Furry Fliers

Nine species of bats live in DuPage County: the little brown, big brown, eastern red, hoary, silver-haired, evening, tricolored and northern long-eared. (The Indiana bat once lived in DuPage, but ecologists have not recorded one in the county for several decades.)

All of the county's bats are insectivores. They have the reputation of eating thousands of mosquitoes in one night, but mosquitoes make up only a small part of their diet. Bats are more likely to feast on moths, June bugs and other larger insects, which are much easier to catch.

Bats are the only mammals in the world that can fly. They navigate in part by emitting high-frequency sounds and then using their funnel-shaped ears to listen for the echoes those sounds make as they bounce off nearby objects. By using this “echolocation,” they can pinpoint tiny insects in complete darkness. This ability has led to the myth that bats are blind, but they actually have excellent eyesight.

Bats like to roost in secluded, warm locations, such as under loose tree bark or in quiet attics or neglected buildings. Females often roost together in maternity colonies, where young bats are born and raised. Their young are born between May and June; they usually have one at a time but will occasionally have two. The females leave the roost at night to forage, but the young do not leave until they are old enough to forage on their own, which is usually after about three weeks.

As winter approaches and the insect supply diminishes, bats migrate to caves, where they enter a state of “torpor,” or decreased activity. Their heartrates can drop from over a thousand beats per minute to one beat every four or five seconds, which allows them to survive for months on very little fat.