Roosting Boxes for Georgia's Bats
Roosting Boxes for Georgia's Bats
Bats are a valuable and fascinating part of Georgia's natural heritage. They provide a beneficial service by foraging on flying insects, many of which are pests. A single bat can eat hundreds of mosquitoes in one hour! They also eat large numbers of moths and beetles that cause agricultural damage.
Roosting boxes are an excellent way to provide much needed habitat for several species of bats that occur in Georgia like the big brown bat (Eptesicus fuscus), Mexican free-tailed bat (Tadarida brasiliensis) and evening bat (Nycticeius humeralis). Historically, caves and large dead trees with slabs of loose bark and hollowed centers provided shelter for roosting. Today, large snags are in short supply so bats are sometimes choosing to roost in buildings or homes. If bats become a nuisance by roosting in a building where they are not wanted, the best method for resolving the problem is to install an excluder. An excluder is simply a one-way door that allows the bats to exit but not re-enter. An excluder can be built by attaching a sheet of plastic or fine netting across the top and down the sides of the hole being used, but leaving it open at the bottom. The excluder should extend several inches below the hole. Once all the bats are out, the hole can be repaired. Exclusions should not be conducted when young, flightless bats are present, which typically would be during the period from May 1 to August 15. If necessary, contact the Georgia Department of Natural Resources for a permit to exclude bats during the months of May through August. Like many mammals, bats can become infected with rabies. Use caution when near bats and try not to touch or harass them, especially those that appear to be sick or behaving abnormally.
Bat Box Design
Bat boxes often are poorly designed with little consideration of the specific criteria required to successfully attract bats. Crevices (chambers) within the box should be around ¾ inch wide, with some variation desirable since bat species vary in size. The chambers must be correctly spaced and the panels need to be roughened to allow bats solid footing. A 1 ½ inch diameter access hole drilled between chambers allows bats to move around within the box. Larger boxes provide more surface area and a range of temperatures so bats can select a position inside the box that meets their needs. Bats generally like much warmer temperatures than humans might find comfortable. Even temperatures in the high 90s are desirable, especially for a maternity colony. Ventilation is important to mitigate excessively high temperatures. Several factors significantly increase the likelihood of a box attracting bats:
Height: Boxes mounted 20-30 feet high have greatest success
If presented in the appropriate habitat, properly designed bat boxes have proven to work consistently to attract bats. A bat box should be mounted as high as possible, but still allow the owner reasonable access for maintenance. A 4 x 4 treated post is acceptable, but the resulting height should be at least 12 feet. Heavy gas pipe 2 ½ inches in diameter is ideal and comes in 20-foot sections. The easiest place to mount a box might be on the side of a house or barn, but be careful not to allow too much shading. And keep in mind that bat droppings will accumulate under the box. The box should be checked each year to remove mud dauber or wasp nests and repainted if necessary. Winter would be the best season for this work, since most boxes are not used in cooler weather, but check to make sure. Untreated wood must be used since chemicals used in treated lumber may be harmful to bats after long exposure. Make sure not to attach the box to a tree, since tree-mounted boxes rarely provide enough direct sunlight. Generally, a dark gray color should be maintained since it allows the box to absorb enough heat in the Georgia climate.
For more information, contact WRD's Nongame Conservation Section, (770) 918-6411.
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