Corynorhinus townsendiiTownsend's big-eared bat

Geographic Range

Corynorhinus townsendii has a broad range in western North America, from southern Canada to southern Mexico. They have significant populations in all Rocky Mountain states (Arizona, Colorado, Utah, Wyoming, Idaho, and Montana) as well as Texas, South Dakota, Kansas, northwest Arkansas and southern Missouri and west through California, Oregon, and Washington. Corynorhinus townsendii townsendii is the subspecies thought to occur mostly in the Pacific Northwest. Corynorhinus townsendii pallescens is a considerably more pale subspecies that inhabits desert habitats. There are isolated populations of the subspecies Corynorhinus townsendii ingens, found in caves in eastern Oklahoma, and Corynorhinus townsendii virginianus, found in east-central Kentucky, West Virginia and westernmost Virginia in the Potomac and James tributary river valleys. (Adams, 2003; Barbour and Davis, 1969; Chapman, 2007; Choate, et al., 1994; Kunz and Martin, 1982; Terwilliger and Tate, 1995)


Most western populations of Corynorhinus townsendii live in montane forest. This type of forest is thick with pine, fir and aspen trees and is bounded by shrub and grasslands. At higher elevations, the surrounding vegetation is subalpine. Corynorhinus townsendii pallescens lives in an arid habitats with limited desert scrub vegetation, but stops short of living in extreme desert environments. Corynorhinus townsendii townsendii inhabit the humid coastal area of the Pacific Northwest. Eastern populations of Corynorhinus townsendii are generally found in oak-hickory forests.

Corynorhinus townsendii individuals choose roosting sites most commonly in caves, cliffs, and rock ledges but have been found in abandoned mines and other man-made structures. Colonies normally choose relatively cold places for roosting, and pick hibernacula with a considerable amount of air movement. Abandoned buildings are usually used only during the summer, while caves and abandoned mines are preferred in the winter.

Roost sites are generally have open ceilings because Townsend's big-eared bats don't crawl well. They prefer habitats that are almost completely dark and are extremely sensitive to human disturbance, which nearly always causes colonies to relocate. (Adams, 2003; Barbour and Davis, 1969; Chapman, 2007; Choate, et al., 1994; Kunz and Martin, 1982; Terwilliger and Tate, 1995)

  • Other Habitat Features
  • caves
  • Range elevation
    457 to 2743 m
    1499.34 to 8999.34 ft

Physical Description

Townsend's big-eared bats are medium-sized bats with broad wings. They have two large, fleshy glands on either side of the muzzle. The snout is short with elongated nostril slits. Coloration varies from population to population, although all fur colors tend to be some hue of brown or gray. Hairs are darker at the base than they are at the tips. The dorsum can be anywhere from pale cinnamon brown to blackish brown to slate gray. The ventral side tends to be buff to pale brown. Ears are large, generally more than 25 mm in length and connected by a low band across the forehead. The ears are usually directed forward while in flight. When these bats are sleeping, the ears are generally rolled down and back across the head, resembling ram horns, which gives these bats one of their nicknames, "ram eared bats". Corynorhinus townsendii can range in mass from 5g to 13g.

Dental formula is I 2/3, C 1/1, P 2/3, M 3/3 = 36. (Adams, 2003; Barbour and Davis, 1969; Chapman, 2007; Choate, et al., 1994; Kunz and Martin, 1982; Terwilliger and Tate, 1995)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    5 to 13 g
    0.18 to 0.46 oz
  • Range length
    90 to 115 mm
    3.54 to 4.53 in
  • Range wingspan
    297 to 320 mm
    11.69 to 12.60 in


Mature males begin spermatogenesis during summer, reaching its peak in September. Females experience a short proestrus in late summer. Estrus occurs in the fall with copulation taking place from November to February. Townsend's big-eared bats mate with multiple partners repeatedly during the breeding season. Males perform a mating display, during which they approach a female making loud, twittering noises. If they are accepted by the female, the male rubs his snout over the female's face, neck, forearms and ventral surface. The glands on the male's snout serve to scent mark the female prior to copulation, during which the female is usually in a state of torpor. The sperm is stored in the female's reproductive tract until the spring, when ovulation, implantation, and gestation occur. (Barbour and Davis, 1969; Chapman, 2007; Kunz and Martin, 1982; Wimsatt, 1977)

