Rocky Times for a Rocky Mountain Toad
by Howard Youth
One of the amphibians most vulnerable to the chytrid fungus is the boreal toad (Bufo boreas boreas), a blotch-bellied amphibian found from southeast Alaska to Colorado and northern California. Over the past 20 years, the southern Rocky Mountain population, now listed as endangered in Colorado and in New Mexico (where none are known to remain), has sharply declined around the lakes, ponds, and streams where they were once common. In 1999, Colorado Division of Wildlife biologists, who had been monitoring their state's dwindling toads for a decade, found animals afflicted with the chytrid fungus for the first time, at a study site west of Denver.
Meanwhile, federal biologists are monitoring a decline in boreal toads living in the nearby Rocky Mountain National Park. "We've witnessed fairly precipitous declines at what have in the past been two of the most robust sites in the state," says U.S. Geological Survey (USGS) zoologist Erin Muths. "We didn't see declines in both sites until this year. These are spots in national parks, and they're considered back country—they're not polluted or over-used. We don't have an easy explanation for the decline," she says. "in fact, that's the million-dollar question. "
After the state biologists discovered chytrid fungus in their toads, Muths and her colleagues tested the park's toads, and detected the fungus too. In 1999, the biologists caught fewer than ten toads at one of the park sites where they had previously caught up to 200.
"My guess is that the decline of boreal toads in Rocky Mountain National Park is a combination of less obvious environmental stressors working in concert with this newly identified disease," says Muths.
She and her colleagues track the toads with tiny transponders the thickness of a pencil, hoping to learn more about the toads' habitat use and about other aspects of their life history. "We're going to keep on monitoring," says Muths. "It's important to see patterns over time. That's what's missing globally—identification of the long-term patterns."
ZooGoer 29(2) 2000. Copyright 2000 Friends of the National Zoo. All rights reserved.
