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NATURAL HISTORY

EASTERN SMALL-FOOTED BAT } Myotis leibii

FAMILY: Vespertilionidae

DESCRIPTION: Adults weigh between three and five grams, and total body length is about three inches. Wingspan is between eight and 10 inches. Even for a bat, the species has very small feet, around one-third of an inch. Defining field marks include a characteristic black mask and black ears. Dorsal pelage varies from pale yellowish brown to darker golden brown; ventral pelage varies from pale buff to white. Sexes are physically similar.

HABITAT: The eastern small-footed bat overwinters in hibernacula located in caves or abandoned/inactive mines, and prefers locations close to cave or mine entrances where humidity is low and temperature fluctuations may be high relative to more interior areas. Individuals have been found hibernating in rock crevices in cave or mine floors and beneath rocks within hibernacula. There is some evidence that this species prefers small caves: in Pennsylvania, a majority of identified hibernacula were less than 500 feet in length. Like most bats, individuals return to the same site year after year.

In summer, the eastern small-footed bat may also use caves or mines as roosting sites, but is most often found on buildings, bridges, within hollow trees, beneath loose bark on trees and in cliff crevices. Roost sites may be at ground level in talus slopes or shale barrens, or in more elevated sites (e.g., cliff crevices). Within these preferred sites, eastern small-footed bats, particularly reproductively active females, tend to select for microsites with the highest solar exposure, presumably to maximize the ambient temperature in maternity roosts. Warm temperatures minimize the maternal energetic output for thermoregulation of young and foster rapid offspring growth rates. This species has been observed at up to 1,800 feet in elevation in the more southerly parts of its range and is commonly found in hilly or mountainous habitat.

RANGE: Eastern small-footed bats are relatively widespread in southeastern Canada and the eastern United States, but their distribution within this range is uneven and populations are generally small. The largest known populations of the speciesoccurred in Pennsylvania, New York, West Virginia and Virginia; white-nose syndrome may have shifted where the largest populations now occur.

MIGRATION: The species is known to migrate regionally between hibernacula and summer roosting or breeding habitat; no estimation of the average migration distance is available in the literature, but recorded migration distances from observational studies vary widely from less than a mile to almost 12 miles. It is likely that the migration distance of any individual or group is contingent on the local availability of suitable habitat.

BREEDING: Mating takes place in late summer or early fall, prior to hibernation. Many bat species, including eastern small-footed bats, use delayed fertilization, wherein females store sperm over the winter and embryo development begins in mid-spring. Gestation lasts approximately 60 days, and parturition occurs in early to mid-summer. Females bear a single offspring annually. Maternity colonies (also known as nursery colonies) comprised of up to 20 females and their offspring form in summer roosting habitat.

LIFE CYCLE: Eastern small-footed bats, like other insectivorous bats in North America, have a very low reproductive rate: one baby per year, born relatively helpless, as well as flightless, and remaining so for the first few weeks. Many bat pups do not survive to their second spring, due to the many challenges they face, including predation, and putting on adequate fat reserves for winter hibernation. They also appear to live a relatively long time for such a small mammal. The oldest recorded specimen was 12 years old at the time of its death.

FEEDING: Both adults and juveniles feed almost exclusively on a variety of aerial invertebrates and are known to be dietary generalists that feed primarily on soft-bodied prey. As nocturnal foragers, they emerge from roosting sites at dusk, and feeding activity peaks shortly thereafter, correspondent with a peak in insect activity. The species’ flight pattern is highly distinctive; their slow, fluttering movement is unusual for small-bodied bats and makes them easy to distinguish from other Myotis species in flight. Eastern small-footed bats use both aerial hawking and gleaning to obtain insect prey.

THREATS: White-nose syndrome; habitat destruction including mineral extraction, logging, residential and agricultural development; environmental contaminants; wind energy; climate change.

POPULATION TREND: This species is declining in the eastern portion of its range due to white-nose syndrome. As the disease spreads westward and southward, it is likely to decline throughout its range.

Eastern small-footed bat photo by Gary Peeples/USFWS