swift 1981), which may result in the death of either the mother or 

her offspring. Although torpor is not an everyday strategy for male bats and may disrupt 

spermatogenesis, males and nonreproductive females may be able to withstand cool, wet 

conditions by entering torpor and conserving energy with little resulting loss in reproductive success (Kurta and Kunz 1988). In the Washington Cascade and Oregon Coast 

3
Ranges, climatic factors apparently affect the spatial distribution of reproductive 

individuals. Of the females trapped by Thomas and West (1991) at elevations from 300 

to 600 meters along the west side of the Washington Cascades, none was pregnant. 

Pregnant females were common, however, at similar elevations on the east side of the 

Washington Cascade Range and in the Oregon Coast Range. This difference in the 

distribution of reproductive females may be due to generally cold and wet conditions 

occurring during the breeding season (April-July) on the west side of the Washington 

Cascades. Thomas and West (1991) hypothesize that such conditions reduce the 

number of suitable foraging days and prevent females from breeding for the 

energy-related reasons outlined above. Similar patterns of reproductive activity have 

been found in the Rocky Mountains and the Cascade Range where nonreproductive 

females and males occupy higher elevations than do reproductive females (Fenton and 

others 1980, Perkins 1983). 

Considering their small body size, bats are extremely long-lived mammals. Myotis bats 

may live from 12 (western small-footed myotis) to 31 (little brown myotis) years, and 

individual little brown myotis over 10 years old are common (Fenton and Barclay 1980, 

Humphrey and Cope 1976, Paradiso and Greenhall 1967). Larger bats seem to have a 

slightly lower potential longevity; the oldest silver-haired bat on record was 12 years old 

(Schowalter and others 1978a), and big brown and Townsend's big-eared bats generally 

live from 15 to 20 years (Goehring 1958, Hitchcock 1965, Paradiso and Greenhall 1967). 

These data represent maximum potential longevity; the average life expectancy of most 

species is not known. 

Pacific Northwest bat species have many predators, but because bats are not a major 

prey item for any animal group, predation does not seem to be a major mortality factor. 

Mortality from predation generally occurs while bats are roosting or hibernating rather 

than when they are active. Most information on predation pertains to the little brown 

myotis and the big brown bat, the most extensively studied bat species in North America. 

Small carnivores, raptorial birds, domestic cats, fish, bullfrogs, and snakes have been 

known to prey on these species (Barbour and Davis 1969, Gillette and Kimbrough 1970, 

Kirkpatrick 1982). Deer mice often live in the hibernacula of little brown myotis and have 

been observed eating torpid, injured bats that have fallen from the ceiling 

(Trevor-Deutsch 1973). Little information exists regarding predation on other bat species, 

but they probably are subject to similar predation pressures (Barbour and Davis 1969). 

Accidents and the influence of people probably kill more bats than predators (see Mohr 

1972). Disturbance of hibernacula through cave exploration and bat banding has caused 

significant declines of bat populations (Gillette and Kimbrough 1970, Mohr 1972). When 

bats are disturbed, they come out of torpor, which causes them to lose weight and 

lessens their chances of survival (Davis and Hitchcock 1965). Other human activities 

also have been linked to widespread declines in bat populations. In the Eastern United 

States, the establishment of dams has flooded hibernacula (DeBlase and others 1965, 

Griffin 1953, Hall 1962), and the application of pesticides to control insect populations 

may affect bats by reducing food supplies and subjecting them to contaminated prey 

(Clark 1981). 

Pacific Northwest bats are insectivorous and nocturnal and use echolocation for hunting 

and orientation. When echolocating, a bat emits pulses of ultrasonic sound (above the 

upper limit of human hearing-about 20 kHz). When the pulses come into contact with an 

object, the sound waves are reflected and received by the bat, thus providing it with information about the size, direction, and nature of the object. Echolocation calls consisting 

predominately of high-frequency sound carry for short distances and are well suited to 

Foraging and Water 

Intake 

4 
Big brown bats (Eptesicus fuscus). 

hunting in structurally complex habitats. Low-frequency calls carry longer distances and 

are efficient in open habitats. There is a rough correlation between the size of bats and 

the frequency of their echolocation calls; small bats tend to use high frequencies and 

large bats, low ones. In addition, the echolocation calls of some species have sufficiently 

unique shapes (patterns of frequency per time) that they can be used to identify 

individual species. The pattern of the echolocation call for a given species also varies, 

however, depending on its purpose; for example, as a bat approaches a prey item, the 

pulse rate of the echolocation call becomes very rapid, thereby creating a sound called a 

"feeding buzz." Researchers can use the number of feeding buzzes as an index of 

foraging activity in different habitats. 

Most species occurring in this region are aerial foragers, but a few (long-eared and 

fringed myotis, big brown, and hoary bats) also glean insects from the ground or foliage 

and rely on vision as well as echolocation when hunting (van Zyll de Jong 1985). Bats 

consume vast quantities of insect pests; a single Myotis bat weighing about 5 grams can 

consume over 600 mosquito-sized insects in an hour (Griffin and others 1960). Insect 

prey apparently is selected by size rather than species (Ross 196; small bats tend to eat 

small insects and large bats eat large ones. Although most bats appear to forage 

opportunistically, often focusing on swarming or emerging insects, moths are an 

important component of the diet in many species2

 (Whitaker and others 1981 a). 

Bats feed throughout the night, but many species exhibit two distinct peaks in foraging 

activity corresponding to peaks in nocturnal insect abundance: one during the first few 

hours after sunset and the second in the last few hours before sunrise (van Zyll de Jong 

1985). The timing of emergence from day roosts differs by species and depends on 

weather and geographic location (Barbour and Davis 1969, van Zyll de Jong 1985). In 

the Pacific Northwest, early emergers (California, long-legged, little brown, and Yuma 

myotis; 

2 Personal communication. 1991. Stephen P. Cross, professor, Southern 

Oregon State College, Department of Biology, Ashland, OR 97520. 

5 
Townsend's big-eared bat (Plecotus townsendii).

big brown and silver-haired bats) may be seen well before sunset but generally emerge 

just at dusk. Late emergers (long-eared myotis; Townsend's big-eared and hoary bats) 

usually appear from 30 minutes to 1 hour after sunset (Maser and others 1981, Whitaker 

and others 1977). Emergence times for the western small-footed and fringed myotis in 

the Pacific Northwest are not known, but information from other parts of the country 

indicates that western small-footed myotis emerge early (just after sunset) and fringed 

myotis emerge late (1-2 hours after sunset) (Cockrum and Cross 1964, 1965; van Zyll de 

Jong 1985; Woodsworth 1981). 

After emerging in the evening, bats often seek open water for drinking (Bailey 1936), 

especially during the breeding season when lactating females have high water 

requirements. To drink, bats fly close to the water with their mouths open, skimming the 

surface with the lower jaw. Myotis bats may be able to drink from a pool as small as a few 

centimeters in diameter, whereas larger, less agile species, such as the hoary and big 

brown bats, need a larger surface area to drink from while in flight (Cross 1986). 

Although bats most often are observed foraging over water, many species also forage in 

forests, and many that occur in urban areas (for example, little brown myotis and big 

brown bat) commonly forage around street lights, over parks, and along city streets 

(Barbour and Davis 1969, Furlonger and others 1987, Geggie and Fenton 1985). 

Thomas and West (1991) found feeding rates of Myotis in Douglas-fir forests of 

Washington and Oregon to be about 10 times greater over water than in the forest 

interior, and in a Cana6 
dian study, little brown myotis were 75 times more active over lakes than in forested 

habitats (Lunde and Harestad 1986). These findings suggest that open water may 

provide critical foraging habitat in Pacific Northwest forests. 

In upland forests, most foraging appears to occur over clearings and roads, although 

when gleaning insects, some species may feed within the canopy. Recently harvested 

areas do not, however, seem to provide suitable foraging habitat; detections of little 

brown myotis were substantially reduced after clearcutting in British Columbia (Lunde 

and Harestad 1986). A few species are observed foraging in upland habitats more often 

than over water. Fringed myotis and hoary and Townsend's big-eared bats commonly 

feed along forest edges, roads, or open areas within the forest, and western small-footed 

bats typically forage along cliffs and slopes in dry areas (Barclay 1985, Black 1974, Kunz 

and Martin 1982, van Zyll de Jong 1985, Whitaker and others 1977). In contrast, Yuma 

myotis are unique among North American bats in that they forage almost exclusively 

over water. I n addition, their roost sites almost always are located close to open water 

(Barbour and Davis 1969, Herd and Fenton 1983, van Zyll de Jong 1985). 

