150 - Hoary Bat

WA East Sunshinegeo GC9GM3D

Claimed by Rick Kinnie 4 years 10 months ago (1h 21m 53s since publication) · visibility Watch (1)

WA-904, Cheney, WA, US

Physical description The hoary bat is the largest bat in Washington . The fur is a mixture of yellowish-brown, dark brown, and white, giving it a distinctive frosty or “hoary” appearance. Individual hairs on the back have four distinct color bands, with blackish-brown at the base followed by yellowish-brown, blackish-brown, and silvery white at the tips. Yellow or white fur occurs on the shoulders and wrists. Yellow fur also encircles the ears and is present on the throat and underside of the wing membranes. Wing membranes are blackish-brown with paler brown strips along the forearm and metacarpals. Wings are long and narrow. The upper surface of the tail membrane is densely furred. Ears are short and rounded with a dark brown or black margin, and the tragus is short and broad. The calcar has a narrow keel.

Food Habits and Foraging This species is commonly considered a moth specialist. The only dietary data for the Pacific Northwest come from Oregon, where several studies suggest a preference for moths, with leaf hoppers, true bugs, mosquitoes, and other insects consumed in lesser amounts. Feeding lasts all night, but often peaks during the middle of the night. Hoary bats are fast straight fliers with less maneuverability than most other bats, and have low frequency echolocation calls that are adapted for long range detection of prey. Thus, foraging occurs mainly in open areas, such as above the forest canopy, over clearings and other open areas, along roads with trees, over lakes and streams, and at street lights. Individuals may forage 1.6 km or more from their day roosts.

Reproduction Mating likely occurs in fall or early winter before, during, or after migration, with ovulation and fertilization delayed until spring. Gestation lasts about 90 days. Females produce one to four pups in a single litter per year, with an average litter size of two. Breeding has not been confirmed in the Pacific Northwest.

Geographic range Hoary bats have the broadest geographic distribution of any bat in the New World, including much of North America and South America, as well as Hawaii. This species has been documented in most of Washington’s counties, but is probably present in all. The sexes are relatively segregated within the species’ summer distribution, with males occurring primarily in the mountainous regions of western North America and females more numerous in eastern regions. This pattern may simply reflect that females tend to migrate farther distances than males from major wintering areas in California and Mexico. Among the few individuals captured during surveys in Washington, nearly all have thus far been males. Examination of bats killed at wind farms in Washington indicate that some females pass through the state during fall migration.

In Washington and elsewhere, hoary bats are mainly associated with a variety of forest types, but also occur in open cover types (e.g., grasslands, deserts, clear cuts, meadows), particularly when foraging and migrating. Urban areas are also used. Late successional forests are often occupied, perhaps because the presence of larger trees provides higher quality roosting habitat. One study suggests that hoary bats were attracted to old-growth forests with relatively open canopies because such habitat may offer improved foraging opportunities. Elevational range varies from sea level to at least 1,620 m in the Pacific Northwest, but reaches 3,100 m elsewhere.

Roosting Hoary bats roost alone or with dependent young primarily in the foliage of coniferous and deciduous trees at heights ranging from 3-16 m above the ground. Roost trees are commonly near the edges of clearings, and may or may not be taller than the adjacent canopy. Easy flight access and concealment from predators are other desirable roost characteristics. Rarely, roosting can occur in tree cavities, caves, buildings, and squirrel nests; beneath rock ledges and bridges; and other locations. Adult females and their nursing young commonly enter torpor while roosting.

Relatively little is known about the night and migration roosts of this species. Hibernating individuals have been found on tree trunks and in tree cavities, squirrel nests, and clumps of Spanish-moss. Other details of hibernation are poorly known.

Picture credit: MICHAEL DURHAM/MINDEN PICTURES, BAT CONSERVATION INTERNATIONAL

2/1.5 Hint - Inside, to the right, low

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