RANGE:

Pipistrells occur in Eastern Washington and Oregon, Western Idaho through Utah and western Colorado to Texas, south into Central American to Columbia and west into Baja California and California. In Idaho, the western pipistrelle is found in Gem, Nez Perce, Twin Falls and likely other western counties.

DESCRIPTION:

This very small bat, which flutters during flight, has dorsal fur that is smoky to a yellowish gray brown color. The face and ears are blackish, the ears broadly rounded and short, not reaching beyond the nostrils when laid forward. The tragus, less than half of the length of the ear, is club-shaped. The calcar is not keeled.

HABITAT:

Pipistrells occur in arid rocky desert canyons near water, but have been collected in lower elevation mixed conifer forests. They roost in crevices, in mines, and buildings emerging in the early evening, especially in canyon areas, where they are often seen over slack water, feeding.

DIET:

An important predator on small swarming insects, pipistrells feed on flying ants, mosquitoes, leafhoppers, and fruit flies, but often select only one kind of insect that is abundant when feeding.

ECOLOGY:

Pipistrells hibernate sporadically, awakening during warm periods to feed. Because they are small, they would appear to be unable to accumulate sufficient fat reserves to migrate to distant hibernal sites. As contrasted to other bat species in Idaho, they are active earlier in evenings and in the morning during early daylight but remain inactive in temporary roosts in the middle of the night. The population ecology of this species is exceptionally difficult to study as a result of the small size of individuals and the type of habitat they occupy.

REPRODUCTION:

This species is known to swarm in large numbers, a condition that is likely important for reproduction. Mating occurs in the fall. Fertilization is delayed to spring and gestation lasts about 40 days. It has been suggested that two young may be produced but one appears to be the most common pattern, at least in California. Maternity colonies are small, comprised of fewer than a dozen individuals.

IMPORTANT STATE REFERENCE:

Keller, B.L. 1995. The status of bat populations in the Craig Mountain Area, Nez Perce County, Idaho. Cooperative Challenge Cost-share Project, Idaho Department of Fish and Game and Bureau of Land Management, Boise, Idaho. 21pp.