Many species fly regular circuits while foraging, moving up and down roads and streams 

or in circular patterns over ponds and lakes (Barbour and Davis 1969, Grinnell 1918, 

Maser and others 1981, Schwartz and Schwartz 1959, van Zyll de Jong 1985). When 

foraging, big brown and hoary bats typically fly high over the water or ground surface (up 

to 50 meters), but most species generally forage below about 10 meters (Barbour and 

Davis 1969, Whitaker and others 1977). 

Migratory patterns differ considerably in bats, both within and among species, and are 

difficult to study. Information on migration comes primarily from reports of seasonal 

appearances and disappearances of species from a given area and from band 

recoveries (see Fenton and Thomas 1984, Griffin 1970). The majority of temperate bat 

species migrate relatively short distances (10-500 kilometers) from their summer ranges 

to winter hibernation sites. A few of the larger species, including the hoary bat, migrate 

much longer distances and may remain active throughout most of the winter. Some 

individuals or populations of any of these species may hibernate within their summer 

range and not migrate at all (Griffin 1970). 

Most species in the Pacific Northwest probably undergo relatively short migrations to and 

from hibernacula each year. Myotis species and Townsend's big-eared and big brown 

bats begin their migration to hibernation sites in October or November (Dalquest 1948). 

Adults generally enter hibernation earlier than juveniles, probably because they do not 

require as much energy for growth and because they are more experienced foragers and 

can acquire more quickly the fat needed for hibernation (Fenton 1970). Bats emerge 

from hibernation in the Pacific Northwest with the onset of warmer temperatures in 

March or April (Maser and others 1981). 

In this region, hoary bats and the majority of silver-haired bats are believed to migrate 

fairly long distances each year, although exact migration routes have not yet been determined (Shump and Shump 1982). A single museum specimen is the only known winter 

record of the hoary bat in the Pacific Northwest (Perkins and others 1990). Most hoary 

bats whose summer ranges are in the Pacific Northwest, Canada, and Alaska apparently 

winter in coastal southern California and Mexico, although they have been found as far 

north as New York in December and January (Shump and Shump 1982). They generally 

are not captured in Washington and Oregon until July and apparently leave Washington 

Migration, 

Hibernation, and 

Movement Patterns 

7
Silver-haired bat (Lasionycteris noctivagans).

by September, but remain in Oregon until November (Dalquest 1943, Findley and Jones 

1964). Sexual segregation of hoary bats in both time and space occurs during migration. 

Females move north in the spring before the males, beginning their migration to summer 

ranges in the North-Central and Northeastern United States in May and early June. 

Males begin their migration later and settle primarily in the Western United States 

(Findley and Jones 1964, Provost and Kirkpatrick 1952). Generally, only male hoary bats 

occur in western Oregon and Washington; no females have been found in this region 

during June and July, when they would be giving birth and rearing young, although 

records do exist for spring and autumn (Cross 1976a, Dalquest 1943, Perkins 1983, 

Perkins and Cross 1988, Thomas and West 1991). 

Silver-haired bats also seem to be migratory, although a small proportion of the population spends the winter in the Pacific Northwest (Johnson 1953, Perkins and others 

1990). No hibernating silver-haired bats were located during cave and mine searches in 

Oregon and Washington from 1982 to 1989 (Perkins and others 1990) but several 

individuals, primarily juvenile males, have been found during winter in both States as 

well as in British Columbia3

 (Schowalter and others 1978b). Females apparently migrate 

farther north than males in the Pacific Northwest, which results in some spatial 

segregation of the sexes

3 Perkins, J.M.; Cross, S.P. 1991. Migratory patterns of Lasionycteris 

noctivagans in Oregon and Washington [Austin, TX: 21 st annual 

American symposium on bat research.] On file with: Bat Conservation 

International, P.O. Box 162603, Austin, TX 78716-2603. 

8 
(Schowalter and others 1978b). Males can be found in Oregon and Washington in May, 

whereas females do not arrive until June (see footnote 3). Sexual segregation also may 

occur on an east-west gradient. As with hoary bats, female silver-haired bats seem to 

dominate numerically in the Eastern United States, whereas males predominate in the 

West and during migration (Kunz 1982a). Although both males and females occur in 

western Oregon and Washington (Cross 1976a, Perkins 1983, Perkins and Cross 1988, 

Perkins and others 1990), reproductive females occupy areas separate from males (see 

footnote 3). In Washington, females generally occur only east of the Cascades during 

spring and early summer, but the distribution of sexes becomes more even in August 

(see footnote 3). 

Bats are capable of traveling long distances between roosting and foraging sites, but 

relatively little is known about this behavior in temperate insectivorous species. Little 

brown myotis have been observed foraging 2 to 5 kilometers from day roosts (Thomas 

and West 1991), big brown bats are known to travel up to 4.1 kilometers to foraging 

habitat (Brigham and Fenton 1986), and adult female Indiana myotis will travel up to 2.5 

kilometers from roosts to foraging areas (Gardner and others 1991). Tattle (1976), 

however, found that growth rates of juvenile gray myotis, which feed almost exclusively 

on aquatic insects, were inversely proportional to the distance of the maternity colony 

from water. Lunney and others (1988a) also found that most activity in small, 

insectivorous bats in Australia was confined to within 1 kilometer of the site of original 

capture, thereby indicating small foraging ranges. Although bats are capable of traveling 

long distances to forage, such movements are energetically draining. Foraging therefore 

apparently occurs within a relatively short distance from roosting sites. 

Pacific Northwest bats often feed over water and then return to the forest to roost, 

thereby transferring nutrients from aquatic to upland habitats and forming an important 

link between these environments (Cross 1988). No other vertebrate group, with the 

exception of certain swifts and swallows, exhibits such a movement pattern. Because of 

their large population numbers, bats may play a unique role in nutrient cycling in forested 

environments. 

Roost sites are a critical resource for bats, and their availability may play a major role in 

determining population sizes and distributions (see Kunz 1982b). Key requirements of 

suitable roost sites include proximity to drinking and foraging habitat, protection from 

predators, and favorable temperature and moisture regimes. Variables such as sex, age, 

and breeding condition of individuals also play a role in roost selection; for example, 

breeding females and young generally require different kinds of roosts than males and 

nonbreeding females. 

During the spring and early summer, adult male and nonbreeding female bats are usually 

solitary roosters, although occasionally they may form small colonies. In late summer, 

they often join breeding females and juveniles in maternity roosts (van Zyll de Jong 

1985). Males and nonbreeding females may or may not roost in the same site each day. 

Selection of a roost to provide shelter from inclement weather and protection from 

predators appears to be rather opportunistic for these individuals. Cracks between 

boards on bridges, crevices in rock cliffs, spaces under tarpaper or siding on buildings, 

and crevices and cavities in live and dead trees provide suitable day roosts for males and 

nonbreeding females (Barbour and Davis 1969, Maser and others 1981, van Zyll de Jong 

1985) (table 2). 

Breeding female and juvenile bats of many species in the Pacific Northwest roost communally in large cavities and crevices, both natural and human-made. Males and nonbreeding 

Roosts and 

Hibernacula 

9
Table Known roost-site characteristics of batsa

 Hardwood Conifer Rock Caves 

Species Buildings Bridges foliage foliage Bark crevices and mines Snags 

California myotis M,S,H M'S S S S M,S,H S 

Western small-footed myotis S S S H 

Long-eared myotis M,S,H S S M,S,H S 

Keens myotisb S S 

Little brown myotis M'S M'S S S M,H M 

Fringed myotis M,S,H S S,H M,S,H 

Long-legged myotis M'S S M'S M'S H M 

Yuma myotis M,S,C M'S M,H 

Hoary Sc

 S S S S 

Silver-hairedd M,S,H S,H S,H S,H M,S,H 

Big brown M,S,C,H M'S S S M,S,H M 

Townsend's big-eared M,H,S M M,S,C,H 

a M = maternity roosts; S = solitary roosts; C = colonial roosts (males and nonbreeding females); H = hibernacula. b Roost characteristics not well described. 

c Unusual occurrence from single account (Bowers and others 1968). d

 Some proportion of hibernation accounts may actually be migrating individuals.

females generally are absent from these maternity roosts, but a few males occasionally 

may be found in the maternity colonies of some species, often roosting separately from 

the female clusters (Cagle and Cockrum 1943, Davis and others 1965). Temperature 

and humidity of maternity roosts must remain within certain, narrow boundaries to 

provide optimal conditions for the development of young. Sites of maternity colonies 

generally are quite warm, and temperature seems to be a major determinant in the 

selection of these sites (Fenton and Barclay 1980). Only a limited number of sites are 

suitable as maternity roosts. Maternity roosts have been found in attics, hollow trees, 

under large bark flakes, under bridges, in caves, and in other natural and human-made 

cavities (Barbour and Davis 1969, Maser and others 1981, van Zyll de Jong 1985) (table 

2). Although adult females are capable of carrying their offspring in the early stages of 

development, they rarely do; maternity roosts generally are used throughout the 

breeding season. Females return to the roost each morning and several times 

throughout the night to nurse their young. Groups of individuals of some species (for 

example, little brown myotis, Townsend's big-eared bat) also will frequently return to the 

same maternity roost year after year (Pearson and others 1952, van Zyll de Jong 1985). 