Most breeding occurs in the winter months at hibernacula, peaking November through February. Some females are inseminated before their arrival at winter roosts. The normal gestation period is 56 to 100 days, depending on ambient temperatures and length of time the female spends in torpor during gestation. In the spring and summer, females form maternity colonies in caves, mines, and buildings while males live solitarily or in small bachelor clusters. Most females give birth to only one young. Maternity colonies usually break up in August, although females who have lost their young typically leave the roost at an earlier date. After maternity colonies disperse, females migrate to hibernacula and reunite with males. Young females typically mate their first autumn, while males don't mate until after their first year of life. (Adams, 2003; Barbour and Davis, 1969; Chapman, 2007; de Magalhaes, et al., 2005)

  • Breeding interval
    Townsend's big-eared bats breed once yearly.
  • Breeding season
    Breeding occurs in the winter, peaking from November through February.
  • Average number of offspring
  • Range gestation period
    56 to 100 days
  • Average weaning age
    6 weeks
  • Range age at sexual or reproductive maturity (female)
    4 (low) months
  • Range age at sexual or reproductive maturity (male)
    1 (low) years

The young are born naked and their ears are folded over their unopened eyes for several days after birth. They cling to their mother's bodies during the day and cluster together in groups when the mothers leave at night to feed. Pups are weaned by at least 6 weeks of age and become independent shortly after. (Adams, 2003; Barbour and Davis, 1969; Chapman, 2007; Kunz and Martin, 1982)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence


Bats have the potential for great longevity. Corynorhinus townsendii individuals have been recorded living over twenty-one years. However, mortality in young is high, averaging 38 to 54%. If the young can survive the first year of life, their chance of survival rises to an average of 80% yearly. It has been noted that the life expectancy of Corynorhinus townsendii is much shorter when kept in captivity. (Barbour and Davis, 1969; de Magalhaes, et al., 2005; Gruver and Keinath, 2006)

  • Range lifespan
    Status: wild
    21 (high) years


Population composition varies according to season. Females form nursery colonies in the summers, while males are typically solitary. Sometimes both sexes live in the same summer roost although they don't normally cluster together. It's not known for certain how new nursery colonies become established, females do not leave to establish new colonies. The entire colony moves from one roost to another. Colony size varies by region. Western populations usually live in colonies of about a dozen to up to a couple hundred individuals. In the east, colonies can have 1,000 or more individuals. Roost sites are usually in an area with dim light, on the edge of the zone of total darkness. Their preference for low light or total darkness is exhibited in their feeding behaviors. Townsend's big-eared bats don't leave their roosts to forage until very late in the evening. Corynorhinus townsendii clusters are never in cracks or crevices, because they don't crawl away from the place that they land. Instead, they cluster on open-ceiling spaces. Often they hang by a single foot. While sleeping, their ears curl back over the head, resembling ram's horns. They are easily disturbed and will most often relocate after a human disturbance to the roost.

Townsend's big-eared bats are also versatile flyers, exhibiting movement ranging from darting to hovering motions. Landing is a delicate but agile maneuver in which the bat swoops from below, folds it's wings and quickly flips over and grasps onto the surface with a foot. This species is extremely adept at avoiding traps and nets and difficult to maintain in captivity.

Mother-young interaction is the most complex social interaction in the colony. During the day, the young cling to their mothers, but when the mothers go out at night to feed, the young remain behind in clusters. Mothers recognize their young through auditory signals, and it's been theorized that females also use the glands on their snout to scent mark their young.

Hibernation roosts occur throughout the colony's range, generally in places where average temperature is 55 degrees Fahrenheit (12.7 degrees Celsius) or less, but above freezing. Individuals may switch between roost sites during hibernation, but still roost in clusters. Individuals begin arriving at hibernacula in late fall and stay into mid spring. It's been observed that males usually choose warmer hibernation sites and also move more frequently than females. Energy sources during the winter months are still unknown. Flying insects are scarce and bats do not store enough fat for the fat stores to be the main energy source. They conserve heat by keeping their large wings folded over the ventral surface and clustering tightly together. During the warm months of the year, Townsend's big-eared bats go through bouts of daily torpor during the day. (Adams, 2003; Barbour and Davis, 1969; Chapman, 2007; Kunz and Martin, 1982)

  • Range territory size
    0.8 to 24 km^2

Home Range

Townsend's big-eared bats do not migrate long distances. Within their range they may have several roost sites for maternity/nursery colonies, bachelor colonies, and hiberancula. Individuals may move between these roosts at any point during the year, but the distances are generally small. Females tend to extend their foraging range during gestation, while the range of males recedes. (Adams, 2003; Barbour and Davis, 1969; Chapman, 2007; Gruver and Keinath, 2006; Kunz and Martin, 1982)

