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Gray Bat

(Myotis grisescens)

Gray Bat
Gray Bat by John MacGregor

Federal Status:  Endangered

Kentucky Status:  Threatened

Description:  The gray bat, measuring up to 4 inches in length, is the largest species of Myotis found in the eastern United States. Its fur is gray, sometimes russet in summer. It is the only Myotis with the wing membrane attached to the ankle (instead of at the base of the toe), and the only bat in its range with dorsal (back) hair that is uniform in color from base to tip.

Range:  The core range of the gray bat encompasses the cave regions of Alabama, northern Arkansas, Kentucky, Missouri, and Tennessee. Populations also occur in portions of Florida, Georgia, Kansas, Indiana, Illinois, Oklahoma, Mississippi, Virginia, and North Carolina.

Distribution in Kentucky:  See Map

Kentucky Occurrence Summary:  The gray bat is found throughout Kentucky with maternity colonies concentrated in the Pennyroyal region and major hibernacula located in Edmonson County.

Habitat:  Gray bats are restricted to caves or cave-like habitats. Few caves meet their specific roost requirements. This results in about 95% of the populations hibernating in less than 20 caves. For hibernation, the roost site must have an average temperature of 42 to 52 degrees F. Most of the caves used by gray bats for hibernation have deep vertical passages with large rooms that function as cold air traps. Summer caves must be warm, between 57 and 77 degrees F, or have small rooms or domes that can trap the body heat of roosting bats. Summer caves are normally located close to rivers or lakes where the bats feed. Gray bats have been documented traveling as far as 26 miles from their colony to feed.

Life History:  Gray bats roost, breed, rear young and hibernate in caves year round. They migrate between summer and winter caves and will use transient or stopover caves along the way. Mating occurs as bats return to winter caves in September and October. By November, most gray bats are hibernating. Adult females begin to emerge in late March, followed by juveniles and adult males. Females store sperm over winter and become pregnant the following spring. A few hundred to many thousands of pregnant females congregate to form maternity colonies. Males and nonreproductive females gather in smaller groups to form “bachelor colonies”. A single pup is born in late May or early June. Young begin to fly 20 to 25 days after birth. Gray bats feed primarily on flying insects over rivers and lakes. Aquatic insects, particularly mayflies, make up most of their diet.

Threats:  Because gray bats are found in caves year round, they are very vulnerable to human disturbance. As with any cave bat, alterations of caves and cave entrances (e.g., commercialization and improper gating) have negatively affected their populations. Gray bat populations have also suffered losses from natural flooding and flooding caused by manmade impoundments. Pollution and siltation of streams causing a reduction in aquatic insects and the overuse of pesticides may also affect gray bat populations. In addition, gray bats are susceptible to white-nose syndrome, a devastating disease that has caused unprecedented mortality in some of our hibernating bat species, especially in the northeastern U.S.

Gray bat in summer Gray bat in summer
Photo by James Kiser
 
Gray bat in summer Gray bat in summer
Photo by James Kiser

Hibernating gray bats Hibernating gray bats
Photo by John MacGregor
 
Cluster of gray bat pups on cave ceiling Cluster of gray bat pups on cave ceiling
Photo by John MacGregor
Gray bats under bridge in gap between concrete beams Gray bats under bridge in gap between concrete beams
Photo by John MacGregor