Guanapo Cave,

Trinidad. Nighttime. It's can't-see-a-thing dark inside the walls of this six-foot-high cave. And it's wicked hot. Ninety degrees and 100 percent humidity that's just fine for the snakes that live there.

In the blackness, about a thousand of one of the Western Hemisphere's largest bats fly around, making a huge racket with their wings and screeches. Bat guano drips from the ceiling and collects on the cave floor into a slippery mess of ankle-deep muck.

But the only thing that really bothers Maryland doctoral student Kirsten "Kisi" Bohn, who spends hours at a time in this B horror-flick setting, studying the cave's greater spear-nosed bats, are the giant cockroaches coming at her in the blackness. "When a giant cockroach lands on my back it's quite startling!"

Bohn is researching how greater spear-nosed bats use social communication. Even among bats, a species with superb hearing and sensing abilities, the greater spear-nosed bat has some unique traits that may shed light on how animal and even human communication evolved.

"The greater spear-nosed bat is one of only a few mammals beside humans that have an extremely stable group of unrelated individuals," says Bohn.

And they seem to use vocal signals in a way that leads to a kind of social cooperation that, in most other mammals, is found only among relatives. "They hear, learn and understand various sounds made by the members of their group, much as the differences in human voices," Bohn says.

One of those sounds is the cry, or isolation call, that babies, called pups, make when they are in distress. That isolation call is the vocalization that Bohn is homing in on in her research.

Teenage Rebel

A born-and-bred California girl from San Diego, Bohn came East to do her doctoral work with Gerald Wilkinson, a Maryland biology professor who studies animal acoustics and communication. Bohn and bats go back to her high school days, when she chose bats as the subject of a zoology project, "because people hated them, and I was a rebellious teenager."

That rebellion has turned into her fulltime work. Bohn keeps several greater female spear-nosed bats on campus. These bats provide a comparison to the data she gathers on the wild cave bats. In the lab, Bohn plays recorded sounds for her bats to see if they can discriminate between recorded isolation calls. It's a controlled setting where the bats have names--Big Mamma, Snit, Nena Freaker, and Pip--and where Bohn speaks gently to them as they sit on her gloved hand. And it's a far cry from the wild scene in Guanapo Cave, where Bohn has trekked every spring for the past four years, at the height of pup birthing season.

Raining Pups

In Guanapo Cave, hundreds of groups of bats hang from the ceiling. Each group consists of a male, 20 to 40 females and their newborn pups, who can't yet fly.

When night falls, hundreds of the adults suddenly take off for the outside world to hunt the night's meal of fruit and insects, leaving behind the kids and, in each group, one or two females who act as babysitters. Like any kids, when the parents leave home, the pups get in trouble.

"They fall from the ceiling," says Bohn, "Hundreds of them. It's raining pups, it's chaos."

The pups can't get off the floor by themselves, so they emit isolation calls for help. It's no small matter, because a pup left on the floor is likely to die or be killed by a female bat from outside the pup's group. While the "babysitters" often sit by fallen pups from their group, apparently protecting them, it's not until the mothers come back from the night's forage that the pups are actually rescued by the returning females.

"Hundreds of bats are making all sorts of noises at once," Bohn says. "Figuring out who's saying what and why is difficult."

Bohn wants to find out if a mother rescues only her own pup because she recognizes the pup's unique isolation call. Covered from head to toe in protective clothing, a respirator over her face and only a head lamp to light her way, the 4'11" Bohn marks babies and mothers with hair bleach to identify them.

She also takes DNA samples to compare back in the lab. If the DNA shows the rescued pups and mothers are related, Bohn will have even stronger evidence that vocalization is critical to the bats' social cooperation and survival.

Bats in Her Future

Bohn will make her last trip to Guanapo Cave this spring and hopes to finish her Ph.D. in December, but she plans to stick with bats. She's taking a position at the University of Texas to study the famed colonies that live around Austin.

"When we figure it out, I think we're going to see that bats have much more complex vocal communication than we ever imagined," Bohn says.