Little is known about the winter roosting habits of most North American forest bats. Most bat research in temperate climates is conducted during summer, and land managers rely heavily on these data for their year-round management strategies. Our research suggests that can be a risky approach for some forest bats.
Summer studies of various tree-roosting species have shown that they typically choose larger-than-average trees. Limited research, however, suggests quite different roost selection in winter, presumably as the bats search for better thermal conditions.
Our study, funded in part by BCI’s North American Bat Conservation Fund grants, examined winter roosts of Seminole bats (Lasiurus seminolus) in a managed forest landscape in South Carolina. The property owner, MeadWestvaco Corporation, practices “ecosystem-based forestry” to maintain diverse habitats for wildlife.
In the winters (January and February) of 2004 and 2005, we used mist nets to capture Seminole bats and attached tiny radio-transmitters to their backs. We radiotracked 12 male Seminole bats to 47 unique roost locations. These included: 13 roosts in the canopy of hardwood trees; two in the canopy of pine trees; six in hanging vines in the overstory; four in midstory trees; nine in pine-needle clusters suspended from understory vegetation; and 13 in the pine-leaf litter on the forest floor.
Bats using overstory hardwoods roosted near the top of the canopy on small branches near clusters of dead leaves, within clumps of Spanish moss or on vines hanging from high branches. Understory roosts were typically located beneath clusters of pine needles that had fallen from taller trees and had become suspended in low-hanging vines or branches. The needles formed a roof-like mat around and over the bats. Bats roosting on the forest floor were under about a half-inch (1 centimeter) of pine-leaf litter. Canopy roosts were usually located near the edge of older stands of mixed pine and hardwood, while roosts among pine needles or leaf litter were located inside young, dense stands of loblolly pine.
Summer studies, by contrast, have found Seminole bats roosting almost exclusively in overstory pine trees.
What we learned during this study has important implications for forest management. Forest managers must consider seasonal differences in roosting behavior. Bats’ use of understory trees and leaf litter in winter suggests that prescribed fire, a common management technique in southern forests, may adversely affect bat populations during certain times.
CRIS HEIN is a graduate research assistant at the University of Georgia’s Daniel B. Warnell School of Forest Resources, where STEVEN B. CASTLEBERRY is an associate professor and KARL MILLER is a professor.