Every summer the monsoons come to southern Arizona. In late afternoon, dark clouds roll in, eclipsing the immense blue sky. And with the summer rain comes Cecil Schwalbe, the frog man of the desert.
"To a biologist, this is mecca, this is heaven," says Schwalbe, a herpetologist with the U.S. Geological Survey. "The amphibians, the reproductive ants and termites, everything's coming out to feed. The scorpions are running around, carrying babies on their backs."
Arizona is one of the nation's driest states, but during its brief rainy season, it becomes an amphibian wonderland. More than a quarter of of the nation's frogs and toads live there, and with amphibians in alarming decline around the world, scientists are working to protect their Arizona habitat.
For National Geographic Radio Expeditions, NPR's John Burnett followed Schwalbe into Arizona's Sonoran Desert for his annual trek to observe the frenzied courtship of its native amphibians.
Of all the vertebrates that live in the great Sonoran Desert, none matches the improbability of the amphibians. For 10 months out of the year, they wait in their burrows, three feet under the burning desert floor, conserving energy and moisture.
But with the first monsoon raindrops, two frantic months of feeding, mating, egg-laying and metamorphosing begin.
During those months, Schwalbe and his assistants spend many nights traipsing around breeding ponds, gathering clues about the population status of six species.
Frogs and toads are regarded as sentinel species. A healthy population can mean a clean bill of health for an ecosystem. The bad news is amphibian numbers are falling around the world. Possible culprits are habitat destruction, climate change, disease and pollution.
Schwalbe's work is part of the U.S. Department of Interior's Amphibian Research and Monitoring Initiative. The project seeks to better understand America's frogs, toads, newts and salamanders, to find out which ones are threatened, and which ones are healthy.
There's one species biologists aren't worried about: the American bullfrog. It's considered a scourge, and is taking over wetlands throughout the West.
"The bullfrog is one of the most amazing predators we've ever run into for its size," says Schwalbe. "In Arizona, over the last 15 years, we've found every vertebrate class in the bullfrog's stomachs. We've found frogs, snakes, lizards, turtles, birds, mammals, rodents, bats, even. "
Bullfrogs cannibalize their young, too. The voracious immigrant was brought from the eastern United States to the West as a game animal and a food source. But with no natural predators, the bullfrog became king of the food chain.
When Schwalbe hears the big, bass calls of a bullfrog, he switches from conservationist to exterminator. He has stolen eggs, speared, hand-captured, shot and trapped bullfrogs. He's drained ponds to dry them out. But the bullfrog is so prolific, so indestructible, it always survives the purges.
And when the monsoons end, the native frogs will burrow back underground. But the bullfrog sticks around. Then, it will just be Schwalbe and his nemesis. And despite its harmfulness, the frog man can't help but admire the animal: It has a great big throaty ribbit.
"I just love it."
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