After weaning, breeding females and juveniles capable of flight join nonbreeding 

females and males and roost opportunistically in individual or group roosts. 

Environmental conditions also are important in the selection of hibernacula. Only certain 

cavities, generally caves, provide the proper conditions of temperature and humidity for 

hibernation, and only specific areas of a cave or cavity will be used. Townsend's big-eared 

bats prefer cold areas near the entrances of caves as hibernacula (Barbour and Davis 

1969, Humphrey and Kunz 1976, Pearson and others 1952), whereas gray myotis only 

use deep, vertical caves with temperatures from 6 to 11 °C (Tattle 1979). Different species 

select different conditions for hibernation and some species require very specific hiber10 
nacula. The entire North American population of the gray myotis, for example, uses only 

nine major hibernation caves in the southeastern United States (Lowe and others 1990). 

Most species in the Pacific Northwest hibernate in caves and abandoned mines 

although several species use buildings as well (Perkins and others 1990, Senger and 

others 1974). Some species readily hibernate in human-made structures. Most 

hibernating California myotis in Washington and Oregon, for example, have been found 

in buildings (Maser and others 1981, Perkins and others 1990); only a few have been 

found in caves and mines (Barbour and Davis 1969, Perkins and others 1990, Senger 

and others 1974, van Zyll de Jong 1985). This apparent preference for buildings as 

hibernacula may reflect only the difficulty involved in locating hibernating individuals in 

crevices and other inaccessible areas in caves and mines (Perkins and others 1990). 

It is common for bats to forage for a short time and then retire to a roost to rest and 

digest food or consume large prey items. These roosts are known as night roosts and 

generally are located at a different site than the day roosts, or in a different area of the 

same structure. Individual bats may spend from a few minutes to several hours at a time 

in night roosts, which often are occupied by several bats of different species that 

ordinarily may not share day roosts. Night roosts have been found in caves and 

buildings, on porches, and under bridges (Barbour and Davis 1969; Maser and others 

1981, van Zyll de Jong 1985). Roosts used at night often are small, with bats packed 

into confined spaces, but they also may be large and open (for example, porches, 

barns). The function of night roosts is unknown, but it has been hypothesized that 

periodically gathering in clusters during the night helps bats maintain high body 

temperatures, which allows extended periods of activity and increases digestive rates 

(Fenton and Barclay 1980). Adult male and nonbreeding females use night roosts 

throughout the spring, summer, and autumn, whereas lactating females and juveniles 

use them only after weaning in the late summer (Anthony and others 1981, van Zyll de 

Jong 1985). 

Most species use crevices and large cavities for roosting. Crevices include cracks in or 

under thick bark of trees, spaces between boards in buildings or bridges and under tarpaper or chimney flashing, fissures in rock cliffs, and spaces between rocks in talus 

slopes. Natural cavities are found in hollow trees and in caves, and human-made 

cavities include attics, barns, and spaces between wooden bridge supports. Most 

species will readily roost in art'rficial structures when natural cavities are unavailable. 

Almost all Pacific Northwest species have been found roosting in buildings and under 

bridges (table 2), and some species, such as the big brown bat and the little brown 

myotis, commonly are encountered in attics and barns (Barbour and Davis 1969, Maser 

and others 1981, van Zyll de Jong 1985). Big brown bats seem to prefer older buildings 

to newer ones, and large colonies tend to locate in buildings constructed before 1925 

(Perkins 1983, Schowalter and Gunson 1979). Unlike buildings with modern insulation 

and heating systems, older buildings probably provide conditions that are warm in the 

summer and cool in winter, which may make such buildings suitable as both summer 

roosts and winter hibernacula (Schowalter and Gunson 1979). Buildings constructed in 

the early 1900s also provide more potential roosting sites (that is, in attics and hollow 

walls) than newer ones (Kunz 1982b). In contrast to natural roost sites, roosts in 

human-made structures are relatively easily located, which probably accounts for the 

preponderance of human-made roosts among known sites. 

A few species select unique or specialized roost structures. Townsend's big-eared 

bats roost almost exclusively in cavity roosts, both in human-made structures (that is, 

buildings, bridges, and mines) and caves (Perkins and Levesque 1987) (table 2). They 

are 

11
Hoary bat (Lasiurus cinereus).

extremely sensitive to disturbance while roosting, because they hang directly from the 

ceiling of the roost and do not go into torpor during the day in summer colonies (Barbour 

and Davis 1969, Dalquest 1948). The hoary bat is the only foliage-roosting bat in the 

Pacific Northwest and, unlike other species, is not known to roost in human-made structures (table 2). In the Midwest and Eastern United States, hoary bats roost in the foliage 

of deciduous or coniferous trees and choose sites that are 3 to 12 meters above the 

ground, open from below, well covered above, and near a clearing (Constantine 1966, 

van Zyll de Jong 1985). Roost sites have not been found in Douglas-fir forests of the 

Pacific Northwest, but it has been hypothesized that roost requirements are best met in 

conifer forests older than 100 years (Perkins and Cross 1988). Older conifers have 

foliage that begins 10 to 20 meters above the ground and needles that are concentrated 

around the edge of the canopy, which together provide the proper combination of 

shelter, open space, and accessibility required by hoary bats for roosting (Perkins and 

Cross 1988). 

Although roost sites are poorly characterized in Pacific Northwest forests, existing 

information indicates that old-growth forests provide higher quality roost sites than do 

younger forests. Thomas and West (1991) found activity levels in old-growth 

Douglas-fir forests to be significantly higher than in young or mature forests for most 

species. Bat activity within forest stands showed a short peak in the early evening 

when bats were emerging; few feeding buzzes were recorded during the night, which 

indicated that bats use old growth for roosting rather than foraging. In other parts of 

the United States and throughout the world, small forest-roosting bats generally roost 

in the oldest available trees (Barclay and others 1988, Gardner and others 1991, 

Lunney and others 1988b). Structural characteristics of old, live trees, such as cracks 

and crevices in thick bark, bark pulling away from the trunk thus forming crevices, and 

holes in the bole where limbs have been shed, offer many potential roosting sites. 

Snags with cracks, peeling bark, bird holes, and hollow interiors also provide ideal 

sites for the large maternity colonies that Myotis bats commonly form in the spring.

12 
Research on Bats in 

Old-Growth 

Douglas-Fir Forests 

Recent interest in old-growth forest ecosystems of the Pacific Northwest has 

stimulated several studies of the habitat preferences of bats with respect to forest age. 

According to these studies, bats show a marked preference for old rather than young 

forests, presumably due to a greater abundance of potential roost sites in large, old, 

hollow trees compared to small, young trees. 

In Oregon, it has been determined that both hoary and silver-haired bats prefer 

Douglasfir/western hemlock forests more than 200 years old over other forest types and 

ages (Perkins and Cross 1988). In this study, three forest types were sampled: 

Douglas-fir/ western hemlock, ponderosa pine/sugar pine, and true fir. These types were 

further subdivided into three age classes (0-50 years, 51-100 years, and > 100 years). 

At each sampling site, mist nets were set up over bodies of water to capture bats while 

they were drinking or foraging. It was assumed that bats were drinking from water 

sources closest to roosting and foraging areas, following Kunz (1982b). Both hoary and 

silver-haired bats were captured almost exclusively in old-growth Douglas-fir forests (old 

growth was defined as stands greater than 100 years of age with most trees over 200 

years) and rarely in younger Douglas-fir forests or ponderosa pine forests of any age. 

Although no roost sites were found, the authors speculated that bats were roosting 

under large bark flakes and in the foliage of old-growth and mature conifers. 

Thomas (1988) and Thomas and West (1991) studied the association of bats with different age classes of Douglas-fir forests in Washington and Oregon as part of the USDA 

Forest Service's Old-Growth Forest Wildlife Habitat Research Program (Ruggiero and 

others 1991). Ultrasonic detectors, which record bat echolocation calls, were used to 

monitor bat activity in young (40-75 years), mature (100-165 years), and old-growth (> 

200 years) forest stands on the western side of the southern Cascade Range in 

Washington and in the Coast Range of Oregon (see Carey and Spies [1991 ] for 

additional information on study design). Each detector consisted of an ultrasonic 

microphone, a divide-by-ten circuit board, a talking clock, and a voice-activated tape 

recorder (Miller and Andersen 1984, Thomas and West 1989). 

