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Bats Northwest

"helping bats in Washington State"

The Hoary Bat - (Lasiurus cinereus)

by Margaret Gaspari

This teddy bear of North American bats is tough and so adventuresome that his explorations have established him as Hawaii's only native mammal - the subspecies Lasiurus cinereus semiotus. His adaptability to diverse habitats allows his range to cover an almost coast-to-coast swath from northern Canada to Argentina and Chile. Lasiurus cinereus is a loner who roosts in trees and foliage, camouflaged by thick, luxuriant fur that covers the entire body and dorsal surface of his tail membrane. His coat of browns and grays is tipped in silvery-white and there are patches of cream on the shoulders and wrists as well as yellow on the throat, ears and underside of his dark brown wings. The short, round ears have a blunt tragus and the calcar sports a narrow keel. His skull is broad, blunt and high. He's big, with an average weight of 28.4 grams (1 oz.), total length of 137 mm (5.4 inches) and a wingspan of 392 mm(15.4 inches).

Lasiurus cinereus appears to be migratory, heading for warmer Pacific and Atlantic coastal regions and the Gulf in the autumn. It is suspected that mating most likely takes place in mid-air during the fall migration. This is the only time when males and females come together. The female will be pregnant when she makes her spring migration northwards, having stored the sperm over winter. Hoaries that hibernate do so out in the open, hanging from foliage or holding tight to a tree trunk - wrapped in their thick, protective fur cape. Their periods of hibernation are probably intermittent, depending on weather, and altogether shorter than most other hibernating bats.

Here in the NW, Hoary Bat mothers give birth about mid-June to two young (providing milk from four mammaries). Three and four pups are not unusual for this bat. The bond between a mother and her young is close and extends past the time they learn to fly well, at about five weeks of age, into their fall migration south. The babies' distinctive chirps allow her to locate them in dense foliage and it has been reported that she will follow distress calls and retrieve a fallen infant. Perhaps the larger brood size may be related to the hazards of a solitary life and rigorous migrations - casualties can be high and the life span of Lasiurus cinereus may be as short as six or seven years.

Hoary Bats fly swiftly and hunt in the open, their favored prey being large moths, although there are reports that a large variety of insects and even on rare occasions small bats are consumed. This is a highly territorial hunter who will emit low-frequency chirps warning other bats to stay away from its hunting turf. These warning chirps, below 10 kHz, are audible to humans, who may be lucky enough to hear and observe a Hoary hunting under a street lamp or in a park. Search with your bat detector in the 15-30 kHz range (hunting frequencies) after dark in fields and woodland clearings for this amazing lone ranger.

Source: Tuttle, Merlin. Winter 1995. BATS. Bat Conservation International.