Townsend's Big-Eared Bat
This bat has remarkable ears that can reach an inch and a half in length.
About This Species
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.
Living with Bats
There are 18 species of bat that call Colorado home. These amazing mammals are not only fantastic insect control, but are also valuable pollinators. Learn more about how humans and bats can live in harmony in our guide.
Bat Conservation
Bats remain one of the most mysterious land mammals, especially in Colorado, where 18 species spend at least part of the year. For example, the little brown bats in our state seem to hibernate differently than those on the east coast, and we are constantly learning about their whereabouts, habitats and behaviors. Our current research suggests that bat populations in Colorado are doing quite well.
One little brown bat can eat up to 18,000 small insects (like mosquitoes) each night. Their economic impact is estimated to be billions of dollars, and much of the agricultural industry relies on their insect control.
Beyond their economic impact, bats flaunt some impressive adaptations. They are the only mammal that truly flies, which requires a very unique anatomy. Their upside-down lifestyle requires adaptations in their “feet” to consistently grip. If people hanged upside down for even an hour, we’d lose consciousness; bats have developed amazing blood pressure accommodations to fit the lifestyle.
We are currently involved in a monitoring partnership called the North American Bat Monitoring Program (NA Bat). The program utilizes acoustic surveys to collect information on bat populations without interfering with their behaviors. We also are using PIT tags, like the chips put in household pets, to monitor a number of maternity sites. While data collection will take years, we’ve already learned new information about Colorado’s bat population, the most heartening of which is that the population appears larger and more widespread than we’d thought. This is an excellent start to learning more about the species, but we’ve got lots of problem-solving and technological innovation left to do.
Our priorities also include learning more about bats so that we are prepared for the potential spread of White-nose Syndrome. Finding and monitoring bats is crucial to this effort, but also comes with its own challenges. Because bats are small, flying mammals, much of the equipment used to track other species is too heavy for them. And during the winter, Colorado bats are very elusive, choosing to hibernate in small groups often in locations that are inaccessible to people.
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Physical Characteristics
Measurements include: total length, 90-112 mm; length of forearm, 39-48 mm; and weight, 9-14 g. Wingspan is approximately 280 mm.
Range
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
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 large rock cavities to elevations above 9,500 feet where they form maternity colonies that may number into the hundreds in rare cases. 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 found in caves, mines, and probably large rock cavities. When hibernating, the bats hang singly or in small clusters in the open, 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 limited by high winter mortality due to the absence of roosts with stable temperatures. Most mortality occurs during the first year of life.
Diet
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 then return to its day roost.
Reproduction
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.
Threats to Species
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 Inactive Mines Project. Predators have not been documented, but snakes, owls and hawks probably take these bats.