Ozark Big-eared Bat

The Ozark big-eared bat (Corynorhinus townsendii ingens) is a regionally endemic subspecies of the Townsend's big-eared bat, a temperate, insectivorous bat that uses caves year-round. The Ozark big-eared batbelongs to the plain-nosed bat family, Vespertilionidae, which is the second largest mammalian family after the Muridae (Old World rats and mice). Ozark big-eared bats only occur in cave and karst areas surrounded by oak-hickory hardwood forests in the Ozark Highlands and Boston Mountains ecoregions. Populations currently occur in northeast Oklahoma and northwest Arkansas. The species also historically occurred in Missouri, but is now considered extirpated. Like other temperate bats, the species exhibits strong roost fidelity, returning to the same maternity sites and hibernacula year after year. Human disturbance is considered to be the greatest threat to cave-dwelling bats like Ozark big-eared bats. Unauthorized human entry into Ozark big-eared bat-occupied caves can cause bats to abandon their roosts. Such abandonment can be detrimental during critical periods such as the maternity season (May through July) and hibernation (November through March).

Ozark big-eared bats weigh from 5 to 13 grams.

The Ozark big-eared bat is the largest and reddest of the five subspecies of C. townsendii. It is a medium-sized bat with forearms measuring 39 to 48 millimeters long. Total body length is 98 millimeters, with the tail measuring 46 millimeters, and the hind foot measuring 11 millimeters long. This bat's long ears, which measure more than 2.5 centimeters, and facial glands on either side of the snout are quite distinctive.

Fur is light to dark brown depending upon the age of the individual and the subspecies. The only other eastern bat that resembles the Ozark or the Virginia big-eared bat is P. rafinesquii, Rafinesque's big-eared bat. Rafinesque's big-eared bat has toe hairs that extend beyond the end of the toes and the dorsal fur is gray rather than brown. Further, the belly fur of Rafinesque's big-eared bat is white or whitish rather than light brown or buff.

Ozark big-eared bats are cave obligates, using caves year round for all life stages. Ozark big-eared bats emerge from their caves to forage shortly after sunset. Female bats likely forage only short distances from maternity caves in order to return several times during the night to take care of non-volant, or flightless, pups. As the season progresses, average distance to foraging sites increases up to 4.9 miles from cave entrances.

The Ozark big-eared bat forages along forested edges, open areas like pastures and native grasslands, and forested habitats. A radio-telemetry study of foraging adult females in Oklahoma conducted during the summer maternity period found that females used edge habitats more than expected based on relative availability of habitats. Females likely selected edge habitat because it provides a relatively less cluttered environment in which to forage - bats do not have to avoid branches while pursuing prey - than adjacent wooded areas. Edge also provides nearby escape cover for both bats and moths.  However, Ozark big-eared bats also have been known to preferentially select forested habitats and to show no preference for particular habitat types, using habitats in proportion to their availability, for foraging. Ozark big-eared bats can readily forage in forested areas because their low ratio of weight to wing area, called wing loading, produces highly maneuverable flight capabilities. Therefore, the Ozark big-eared bat’s relatively high level of flight maneuverability does not restrict use of habitat types, including clustered forests, as it does in other less maneuverable species. Surface habitat use is likely strongly influenced by current prey distribution.

Ozark big-eared bats use limestone and sandstone talus caves and crevices that are surrounded by oak-hickory hardwood forest. These bats are known to hibernate both in twilight areas, near the entrance of caves, as well as areas of total darkness, deep within the coldest regions of caves. Bats select sites with the appropriate microclimate to ensure that their metabolic rate will not deplete the fat reserves which are required to sustain them through the winter. When temperatures near the entrance become too extreme, Ozark big-eared bats relocate to a more optimal roost site. The Ozark big-eared bat selects areas for hibernation with temperatures ranging from 4° to 11°C (40° to 52°F) and humidity from 83% to 95%.

Ozark big-eared bats are cave obligates, meaning that they use caves year-round for all life stages. Ozark big-eared bats emerge from their caves to forage shortly after sunset. Female bats likely forage only short distances from maternity caves in order to return several times during the night to take care of non-volant, or flightless, pups. As the season progresses, average distance to foraging sites increases up to 4.9 miles from cave entrances.

The Ozark big-eared bat forages along forested edges, open areas like pastures and native grasslands and forested habitats. A radio-telemetry study of foraging adult females in Oklahoma that was conducted during the summer maternity period, found that females used edge habitats more than expected based on relative availability of habitats. Females likely selected edge habitat over that of adjacent wooded areas, because edge habitat provides a relatively less cluttered environment in which to forage; bats do not have to avoid branches while pursuing prey. Edge habitat also provides nearby escape cover for both bats and moths. However, Ozark big-eared bats also have been known to preferentially select forested habitats and to show no preference for particular habitat types. They use habitats in proportion to their availability, for foraging. Ozark big-eared bats can readily forage in forested areas, because their low ratio of weight to wing area. This phenomenon, referred to as wing loading, produces highly maneuverable flight capabilities. Therefore, the Ozark big-eared bat’s relatively high level of flight maneuverability does not restrict use of habitat types, including clustered forests, as it does in other less maneuverable species. Surface habitat use is likely strongly influenced by current prey distribution.

Based on recovery of banded individuals, the maximum lifespan of the Ozark big-eared bat is estimated to be about 16 years. 

Ozark big-eared bats mate during fall and winter. Females become reproductively active during their first fall, while young males do not reach sexual maturity until their second autumn. Ozark big-eared bats give birth to a single offspring in May or June. Young bats grow rapidly and are volant, or capable of flight, at 3 weeks and are weaned by 6 weeks of age.

The Ozark big-eared bat is a temperate, insectivorous bat that uses caves year-round. Like other temperate bats, the species exhibits strong roost fidelity, returning to the same maternity sites and hibernacula year after year.

Both sexes hibernate together in clusters that typically range from two to 135 individuals. Ozark big-eared bats also will hibernate singly and in larger groups that have consisted of up to about 400 individuals.

The Ozark big-eared bat is known to exhibit winter activity. Because insect activity is typically very low during cold nights, winter activity likely occurs in order to relocate within the same hibernaculum or among hibernacula to find a more thermally stable location when temperatures at the initial location become too extreme. They may also be active to fly to open water to drink.  

Hibernating colonies gradually begin to break up in spring from April through May. Females also become pregnant during this time and slowly begin to congregate at warm maternity caves to give birth and rear their young over the summer. The exact timing of the formation of maternity colonies varies from year to year, but it usually occurs between late April and early June. Distances between hibernacula and summer caves are known to range from 6.5 to 65 kilometers, about 4 to 40 miles.