Gray Bat - Cave Characteristics

Cave Characteristics

Although the habitat range of the gray bat incorporates much of the southeastern United States, the largest summer colonies of gray bats are located within the Guntersville Reservoir. This reservoir, found in northeastern Alabama, contains the Sauta (formerly Blowing Wind) and Hambrick caves which can accommodate over 100,000 gray bats. Gray bats use caves differently at different times of the year. For example, populations of gray bats tend to cluster in caves known as hibernacula to prepare for winter hibernation. In contrast, their populations disperse during the spring to establish sexually segregated colonies. Females form maternity colonies (also known as summer maternity roosts) while males aggregate in non-maternity, or bachelor colonies. These bachelor colonies also house yearlings of both sexes. Gray bats also utilize a third type of cave, the dispersal cave, which they inhabit only during migration. For their hibernacula, gray bats prefer deep, cool caves with average temperatures ranging from 5 to 11 °C. Multiple entrances and good airflow comprise the other characteristics that gray bats find desirable. Winter hibernacula are already cold when gray bats begin arriving in September. Summer caves are usually located along rivers and have temperatures that range from 14 to 25 °C. Summer caves typically contain structural heat traps (including domed ceilings, small chambers, and porous rock surfaces) that capture the metabolic heat from the clustered gray bats, allowing the nursery populations to succeed. Preferred summer colony caves are within 1 km of a body of water and are rarely further than 4 km away from a lake or major river. The average roosting density of gray bats is 1828 bats/m².