The gray bat, Myotis grisescens, is listed as endangered by the United States Fish and Wildlife Service. Unlike many of species of bats that inhabit Tennessee, the gray bat uses caves throughout the year in Tennessee.
During the summer, gray bats form large maternity colonies in caves where the females give birth to the pups, raising them until they can fly, or become violant. At this same time, male gray bats form bachelor colonies in the same caves as the females or these colonies may be found in different caves.
In the winter, gray bats, like many species of bat in Tennessee, enter caves to hibernate; however, this species requires specific temperature and humidity levels and the reason gray bats only have three primary caves used for hibernation within the state.
Each of these three caves is protected by TWRA or The Nature Conservancy of Tennessee. Winter colony sizes may range from 160,000 bats to well over 500,000 bats during this critical period of the year.
Biologists perform routine surveys of wintering gray bats biennially. Historically, these surveys were performed every three years to minimize disturbance.
Because of white-nose syndrome, surveys were performed annually for a short period to assess any impacts from this devastating disease. During these surveys, biologists try to determine the density of gray bats within each square foot of cave wall where bats are found. At the end of the survey, all estimations are tallied to determine the approximate number of wintering bats within the cave.
Wildlife Diversity personnel began capturing gray bats during nightly emergences to apply bands, determine the demographics of the colony, reproductive statuses, and assess the impacts from white-nose syndrome. Captures are made with a large trap design to safely capture these flying mammals as they emerge to feed on insects.
The banding of gray bats allows Wildlife Diversity personnel to determine site fidelity, migration distances, and longevity for the species. Many of the bands recovered are made within the same cave in which they were placed or within one of the primary caves within the state. These recoveries indicate a strong preference for these caves and movement between the caves.
Wildlife Diversity personnel have recovered bands in Tennessee from as far north as the Shawnee National Forest in Illinois, and TWRA bands have been recovered in a cave in north Alabama. These recoveries indicate gray bats migrate great distances between caves.