THE SKY IS NOT yet black, but already small bats dart about in the humid air above a murky, isolated pond. A high-pitched symphony of chirping crickets, eerie background music suitable for a "Twilight Zone" episode, is broken by the buzz of a bloodthirsty mosquito as it hovers at ear level. The ear is mine, and, within minutes, the mosquito bites will be mine, too.
On this summer evening, one of the hottest in Southern California history, I am watching five grown men relive their boyhoods at the pond's edge. Every few minutes, someone focuses his flashlight on a spot, smacks his hand down on the water and raises a squirming frog in triumph. "Here's another one!" a man shouts from the far end of the pond.
The members of this expedition have journeyed to a nature preserve in the southwest corner of Riverside County to hunt California red-legged frogs. Some of the men are longtime friends; others are new acquaintances. But they all share a passionate interest in one of the oldest classes of creatures on Earth, and their mission tonight is to conduct part of a census of frogs that may face extinction.
Leading the group is Mark Jennings, a tall, sandy-haired, mustachioed naturalist in waders and a wide-brimmed felt hat. As his buddies grab frogs from the pond, he lays his bulky day pack in a dry spot a few feet up the bank and pulls out a handful of plastic freezer bags to hold the frogs. All the while, Jennings calmly offers instructions: "Try to clean the pond out... Once you get everybody, then you can let them go again."
Then he wades into the thigh-high water himself, scanning the edges of the pond with a miner's lamp he holds at eye level. Small, jewel-like eyes flash under the light. It's one of the muddy, green red-leggeds, now sitting placidly in shallow water.
When it comes to California red-leggeds, Jennings is an expert. At 34, he is an ichthyologist and herpetologist who holds a doctorate in wildlife and fisheries science from the University of Arizona. But in recent years, he has been less concerned with fish than with amphibians, and he has visited virtually every spot in the state where red-legged frogs are known to live. He has tracked them, counted them, published papers and lectured about them.
Jennings counts himself among a growing number of scientists who in the past decade have noticed dramatic, sometimes sudden decreases in the worldwide population of frogs, toads and salamanders. Declines have been documented in dozens of species in at least 16 countries. In Australia, for instance, there has been a serious drop in at least 10% of that country's 194 frog species, one specialist in amphibians estimates. And at least two frog species in that country, including one novel creature that bore its young through regurgitation, are thought to have disappeared entirely.
In Southern California, many areas, including undeveloped canyons and mountains, that once teemed with tadpoles and several frog species now have few or none. If you can still find a frog in your back yard, it's probably the ubiquitous bullfrog or tree frog. The days of easily finding something other than those two species are over.
Sometimes the reasons for the declines here and around the world are clear and simple. Wetlands have been drained for housing projects; forests have been destroyed by logging; tadpole-eating trout have been introduced into ponds and streams, droughts have dried up water holes. Other culprits include pesticides, acid rain and air pollution. But for every drop in the frog population identified and explained, the disappearance of another species in some apparently pristine wilderness remains a confounding mystery.
"There are so many variables, I think it's really tough to say 'OK, the decline is keyed to this particular phenomenon," says Mike Hamilton, a UC Riverside ecologist and director of the university's James San Jacinto Mountains Reserve study center near Idyllwild. "Very few things in nature are cause and effect. Almost every ecological relationship is so multivariate that it's hard to pin it down to 'this has an effect on that."
In the grand scheme of things, many other animal species are disappearing as humans encroach on wildlife habitats. But the decreases in the amphibian population are so sudden and inexplicable that many herpetologists believe that frogs, toads and salamanders may have become like the proverbial miner's canary. The declines, scientists say, could be a sign that environmental degradation has slipped from problem to crisis.
"If you lose these things, it's really telling you that something's wrong," Jennings says. Amphibians' smooth, porous skin and the fact that they live part of their life in water and part on land may make them more vulnerable than other animals to environmental pollutants and changes. Moreover, their place in the ecosystem, as insect predator and bird and mammal prey, make them especially important to its smooth operation.