Silver-haired Bat (Lasionycteris noctivagans)
Description:
The silver-haired bat is a medium-sized bat (smaller, that is, than the similar hoary bat) with a darkly-pigmented tail membrane that is only lightly furred.
Color:
Silver-haired bats have pelage that is dark brown or, more commonly, black with silver tips to each hair, which gives this species its well-deserved name.
North American Range:
The species is found throughout the United States outside its hottest deserts and peninsular Florida. It occurs broadly across southern Canada and has an extremely limited range into the northeastern corner of Mexico.
Roosting:
Silver-haired bats may roost singularly and occasionally in groups of three to five individuals. They may be found deep in rock crevices or under loose bark.
Characteristics:
The silver-haired bat is one of the slowest flying bats in the U.S., often flying close to the ground. Abundant, especially in old-growth forests, they may also be found foraging over grasslands and meadows. They feed and often drink in the vicinity of woodland ponds and streams and often forage in open areas adjacent to forest canopies, especially in coniferous forests.
Feeding:
They feed on small flying insects, especially moths, using echolocation to navigate and hunt. They start foraging after sunset, finding their prey at treetop level or over streams and ponds.
Migration:
In general, northern populations are migratory; however, these bats can enter torpor for energy conservation, and some individuals/populations may not migrate.
Breeding:
Silver-haired bats breed in the fall, and young are born during a relatively short period between April and May. Typically, two pups are born to each female.
Scientific Notes:
Distinguishing echolocation calls: silver-haired bat vs. hoary bat
Robert M. R. Barclay (Barclay 1986) found support for the theory that, at least among aerial-feeding insectivorous bats, differences in the design of echolocation calls appear to be associated with differences in foraging strategy. Barclay found that the silver-haired bat (Lasionycteris noctivagans) uses multi-harmonic search–approach calls with an initial frequency sweep and a constant frequency tail. Such calls are suited for bats foraging in the open but near obstacles and pursuing prey detected at relatively close range. This is the foraging strategy employed by the silver-haired bat, a relatively slow, maneuverable species.
Conversely, the hoary bat (Aeorestes cinereus) employs single harmonic search–approach calls that are low (17-20 kHz), essentially constant frequency signals. Calls of this design are suited for long-range target detection in open-air situations, which is the foraging strategy used by the hoary bat.
Reference
Barclay, R. M. B. 1986. The echolocation calls of hoary (Lasiurus cinereus) and silver-haired (Lasionycteris noctivagans) bats as adaptations for long- versus short-range foraging strategies and the consequences for prey selection Canadian Journal of Zoology. 64(12): 2700-2705.