Detectors were placed in the canopy and near the forest floor in several stands of each 

age class, and activity was monitored from dusk until dawn each day. Once reduced to 

a frequency within the range of human hearing by the divide-by-ten circuit board, calls 

were recorded on tape along with the time of day from the talking clock (Thomas and 

West 1989). Recorded calls then were passed through a period meter to convert them 

into frequency-time spectrograms displayed on an oscilloscope screen (Fenton 1988, 

Simmons and others 1979, Thomas and West 1989). To identify calls, the minimum 

frequency, duration, and shape of the calls were compared with recordings from captive 

bats or previously published characteristics (see Fenton and Bell 1981, Thomas and 

others 1987). 

Several species, especially among the myotis bats, have similar echolocation call characteristics, and it was not possible to distinguish the calls of all species present. Consequently, species whose calls overlapped were classified into groups for analysis: Myotis 

A (little brown and Yuma myotis); Myotis B (California, Keens, long-eared, and western 

small-footed myotis); and big brown bat (big brown bats and fringed myotis) (table 3). 

Echolocation calls could be individually distinguished for the long-legged myotis, silverhaired, hoary, and Townsend's big-eared bats. With additional research, further resolution of the groups into constituent species may be possible. 

13
Table 3-Detection rates of bats in old-growth, young, and mature stands in the 

southern Washington Cascade and the Oregon Coast Ranges 

 Mature and Old-growth/ 

Species or groupsa Old-growth young youngerb P

c 

Washington: 

Myotis A 1.23 t 0.27d 0.33 t 0.09 3.73 <0.005 

 Myotis B 2.41 t 1.75 .91 t .25 2.65 < .001 

Long-legged .34 t .08 .06 ± .02 5.67 < .01 

Silver-haired .27 .27:t .11 .15 :t .64 - Ns 

Oregon: 

Myotis A 6.29 t 1.98 2.48 t 1.13 2.54 < .001

Myotis B 6.54 ± 1.81 1.48 ± .50 4.42 < .001 

Long-legged 1.46 t .50 .53 t .30 2.75 < .01 

Silver-haired 2.73 t 1.15 .28 ± .22 9.75 < .005 

Big brown .53 ± .26 .16 ± .08 3.31 `

< .05 

Ns = not significant. 

a Myotis A includes the little brown and Yuma myotis; Myotis B includes the California, long-eared, Keens, and 

western small-footed myotis; big brown includes the big brown bat and fringed myotis. b Detection rates are expressed as a ratio of old-growth to younger stands. 

c Differences between detection rates in old-growth and younger stands were tested by a Mann-Whitney test; P is 

the resulting probability.

d Detection rates as bats per 100 sample minutes (x ± SE). 

Source: Thomas and West 1991. 

Although not all bat species are readily captured in mist nets, some idea of the relative abundances of 

species within each group was obtained by using mist nets in areas censused by echolocation call. 

Captures within each group were dominated numerically by one species. Among the Myotis A group, 

most captures were of the little brown myotis; the Myotis B group was dominated by California myotis; 

and big brown bats comprised the majority of the big brown bat group. 

The main peak in activity was short and predictable and generally occurred in the first 15 minutes after 

dusk; a second activity peak occurred at dawn (Thomas and West 1991). Feeding rates in old-growth 

forests, determined by counting the number of feeding buzzes, were low. Low feeding rates, combined 

with high detection at dawn and dusk, indicated that bats were using old-growth forests primarily for 

roosting rather than feeding (Thomas and West 1991). 

Because activity levels did not differ significantly between young and mature stands, the calls in these 

age classes were combined for further analysis. Most groups had significantly higher abundances in 

old-growth forest (table 3). Although detection rates for the silver-haired bat did not differ significantly 

between age classes in the Washington Cascades, detection rates were higher in old growth than in 

young and mature forests (table 3). Detection rates for big brown bats or fringed myotis were too low 

to be included in the analysis for the Washington Cascades. 

14 
As part of the old-growth research program, relations between activity levels and 

vegetative parameters were examined to determine habitat characteristics of importance 

to forest-dwelling bats (Thomas and West 1991). The density of damaged or diseased 

trees, snag size and decay class, elevation, and stand age were all weakly associated 

with higher activity levels. These regression variables did not explain observed 

associations with old growth because 83 percent of the total among-sample variation 

was not accounted for in the regression. The relation between measured vegetative 

characteristics and activity levels was too weak to draw any conclusions. According to 

Thomas and West (1991), the weakness of the association indicates that critical habitat 

variables associated with natural roost-site characteristics were not measured and 

remain unknown. This information gap severely constrains our ability to describe the 

habitat relations of bats in the Pacific Northwest. 

Regional differences in abundance and reproductive activity were clearly evident in the 

Washington Cascade and Oregon Coast Ranges. Population sizes of all species 

(except the tong-legged myotis) in old-growth forests of the Washington Cascades seem 

to be much lower than in the Oregon Coast Range (Thomas and West 1991). Along the 

west side of the Washington Cascades, only 11 percent of the bats captured were 

female and none of these females was reproductively active. In contrast, along the east 

side of the Washington Cascades and in the Oregon Coast Range, breeding females 

and juveniles were much more abundant. These results suggest that in the Pacific 

Northwest, only relatively warm environments provide suitable conditions for 

reproduction in bats. 

In general, few studies have been done on the bat fauna of the Pacific Northwest, especially in Washington. Previous work consists primarily of population surveys in southern 

(Cross 1976a) and northwestern (Perkins 1983) Oregon. In each of these surveys, roost 

sites were located through public input gathered through radio and newspaper requests 

for roost locations, as well as information from various State and Federal land management agencies. Species composition and relative abundances of bats in different 

habitats were determined by capture with mist nets. In southern Oregon, habitat 

variables (for example, vegetation types, number of snags, amount of available rimrock) 

also were measured to identify habitat characteristics of importance to different bat 

species. 

In southern Oregon, the fringed myotis, big brown, hoary, and silver-haired bats were 

found most commonly in the west, whereas the western pipistrelle, western small-footed 

myotis, and little brown myotis were more common in the east. The pallid bat, 

long-legged myotis, and long-eared myotis were caught most frequently in ponderosa 

pine forests but were found across the State. Townsend's big-eared bats, California 

myotis, and Yuma myotis occurred in equal frequency throughout the study area. 

Captures of both the big brown and silver-haired bats were most frequent in areas of 

high snag density and forest cover. A single spotted bat was captured in a ponderosa 

pine forest during this study. This species is most common in the Southwestern United 

States and is found as far north as the Okanagan Valley of British Columbia but has 

been neither captured nor sighted in Washington; this account represents the only 

record of the species from Oregon. 

In northwestern Oregon, the little brown bat was the most common and widespread 

species, and big brown bats, California, long-eared, fringed, long-legged, and Yuma 

myotis also were distributed widely. Other species were more restricted in distribution: 

silverhaired, hoary, and Townsend's big-eared bats were caught only in old-growth or 

mature Douglas-fir forests, and the pallid bat was found only in oak-woodland habitats. 

N t f d f i d ll l t d i b ildi

Review of Other

Bat Studies in the 

Pacific Northwest 

15
Long-eared myotis (Myotis evotis).

Roost sites and capture locations for all bat species occurring in Oregon have been 

mapped in relation to habitat and physiography (Maser and Cross 1981). Data on bat 

distribution were collected from 1970 to 1980 by using mist nets, shooting, and 

collecting bats from day and night roosts. Range maps of Oregon bats were compiled 

from this data and previously published accounts. 

Bats at Oregon Caves National Monument in southwestern Oregon have been surveyed 

several times from 1958 to 1989 (Albright 1959; Cross 1976b, 1977; Cross and Schoen 

1989). A mark-recapture technique, in which bats were captured in Tattle traps (Tattle 

1974) at the main cave entrance and marked on the wings with punchmarks, was used 

to estimate numbers of bats using the caves. Eight species were captured: Townsend's 

big-eared and big brown bats, long-eared, Yuma, little brown, California, fringed, and 

longlegged myotis. The caves most commonly were used as night roosts although a few 

individuals used them during the day or for hibernation. Confidence limits for population 

estimates were large and, although it appeared that a decline has occurred since 1958, 

this could not be verified. 

The distribution, status, and habitat affinities of Townsend's big-eared bat in Oregon are 

described by Perkins and Levesque (1987). A distribution map was constructed by 

using data from captures, museum specimens, and literature sources. The total Oregon 

population was estimated at 2,300-2,600 bats, with a fragmented distribution centering 

around areas with suitable cave or cavelike habitat. Comparison of counts at known 

hibernacula with historical records suggested that population declines may have 

occurred in some areas. Management recommendations included habitat protection, 

population monitoring, and public education. 