Communication and Perception

Most navigation and perception in this species is guided by echolocation. The large ears of Corynorhinus townsendii reflect the low-frequency echolocation calls they use and their sensitivity to detecting sounds. These bats can swivel their ears to concentrate on a directional or moving source of sound. Echolocation is accomplished by emitting a rapid series of intense sounds in the larynx. Unlike other mammals, whose auditory organs are connected to the skull, bats' auditory organs are surrounded by fatty tissue or sinuses, which helps dampen the conduction of sounds from the larynx. The middle inner-ear muscles contract before each sonar pulse so that the noises produced by the bat don't drown out the sounds that are being received by the ears. Pulses of high-pitched signals are sent out, ranging from several to a couple hundred pulses per second. The pulses only last a few thousandths of a second. Pulse rate, duration, pitch, and frequency vary based on the situation. High frequency sounds (above 20kHz) are the sounds produced for the purposes of echolocation. When foraging, Townsend's big-eared bats use low frequency pulses with longer durations until they locate a meal. When an insect is located, the pulse rate is increased and shortened and the pitch is lowered to help locate the insect more precisely. When the pulse strikes an obstacle, it is reflected back towards to bat, and the bat can determine the size, shape, texture, distance, direction, and movement of an object.

Auditory perception plays an important part in social interaction as well. Low frequency sounds (under 20 kHz) are within the range of human recognition and usually are used for social interactions. These interactions include spacing between individuals in the colony, mother-young interactions, communication, and warning calls. Males, when performing a courtship display, make high pitched twittering noises to their intended mate. Young bats produce unique calls which help their mothers locate them if they become separated in the colony. Studies have shown that over time, the calls of the young evolve into chirping noises, but when a mother heard a recording of the call of her infant that had been made a week earlier, she still responded.

The importance of olfactory signals to Townsend's big-eared bats is unclear. It is probable that scent plays a role in recognizing individuals within a colony as well as mother-infant recognition. It has been shown that acoustic emissions are key in mother-infant associations in Corynorhinus townsendii, especially when the infant might be beyond the range of olfactory reception. Males have been observed scent-marking females before copulation using excretions from the glands on their muzzles. (Fenton, 1985; Hill and Smith, 1984; Kunz and Racey, 1998; Lacki, et al., 2007; Mohr, 1976; Wimsatt, 1977)

Food Habits

Townsend's big-eared bats feed almost exclusively on moths (Lepidoptera), but they've also been known to eat beetles (Coleoptera), flies (Diptera) and other small insects. Small moths 3 to 10 mm in length are the most common prey. Western bat populations typically forage in dense foliage, using low frequency signals to pinpoint the location of insects among the branches of trees. Populations in Virginia and Kentucky, however, have been observed foraging among the forest but also in open fields and along low cliff walls. They generally glean prey off the branches of trees and can drink in flight from the surface of ponds and pools. After feeding, they return to night roosts to digest and may make a second foraging trip before dawn. Townsend's big-eared bats are also recognized as one of the most effective "food specialists" in North America, with a diet compromised of over 80% moths. The availability and size of moth populations are significant factors in the sustainability of any population of Corynorhinus townsendii. (Adams, 2003; Burfod and Lacki, 1995; Dodd, et al., 2008; Hill and Smith, 1984; Lacki, et al., 2007)

  • Animal Foods
  • insects


The nocturnal habits of Townsend's big-eared bats, their ability to fly, and their occupation of difficult to access roosting areas, makes them unlikely prey for most predators. Nocturnal birds of prey, snakes, and rats will prey on big-eared bats occasionally. Specific reports of predation include Pacific gopher snakes (Pituophis catenifer catenifer), domestic cats (Felis catus), and raccoons (Procyon lotor). A California study of a colony of Corynorhinus townsendii that had taken up residence in an abandoned multi-story house reported Rattus rattus> preying on the colony and the tracks and markings made by these rodents were discovered in the rafters closest to the roosting site of the bats. Colonies threatened by a predator may use warning vocalizations varying from loud cries to twittering. (Barbour and Davis, 1969; Fellers, 2000; Fenton, 1985; Gruver and Keinath, 2006)

