Silver-haired bats are medium sized bats, weighing 8 to 12 grams. Measurements of these bats include: total length, 90 to 115 mm; tail length, 35 to 50 mm; wingspread, 270 to 310 mm; forearm, 37 to 44 mm; head size, 60 mm long; and a hind foot length of 6 to 12 mm. Silver-haired bats receive their name from their dark, silver-tipped fur. The fur is usually black in color, however some individuals may be dark brown with yellow-tipped fur. The ears of these bats are relatively short (15 to 17 mm in height), round, and naked. The top of the tail membrane is lightly furred, with 50 to 75% of the tail being naked.
Silver-haired bats are found throughout the United States (with Florida as a possible exception), northward into southern Canada up to the treeline, and reach their northern limits in Alaska. The range may also include extreme northeastern Mexico (due to similar habitat conditions), although they have not been seen there.
Silver-haired bats prefer northern deciduous forests with ponds or streams nearby. The typical day roost for the bat is behind loose tree bark. Silver-haired bats appear to be particularly fond of willow, maple and ash trees (most likely due to the deep crevices in the bark). Hollow trees and bird nests also provide daytime roosting areas for silver-haired bats. Less common daytime roosts include buildings, such as open sheds and garages; however, due to their solitary nature and adaptation to woodland roosts, these bats rarely invade buildings in large enough numbers to cause alarm. During the winter months, silver-haired bats that hibernate find shelter in northern areas inside trees, buildings, rock crevices, and similar protected structures.
Courtship and mating of silver-haired bats occurs in autumn when both sexes gather together for migration. The embryos do not begin developing during the winter when the mother is hibernating; instead, fertilization happens the next spring. Births occur after a pregnancy of 50 to 60 days. While giving birth, the female roosts with her head facing upward. The tail membrane is bent forward to form a basket, in which the young are caught as they leave the birth canal. Two young are produced, usually between late June and early July.
Newborns weigh about 2g. The litter weight equals 36% of the mother's body weight. Young are born with their eyes closed, ears folded over, and most of their 22 baby teeth in place. Within a period of 21 to 36 days, young are able to find food for themselves.
Tooth wear of silver-haired bats suggests that these bats can live up to 12 years.
Silver-haired bats have been reported to be one of the earliest fliers in the evening, sometimes appearing in broad daylight. However, other sources claim that these bats are late-evening fliers. The flying time of silver-haired bats is believed to be adjusted by the bat so that it will not conflict with the flying times of the red, hoary, or big brown bats. Silver haired-bats are believed to be one of the slowest flying bats in North America (possibly second to western pipestrelles), with a flight speed of 4.8-5.0 m/s.
The adults usually appear singly, but can occasionally be found in pairs or small groups. During the summer, the bats are believed to segregate by sex. During late summer and autumn, however, silver-haired bats join in groups containing both sexes to migrate to the southern parts of their range. Some silver-haired bats are also known to hibernate in the northern locations.
Silver-haired bats use echolocation to find their prey. They have acute hearing, and communicate with one another using sound. Baby bats give high-pitched chirps when they become separated from their mothers.
Silver-haired bats are insectivorous. Their diet is mostly made up of flies, beetles, and moths. However, these bats take the opportunity to feed on any concentration of insects they come across. They have a short-range feeding strategy, traveling over woodland ponds and streams. Silver-haired bats do not always feed in mid-flight; they have been caught in mouse traps, suggesting that they look for food on the ground, and they have been reported to eat insect larvae on trees.
Silver-haired bats have an important role in the food chain, because they eat large amounts of insects.
Silver-haired bats are sometimes thought to give rabies to humans.
Silver-haired bats help with insect control, consuming large numbers of insects each night.
Silver-haired bats have no special endangered or threatened status; however, activities such as logging and deforestation may pose a threat for the bat in the future.
Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%. While there are currently no reports of Lasionycteris noctivagans mortalities as a result of white-nose syndrome, the disease continues to expand its range in North America. (Cryan, 2010; National Park Service, Wildlife Health Center, 2010)
Fisherman occasionally snag silver-haired bats in mid-air while casting their fishing lines.
Allison Poor (editor), University of Michigan-Ann Arbor.
Robert Naumann (author), University of Michigan-Ann Arbor.
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