Bats are most easily censused in their hibernacula, and several researchers have compiled winter records of bats in the Pacific Northwest from cave, mine, and house searches 

and museum specimens (Perkins and others 1990, Senger and others 1974). Over-wintering California, long-eared, little brown, fringed, and long-legged myotis as well as 
Townsend's big-eared and Mexican free-tailed bats were found in caves or mines, or 

both, in Washington and Oregon. Winter records from museum specimens of the aforementioned species plus big brown, silver-haired, and hoary bats also were listed. The 

number of bats in a given hibernaculum generally was less than 10. California myotis 

and big brown and Mexican free-tailed bats were found most commonly in buildings; 

little brown myotis were found with equal frequency in buildings and in caves or mines; 

Townsend's big-eared bats and long-eared, western small-footed, fringed, and 

long-legged myotis were found primarily in caves and mines; and silver-haired bats 

rarely were found 

The food habits of bats in western and eastern Oregon have been studied by stomach 

or scat analysis (Whitaker and others 1977, 1981 a, 1981 b). Several species showed 

similar patterns of prey selection across the State. Townsend's big-eared and 

silver-haired bats and long-legged, long-eared, and fringed myotis ate primarily moths; 

little brown myotis and western pipistrelles ate flies; big brown bats ate beetles; and 

silver-haired bats and western small-footed myotis did not specialize but fed on a wide 

variety of insects. A few species showed a different pattern for the west than for the east 

side of the State, possibly reflecting differences in prey availability. Yuma and California 

myotis ate flies in western Oregon, whereas the Yuma was a generalist and the 

California ate primarily moths on the east side. The pallid bat fed heavily on beetles in 

western Oregon but ate mainly moths and grasshoppers in the east. 

The effects of pesticide application on bats were studied in the Pacific Northwest by 

examining the residue patterns from a 1974 spray application of DDT to forests in 

northeastern Oregon, eastern Washington, and northern Idaho (Henny and others 

1982). Levels of DDT in the control group were extremely low or absent. Four of five 

species showed significant changes in DDT residues after the forests were sprayed. 

California and longlegged myotis showed the highest residues, silver-haired and big 

brown bats showed a moderate increase in residues, and long-eared myotis exhibited 

no postspray change. Three years after spraying, only California and long-legged myotis 

exhibited DDT levels above control levels. Although it was not determined whether 

these elevated levels of DDT had adverse effects on the bats in this study, insecticides 

have been linked with population declines and toxicity in other areas (Clark and others 

1978, Geluso and others 1976; see review in Clark 1981). 

Biologists suspect that bat populations have been declining in recent years, but this is 

difficult to document because few data exist on historic population sizes. The status of 

only 3 percent of bats worldwide is well known (Stebbings 1980) but 7 of the approximately 40 species in the United States are listed Federally as endangered (Lowe and 

others 1990). None of the Federally listed species are found in the Pacific Northwest; 

however, the Townsend's big-eared bat has been nominated for federal listing, and 

both the Washington State Department of Wildlife and the Oregon Department of Fish 

and Wildlife have listed it as a Species of Concern or Sensitive Species. Documented 

population declines of bats worldwide are due primarily to disturbance in maternity 

colonies and hibernacula and loss of habitat (Cockrum 1969, Edgerton and others 

1966, Mohr 1948, Tuttle 1979). Forest harvest in particular has been shown to have 

detrimental effects on populations of little brown myotis in that activity is substantially 

reduced after clearcutting (Lunde and Harestad 1986). Because most Pacific Northwest 

bat species are closely associated with old-growth Douglas-fir forests (Thomas and 

West 1991), the recent, rapid decline in old-growth forests on the west coast probably 

has had detrimental effects on bat populations. 

Conclusion and 

Research Needs 

17
Yuma myotis (Myotis Yumanensis).

Mitigation for the effects of forest harvest on bat populations is difficult to prescribe 

because critical aspects of their basic ecology are poorly understood. Conservation of 

bat species in the Pacific Northwest should center on preserving suitable roost sites and 

foraging areas, but attaining this goal is hampered by our rudimentary knowledge of 

these requirements. Recent advances in miniaturization of radiotelemetry components 

have now made radio tracking of bats feasible. This technique holds promise for 

gathering significant new information on roost characteristics and home range sizes. 

Three studies involving radio tracking of Myotis bats currently are underway in 

Washington State. They should provide significant new information on natural roost 

sites in second-growth and old-growth forests of the Pacific Northwest. Although 

radio-tracking studies are expensive and time consuming, they are the only practical 

means of gathering information on roosting behavior in forest-dwelling bats. More 

studies of this kind are necessary. 

Bats often have been excluded from general vertebrate surveys because they are 

difficult to study; specialized equipment and expertise are required. Responses of bat 

populations to various forest management practices (for example, riparian buffer strips, 

clearcutting) and habitat variables (for example, forest fragmentation) therefore are 

virtually unknown. Two large-scale studies of vertebrate responses to logging practices 

and landscape patterns recently have begun in Washington. Automated ultrasonic 

detectors are being used to assess bat activity patterns in both studies. Inclusion of bats 

in other vertebrate studies in the Pacific Northwest would provide valuable information 

both on the effects of forest practices on bat populations and the distribution and habitat 

preferences of individual species. 

The lack of information on basic geographic distributions, habitat associations, and the 

population status of Pacific Northwest bat species is a major factor hindering the development of alternative forest management procedures that might protect bat populations. 

General bat surveys to document distribution and estimate population sizes have been 

performed in various areas in Oregon (Cross 1976x, Perkins 1983), and fairly current 

distribution maps exist for the State (Maser and Cross 1981). The bat fauna of 

Washington 

18 
remains virtually unstudied, however; no recent distribution maps have been published 

for the State and localized trapping efforts and cave exploration provide the only 

information. General surveys (consisting of cave and building searches, trapping efforts, 

and ultrasonic detection) in state parks, national forests, and wildlife refuges would 

greatly enhance the current information base. Although we lack critical information for all 

bat species, this deficit is most acute for Keen's myotis4

. Virtually no research has been 

conducted on the basic ecology of Keen's myotis since it was proposed as a distinct 

species by van Zyll de Jong (1979). It is found exclusively in the Pacific Northwest and 

occupies a restricted range within western Washington and western British Columbia. It 

is considered a forestdwelling species and most likely has a strong association with 

old-growth forests, as it was part of a group of Myotis species identified as closely 

associated with old-growth Douglas-fir forests (Thomas and West 1991). Keen's myotis 

has not been found roosting in human-made structures and may rely entirely on natural 

roost sites, such as bark flakes and rock crevices. Forested habitat within the range of 

this species has declined substantially in the past two decades. Basic information on 

population sizes, roost sites, migration, and feeding habits of Keen's myotis will be 

necessary to assess the status of this species and ensure its long-term survival. 

To evaluate the effects of forest management on bat populations of the Pacific 

Northwest, we need to accurately describe current geographic distributions, monitor 

population sizes, and determine the habitat characteristics of sites used for roosting, 

maternity colonies, and foraging. Distributional records for many species are incomplete 

and information on population sizes for most species is virtually nonexistent. Some 

progress is now being made in understanding habitat-use patterns, but this work has 

only begun. Critical habitat elements, especially the characteristics of naturally occurring 

roost sites and the size and variation in foraging ranges, need to be described. Until key 

characteristics of roost sites and foraging areas are known, it will be very difficult to 

manage forests for the persistence of native bat populations.

4 A recent taxonomic revision separated Keen's myotis into two 

species: Keen's myotis (Western United States) and the 

northern myotis (Eastern United States).

19 
Scientific Names5 Common name Scientific name 

Bats: 

 California myotis6 

 Western small-footed myotis6 

 Long-eared myotis6 

 Gray myotis 

 Keen's myotis6 

 Little brown myotis6 

 Northern myotis 

 Indiana myotis 

 Fringed myotis6 

 Long-legged myotis6 

 Yuma myotis6 

 Hoary bats 

 Silver-haired bats 

 Spotted bat 

 Big brown bats 

 Townsend's big-eared bat6 

 Pallid bat 

 Western pipistrelle 

 Mexican free-tailed bat 

Myotis californicus 

Myotis ci1iolabrum7 

Myotis evotis 

Myotis grisescens 

Myotis keenii 

Myotis lucifugus 

Myotis septentrionalis 

Myotis sodalis 

Myotis thysanodes 

Myotis volans 

Myotis yumanensis 

Lasiurus cinereus 

Lasionycteris noctivagans 

Euderma maculatum 

Eptesicus fuscus 

Plecotus townsendii 

Antrozous pallidus 

Pipistrellus hesperus 

Tadarida brasiliensis 

Other animals: 

 Deer mouse 

 Bullfrog 

Vegetation: 

 Douglas-fir 

 Western hemlock 

 Ponderosa pine 

 Sugar pine 

 True fir 

Peromyscus spp. 

