The Townsend's big-eared bat (Corynorhinus townsendii) is a species of vesper bat found in North America.
Townsend's big-eared bat is a medium-sized bat (7-12 g) with extremely long, flexible ears, and small yet noticeable lumps on each side of the snout. Its total length is around 10 cm (4 in.), its tail being around 5 cm (2 in) Its wingspan is about 28 cm (11 in).
These bats have low wing loading, which means a large wing area to mass ratio. This morphology allows for a large amount of lift, high maneuverability, low-speed flight, and hovering during flight.
Their large pinnae are usually in line with the body during flight; this indicates one of the roles of the pinnae is to impart lift during flight. The ears are also used to transmit sound into the bat's external auditory meatus, effectively distinguishing between ambient noise and the sounds of predators or prey.
These bats are found in Canada, Mexico, and United States. They inhabit coniferous forests and woodlands, deciduous woodland, riparian areas with trees, and semi-desert and montane shrublands. They require large cavities for roosting in abandoned buildings and mines, caves, and basal cavities of trees. During summer, these bats inhabit rocky crevices, caves, and derelict buildings.
In winter, Townsend’s big-eared bats hibernate in rocky crevices, caves, tunnels, mineshafts, spaces under loose tree bark, hollow trees, and buildings. During the summer, males and females occupy separate roosting sites; males are typically solitary, while females form maternity colonies, where they raise their pups. A maternity colony may range in size from 12 bats to 200, although in the eastern United States, colonies of 1,000 or more have been formed. During the winter, these bats hibernate, often when temperatures are around 32 to 53 °F (around 0 °C to 11.5 °C.) They prefer to roost singly during hibernation, forming small clusters only rarely. Males often hibernate in warmer places than females and are more easily aroused and active in winter than females. The bats are often interrupted from their sleep because they tend to wake up frequently and move around in the cave or move from one cave entirely to another. Before hibernation, they increase their body mass to compensate for the food they do not eat during the winter. Townsend’s big-eared bats have 2-3 feeding periods between dark and dawn, with periods of rest in between. They rest in areas different from where they roost during the day. When hunting, these bats echolocate at much lower intensities than other bats; this may be partly because they specialize in moths because some moths have the ability to hear bats, possibly producing their own noises to 'jam' a bat's echolocation in an effort to thwart predation.
Townsend’s big-eared bats are carnivores (insectivores) and are moth specialists. However, their diet may include small moths, flies, lacewings, dung beetles, sawflies, and other small insects.
Townsend’s big-eared bats have a polygynandrous (promiscuous) mating system in which both the males and the females have multiple partners. Their breeding season takes place in late fall. The females delay implantation after mating, and fertilization occurs in the spring. Gestation lasts from 50 to 60 days and pups are born without the ability to fly. Only one pup is birthed per female. The young are weaned at the age of 6 weeks and become independent shortly after.
The main threats to this species include disturbances caused by humans and pesticide poisoning.
The IUCN Red List and other sources don’t provide the number of the Townsend’s big-eared bat total population size. Currently, this species is classified as Least Concern (LC) on the IUCN Red List and its numbers today are stable.
