Here's an idea worth trying. . .
Here's an idea worth trying. . .
by Richard L. Clawson and Gene Gardner
In 1963 when wildlife biologists at Duck Creek Wildlife Area in southeastern Missouri wrapped aluminum sheets around cypress trees to protect nesting wood ducks from predators, they also inadvertently created ideal bat roosts. With abundant insects and water, Duck Creek was already well suited for bats. It took them less than three years to discover the predator guards, and a nursery population of little brown bats (Myotis lucifugus) has been living beneath them ever since.
We visited Duck Creek during the summer of 1992 and looked at 49 predator guards beneath wood duck nest boxes. Some were made of corrugated sheet metal, and some were flat aluminum, ranging in size from 20 to 80 inches wide, and about two to four feet above the surface of the water.
We discovered that bats used only those collars that fit loosely and had crawl space underneath, mostly created by irregularly shaped tree trunks. Bats preferred corrugated collars, which, because of their stiffness, had been more difficult to wrap tightly around the trees. Twenty
-seven guards, all with openings at the bottom, supported bats or had guano accumulations. Some were so full of guano, in fact, that bats could no longer use them. Most bats were in groups of 25 to 40, primarily females and young. We observed only two adult males.
Sheet metal collars similar to those used at Duck Creek may provide inexpensive and easily built bat habitat worth trying in other situations. Endangered Indiana bats (M. sodalis) and other species that roost under tree bark might especially benefit. Corrugated sheet metal may even have advantages over natural bark. Its ripples imitate the exfoliating bark that bats find so attractive but is far more durable because such bark soon falls from dead trees. Collars can be placed where needed, and they allow bats to regulate their temperature by moving around the tree to the sunny or shady side.
Although bats used some narrow collars, we believe that wider is better at least 48 inches. Nail collars securely at the top and along the seam, using aluminum nails. Aluminum will not rust, is inert, and will not destroy a saw blade if the tree is later cut. Be sure to leave one-half to an inch of space under the collar for the bats to enter and move around. Inspect the collar during the off-season to check for evidence of bats and to remove excessive guano. Finally, if a tree is so irregular in shape that sizeable gaps are left at the top, be sure to crimp it closed to prevent wood ducks or other cavity nesters from being trapped.
Over 25 years of bat use of sheet metal predator guards at the Duck Creek Wildlife Area proves that they provide excellent habitat and are a potential tool for bat management. We do not know if there are geographic or other limits to the usefulness of metal collars as bat roosts, but we encourage other wildlife managers and BCI members to give them a try. If you do, you can help us evaluate the effectiveness of this type of artificial habitat by keeping careful records and reporting on the results.
Richard L. Clawson is a research biologist with the Missouri Department of Conservation. Gene Gardner is an endangered species specialist with the Missouri Department of Highways and Transportation. Both are members of the Indiana/Gray Bat Recovery Team.
Gene Gardner examines one of the wood duck predator guards used by bats at the Duck Creek Wildlife Area.