Decline in the Winter Population of Gray Bats (Myotis grisescens) in Florida

The number of Myotis grisescens (Gray Bat) observed at hibernacula has increased across most of the species' range in recent years as more roost caves have been protected from humans. In Florida, most Gray Bats have been found to hibernate in one primary cave, where the number of hibernating individuals decreased from several thousand in the 1950s to zero in 1975 due to disturbance by humans and improper gating of the cave. After removal of the gate in 1982, the number of hibernating Gray Bats increased, averaging 166 bats during 1990-1998. The number then declined again, and <10 Gray Bats per year were counted during 2002-2011. The cause of this recent decline is uncertain. Temperatures in the cave remain suitably cold, visitation by humans is restricted, and no mortality from floods or disease has been observed. Most of the Gray Bats may have moved to larger and more suitable hibernacula in northern Alabama and Tennessee.