Rana catesbeiana 

Pseudotsuga menziesii (Mirb.) Franco 

Tsuga heterophylla (Raf.) Sarg. 

Pinus ponderosa Dougl. ex Laws. 

Pinus lambertiana Dougl. 

Abies spp. 

Acknowledgements We thank Stephen Cross and Richard Johnson for comments on the initial draft of the 

manuscript and Bat Conservation International for photographs. We especially 

acknowledge Keith Aubry for extensively editing several drafts and Mark Huff for editing 

the manuscript and preparing the species identification table. 

5 All taxonomy of North American species follows Jones and others (1992). s 

6 Bat species occurring in Douglas-fir forests in the Pacific Northwest. 7 7 Previously known as M. lebiii or M. subulatus. 

20 
Literature Cited Albright, Ray. 1959. Bat banding at Oregon caves. Murrelet. 40: 26-27.

Anthony, E.L.P.; 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. 

Bailey, Vernon. 1936. The mammals and life zones of Oregon. North American Fauna 

55. Washington DC: U.S. Department of Agriculture, Bureau of Biological Survey. 

416 p. 

Barbour, Roger W.; Davis, Wayne H.1969. Bats of America. Lexington: University of 

Kentucky Press. 286 p. 

Barclay, Robert M.R. 1985. Long- versus short-range foraging strategies of hoary 

(Lasiurus cinereus) and silver-haired (Lasionycteris noctivagans) bats and the 

consequences for prey selection. Canadian Journal of Zoology. 63: 2507-2515. 

Barclay, Robert M.R.; Faure, Paul A.; Farr, Daniel R. 1988. Roosting behavior and 

roost selection by migrating silver-haired bats (Lasionycteris noctivagans). Journal 

of Mammalogy. 69: 821-825. 

Black, Hal L.1974. A north temperate bat community: structure and prey populations. 

Journal of Mammalogy. 55: 138-57. 

Bowers, J.R.; Heidt, G.A.; Baker, R.H. 1968. A late autumn record for the hoary bat in 

Michigan. Jack-Pine Warbler. 46: 33. 

Brigham, R. Mark; Fenton, M. Brock 1986. The influence of roost closure on the 

roosting and foraging behavior of Eptesicus fuscus (Chiroptera: 

Vespertilionidae). Canadian Journal of Zoology. 64: 1128-1133. 

Cagle, Fred R.; Cockrum, Lendell. 1943. Notes on a summer colony of Myotis 

lucifugus lucifugus. Journal of Mammalogy. 24: 474-92. 

Carey, Andrew B.; Spies, Thomas A. 1991. Sampling design of the Old-Growth Forest 

Wildlife Habitat Program. In: Ruggiero, Leonard F.; Aubry, Keith B.; Carey, Andrew B. 

[and others], tech. coords. Wildlife and vegetation of unmanaged Douglas-fir forests. 

Gen. Tech. Rep. PNW-285. Portland, OR: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station: 9-16. 

Clark, Donald R., Jr. 1981. Bats and environmental contaminants: a review. Special 

Rep.-Wildl. 235. Washington, DC: U.S. Department of the Interior, Fish and Wildlife 

Service. 27 p. 

Clark, Donald R.; Laval, Richard K.; Swineford, Douglas M. 1978. Dieldrin-induced 

mortality in an endangered species, the gray bat (Myotis grisescens). Science. 199: 

1357-1359. 

Cockrum, E. Lendell. 1969. Migration of the guano bat Tadarida brasiliensis. In: Contributions in mammalogy. University of Kansas Museum of Natural History Misc. Publ. 

51. Lawrence, KS: University of Kansas Printing Service: 303-336. 

Cockrum, E. Lendell; Cross, Stephen P. 1964. Time of bat activity over water holes. 

Journal of Mammalogy. 45: 635-636. 

Cockrum, E. Lendell; Cross, Stephen P. 1965. Time of bat activity over water holes. 

Journal of Mammalogy. 46: 356. 

21
Constantine, Denny 6.1966. Ecological observations on lasiurine bats in Iowa. 

Journal of Mammalogy. 47: 34-41. 

Cross, S.P., ed. 1976a. A survey of bat populations and their habitat preferences 

in southern Oregon: a student originated studies project of the National 

Science Foundation. Ashland, OR: Southern Oregon State College. 40 p. 

Cross, Stephen P.1976b. A survey of the bats of Oregon Caves National 

Monument. [Place of publication unknown]:[Publisher unknown]; contract 

report; NPS contract CX-9000-6-0051. 25 p. Available from: Stephen P. Cross, 

Department of Biology, Southern Oregon State College, Ashland, OR. 

Cross, Stephen P. 1977. A survey of the bats of Oregon Caves National 

Monument. [Place of publication unknown]: [Publisher unknown]; contract 

report; NPS CX-90006-0051. 40 p. Available from: Stephen P. Cross, 

Department of Biology, Southern Oregon State College, Ashland, OR. 

Cross, Stephen P. 1986. Bats. In: Cooperidge, Allen Y.; Boyd, Raymond J.; Stuart, 

Hanson R., eds. Inventory and monitoring of wildlife habitat. Denver, CO: U.S. 

Department of the Interior, Bureau of Land Management Service Center: 

297-517. 

Cross, Stephen P.1988. Riparian systems and small mammals and bats. In: 

Raedeke, Kenneth J., ed. Streamside management: riparian wildlife and forestry 

interactions. Seattle, WA: University of Washington Press: 93-112. 

Cross, Stephen P.; Schoen, Curtis. 1989. Bats at Oregon Caves: 1988 status 

report. [Place of publication unknown]: [Publisher unknown]; contract report; 

NPS CX-90006-0051. 25 p. Available from: Stephen P. Cross, Department of 

Biology, Southern Oregon State College, Ashland, OR. 

Dalquest, Walter W.1943. Seasonal distribution of the hoary bat along the Pacific 

Coast. Murrelet. 24: 21-24. 

Dalquest, Walter W. 1948. Mammals of Washington. Lawrence, KS: University of 

Kansas: Publication of the Museum of Natural History: 1-444. 

Davis, W.H.; Hassell, M.D.; Rippy, C.L. 1965. Maternity colonies of the bat 

Myotis lucifugus in Kentucky. American Midland Naturalist. 73: 161-165. 

Davis, Wayne H.; Hitchcock, Harold B. 1965. Biology and migration of the bat, 

Myotis lucifugus, in New England. Journal of Mammalogy. 46: 296-313. 

DeBlase, Anthony F.; Humphrey, Stephen R.; Drury, K. Susan. 1965. Cave 

flooding and mortality in bats in Wind Cave, Kentucky. Journal of Mammalogy. 

46: 96. 

Doutt, J.K.; Heppenstall, C.A.; Guilday, J.E. 1966. Mammals of Pennsylvania. 

Harrisburg: Pennsylvania Game Commission. 273 p. 

Edgerton, H.E.; Spangle, R.F.; Baker, J.K.1966. Mexican free-tailed bats: 

photography. Science. 153: 201-203. 

Fenton, M.B. 1970. Population studies of Myotis lucifugus (Chiroptera: 

Vespertilionidae) in Ontario. Life Sciences Contributions of the Royal Ontario 

Museum. 77: 1-34. 

Fenton, M.B.; Bell, G.P. 1981. Recognition of species of insectivorous bats by 

their echolocation calls. Journal of Mammalogy. 62: 233-43. 

22 
Fenton, M.B.; van Zyll de Jong, C.G.; Bell, G.P. [and others]. 1980. Distribution, 

parturition dates and feeding of bats in south-central British Columbia. Canadian 

Field-Naturalist. 94: 416-20. 

Fenton, M. Brock. 1988. Detecting, recording, and analyzing vocalizations of bats. In: 

Kunz, T.H., ed. Ecological and behavioral methods for the study of bats. Washington, 

DC: Smithsonian Institution Press: 91-104. 

Fenton, M. Brock; Barclay, Robert M.R. 1980. Myotis lucifugus. Mammalian Species 

142. New York, NY: American Society of Mammalogists. 8 p. 

Fenton, M. Brock; Thomas, Donald W. 1984. Migrations and dispersal of bats 

(Chiroptera). In: Checkley, D.; Cullen, J.; Kitting, C. [and others], eds. Migrations: 

mechanisms and adaptive significance. Contributions in Marine Science. 27: 

409-424. 

Findley, James S.; Jones, Clyde. 1964. Seasonal distribution of the hoary bat. Journal 

of Mammalogy. 45: 461-470. 

