v1-Townsend’s Big-eared Bat (Corynorhinus townsendii)

Townsend’s Big-eared Bat (Corynorhinus townsendii)


Townsend’s Big-eared Bat is a medium-size bat with enormous ears (about one half its body length) and two prominent, glandular swellings on its nose. It measures from 83-113 mm in length and weighs 6.0-13.5 g. Its long dorsal fur varies from pale brown to blackish-grey. The underside of the Townsend’s Big Bats is paler than the dorsal side of the body. The tragus is long (about one third the ear length) and pointed. The calcar lacks a keel. The skull is relatively narrow and the profile of the brain-case is curved.

Natural History

In the western United States, the Townsend’s Big-eared Bat uses caves, old mines and buildings as both summer day roosts and night roosts, with buildings being used more often in humid coastal areas. Females form colonies of a dozen to several hundred in dimly lit areas in buildings, caves or mines. This species is particularly sensitive to human disturbance and a number of biologists have noted that females will permanently abandon a traditional summer roost if disturbed. Males roost alone during summer, separate from females. In August, nursery colonies break up and individuals begin to migrate to caves and mines for hibernation. Townsend’s Big-eared Bat is relatively sedentary, moving 10 to 65 km between the summer roost and the winter hibernaculum. This is one of the few bats that has been consistently found hibernating in British Columbia.  When in a state of deep torpor this bat hangs from a horizontal surface by its feet; its ears are curled back along the head in a shape resembling a ram’s horn. Folding the ears may reduce heat loss. Curiously, the tragus remains erect when the ears are folded-it has been suggested that the tragus acts as a heat sensor. The Townsend’s Big-eared Bat emerges an hour or so after dark to feed. It is an agile bat that is capable of flying at slow speeds. Food habits have not been studied in British Columbia however in the western United States; small moths (body length, 3-10 mm) form most of its diet. It also eats lacewings, dung beetles, flies and sawflies. This species feeds several times during the night so it is often near dawn before it returns to the day roost.

Range: The Townsend’s Big-eared Bat is found throughout the western United States; there are isolated populations on the southern Great Plains and in the Ozarks and Appalachians. In Canada, it is restricted to British Columbia. On the coast, it inhabits Vancouver Island, the Gulf Islands and the Vancouver area; in the interior, it has been found as far north as Williams Lake and east to Creston.

Habitat: In British Columbia this species is associated with a variety of habitats from coastal forests to arid grasslands of the interior. It ranges in elevation in the province is from sea level to 1070 m, although most occurrences are from low elevations.


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