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  The Mammals of Texas - Online Edition

Townsend's Big-eared Bat
Order Chiroptera : Family Vespertilionidae : Plecotus townsendii Cooper

Townsend's Big-eared Bat (Plecotus townsendii).  Photo by Merlin D. Tuttle, Bat Conservation International.Description. A medium-sized bat with extremely long ears and a small glandular outgrowth on each side of the snout. Upperparts near clove-brown on back, wood-brown on sides, underparts slightly paler; membrane between hind legs full, wide and hairless. The combination of large flexible ears, nearly uniform color, and the lumps on the snout identify this bat. Dental formula: I 2/3, C 1/1, Pm 2/3, M 3/3 X 2 = 36. External measurements average: total length, 100 mm; tail, 46 mm; foot, 11 mm; ear, 35 mm; forearm, 44 mm. Weight, 7-12 g.

Species distribution mapDistribution in Texas. Suitable habitat in western one-half of state.

Habits. The distribution of this bat is correlated largely with rocky situations where caves or abandoned mine tunnels are available. They do not seem to utilize crevices in such sites, and may occasionally inhabit old buildings. In the Trans-Pecos, this is probably the most characteristic bat of caves and mines.

Townsend’s big-eared bats hibernate throughout their range during winter months when temperatures are between 0C and 11.5C. The bats hibernate in tight clusters, which may help stabilize body temperature against external changes in temperature. While torpid, the large ears are "rolled up" and laid back against the animal’s neck. Males may select warmer hibernacula than do females and are more easily aroused and active in winter than are females. Their winter sleep is interrupted by frequent periods of wakefulness during which they move about in the caves or from one cave to another. They become very fat before hibernation. This fat provides them with sufficient food to maintain their lowered metabolism during the winter months when they do not eat. Males and females occupy separate roosting sites during summer. During this season, males appear to lead a solitary lifestyle while females and young form maternity colonies which may number 12-200, although in the eastern United States colonies of 1,000 or more are known.

These bats emerge late in the evening to forage and are swift, highly maneuverable fliers. Prey items include small moths, flies, lacewings, dung beetles, and sawflies.

The single young is born in late May to early June, at least in Texas. The baby bat weighs approximately 2.4 g at birth and is pink, naked, and completely helpless. At 4 days of age the newborn bat begins to display hair growth and by 1 month of age is volant and nearly adult size. At 2 months of age the juveniles are weaned and the nursery colonies begin to disperse.

Photo credit: Merlin D. Tuttle, Bat Conservation International.