Bats: Chiroptera

Bats as a group are crepuscular (kri-PUS-kyuh-lur), meaning they are active at dawn and dusk, or nocturnal, meaning they are active at night. When they are roosting, bats generally hang upside down by their claws. This allows them to simply let go of whatever they are hanging onto and start flying.

With their large ears and small eyes, microchiropteran bats depend upon a complex sound technique called echolocation (eck-oh-loh-KAY-shun) to help them find prey and move. While flying, these bats send out high-frequency sounds that bounce off of other objects. The bat listens for the bounced sound, and then determines the location, size, distance, and speed of the object—all within a split second. In most bats, the echolocation is at such a high pitch that it is beyond the human hearing range, though humans can hear the sounds of some bats. Researchers are still working to understand exactly how echolocation works. Megachiroptera generally depend upon their eyes to navigate, but some of these bats also use echolocation.

Like all mammals, bats are warm-blooded, meaning they maintain their body temperature. Bats roost in warm places during the cool months to conserve the energy it takes to keep warm. Unlike other mammals, bats can allow their body temperature to drop to the ambient temperature, or surrounding temperature, when they are not active. As their temperature drops, metabolism slows down.

During the winter, some bats will drop their body temperatures for months at a time and go into hibernation, meaning they go into a resting state in a safe place, typically without eating or passing wastes. A bat's body temperature can drop to as low as 35.6°F (2°C). These bats survive the winter by living off their storages of fat and making occasional food trips during warmer weather.

Other bat species follow an annual migration pattern, traveling to warmer climates in the cool months and cooler climates in the warm months.

Bats are generally social animals and gather together in roosts. Bats can roost in colonies of several hundred to tens of millions. The number of bats in a roost depends upon the type of bat. Pipistrelle maternity, or motherhood, roosts usually contain between fifty and two hundred bats. Brown long-eared bats usually live in colonies of twenty-five up to fifty bats. Mexican free-tailed bats are one of the more social bat species and found in huge populations throughout their range. In Bracken Cave, Texas, the population of Mexican free-tailed bats was estimated at twenty million bats!

Like all mammals, female bats give birth to live young and feed their newborns milk. Females often roost in large colonies, with many females giving birth in the same area. Bats usually give birth to only one young per year. During their first weeks of life newborn bats cling to their mothers while in flight. Only the mother cares for the young, and there is no lasting relationship between the mother and father.

Bats grow quickly; the young are often flying at four weeks. Young microchiropterans become independent at approximately six to eight weeks, megachiropterans at about four months old. At the age of two years bats are sexually mature. Bats live about twenty-five years, far longer than most mammals of a comparable size.