Lasiurus cinereus
(Hoary Bat)

Order: Chiroptera
Order Description: Bats
Family Description:

The dorsal fur is yellowish to brownish with white tipped hairs producing a frosted appearance. The furred ears have black rims, are wide and fully rounded. The tragus Click word for definition, curved forward and wide at the base, is less than one-half the length of the ear. The tail membrane is heavily furred, usually to the margin. A tan throat patch is present and a cream-to-white spot in just behind the thumb. Newborn bats are covered with fine silvery-gray hair. This is the largest bat found in Idaho.

Southern British Columbia east across Northern Canada to Nova Scotia, southward along the Atlantic Coast to Northern Florida, west into Texas and South into Mexico, west to Baja California and North along the Pacific coast. Collected sites in Idaho include 13 counties but the hoary bat it is likely resident in all areas containing forested habitat but may be less common in urban areas.

Hoary bats usually roost at the edge of clearings preferring foliage of both coniferous Click word for definitionand deciduous Click word for definitiontrees. Less common sites include cavities or, in unusual situations, caves or anthropomorphic structures.

Grasshoppers, dragonflies, wasps, beetles, flies, and moths, apparently the preferred food, are eaten.

Hoary bats are most common in the southwest. They roost individually in trees, usually at the end of branches where they often choose a site that is not visible from above. The area below the roost is open and likely is along the edge of a clearing. Jays appear to be significant predators on this species. Hoary bats may fly in waves from northern forests to southern latitudes, usually in the late fall. Spring return migrations do not appear to be organized, but more needs to be learned about the migratory pattern of this species. This bat has a swift flight pattern. It usually flies high and direct to feeding areas along watercourses and meadows. Hoary bats enter torpor Click word for definitionduring cold periods and may feed in cold weather.

Swift flier. Usually emerges after dark, though one source states that emergence occurs early in evening. Feeding activity peaks 4-5 hr after sunset, with secondary peak occurring several hr before dawn. Frequently forages around clearings, but may forage around lights in nonurban situations. May forage at considerable distances (a mile or more) from diurnal Click word for definitionroost Click word for definitionsite. Usually roosts in tree foliage 3-5 m above ground with dense foliage above roost and open flying room below, often at edge of clearing. Sometimes roosts in rock crevices; rarely uses caves. Generally dispersed population allows little chance to obtain density Click word for definitionfigures.

Females do not form nursery colonies and males and females rarely occur together, except during breeding which appears to occur during migration. Individual females give birth to one to four pups in May to July. The average number of young is two.

Breeds from September-November in North America. fertilization Click word for definitionis delayed. Gestation Click word for definitionlasts 90 days. Female produces 1 litter Click word for definitionof 1-4 young (average 2) in mid-May to early July (May or June in Idaho). Young are able to fly at 4 wk, and probably become sexually mature in first summer. Female sometimes may carry young during feeding flight.

Status: Unprotected nongame species
Global Rank: G5
State Rank: S4

Important State References:
Keller, B.L. 1987. Analysis of the bat species present in Idaho, with special attention to the spotted bat, Euderma maculatum. Dept. Biol. Sciences, Idaho St. Univ., Pocatello. 25pp.

Information written by Barry Keller,© 2000
Map image provided by
Stephen Burton,© 2000
Design by Ean Harker©1999, 2000.