Nine species of bats live at least part of the year in the northeastern United States, and two southern species reside infrequently in Pennsylvania. (See box.) Northeastern bats range in size from the hoary bat (length 5.1 to 5.9 inches from nose to tail; wingspan 14.6 to 16.4 inches; weight 0.88 to 1.58 ounces) to the pipistrelle bat (length 2.9 to 3.5 inches; wingspan 8.1 to 10.1 inches; weight 0.14 to 0.25 ounces). Colors range from the drab brown of the little brown bat to the striking frosted red coat of the red bat.

Although some mammals are able to glide, bats are the only mammals that truly fly. That is, they actually flap their wings to propel them in flight. They belong to their own unique order of mammals, called Chiroptera, meaning “hand wing,” which refers to how the finger bones of a bat support its wings. The wings of a bat are actually thin membranes of skin that stretch between the fingers of the front leg and extend to the hind legs and tail. The bat’s finger bones are greatly elongated and serve a purpose similar to struts on an airplane wing, providing support and maneuverability during flight. When at rest, a bat folds its wings alongside its body to protect the delicate finger bones and wing membranes.

Bats live in a variety of habitats, including wetlands, fields, forests, cities, suburbs, and agricultural areas. They usually feed in areas where insects swarm, such as over water and agricultural fields, in forest clearings and along forest edges, and around street lights. All northeastern bats eat insects and take their prey on the wing. Bats use their mouths to scoop small insects out of the air. Larger insects are often disabled with a quick bite and then carried to the ground or to a perch for eating. If an insect takes last-second evasive action, a bat can flick out a wing to nab the insect and draw it into its mouth. This maneuverability makes bats very efficient insect predators: A bat may consume nearly 50 percent of its body weight in insects in a single night!

Although bats can see quite well, they rely on their hearing for night flying. A highly sophisticated
adaptation, called echolocation, enables bats to use their large and well developed ears to navigate and catch prey in total darkness. A bat’s echolocation system makes use of ultrasonic sound pulses and echoes to locate objects. Bats open their mouths in flight and emit a series of ultrasonic sound pulses. These pulses bounce off nearby objects— such as bushes, fences, branches, and insects—then return as echoes to the bat’s ears. Using the information gathered from these echoes, a bat can maneuver to capture an insect or avoid flying into an object. Bats have one of the lowest reproductive rates for animals their size. Most northeastern bats have just one or two pups per year, and many females do not breed until their second year. This low reproductive
rate is partially offset by their long life span.