Ecosystem Roles

The most common parasites found on Corynorhinus townsendii are parasitic flies from the family Streblidae. These flies are large, yellow, and extremely visible. They use the bats as hosts throughout the year. Another kind of wingless fly has been found on western populations, from the family Nycteribiidae. Mites are common across all populations. Corynorhinus townsendii share roost sites with other species, sometimes, including Rafinesque’s big-eared bats (Corynorhinus rafinesquii) in southern populations, eastern pipistrelles (Pipistrellus subflavus), northern long-eared myotis (Myotis septentrionalis), and eastern small-footed myotis (Myotis leibii). Woodrats (Neotoma) are sometimes also found in roosting areas with these bats. Corynorhinus townsendii populations help to control moth populations because they are moth dietary specialists. (Barbour and Davis, 1969; Chapman, 2007; Hill and Smith, 1984)

Commensal/Parasitic Species
  • mites (Acari)
  • streblid flies (Streblidae)
  • bat flies (Nycteribiidae)

Economic Importance for Humans: Positive

By far the most recognizable benefit humans gain from the presence of Corynorhinus townsendii is pest-control. They are highly effective predators of moths especially. As a result, there is less environmental and agricultural damage due to insects. In some areas they are important predators of destructive gypsy moths (Lymantria dispar). (Hill and Smith, 1984; Mohr, 1976)

  • Positive Impacts
  • research and education
  • produces fertilizer
  • controls pest population

Economic Importance for Humans: Negative

While it is popular belief that bats are diseased and dangerous animals, this is largely erroneous. Bats can carry rabies and histoplasmosis, which can infect humans and other warm-blooded species, but reports of disease transmission to humans are uncommon. Bacterial, fungal, viral and mycotic agents have all been associated with bats, and they can be a host to many endo- and ecto-parasitic organisms. In 2001, the Center for Disease Control reported that 17.2% of all rabies cases were bats, there are no estimates for the prevalence of rabies within the species Corynorhinus townsendii. Although Corynorhinus townsendii generally does not take up residence near human populations, their presence in human structures can deteriorate the sanitation and the structural quality of the roost site. The accumulation of feces and the presence of parasites and bacteria represent a real health hazard to people who wander into a roost site. However, the greatest problems seem to be the noise the colony produces as well as the inconvenience of accumulated fecal matter. (de Magalhaes, et al., 2005; Gruver and Keinath, 2006; Hill and Smith, 1984; Mohr, 1976)

  • Negative Impacts
  • injures humans
    • carries human disease

Conservation Status

Corynorhinus townsendii is recognized by many sources as a endangered species, although it has a global rank of Apparently Secure. Its low tolerance for human disturbance often causes the entire colony to relocate if it is interrupted, particularly during hibernation. The presence of humans in their environment can be so stressful to big-eared bats that mortality rate might increase as a result of disturbance. As such, many national parks and other protected lands take precautions to prevent the disturbance of any populations present on their land by placing warning signs outside of roost caves or other sites. Some have installed metal gates that bar passage to people but allow the bats to move freely in and out of their caves.

Populations that roost in abandoned mines are threatened by demolition of those mines. Roosting bats are buried alive in the mine shaft. Researchers have taken steps to work with mining companies to ensure that no populations exist before shafts are destroyed, and with populations that do exist, they usually place grates over the entrance to the shaft, similar to those used to protect cave sites. While protection of their roost sites are key, Corynorhinus townsendii also needs protection of the forested areas where they forage. Deforestation represents a real problem for big-eared bats. (Chapman, 2007; Hill and Smith, 1984; Kunz and Racey, 1998)

Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Corynorhinus townsensii mortalities as a result of white-nose syndrome, the disease continues to move westward across North America. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)

Other Comments

Townsend's big-eared bats were previously known as Plecotus townsendii.


Tanya Dewey (editor), Animal Diversity Web.

Jen Sullivan (author), Radford University, Karen Powers (editor, instructor), Radford University.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map


uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate

delayed fertilization

a substantial delay (longer than the minimum time required for sperm to travel to the egg) takes place between copulation and fertilization, used to describe female sperm storage.


The process by which an animal locates itself with respect to other animals and objects by emitting sound waves and sensing the pattern of the reflected sound waves.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.


having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.


the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.


An animal that eats mainly insects or spiders.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


having the capacity to move from one place to another.


This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.


active during the night


the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


lives alone


mature spermatozoa are stored by females following copulation. Male sperm storage also occurs, as sperm are retained in the male epididymes (in mammals) for a period that can, in some cases, extend over several weeks or more, but here we use the term to refer only to sperm storage by females.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


Living on the ground.


uses sound above the range of human hearing for either navigation or communication or both


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


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