D e s e r t E x p o s u r e
April
2008
Going Batty
Misunderstood and often maligned, bats count on the work of a few good scientists — and the cooperation of all of us — to survive in the Southwest.
By Donna Clayton Lawder
As the sun sinks in a red blaze below the Guadalupe Mountains, a range jutting across western Texas and southeastern New Mexico, a swarm of Mexican Free-Tail bats streams out of their limestone caves into the darkening sky. Numbering in the millions, the bats show up as storm clouds on weather radar systems.
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USFS bat expert Marikay Ramsey |
"Oh, it's something to see," Marikay Ramsey says of this nightly show — called a "fly-out" — that occurs every warmish evening in Southwest bat havens. "They just go on and on, streaming out at you, over your head. People can't believe it the first time they witness it. It really gives you a sense of awe."
Once clear of the caves where they roost, the bats swarm down into canyons, across fields, swooping after their dinner. From sundown to sunup, sometimes traveling 40 miles for its nightly meal, the half-ounce Mexican Free-Tail bat — whose name comes from the way its tail is formed by a membrane between the bat's hind legs rather than growing directly from its body — will eat half its body weight in insects each day. Multiplied by millions of bats, that adds up to nearly four tons of potential pests to crops and humans devoured every 12 hours.
One of the more common bats in forest service biologist Ramsey's southwestern territory, the species is estimated to number many millions. A colony of Mexican Free-Tails living in the lava tubes on Ted Turner's Armendaris Ranch, for example, is the second-largest in North America and is estimated at several million.
Ramsey currently is transitioning into a new position within the US Forest Service. She has worked as the Bat Conservation Coordinator in Truth or Consequences for the past four years and in Silver City for the six years prior to that, making her the region's USFS bat expert for the past decade.
That experience leads her to caution that not all of the West's 35 species of bats are as numerous as the Mexican Free-Tails. Many area breeds of bat, in fact, are on the federal endangered-species list, designated as sensitive or threatened with extinction.
Locally, Ramsey notes, there is concern over the endangered listing for the Lesser Long-Nosed bat and the Mexican Long-Nosed bat. Four others — the Western Red bat, the Spotted bat, Allen's Lappet-Browned bat and Townsend's Big-Eared bat — are listed as "sensitive" species, according to the forest service. Of the Townsend's Big-Eared species, Ramsey says, "Large numbers would be captured in an average night of netting. Now it's getting much harder to find them, so we can surmise that they are in trouble."
It's not a good time to be a bat. Nearly 40 percent of all bat species in North America are included on state or federal threatened, endangered or sensitive species lists or are candidates for listing. Gray bats, which were among America's most abundant bats in the early part of the 20th century, are now endangered. Indiana bats declined by 55 percent in less than 10 years and also are listed as endangered. In the early 1960s, Eagle Creek Cave in Arizona housed the world's largest known bat colony, approximately 30 million Mexican Free-Tail bats. Yet that population declined over 99 percent in only six years.
While that's bad news for bats, it's equally bad news for humans, Ramsey says. Their extinction — the bats, that is — would have a devastating ripple effect on crops and the economy.
"One of the major things that people can relate to is that bats are the primary predators of nighttime flying insects," she explains. Depending on the species, bats eat up to several thousand insects apiece per night, about one-third to half their body weight. While the biggest Eastern US bat weighs only as much as 17 dimes, that's still a lot of mosquitoes you won't have to swat or deter by slathering yourself in Deet.
But bugs chomp on more than human flesh. Crop damage is the much more serious problem, Ramsey says. "In Bosque del Apache, for example, there are millions of bats swooping around eating flies, mosquitoes, grasshoppers and more. There are millions of bats that eat the Corn-Borer moth. We cannot even imagine the damage our crops would incur if we didn't have those bats alone."
Ernest W. Valdez, a wildlife biologist with the US Geological Survey in Albuquerque and co-chair of the New Mexico Bat Working Group (NMBWG), has studied the diets of local bats in the wild. He's found an interesting link between the flying animals and their local habitat — particularly the conifers now threatened by bark-beetle infestation.
"We have found that bats are very important in consuming forest and agriculture pests in New Mexico, including bark beetles and click beetles (adult forms of wireworms)," Valdez says. With concern growing over the spreading damage of bark beetles through local forests, documenting the bats' appetite for the onerous pests adds to bats' perceived value. "Understanding food habits of bats and their effects on insect pests has been a great way to promote conservation of bats, including protecting known roosts and supporting efforts for bat-house construction near areas with agriculture," Valdez says.
Bats also are pollinators and seed dispersers. Next time you're throwing back a shot of tequila, thank a bat. In the Sonoran Desert of the southwestern US and Mexico, the Long-Nosed bat plays a critical role in the lives of several species of agaves — from which tequila comes — as well as giant cacti.
According to the Western Bat Working Group (WBWG), a coalition of laypersons, scientists and academicians, the loss of plant and animal diversity is one of the most serious long-term global problems humanity faces. Many of the world's most economically important plants rely on bats. Some crops from these plants are valued in the hundreds of millions of dollars each year and are crucial to the economies of cash-poor developing countries.
Beyond economics, the delicate "web of life" between species is at issue. The giant cacti in the Southwest provide food and shelter for countless other animals. The relationships between plants and their animal pollinators and seed dispersers are the result of millions of years of evolutionary interplay. If the bat pollinators disappear, the plants and the wildlife that rely on them could be seriously threatened.