Southern Bats Like Hardwoods
by Perdita Spriggs
Bats are one of the most numerous and diverse groups of mammals, existing on every continent except Antarctica. The world’s current bat fauna represents over 50 million years of adaptation to a variety of environmental conditions and unique niches. The only true flying mammals, bats are fascinating for a variety of reasons, including the ways their bodies have evolved for flight. Millions of years ago, bat forelimbs evolved into wings and their hips rotated 180 degrees, allowing the animals to hang by their feet. Bats also developed the ability to echolocate, or use sound to locate objects and orient themselves in their environment, which helps them navigate through caves and forests as well as locate prey.
There are over 1,000 species of bats, each playing an essential role in their environment— including consuming vast quantities of insects. As an additional perk, bats redistribute nutrients throughout the forest in their guano. Many bat species also feed on pollen and fruit, serving as pollinators and seed dispersers. Though abundant in the United States before 1900, 13 percent of bat species are now at risk of extinction due to human disturbance. Studying and understanding the lifestyle patterns of these animals is essential to reversing species decline.
How Do You Track a Bat?
Researchers at the SRS upland hardwoods unit located in Clemson, SC, are particularly interested in learning more about the lives of bats in the South, where four species—gray bat, Indiana bat, Virginia big-eared bat, and Ozark big-eared bat—are on the Federal endangered species list. Four additional species—Rafinesque’s big-eared bat, southeastern myotis, small-footed bat, and Florida bonneted bat—are considered species of special concern.
“Because bats are small, nocturnal, and fly over large distances, they can be very difficult to study,” says Susan Loeb, research ecologist who initiated SRS bat research in 2000. “However, technological advances over the past 10 to 15 years have opened a new window on their ecology and habitat relationships.”
This technology includes very small radio transmitters and field-hardy bat detectors. The tiny transmitters, which are literally glued onto the body of the bat, give researchers the ability to track foraging and roosting patterns. Because bat echolocation calls are species-distinct, researchers can use detectors to identify which bat species are foraging in a particular area. These tools help researchers look at how the landscape affects habitat use, whether bats prefer certain forest types or age classes over others, or if they are affected by silvicultural treatments such as thinning and prescribed fire.
Picky About Habitat
Loeb and her Clemson research team collaborate with other SRS units, universities, and Federal and State agencies to discover more about bat behavior in hardwood forests. Studies in the upper Piedmont and South Carolina mountains have shown that bats use habitats with an open structure, such as early succession or
mature forests, more than forests with cluttered structures. Collaboration with Clemson University on roosting habits of red bats and eastern pipistrelles on the Clemson Experimental Forest have confirmed that both species roost exclusively in hardwoods, primarily oaks and hickories.
Another cooperative study with Clemson University examines the importance of riparian zones and effects of riparian zone management on bat foraging and roosting ecology in upland hardwoods in the Nantahala National Forest. Additional research on the effects of silvicultural practices associated with gypsy moth suppression and oak decline on habitat use are being conducted in conjunction with Eastern Kentucky University, Kentucky Department of Fish and Wildlife Resources, and several other research work units.
Bats can be pretty particular when choosing their habitats, especially when selecting roost sites. However, little is known about how forest management affects bat habitat use or selection, particularly in hardwood forests. Some studies in the Midwest suggest that bats prefer to roost in hardwood areas after a prescribed burn. “Bats usually prefer to roost in trees that get a lot of sunlight,” says Loeb. “Burning increases light while decreasing clutter in the forest, resulting in more solar exposure and greater access to potential roost trees.” Many more studies are needed to determine how forest management activities affect roost site availability, insect abundance, and foraging.
Researchers are also trying to determine whether the decline in some bat populations is due to factors in their summer or winter habitats. Many bats migrate in the spring and fall; some fly less than 50 miles, others over 500. Migration can be very risky; bats go into unfamiliar territory with unpredictable weather and predators— all factors that could significantly reduce their populations. Very little is really known about the migratory patterns of bats; linking summer and winter habitats could help scientists determine factors in each seasonal environment, and potentially both, responsible for population declines. Loeb and colleagues at several universities are currently testing whether a technique called stable isotope analysis can provide more specific information on migratory patterns.
Loeb is always on the lookout for new and interesting opportunities to study bats and to open their nocturnal world to natural resource managers, students, and the public. In 2002, she took part in the first annual bat blitz sponsored by the Southeastern Bat Diversity Network. Held in the Great Smoky Mountains National Park, the blitz brought together bat enthusiasts from State and Federal agencies, universities, and private industry to exchange information, ideas, and share techniques for studying bats.
“The blitz is an excellent way to inventory the bat community of a specific area,” says Loeb. “During a 3-night intensive survey, biologists from around the country network, receive training, and share current research methods.” SRS jointly hosted the 2006 blitz with the Francis Marion and Sumter National Forests, the Chattahoochee National Forest, and the South Carolina and Georgia Departments of Natural Resources. The 2007 blitz was held in late summer on the Cherokee National Forest in Tennessee.