MEXICO CITY – Shortly before sundown they make their first foray, cruising up to 5,000 feet aboveground in search of mosquitoes, moths and other tasty treats. A few hours later, they return home to rest and feed their young before heading out again around midnight.
By daybreak, when Mexican free-tailed bats finally return to their cave, named Cueva de la Boca, the colony will have traveled as far as 62 miles and gobbled some 12 tons of bugs out of the skies near the U.S. border. And in cornfields from Texas to Iowa, farmers are giving thanks.
Or at least they should be.
Sure, bats are creepy. They hang upside down, squeal at high decibels and turn up in movies as blood-sucking fiends. Some even spread rabies. But, it turns out, that in the global ecosystem, bats are humanity’s allies.
Every night, all night, as humans sleep, the flying mammals work feverishly. They pollinate plants such as the agave, the source of Mexican tequila. Their excrement, called guano, is a valuable fertilizer. And bats eat up to one-quarter of their body weight in insects every night, making them one of the simplest, safest, most cost-effective forms of pest control available.
Somehow, that message has not reached most people. For decades, intentionally or otherwise, property owners, hikers and sightseers have trampled habitat, dumped garbage and set fires, decimating the bat populations in many parts of the world.
“We scientists missed a chance to give farmers the right information in the right way at the right time,” said A. Nelly Correa, a bat expert at the Center for Environmental Quality at the Monterrey Institute of Technology in Mexico. “Most of us were too busy giving the information to our peers in journals and not to the people who could be our partners.”
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Now, in a unique cross-border alliance, bat lovers have embarked on a multiyear effort to quantify the damage and replenish the bat population of northern Mexico. The project, being spearheaded by the nonprofit Texas-based Bat Conservation International (BCI), includes detailed mapping of hundreds of present and former bat roosts, educational programs for farmers and even purchases of land to protect the most vulnerable colonies.
In late September, armed with BCI data, the Mexican environmental group Pronatura Noreste bought the Cueva de la Boca cave outside Monterrey for about $500,000. It is believed to be the first purchase of a bat cave by Mexican conservationists, said Magdalena Rovalo, a biologist and director of the organization. Access is now limited to researchers, and plans are underway to build an observation tower in the hopes of generating tourism revenue at the cave, which takes its name from the Spanish word for “mouth.”
“If we had a healthy population of bats, we would have pest control and healthy crops at no cost to society and no bad effects on health,” Correa said. “And it would be a plus for the economy as bats can become a tourist attraction.”
Scientists have identified more than 1,000 species of bats worldwide, representing about one-fourth of all mammal types. Latin America is home to 290 species, 140 of them in Mexico, making the region one of the most diverse bat habitats on the globe. Of all those bats, just two species feed on wild bird blood and only one eats cattle blood, said Correa, who tries at every opportunity to disabuse the public of those blood-sucking stereotypes.
“They have given all bats a bad image very unfairly,” Correa said. “Bats are really great guys!”
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.”
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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, Texas, 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.
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.
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