No Vampires, These Bats Are Friends
Preserving abundant species of bats draws thousands of volunteers and helps the economy and the environment
AUSTIN, TEXAS — BUILD a better bat house, and winged mammals will flap to its door.
That's the goal of the North American Bat House Research Project, which uses volunteers in 49 states to erect bat houses. They report the results to Bat Conservation International (BCI), which directs the two-year-old effort.
``The project thrives, and we learn as we enlist new people - the more the better,'' says ecologist Merlin Tuttle, BCI's founder and executive director.
People familiar with bats only as creepy Halloween cliches will wonder why anyone would want to attract the rabid bloodsuckers. Aren't bad hair days frequent enough without encouraging the tress-tantalized critters to roost nearby?
Dr. Tuttle scuttles these myths. Bats have no interest in human hair and capably avoid it during flight, he says. Bats are no likelier than pets or other animals to become rabid. Just don't pick them up, he says, since a bat lying on the ground may be unwell.
As for vampire bats, they live only in Latin America and are content to stay there. The bats farther north spend summer evenings devouring their body weight in airborne bugs such as beetles, moths, mosquitos, and even roaches. They hibernate in winter.
In one of the most authoritative studies yet, 25 million to 50 million Mexican free-tail bats living in Arizona's Eagle Creek Cave were confirmed to dine nightly on 200 tons of bugs that had gnawed on crops. Says Tuttle: ``It doesn't take much extrapolation to say that those bats had a huge economic impact.''
But that population declined to 30,000 bats in only six years.
The reason was human interference, Tuttle says. All too often, amateur spelunkers disturb bats or developers pave over their cave entrances, as has happened in Austin, Texas.
``Most bats can get along fine around people if we leave them a place to live,'' Tuttle says.
Houses replace habitat
Humans are destroying all kinds of bat habitat, from old-growth forests, where bats roost in dead trees, to abandoned mines that are being sealed. Last year Tuttle was just in time to prevent the sealing of a Michigan mine where a million bats were hibernating. But some states have sealed thousands of mines without checking for bats.
North America would have to lose millions more Mexican free-tail bats before they could be officially listed as endangered. ``But at that point [the species] will be biologically and economically irrelevant,'' Tuttle says. ``It's just as important [to the environment] to keep abundant species abundant.''
BCI hopes to help by halting habitat destruction and creating new habitat to replace what has been lost. The Congress Avenue bridge over Town Lake in Austin shows what's possible.
A 1980 reconstruction created spaces an inch wide and 16 inches deep between concrete beams. The size of those gaps and the humidity and temperature inside them attracted a northward spring migration of 1.5 million Mexican free-tail bats to the bridge. The bats raise their young there.
That makes Austin's bats the largest urban colony in North America. Headlines like ``Bat Colonies Sink Teeth Into City'' brought Tuttle to Austin from Milwaukee in the hopes of educating the public about the benefits of bats. In 1986 he founded BCI, which now has 12,500 members in 55 countries.
Hoping to copy the serendipitous success of the Congress Avenue bridge, BCI has enlisted the Texas Department of Transportation in a study of ``bat friendly'' bridge design. A BCI researcher has visited 370 bridges so far. She has found 6 million bats living under 10 percent of them.
``There are good reasons why they're not using the other 90 percent,'' Tuttle says. Temperature, height, size of openings, accessibility to predators, surface smoothness, exposure to wind, and access to food and water are major variables. But there's much more to be learned. ``It shouldn't come as any surprise that we're scratching around in the dark,'' Tuttle says. Although bats make up one-quarter of all mammal species, they are the least-studied mammals on Earth.
That's why BCI is turning to the public to help with bat house research. ``The beauty of having an amateur research project is that amateurs are all the time doing seemingly stupid things that turn out to work,'' says Tuttle. For instance, 50 years ago a scientist concluded that bats prefer houses made of unpainted wood. The scientific community took that for granted until volunteers in BCI's bat house project painted some anyway, Tuttle says. The painted houses attracted bats 2-1/2 times more often than unpainted ones.
Bat houses only 2 ft. tall and wide and only 6 in. deep can attract nursery colonies of up to 300 bats.
Tuttle warns against buying commercially made bat houses not accompanied by complete instructions. Almost all have no chance of attracting bats, he says. Those unnecessary failures, he worries, will cause people to lose enthusiasm.
Instead, he recommends ``The Bat House Builder's Handbook,'' a publication he co-authored that contains detailed instructions and designs incorporating the latest findings. The guide ($6.95, University of Texas Press) can be ordered from bookstores. Or send any size donation to BCI (P.O. Box 162603, Austin, TX, 78716) and it will send a copy and information on how to join the project.
``We're honing in really fast on what makes these work,'' Tuttle says. For instance, in northern latitudes the choice of exterior paint has been narrowed to dark brown or black. Other improvements to old designs include ``landing pads'' and ventilation slots. Nonetheless, BCI hopes volunteers will experiment with the design, placement, or orientation of their bat houses.
``We'll know we've arrived when we put up these houses in areas where bats already have plenty of alternatives and they move into our houses anyway,'' Tuttle says.