As I stood under a thatched roof in the middle of a Central American rain forest, zoologist Bruce Miller approached from the evening shadows with something wriggling in his cupped hands. “This,” he said, “is the smallest bat in Belize–a black-eared yellow bat.”
Miller gently stretched the bat’s wing so I could see that it had a wrist, a thumb, and four long, needle like fingers. The fur of this flying mammal was incredibly soft. I once thought bats were scary, but this one was cute.
I was in Central America for a few days last spring to learn about the pioneering research Miller and his wife, Carolyn, are doing. The Millers first landed in Belize more than 14 years ago intending to study nothing but birds. Gradually, their interests expanded to include mammals. Now Carolyn spends her mornings scouring the ground for the tracks of jaguars, and Bruce spends his nights combing the sky for bats.
On most nights, Miller doesn’t see or hold the bats he studies. Instead, he waves a small yellow and white box, called an Anabat detector, above his head. The Anabat detector functions as an electronic ear, picking up inaudible bat sounds.
Bats use echolocation to navigate. They produce high-frequency sounds that echo off surrounding objects. The echoes enable the bats to detect trees in their path or the tiny insects they eat.
When the Anabat is plugged into a laptop computer equipped with special software, bat voices become squiggles, dots, and lines on the laptop’s screen. Each distinctive pattern and shape, known as a vocal signature, represents the unique sound waves emitted by a particular species of bat.
Some bats found in Belize, called leaf-nosed bats, don’t echolocate; they find their way with old-fashioned eyesight. Bat researchers have been studying leaf-nosed bats for more than 30 years. Like birds, leaf-nosed bats are easily caught in invisible nylon nets.
Until recently, not much was known about the other families of bats in Belize. “These bats use echolocation, allowing them to `see’ nets like a big wall in their path and say, `I don’t want to go there,'” Miller told me.
FACES AND VOICES
Imagine the excitement when Miller received his first Anabat detector five years ago. “We turned the Anabat on and immediately `heard’ bats,” Miller said. “Then we hooked it up to the computer and saw five or six different shapes of signals.”
Then came the work of deciphering the signals. “Initially everything was an unknown” Miller said. “We started naming [the species] Unknown 1. Unknown 2, Unknown 3….” To match faces to the signals, the Millers had to catch some bats and fly them in their “sound lab”–their kitchen.
“We just let them fly laps around the kitchen and made recordings with the Anabat.” said Miller. “After we had enough, we opened the sliding door, and on their next lap, they went right out.”
So far, Miller has identified the vocal signatures of 28 of the 33 echolocating bat species known to live in Belize. “Everywhere we go, we find species of bats we just never knew were there before,” he said. By storing the data on his computer, Miller is well on the way to his next goal: developing regional bat project to determine which habitats are crucial for the bats’ survival.
“If we lose the bats, we’re going to lose the tropical forest.” he said. “In the tropics, the birds are the day crew, and the bats are the night crew.” Everything that birds do during the day–from pollinating plants to transferring seeds to eating insects that gobble plants–the bats do at night. “It keeps the tropical system going,” he added.
Though bats are key players in the maintenance of the tropical forest, many species are on the decline. “A lot of people assume all bats are [bloodsucking] vampire bats and that they’re bad.” Miller said. “So people kill them.”
In reality, only three species of vampire bat exist. Two are extremely rare and only feed on birds. The third wasn’t common until humans began converting forests to fields populated by cows. Sucking blood from wild animals that move around a lot is difficult for vampire bats and keeps their numbers low. But with cows and other domestic animals, the vampire bats can just fly right up to an easy 20-minute meal. As a result, their numbers have swelled.
Labeled as pests, vampire bats are often burned out of their caves. But caves are like apartment buildings: All kinds of bats, not just vampire bats, reside in them. When caves are burned. everything in them, including other bats, are killed.
“Bats perform a really valuable role,” said Miller. “But because it’s in the dark, it’s like `out of sight, out of mind.’ The average person just doesn’t know about them.”