||The Mammals of Texas -
Townsend's Big-eared Bat
Chiroptera : Family
Vespertilionidae : Plecotus townsendii Cooper
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.
Distribution 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
Townsends big-eared bats
hibernate throughout their range during winter months
when temperatures are between 0°C and 11.5°C. 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 animals 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
Photo credit: Merlin D. Tuttle, Bat Conservation