Building your bats a house of their own

Plagued by bats? Dr. Tuttle suggests exclusion as a safe, simple alternative to extermination, which involves highly toxic chemicals. The experience of some St. Louis wildlife enthusiasts is a case in point. This group had no misconceptions about bats, but when they arrived at their wilderness preserve one spring to find that a colony had taken over their cookhouse, they decided something had to be done. How they solved the problem made a significant contribution to the save-the-bats campaign: They built a bat-house that proved acceptable to the Little Brown Bat, something considered no easy task. Then one evening, after the bats had flown off, the members of the group caulked up or otherwise blocked every chink and crack in the cookhouse that might allow the bats to get back in.

When the bats returned at dawn to find every entrance blocked, they had to look elsewhere for shelter. The nearby ``Bat Towers'' complex proved inviting enough and they moved in. A few weeks later, wildlife expert Dr. Richard LaVal examined the bat-house and found 70 sleeping bats. There was room, he said, for several hundred more.

Now, the Missouri Department of Conservation and the Washington-based magazine Defenders, that broke the bat-house success story in 1985, are providing plans of the St. Louis group's bat-house free to anyone who might like to build one.

How did the St. Louis conservationists design a shelter that proved attractive to bats? They started by reading up on everything they could find about bat roosting sites. They found that bats are attracted to small nooks and crannies where they can crawl in, hang upside down, and go to sleep. So they came up with a roof-type structure, designed to shelter the bats from the weather, with special sleeping quarters (a series of parallel slats) inside. The slats were made from vertical rows of cedar shingles spaced at various intervals to give the bats a choice of sleeping crevices ranging from one-half inch to 1-inches wide. The bats crawl through the narrow opening of their preference, cling to the rough cedar sides, and go to sleep.

The key to bat acceptance is the slat structure inside. How decorative or plain the protective roof is of no consequence to the bats. (The plans put out by the Missouri Department of Conservation, however, call for a bat-house that would look handsome in any garden. It includes a sloping, shingled roof complete with cupola and weathervane.)

Some bat species live permanently in caves, others hibernate through the winter in distant caves and emerge in the spring to fan out in search of food. Once in their preferred ``hunting grounds,'' the latter species search around for appropriate roosting sites where they also raise their young -- one a year. These roosting sites sometimes include barns and attics. Because even the largest bat species can crawl through an opening less than three-quarters of an inch wide, they can readily enter many older buildings.

If you plan to build a bat-house for yourself, David Robinson of the National Geographic Society suggests doing so in the summer or winter, and waiting until early spring to set it up, just before the bats fan out in search of roosting sites. If few bats have been sighted in your area, you may have to wait some time, several years perhaps, before any locate your structure. On the other hand, if bats currently roost in a building on your property, they may soon take over your bat-house if you erect it near the building they use and then caulk over or block up all possible openings in that building.

The best time to block these entrances is during the winter, when bats hibernate elsewhere. Otherwise, block them up any time after dark when the bats are out flying. Don't do this during June and July, Dr. Tuttle cautions, or you will separate the mothers from their flightless babies inside.

Bat-house plans are available free from: Defenders Magazine, Defenders of Wildlife, 1244 Nineteenth St., NW, Washington, DC 20036 or from Missouri Department of Conservation, 1221 South Brentwood Blvd., St. Louis, MO 63117. Bat Conservation International, c/o Brackenridge Field Laboratory, University of Texas, Austin, TX 78712, also offers plans of smaller bat-houses.