My Bantam Lake

Hoary Bat

Written on 06/27/2018

Lasiurus cinereus

Hoary bats are thought to prefer trees at the edge of clearings, but have been found in trees in heavy forests, open wooded glades, and shade trees along urban streets and in city parks. The body of hoary bats is about the size of a fat mouse. Hoary bats weigh 20 to 35 g. The length from the tip of the nose to the end of the tail vertebrae is 13 to 15 cm. The wingspan is 43 cm. These bats have blunt, rounded noses and small, beady eyes. The ears are short, thick, broad, and rounded. The coloring of the dorsal area (including the tail membrane) is a mixed brown-gray with a heavy white tinge, giving these bats a frosty appearance. In fact, these bats' name means "frosty or ash colored hairy tail." The individual silky hairs are basally dark, medially yellowish, and distally black with white tips. The belly of these bats is not heavily frosted. The throat has a distinct yellow patch. Hoary bats give birth to their young while hanging upside down in the leafy shelter of their daytime retreat. The newborn's skin is brown, darker on the body than on the wings, and lighter beneath. Purposeful flight is possible for the infants by the thirty third day. The young cling to the mother in the day, while she sleeps, and hang on a twig or leaf while she hunts at night. Hoary bats are solitary. They roost 3 to 5 m above ground during the day, usually in the foliage of trees. They prefer dense leaf coverage above and an open area below. They also prefer trees that border clearings. Hoary bats reach their peak activity at about five hours after sunset, although they may occasionally be seen flying on warm winter afternoons. Their flight is stong and direct, reaching speeds of thirteen miles/hr. While hunting, they soar and glide. They forage about the tree tops, along streams and lake shores, and in urban areas where there are lots of trees. These bats stop to rest between meals at night. Feeding is the only time that hoary bats appear to associate with other bat species. Hoary bats often form groups when hunting for insects. Like all microbats, hoary bats use echolocation while flying. They make a shrill, hissing sound when disturbed. Moths make up the bulk of the diet of hoary bats. These bats are also known to feed on flies, beetles, small wasps and their relatives, grasshoppers, termites, and dragonflies. The bat approaches the insect from behind, taking the abdomen and thorax in its mouth and biting off and swallowing this area of the insect, while dropping the wings and head. Temperate North American bats are now threatened by a fungal disease called “white-nose syndrome.” This disease has devastated eastern North American bat populations at hibernation sites since 2007. The fungus, Geomyces destructans, grows best in cold, humid conditions that are typical of many bat hibernacula. The fungus grows on, and in some cases invades, the bodies of hibernating bats and seems to result in disturbance from hibernation, causing a debilitating loss of important metabolic resources and mass deaths. Mortality rates at some hibernation sites have been as high as 90%.


Source: Lasiurus cinereus Hoary Bat, Animal Diversity Web, University of Michigan Museum of Zoology