Furlonger, C.L.; Dewar, H.J.; Fenton, M.B.1987. Habitat use by foraging insectivorous 

bats. Canadian Journal of Zoology. 65: 284-288. 

Gardner, James E.; Garner, James D.; Hofmann, Joyce E. 1991. Summer roost 

selection and roosting behavior of Myotis sodalis (Indiana bat) in Illinois. Twin cities, 

MN: U.S. Department of the Interior, Fish and Wildlife Service; final report; [contract 

no. unknown]. 56 p. 

Geggie, J.F.; Fenton, M.B. 1985. A comparison of foraging by Eptesicus fuscus 

(Chiroptera: Vespertilionidae) in urban and rural environments. Canadian Journal 

of Zoology. 63: 263-267. 

Geluso, Kenneth N.; Altenbach, J. Scott; Wilson, Don E. 1976. Bat mortality: 

pesticide poisoning and migratory stress. Science. 194: 184-186. 

Gillette, David D.; Kimbrough, John D. 1970. Chiropteran mortality. In: Slaughter, 

B.H.; Waltin, D.W., eds. About bats. Dallas, TX: Southern Methodist University Press: 

262-283. 

Goehring, H.H. 1958. A six year study of big brown bat survival. Proceedings of the 

Minnesota Academy of Science. 26: 222-24. 

Griffin, Donald R. 1953. Deluge underground. Bulletin of the National 

Speleological Society. 15: 34-37. 

Griffin, Donald R. 1970. Migrations and homing of bats. In: Wimsatt, W.A., ed. Biology 

of bats. New York: Academic Press: 233-64. Vol. 1. 

Griffin, Donald R.; Webster, Frederic A.; Michael, Charles R. 1960. The 

echolocation of flying insects by bats. Animal Behaviour. 8: 141-154. 

Grinnell, Hilda Wood. 1918. A synopsis of the bats of California. University of 

California Publications in Zoology. 17: 223-404. 

Hall, J.S. 1962. A life history and taxonomic study of the Indiana bat Myotis sodalis. 

Scientific Publications of the Reading Public Museum and Art Gallery. 12: 1-68. 

23
Herd, Robert M.; Fenton, M. Brock. 1983. A genetic, morphological and ecological 

investigation of a putative hybrid zone between Myotis lucifugus and Myotis 

yumanensis (Chiroptera: Vespertilionidae). Canadian Journal of Zoology. 61: 

20202050. 

Henny, Charles J.; Maser, Chris; Whitaker, John O., Jr.; Kaiser, T. Earl. 1982. 

Organochlorine residues in bats after a forest spraying with DDT. Northwest 

Science. 56: 329-337. 

Hitchcock, Harold 8.1965. Twenty-three years of bat banding in Ontario and Quebec. 

Canadian Field-Naturalist. 79: 4-14. 

Humphrey, S.R.; Cope, J.B. 1976. Population ecology of the little brown bat, Myotis 

lucifugus, in Indiana and southcentral Kentucky. Stillwater, OK: American Society 

of Mammalogists. 81 p. 

Humphrey, Stephen R.; Kunz, Thomas H. 1976. Ecology of a Pleistocene relict, the 

western big-eared bat (Plecotus townsendii) in the southern great plains. Journal 

of Mammalogy. 57: 470-484. 

Johnson, Murray L.1953. Fall and winter record of the silver-haired bat for Washington 

State. Murrelet. 31: 32. 

Jones, J. Knox, Jr.; Hoffmann, Robert S.; Rice, Dale W. [and others]. 1992.

Revised checklist of North American mammals north of Mexico. Occasional Papers 

of the Museum of Texas Tech University 146. Lubbock: Texas Tech University Press. 

23 p. 

Kirkpatrick, Ralph D. 1982. Rana catesbeiana (bullfrog) food. Herpetological 

Review. 13: 17. 

Kunz, Thomas H. 1982a. Lasionycteris noctivagans. Mammalian Species 172. 

New York, NY: American Society of Mammalogists. 5 p. 

Kunz, Thomas H. 1982b. Roosting ecology of bats. In: Kunz, Thomas H., ed. Ecology 

of bats. New York, NY: Plenum Press: 1-55. 

Kunz, Thomas H.; Martin, Robert A. 1982. Plecotus townsendii. Mammalian Species 

175. New York, NY: American Society of Mammalogists. 6 p. 

Kurta, Allen; Baker, Rollin H. 1990. Eptesicus fuscus. Mammalian Species 356. New 

York, NY: American Society of Mammalogists. 10 p. 

Kurta, Allen; Kunz, Thomas H. 1988. Roosting metabolic rate and body temperature 

of male little brown bats (M. lucifugus) in summer. Journal of Marnmalogy. 69: 

645-651. 

Lowe, David W.; Matthews, John R.; Moseley, Charles J., eds. 1990. The official 

world wildlife fund guide to endangered species of North America. Washington, 

DC: Beacham Publishers. 1180 p. 

Lunde, Robert E.; Harestad, Alton S. 1986. Activity of little brown bats in coastal 

forests. Northwest Science. 60: 206-209. 

Lunney, D.; Barker, John; Leary, Tanya. 1988a. Movements of banded bats 

(Microchiroptera: Vespertilionidae) in Mumbulla State Forest near Bega, New South 

24 
Lunney, Daniel; Barker, John; Priddel, David; O'Connell, Micheal. 1988b. Roost 

selection by Gould's long-eared bat, Nyctophiius gouldi Tomes (Chiroptera: Vespertilionidae) in logged forest on the south coast of New South Wales. Australian 

Wildlife Research. 15: 375-384. 

Manning, Richard W.; Jones, J. Knox, Jr. 1989. Myotis evotis. Mammalian Species 

329. New York, NY: American Society of Mammalogists. 5 p. 

Maser, Chris; Cross, Stephen P. 1981. Notes on the distribution of Oregon bats. 

Research Note PNW-379. Portland, OR: U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Forest and Range Experiment Station. 31 p. 

Maser, Chris; Mate, Bruce R.; Franklin, Jerry F.; Dyrness, C.T. 1981. Natural history 

of Oregon Coast mammals. Gen. Tech. Rep. PNW-133. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Forest and Range Experiment 

Station. 496 p. 

McNab, Brian K. 1982. Evolutionary alternatives in the physiological ecology of 

bats. In: Kunz, Thomas H., ed. Ecology of bats. New York: Plenum Press: 

151-200. 

Merriam, Clinton Hart. 1884. Mammals of the Adirondack region. New York: Press of 

L.S. Foster. 316 p. 

Miller, Lee A.; Andersen, Bent Bach. 1984. Studying bat echolocation signals 

using ultrasonic detectors. Zeitschrift fur Saugetierkunde. 49: 6-13. 

Mohr, Charles E. 1948. Texas bat caves serve in three wars. Bulletin of the National 

Speleological Society. 14: 3-13. 

Mohr, Charles E. 1972. The status of threatened species of cave-dwelling bats. Bulletin 

of the National Speleological Society. 34: 33-47. 

Nowak, Ronald M. 1991. Walker's mammals of the world. Baltimore: Johns Hopkins 

University Press. 642 p. Vol. 1. 

O'Farrell, Micheal J.; Studier, Eugene H.1980. Myotis thysanodes. Mammalian 

Species 137. New York, NY: American Society of Mammalogists. 5 p. 

Paradiso, John L.; Greenhall, Arthur M. 1967. Longevity records for American bats. 

American Midland Naturalist. 78: 251-252. 

Parsons, Harold J.; Smith, Donald A.; Whittam, Robert F. 1986. Maternity colonies 

of silver-haired bats, Lasionycteris noctivagans, in Ontario and Saskatchewan. 

Journal of Mammalogy. 67: 598-600. 

Pearson, Oliver P.; Koford, Mary R.; Pearson, Anita K. 1952. Reproduction of the 

lump-nosed bat (Corynorhinus rafinesquh) in California. Journal of Mammalogy. 

33: 273-320. 

Perkins, J. Mark. 1983. Northwest Oregon bat survey. Portland, OR: Oregon 

Department of Fish and Wildlife; draft report; contract 82-0-4. 51 p. 

Perkins, J. Mark; Barss, John M.; Peterson, Joshua. 1990. Winter records of bats in 

Oregon and Washington. Northwestern Naturalist. 71: 59-62. 

25
Perkins, J. Mark; Cross, Stephen P.1988. Differential use of some coniferous forest 

habitats by hoary and silver-haired bats in Oregon. Murrelet. 69: 21-24. 

Perkins, J. Mark; Levesque, Connie. 1987. Distribution, status and habitat affinities 

of Townsend's big-eared bat (Plecotus townsendii) in Oregon. Portland, OR: 

Oregon Department of Fish and Wildlife, nongame wildlife program; technical report 

86-5-01. 49 p. 

