Hoary bat

Hoary bat

Lasiurus cinereus. By Susie Wall

This story is featured in Montana Outdoors March–April 2014 issue

Scientific name
Lasiurus is from the Greek lasios, meaning “shaggy” or “hairy,” and ursus, for “tail.” The species name, cinereus, is Latin for “ashen,” referring to the bat’s fur color.

With a wingspan stretching 15 to 16 inches and a total body length of 5 inches, the hoary bat is the largest bat in the United States. Its long, narrow wings make it one of the fastest bats, too. Due to its large size and dense fur coat, the hoary bat is also the most hardy, hunting when the thermometer drops to as low as 32 degrees (a temperature that puts most other bat species into a stupor).

The hoary bat is named for its grizzled (grayish-white) coat and furred “pinnae,” or outer ears. The wrists and shoulders have white patches, the throat sports a bright yellow patch, and the ears are short and rounded. These characteristics make it easy to differentiate the hoary bat from other species if you are lucky enough to spot one. The wings of most other bats in Montana are hairless and their ears are long. What’s more, “the fast, straight flight of the hoary bat makes it easy to identify on the wing,” writes Kerry Foresman, University of Montana emeritus professor of biological sciences, in his book Mammals of Montana.

Habitat and Range
In North America, few bat species are more widespread than the hoary. It is found throughout Montana, though not in high numbers and mainly in coniferous and deciduous forests. Solitary creatures, hoary bats roost alone in foliage and under the thick bark of Douglas firs, ponderosa pines, and cottonwoods. Less often, they nest in caves, in gray squirrel nests, and tucked under driftwood.

The bats roost 10 to 40 feet above the ground, the males choosing lower sites and the females higher ones, especially females that have young. The bats begin arriving in Montana each spring during May, and in September fly south for warmer climates, most likely (no one is certain) to the southern United States, Mexico, and parts of South America.

Diet and Feeding
Montana’s hoary bats mainly dine on scarab beetles, moths, and other flying insects, though they may also kill and eat smaller bats, as has been witnessed in other states. Using its “propatagium” (wing membrane) or tail membrane as a net, the bat catches an insect in flight and pulls it to its mouth.
The hoary bat feeds later in the evening than most other bats, showing up in the night sky about one hour after sunset. Because its long wings lessen maneuverability, the hoary bat feeds in open spaces such as over water and roads, in forest clearings, and along forest edges.

Like all bats, the female hoary exhibits “delayed fertilization.” After mating in early autumn, the female stores the male’s sperm through winter hibernation until spring, when she ovulates and the eggs are fertilized. After a gestation period of 90 days, the young are born in early to midsummer. A litter is composed of one to four young, which are covered in a coat of fine, silver-gray hair. Baby hoaries cling to their mother during the day but are left in the nesting roost at night when she leaves to feed. The young bats can fly within 33 days of birth.

Conservation Status
The hoary bat has escaped the insidious white-nose syndrome that has plagued populations of other bat species across the eastern United States. This good fortune, combined with both a widespread range and a large population outside Montana, means the hoary bat has no pressing need for conservation. However, it is listed as a Species of Concern within Montana because the population here, though widespread, is relatively small.Bear bullet

Susie Wall is a writer in Missoula.