BOSTON — The tiny radio transmitter weighs only seven-tenths of a gram. With a dab of surgical glue, it is pressed gently against a small shaved area between the shoulder blades of a furry Virginia Big-Eared Bat. A flexible four-inch antenna trails down the little creature's back.
"You let the bat go," says Bob Currie, a biologist with the United States Fish and Wildlife Service in Asheville, N.C., "and basically you don't get any sleep for two or three weeks."
Because the Virginia Big-Eared Bat is an endangered species - one of eight bat species so designated in the US - biologists are turning to micro-technology to learn as much as possible about a bat's night out to save some bats from extinction.
Driving over country roads for hours, Mr. Currie and fellow biologists use directional antennas to track a half-dozen of the radio-equipped winged insect eaters.
"We learn how widely they range from the roost," Currie says, "and what kind of vegetation they are foraging in. By analyzing bat scat we know what kind of insects they eat."
The tiny transmitters deteriorate and fall off the bats within two to three weeks. Other experiments include attaching inch-long, glowing "cyalume" rods to their backs for easy tracking.
At their best, bats function as low-tech, omnivorous vacuum cleaners of insects, often protecting farmers from the ravages of destructive nocturnal beetles, moths, leafhoppers, and other pests. Bats may look like the warthogs of the night, but they are an important part of the food chain.
"One study found that three Mexican Free Tail Bat colonies near San Antonio, Texas, eat an estimated 250 tons of insects a night," says Merlin Tuttle, founder of Bat Conservation International (BCI) in Austin, Texas.
Despite an amazing ability to use "echolocation," a kind of in-flight sonar that can detect the flutters and footsteps of insects, bats have been no match for human invasion of their habitats. Since the turn of the century, when eyewitnesses saw tens of millions of bats flying in and out of caves in clouds that lasted for hours, bat numbers have plummeted.
Old wives' tales
Fear and ignorance contributed heavily to their decline. Old-wives' tales about bats being tangled in human hair, the negative image of bats in the movies, and the myth that all bats are rabid vampires, have persisted for decades. Pesticides also played a part in their decline. And few scientists studied bats exclusively until the 1960s.
Ignorance of bats led to disturbances and widespread vandalism in caves and abandoned mines across the US where bats live and breed. Many caves and mines were sealed by private owners or local agencies with the bats inside.
But some biologists have seen hopeful signs of recovery during the last 15 years as awareness of bat needs has increased. Most significant in the recovery efforts are the steel grates, or "bat gates" that have been constructed over many cave entrances to keep humans out and allow bats to come and go.
Many caves have been purchased by the US Fish and Wildlife Service, state and federal agencies, and the Nature Conservancy in Arlington, Va. Along the Tennessee River, the number of endangered Gray Bats has risen over the last few years since a few caves are now managed by the Tennessee Valley Authority.
"At one cave, there are some 75,000 Gray Bats where there used to be a few thousand," Currie says, "and another cave has perhaps a million, up from 20,000."
On the other hand, the population of the endangered Ozark Big-Eared Bat is down to around 1,500 in Oklahoma, where the US Fish and Wildlife Service has recently created a refuge for their protection.
No fly-by-night operation
Bats use caves because temperatures there are relatively stable for hibernation and maternity. The Virginia Big-Eared Bat, for instance, hibernates by lowering body temperature to 40 degrees. In summer, females find warmer maternity caves to give birth to a single "pup." The males leave and roost in clusters away from the caves.
If the winter cave is disturbed even slightly by humans, air pressure and temperature can change. The bats awaken. In the disturbance, the creatures then consume much of the body fat intended to get them through the winter.
"There was a sort of trial-and-error period when we weren't sure the grates were going to work, " says Thomas Kunz, a biology professor at Boston University who studies bats. "And by working with some of the spelunking societies, some of the caves have been managed to the point where colonies are returning."
One of the strategies used by BCI is to protect the crucial hibernation sites. "As we protect these sites where really large numbers of bats assemble for most of the year," Mr. Tuttle says, "they become centers for dispersal into other sites."
Tuttle, who has written four articles on bats for the National Geographic magazine, has seen BCI membership jump to 14,000 recently because of rising public interest in bats and in building small bat houses to attract them.
BCI has held workshops for the last five years to train some 100 wildlife managers from all over North America about bat conservation and how to include low-cost bat projects in ongoing programs. "We have a number of collaborative projects under way now," says Tuttle, "and next year we are establishing the National Bat Conservation Partnership with the US government."
Major challenges remain to prevent extinction of some bats. The Mexican Free Tail Bat, which winters in Mexico and summers in the US southwest, has been scorned in Mexico for years. "People dynamited the bats or burned them in caves there because they think all bats are vampires," Tuttle says.
The population of the migrating bats had once been estimated at 25 million some 10 years ago in a cave in Arizona.
"Now there are only around 30,000," he says. "Over the last two years we have had a collaborative-education program with Mexico, and we are lining up some of the biggest bat caves there for protection and purchase."