Recognition: This bat's ears are remarkable -- reaching a length of 38 mm. The face is marked by a large lump on either side of the snout. Color ranges from pale brown to slate gray. Females are larger than males. Measurements include: total length, 90-112 mm; length of forearm, 39-48 mm; and weight, 9-14 g. Wingspan is approximately 280 mm.
Distribution: This is a bat of western North America, ranging from southern British Columbia to southern Mexico. Townsend's big-eared bat can be found throughout Colorado except on the eastern plains. Its distribution seems to be determined by availability of roosts, such as caves, mines, tunnels, crevices and masonry structures with suitable temperatures, making the conservation of suitable roosts essential to the management of this species.
Habitat and Habits: This bat is generally solitary or gathers in small groups, although during summer females may form larger maternity colonies. Townsend's big-eared bat can be found in mines, caves and structures in woodlands and forests to elevations above 9,500 feet. They often hang near the entrances to roosts, in the "twilight zone." The animals do not make major migrations and appear relatively sedentary. Hibernacula have low and stable temperatures -- sometimes with moderate airflow -- during late October to April. Hibernating, the bats hang singly or in small clusters in the open, not in crevices, with pelage erect to provide maximum insulation and the ears coiled back like a ram's 
horns, perhaps to reduce heat loss. The bat is quite sensitive to changes in temperature and humidity within the hibernaculum and may arouse to move to a more favorable location. Care should be taken not to disturb them because paying the price of accidental arousal in winter could deplete energy stores and prevent arousal in spring. Populations may be principally limited by high winter mortality due to the absence of roosts with stable temperatures. Most mortality occurs during the first year of life. Predators have not been documented, but snakes, owls and hawks probably take these bats.
Breeding: Copulation, which occurs in late fall, is preceded by ritualized courtship behavior by the male. The female stores sperm in the reproductive tract until spring when ovulation and fertilization happen. Gestation takes 50-60 days. Young are born in mid-June, and strong bonds form between mother and offspring. About 90 percent of all females in the nursery colonies produce young. Young fly in 2 to 3 weeks and are weaned by 6 weeks. Only one young is born per female.
Food: This bat feeds mainly on small moths, but also eats beetles, flies and wasps. Townsend's big-eared bat usually is a late flier (except for females from maternity roosts) and forages along the edge of vegetation. The animals sometimes glean insects from the vegetation. Like other species, this bat may use a night roost and then feed a second time just before dawn and the return to its day roost.
Remarks: Populations, especially in the nursery and hibernaculum, are highly susceptible to disturbance and have been reported to be declining. Little is known of the natural history of this species in Colorado, but the animals certainly stand to benefit from the Bats/Inactive Mines Project of the Colorado Parks and Wildlife.
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