Myotis leibii, or small footed myotis, is the smallest bat in eastern North America. This species is listed as threatened by the Pennsylvania Game Commission. Only three inches long, M. leibii weighs 0.1 to 0.3 onces -- about the same as a hummingbird. Its golden-brown fur, small feet and forearms, black ears and a black "mask" across the face all help to distinguish it from its more common relative, the little brown bat.

Although little is known about the ecology of M. leibii, scientists believe that in the summer it roosts in buildings, where, after a two-month gestation period, it bears a single offspring. M. leibii forage at or

In the winter, M. leibii hibernates in caves and mines most often located in hemlock forests. It enters hibernation later than most bats in Pennsylvania and tends to stay near the entrance, nestled in cracks and crevices and even under rocks on the cave floor.

Because so much is unknown about M. leibii, it's hard to pinpoint the cause of its decline. However, since the gating of Aitkin Cave at the Rowlands Preserve, Conservancy scientists have seen more than a 300 percent increase in the number of M. leibii found at the preserve. This suggests that eliminating disturbance during hibernation may be one way to reverse their decline.