Biologist Laurie Lomas of the U.S. Fish and Wildlife Service swept the red beam of her flashlight across the ceiling of the cinder-block tower. “Up there. Look up in the corner,” she said. A group of female bats and pups stared back at her. Their oversized ears left no doubt that these were Rafinesque’s big-eared bats, exactly what this “artificial tree” was designed for.
This “tower roost” at the Trinity River National Wildlife Refuge in East Texas shows the most promise of the string of experimental designs so far developed by Bat Conservation International and its partners over the past six years. The idea is to mimic the bats’ traditional roosts: hollow cavities in extra-large, old-growth trees, which are fast disappearing from the nation’s woodlands.
For the past two years this tower, one of two at the Refuge, has housed 10-15 Rafinesque’s big-eared bat mothers and pups during the mid-summer months. The mothers gave birth in a ramshackle old abandoned farmhouse nearby, then moved into the tower roost after the young bats learned to fly. In a healthy forest, Rafinesque’s big-eared bats alternate among several roosts to reduce parasite loads and confuse predators.
This is a forest-dwelling species that naturally roosts in small colonies (typically 5 to 50 females, rarely more than 200) in hollows of old-growth black gum, water tupelo, American beech and bald cypress trees. Rafinesque’s big-eared bats face widespread loss of habitat and roosting sites and are thought to be in decline range-wide.
They do not roost in tight crevices, so do not use the traditional bat houses that BCI’s Bat House Project has dramatically improved and popularized for at least 14 species of crevice-roosting bats in North American. The Project still works with bat houses, but it is adding a new emphasis on innovative roosting options for bat species cannot use the kinds of crevices provided by traditional bat houses.
Our challenge with the Rafinesque’s big-eared bat is to create an artificial environment that is suitable for this extremely shy and rare species.
Much work remains to perfect these “artificial trees,” improving their suitability for bats while reducing costs. But, through our field tests and several lines of systematic research, we are constantly adding to the information that will help us achieve this goal. Wildlife researchers from Stephen F. Austin State University, Texas A&M University and Texas Parks and Wildlife are collaborating on a East Texas study to identify in detail the distribution and habitat needs of Rafinesque’s big-eared bats. And Trinity River National Wildlife Refuge biologists, with a Science Support Grant from the U.S. Geologic Survey, are studying the species’ local population.
Both studies are recording conditions inside current bat roosts (both natural tree roosts and artificial roosts) and defining habitat conditions around the roosts. The results will help guide forest managers in protecting habitat for this widely threatened species. And BCI’s Bat House Project will use the data to continue improving our tower designs.
The generosity of these partners have made possible BCI’s artificial tree program possible: Angelina National Forest, Bar-M Plantation, Lower Suwannee National Wildlife Refuge, Lumber River State Park, Mammoth Cave National Park, Offield Family Foundation, Pebble Hill Grove, Saint Catherine Creek National Wildlife Refuge, Shangri La Botanical Gardens and Nature Center, South Mountains State Park, Texas Parks and Wildlife Department, Trinity River National Wildlife Refuge, and Alison Sherman (Mississippi Museum of Natural Sciences).
BCI members can the read the complete story of this promising new direction in artificial bat roosts in the Fall 2006 issue of BATS magazine.