Vespertilionid Bats: Vespertilionidae

Like other bats, the vespertilionid bats use sound waves to find their way through their habitat and to find food. They make high-pitched sounds, ones that we cannot hear, and then listen as the waves bounce off of objects and return to them as echoes. Using this method of "seeing" with sound, they can fly quickly between tree limbs and around objects, while also finding and identifying prey insects. It is common for a vespertilionid bat to notice a moth or other flying insect while both the bat and insect are in flight, then swoop in and capture the insect in midair. Using echolocation (eck-oh-loh-KAY-shun), they can also spot insects on plants and pick them off of leaves. Echolocation is particularly useful in these animals that rest during the day and look for food in the dark of night. A few species become active around sunset, sometimes even a little earlier, but most wait until the skies darken before they leave their roost and begin looking for food. Because they are such excellent and swift fliers, the vespertilionid bats avoid most predators. Occasionally an owl is able to catch one at night, but their biggest threat of predation (hunting by animals that eat them for food) comes from larger land animals that stumble upon a roost while the bats are resting.

Bats have a fairly set schedule with certain activities occurring during specific seasons. Mating occurs in the fall in most species. Some bats don't engage in any courtship rituals, but for the most part, scientists know little about these behaviors in most bats. In the fall, bats that live in cooler climates begin to disappear, probably to start migrating to warmer climates for the winter. Cool- and warm-climate bats typically participate in hibernation, although some warm-weather bats remain active all year. Some vespertilionid bats hibernate alone, and others hibernate together in large groups, often numbering a hundred or more. If the temperature rises sufficiently in the winter, the bats may awaken and fly about in search of food. When spring arrives, males typically strike out on their own, but females usually form colonies in roosts, which may be in caves or other hideaways, and share the duties associated with raising young, which are born in late spring to early summer. (A few warm-weather species may be able to have young at other times of the year.) Most mothers have one or two young, called pups, a year. A few species may have up to four pups at a time. The pups begin flying in about a month and then start hunting for insects on their own. Some remain with the colony for their first year, but others leave earlier.

Bat behavior is a field with many unanswered questions. Although scientists know a good deal about the behavior of a few species, they know little about most of the vespertilionid bats.