Provost, Ernest E.; Kirkpatrick, Charles M. 1952. Observation on the hoary bat in 

Indiana and Illinois. Journal of Mammalogy. 33: 110-113. 

Racey, P.A.1973. Environmental factors affecting the length of gestation in 

heterothermic bats. Journal of Reproduction and Fertility Supplement. 19: 175-189. 

Racey, P.A. 1982. Ecology of bat reproduction. In: Kunz, Thomas H., ed. Ecology of 

Bats. New York: Plenum Press: 57-104. 

Racey, P.A.; Swift, Susan M.1981. Variations in gestation length in a colony of 

pipistrelle bats (Pipistrellus) from year to year. Journal of Reproduction and Fertility. 

61: 123-129. 

Ross, Anthony. 1967. Ecological aspects of the food habits of insectivorous bats. 

Proceedings of the Western Foundation of Vertebrate Zoology. 1: 205-63. 

Ruggiero, Leonard F.; Aubry, Keith B.; Carey, Andrew B. [and others], tech. 

 coords. 1991. Wildlife and vegetation of unmanaged Douglas-fir forests. Gen. Tech. 

Rep. PNW-285. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific 

Northwest Research Station. 533 p. 

Schowalter, David B.; Dorward, William J.; Gunson, John R.1978a. Seasonal occurrence of silver-haired bats (Lasionycteris noctivagans) in Alberta and British 

Columbia. Canadian-Field Naturalist. 92: 288-291. 

Schowalter, David B.; Gunson, John 8.1979. Reproductive biology of the big brown 

bat (Eptesicus fuscus) in Alberta. Canadian Field-Naturalist. 93: 243-251. 

Schowalter, David B.; Harder Lawrence D.; Treichel, Bruce H. 1978b. Age composition of some vespertilionid bats as determined by dental annuli. Canadian Journal of 

Zoology. 56: 355-358. 

Schwartz, Charles Walsh; Schwartz, Elizabeth Reader. 1959. The wild mammals of 

Missouri. Columbia: University of Missouri Press and Missouri Conservation 

Commission. 339 p. 

Senger, Clyde M.; Senger, Robert; Senger, David; Senger, Stuart. 1974. Winter 

records of myotid bats in western Washington. Murrelet. 55: 13-14. 

Seton, Ernest Thompson. 1907. Life-histories of northern animals. New York: Charles 

Scribner's Sons. 1264 p. 

Shump, Karl A., Jr.; Shump, Ann 0.1982. Lasiurus cinereus. Mammalian Species 185. 

New York, NY: American Society of Mammalogists. 5 p. 

Simmons, James A.; Fenton, M. Brock; Ferguson, William R. [and others]. 1979. 

Apparatus for research on animal ultrasonic signals. Life Sciences Misc. Publi. 

Toronto, ON: Royal Ontario Museum. 31 p. 

26 
Stebbings, R.E.1980. Conservation of European bats. Kent, United Kingdom: 

Christopher Helm, Ltd. 246 p. 

Thomas, Donald W.1988. The distribution of bats in different ages of Douglas-fir 

forests. Journal of Wildlife Management. 52: 619-626. 

Thomas, Donald W.; Bell, Gary P.; Fenton, M. Brock. 1987. Variation in echolocation 

call frequencies recorded from North American vespertilionid bats: a cautionary note. 

Journal of Mammalogy. 68: 842-847. 

Thomas, Donald W.; West, Stephen D. 1989. Sampling methods for bats. Gen. Tech. 

Rep. PNW-243. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific 

Northwest Research Station. 20 p. (Ruggiero, Leonard F.; Carey, Andrew B., tech. 

eds.; Wildlife-habitat relationships: sampling procedures for Pacific Northwest 

vertebrates). 

Thomas, Donald W.; West, Stephen D. 1991. Forest age associations of bats in the 

Washington Cascade and Oregon Coast Ranges. In: Ruggiero, Leonard F.; Aubry, 

Keith B.; Carey, Andrew B. [and others], tech. coords. Wildlife and vegetation of 

unmanaged Douglas-fir forests. Gen. Tech. Rep. PNW-285. Portland, OR: U.S. 

Department of Agriculture, Forest Service, Pacific Northwest Research Station: 

295-303. 

Trevor-Deutsch, B. 1973. The role of hibernating bats in the winter diet of Peromyscus 

spp. (Rodentia: Cricetidae) in Ontario. Ottawa, ON: Carleton University. 127 p. Ph.D. 

thesis. 

Tuttle, Merlin D. 1974. An improved trap for bats. Journal of Mammalogy. 55: 475-477. 

Tuttle, Merlin D. 1976. Population ecology of the gray bat (Myotis grisescens): factors 

influencing growth and survival of newly volant young. Ecology. 57: 587-595. 

Tuttle, Merlin D. 1979. Status, causes of decline and management of endangered gray 

bats. Journal of Wildlife Management. 43: 1-17. 

van Zyll de Jong, C.G. 1979. Distribution and systematic relationships of long-eared 

Myotis in western Canada. Canadian Journal of Zoology. 57: 987-94. 

van Zyll de Jong, C.G.1985. Handbook of Canadian mammals: Volume 2: Bats. 

Ottawa: National Museums of Canada. 212 p. 

Warner, Richard M.; Czaplewski, Nicholas J.1984. Myotis volans. Mammalian 

Species 224. New York, NY: American Society of Mammalogists. 4 p. 

Whitaker, John O., Jr.; Maser, Chris; Keller, Laurel E. 1977. Food habits of bats of 

western Oregon. Northwest Science. 51: 46-55. 

Whitaker, John O., Jr., Maser, Chris; Cross, Stephen P.1981 a. Food habits of 

eastern Oregon bats, based on stomach and scat analysis. Northwest Science. 55: 

281-92. 

Whitaker, John O., Jr.; Maser, Chris; Cross, Stephen P. 1981 b. Foods of Oregon 

silver-haired bats. Northwest Science. 55: 75-77. 

Woodsworth, G.C. 1981. Spatial partitioning by two species of sympatric bats, Myotis 

californicus and Myotis leibii. Ottawa, ON: Carleton University. M.S. thesis. 

27
Glossary Calcar-Extension of heel bone that supports the tail membrane between the foot and 

the tail. 

Day roosts-Structures used by bats to sleep or rest in during the day. 

Glean-To pick insects from the ground or foliage rather than from the air. 

Hibernacula-Sites used by bats for hibernation in winter months (for example, caves, 

mines, hollow trees, attics). 

Hibernation-Long-term decrease in metabolic rate during winter in response to seasonal changes in environmental conditions and resource availability. 

Keel-Ridgelike expansion of the calcar, which gives added support to the tail membrane. 

Kilohertz (kHz)-Unit of sound frequency equal to 1000 cycles per second. The human 

ear can pick up sounds from 0.05 to 20 kHz. Bat echolocation frequencies range from 

10 to 180 kHz. Species in the Pacific Northwest echolocate at 20 to 100 kHz. 

Maternity roosts-Structures used by colonial female bats and their young during the 

spring and summer months. Males often join females and young in maternity roosts in 

autumn after young are weaned. 

Mist netting-Capture of bats (or birds) in fine nylon nets. 

Night roosts-Structures used briefly by bats at night. Bats will retreat to night roasts to 

rest between feeding periods or to feed on large insects that cannot be eaten while in 

flight. Night roosts usually are found in different locations than day roosts. 

Torpor-Short-term decrease in metabolic rate for energy conservation that may occur 

during any season of year. 

Vespertilionidae-Evening bats or plain-nosed bats. Taxonomic family that includes all 

Pacific Northwest bats. 

Wingspan---Length of wing spread. Measured from wing tip to wing tip, including width 

of the body. 

28 
Christy, Robin E.; Stephen D. West. 1993. Biology of bats in Douglas-fir 

forests. Gen. Tech. Rep. PNW-GTR-308. Portland, OR: U.S. Department 

of Agriculture, Forest Service, Pacific Northwest Research Station. 28 p. 

(Huff, Mark H.; Holthausen, Richard M.; Aubry, Keith B., Tech. coords. 

Biology and management of old-growth forests). 

Twelve species of bats occur in Douglas-fir forests of the Pacific Northwest, of 

which nine are known to roost in tree cavities, bark crevices, or foliage, and 

several are closely associated with old-growth forests. Thus bat populations 

may be detrimentally affected by forest management practices involving the 

removal of large, old trees and snags. We review the life history 

characteristics and habitat relations of bats in the Pacific Northwest and 

provide information useful in managing forests for the persistence of native bat 

populations. 

Keywords: Bats, Pacific Northwest, natural history, old-growth forests. 

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