Mexican Bats Find Cross-Border Benefactors

Cueva de la Boca caught the attention of conservationists after researcher Arnulfo Moreno surveyed 10 major publicly accessible caves in northern Mexico and found that the bat population had fallen by 90 percent in five of them.

"They are especially vulnerable when they are concentrated in a single place and only produce one pup a year," said Moreno, who is based at the Technological Institute of Victoria City in Monterrey. In addition, Boca is a "maternity cave," where young pups were being suffocated to death by smoke from the torches that hikers fashioned with halved plastic bottles and old rags.

"If you're an adult bat and you cannot breathe, you just fly away," Correa said. "If you are a newly born baby bat waiting for your mom to feed you, you just fall down and die."

A Shrunken Population

At one time, Cueva de la Boca was home to an estimated 20 million Mexican free-tailed bats, known to scientists as Tadarida brasiliensis . By last year, the colony had shrunk to 600,000. Pug-nosed, with a wrinkly lower lip and long, loose tail, the bats prefer warmer climes, choosing to live along the border from April to early November. There is evidence they continue south through the winter, but details of their migratory patterns are not well known.

Three other species live in the cave in smaller numbers, including the ghost-faced bat, which has folds of skin below its chin and eyes that appear to be tucked inside its ears, and the naked-back bat, so named for its smooth, almost rubbery-looking skin.

But Boca became a high priority because of the Mexican free-tailed bat and its proclivity to eat the corn earworm, a vicious moth that devours corn crops as it migrates and lays eggs all the way from Winter Garden, Tex., to the Canadian border. As a pest control, bats are more attractive than chemicals because they cost little, pose almost no risk to human health and target specific bugs, leaving the rest of nature undisturbed, Correa said. And because of their location along the border, Mexican free-tailed bats are well-positioned to eliminate earworms before they strike vital crops.

"These bats are of enormous ecological and economic benefit on both sides of the border," Merlin Tuttle, founder and president of Bat Conservation International, said in an e-mail. BCI and Fondo Mexicano, a private organization focused on biodiversity projects, have commissioned assessments of an additional 150 hard-to-reach caves along the border. The bat population in those has fallen from about 55 million to 15 million, Moreno said.

Though modest in size, the 20-acre Boca property offers conservation opportunities beyond bats. It is home to a pair of endangered peregrine falcons, a threatened cypress species and a few endangered American beaver, according to Pronatura. From a single location, visitors can take in an entire ecosystem -- the insects feeding on the plants, the bats eating the bugs and the falcons feeding on the bats.

Since Pronatura began informing visitors about the fragile residents of Cueva de la Boca last year, the number of Mexican free-tailed bats has doubled to about 1.2 million, Correa said. It is quite a sight, she marveled, when the colony departs for another night of hunting and dining. When they emerge in one burst, their presence in the skies shows up on Doppler radar.

She can only imagine what 20 million or so would look like.