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Species: Plecotus townsendii
Common Name: Western big-eared bat
Spanish Name: Murcielago de Townsend
Townsend's big-eared Bat
Author: Richard Plunkett
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Species: Plecotus townsendii |
Description:
Townsend's big-eared bat, as its name suggests, has very large ears—nearly half the length of its body. These big ears are used in flight to add lift and aid maneuverability, and in echolocatin of prey. It has pale reddish-brown to dark brown dorsal fur and pale buff to grey underparts. Although it looks very similar to other bats in the same genus, Townsend's big-eared bat can be distinguished by two prominent lumps on either side of its nose. Adults are 89-116 mm in length, with forearm length 39-47 mm and tails from 35-54 mm long, and weigh 9-12 g. The females are slightly larger than the males.
Geographic range:
Even though they are found across a wide geographic area, big-eared bats are not very common. Where these bats are found depends very largely upon the availability of caves and cave-like roosting habitat (such as old mines). Townsend's big-eared bats occur throughout western North America . Their range extends from southern British Columbia , through the western United States from California to Colorado and west Texas and Oklahoma . They are found in northern and central Mexico to as far south as the Isthmus of Tehuantepec . A few isolated populations of Townsend's big-eared bats exist in the eastern United States . The subspecies P. t. pallescens is found from New Mexico to southeast California , and north to Utah , Wyoming and Colorado . These bats are extremely vulnerable to disturbance. Loss of roosting habitats (e.g. mine closings), vandalism and increased visitation by humans have been causes of the declin of big-eared bat populations.
Habitat:
Townsend's big-eared bats are found where roosting habitats such as caves or abandoned mines are available, and do not seem to be particular about the the geography of where they live. If roosting sites are available, they can be found in low deserts, high mountains, riparian areas, and anywhere in between. Mines and caves provide good places for roosting and hibernating, but these bats have also been found in abandoned buildings, crevices in rock cliffs, and under large boulders or overhangs which provide refuge.
Big-eared bats are relatively sedentary. They do not tend to move great distances between their hibernacula and their summer roosting sites, nor do they stray far from their roosts each night while foraging. Because of this, preservation of suitable habitats is crucial to the survival of the populations of bats which use them—if the roosts are disturbed or destroyed, the bats do not simply move on to find new homes.
Townsend's big-eared bats are insectivores. They feed at night, mostly on moths, though they also eat flies, beetles and some other insects. The bats take their catch to caves, buildings or other safe night roosts, where they remove the wings from the moths (85 percent of their diet) and eat the abdomens. Townsend's big-eared bats generally wait about 45 minutes after sundown before leaving their day roosts, and thus are rarely seen. Often they circle inside the cave opening before embarking on their nightly forage. Female bats generally make one foraging bout each night, but during pregnancy and while lactating, they make two or even three trips per night.
Carnivores may prey on Townsend's big-eared bats. Some animals seen eating these bats include a black rat snake ( Elaphe obsoleta ), a spotted skunk ( Spilogale putorius ), house cats ( Felis domesticus ) and even rats ( Rattus rattus ).
Reproduction and Development:
Townsend's big-eared bats generally mate between November and February. The females store the male sperm in their reproductive tracts until late spring. Gestation can take from 56 to 100 days, depending on the temperature and activity of the bats. Female bats form maternity colonies in warmer parts of caves or buildings; these colonies may contain over 1,000 bats, but typically are made of several hundred individuals. The females give birth to a single pup each year, which grows very rapidly, and is weaned in 4-5 weeks.
Behavior:
Townsend's big-eared bats are nocturnal feeders, and spend their days in roosts, such as caves or abandoned mines and buildings. They are active at night, emerging about 45 minutes after sunset to forage for insects. Their large ears provide extra lift, and big-eared bats are able to fly at low speed and even hover with great maneuverability. The big ears are also used in the echolocation of prey. Often thought of as “radar,” the term “sonar” is more appropriate because the bats use reflected sound waves from their vocalizations to sense objects around them.
During the winter months, Townsend's big-eared bats hibernate in cool humid caves or mines. Depending upon the climate, the bats may hibernate in the twilight areas near the cave opening, or if the temperatures are too extreme, they may move to deep within the cave, where the temperature remains stable. Big-eared bats hibernate huddled tightly together in clusters. One group of big-eared bats numbering over 1,000 individuals was discovered once! More commonly, however, Townsend's big-eared bats are found in groups of less than 25. If temperatures drop below freezing the bats may move around within the caves, and sometimes between different caves, but they generally spend most of their time in a state of torpor. During the winter the bats' big ears may be folded, and look like curled ram's horns.
Conservation:
Considered to be rare or uncommon, Townsend's big-eared bat numbers are being tracked by the Federal government and by the State of New Mexico . In the southwest United States it is a species of special concern, and because of declining populations, Townsend's big-eared bat is being considered for threatened or endangered species classification. These bats are extremely sensitive to disturbance of their maternity roosts and hibernation sites, and do not produce very many offspring. Because of their insect diet, big-eared bats are also vulnerable to chemical pesticides and herbicides.
The biggest threats to the existence of Townsend's big-eared bats are disturbance by humans and vandalism of their roosts and hibernation sites. The bats' roosting habitats can be lost to mine closings, and their foraging habitats can disappear from deforestation. Rather than closing mines and caves, gates may be installed to keep people out which still allow the bats to enter and leave. Careful monitoring of local bat populations can help determine where conservation efforts are most needed, and alternative or even artificial roosts may be identified for the bats.
Townsend's big-eared bats are being studied for several reasons. Their populations are of interest not only for conservation, but also because of economic and public health concerns. Bats may be associated with diseases such as rabies, for which they may host the causative agents. Bat guano, on the other hand, has proved useful as a source of antibiotics, and is an important source of fertilizer for agriculture.
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Taxonomy:
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order:
Chiroptera
Family:
Vespertilionidae
Genus:
Plecotus
Species:
townsendii
References:
Species information was obtained from the Biota Information System of New Mexico (BISON) and the following sources:
The Smithsonian book of North American Mammals . D.E. Wilson and S. Ruff (eds.). The Smithsonian Institution, 1999.
Mammals of North America . E.R. Hall and K. R. Kelson. The Ronald Press Company, 1959.