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Editors: For a link to reproducible pictures and to other amphibian releases, please go to http://www.usgs.gov/amphibians.html
Even as the Chiricahua leopard frog has disappeared from 80 percent of its former habitat, scientists, resource managers, ranchers, volunteer naturalists and even teachers and schoolchildren are striving to discover what is killing this frog and to sustain its populations in southeast Arizona until answers are found.
For the first time, however, new research is linking chytrid fungus - which has been implicated as a probable cause of major amphibian die-offs in pristine areas around the globe - as a factor in the declines of some of the state’s frog populations, according to recent studies by researchers with the U.S. Geological Survey, the U.S. Fish and Wildlife Service, Arizona Game and Fish Department, and the University of Arizona. These die-offs of amphibians in the Southwest and around the globe are of great concern because amphibians are good barometers of significant environmental changes that may go initially undetected by humans.
"Childhood memories of the frogs we put in our pockets and carried around are linked to our early awareness of the natural world. Will this generation of schoolchildren be the last to have such associations?" asked Cecil Schwalbe, a research scientist of the USGS Western Ecological Research Center in Tucson, Ariz.
Since the 1970’s all seven native true frog species in Arizona have declined to some degree - and some precipitously. Introduction of non-native predators or competitors -fishes, bullfrogs and crayfishes - has been the single most important factor in recent declines of native frog populations in the Southwest, said Schwalbe. Previous loss and degradation of wetland habitat have also affected many populations, but recent studies implicate chytrid fungus as a player in the declines as well.
"We have learned to exclude bullfrogs from ponds used by the native leopard frogs, but we are still trying to understand all of the factors that are causing leopard frog declines," Schwalbe said. Researchers are examining the roles of chytrid fungus disease and air quality, but note that at the same time, viable populations of leopard frogs will need to be maintained through conservation efforts until the causes of decline are understood and can be fully addressed.
Mike Sredl, a herpetologist with the Arizona Game and Fish Department, noted that the Chiricahua leopard frog is gone from 80 percent of its historical localities in southeastern and central Arizona and southwestern and west-central New Mexico. According to Jim Rorabaugh, a U.S. Fish and Wildlife Service biologist, the frog is found now at only about 79 wetland sites.
From 1993 to 1996, researchers from the USGS, the USFWS, AGFD, and the University of Arizona conducted intense conservation efforts in extreme southeastern Arizona on San Bernardino National Wildlife Refuge, at Douglas High School in the nearby town of Douglas, Ariz., and on the Magoffin Ranch, near the refuge. They introduced leopard frogs to new sites where bullfrogs - which are voracious predators on the leopard frogs - were absent. Leopard frogs increased in number exponentially, but in 1997, a rapid, mysterious and alarming die-off of leopard frogs occurred at some of the sites, Schwalbe said.
"We knew then that non-native species were not the only cause of leopard frog decline," said Phil Rosen, the University of Arizona researcher who found that some of the dying and dead frogs at the study sites had a chytrid fungal skin infection that was identified microscopically by Greg Bradley, a veterinary pathologist at the university’s Veterinary Diagnostic Laboratory. This was the first report of deaths in wild amphibians in the United States that was associated with the chytrid fungus disease.
Chytrid fungus in amphibians was first identified in 1998 by an international team of scientists from Australia, the United States and Great Britain. This team, which included D. Earl Green, a USGS wildlife pathologist, discovered that the fungus had most likely been responsible for large amphibian die-offs in pristine areas of Panama and Australia. It also was a factor and probable cause of recent die-offs in remaining populations of the endangered boreal toad in the southern Rocky Mountains this year. The disease is now being studied in detail to understand its origin, incidence, distribution and control methods. Researchers at the USGS, Arizona Game and Fish Department and Arizona’s universities, as well as other interested naturalists, are collaborating in field and laboratory studies of this disease in southwestern frogs, Rosen said.
"This disease, added to past habitat desiccation and ongoing non-native species problems, may wreak havoc with a number of frog species, especially the Chiricahua leopard frog," Rosen said. "Another question is whether pollution or some other stressor aids the disease’s impacts."
Air quality, possibly in conjunction with disease, may have been involved in the disappearance of the Tarahumara frog from its last known locality in the United States in 1983, said Schwalbe. All declining populations of this former Arizona frog were downwind of a copper smelter that produced acid rain and heavy metal deposition in the areas of frog decline. At the same time, populations of the Chiricahua leopard frog also declined or disappeared at the same localities, Schwalbe said. The discovery in October 1999 of chytrid fungus in live Tarahumara frogs from northern Mexico, said Schwalbe, does implicate disease as a likely factor in those declines. The relationship among air and water quality, disease and declines in frog populations needs further study, he added.
USFWS scientists are monitoring air quality at San Bernardino National Wildlife Refuge near Douglas, Ariz., and Buenos Aires National Wildlife Refuge west of Tucson. National Park Service resource managers at Chiricahua National Monument and Organ Pipe Cactus National Monument, will provide additional sources of air quality information.
"Episodes of frog die-offs at San Bernardino National Wildlife Refuge appear correlated with low-pressure meteorological inversions that trap smelter emissions in the valleys," said Tony Velasco, a USFWS scientist. In this phase of the study, researchers will analyze dead frogs and compare tissue contaminant levels with air quality information obtained near the time of death, said Velasco.
While the air quality studies are being conducted, Rosen and Schwalbe are implementing research and management plans to re-establish leopard frogs in wetlands at Buenos Aires National Wildlife Refuge with funding from Arizona Water Protection Fund and USFWS, and assistance from wildlife refuge staff. The plans entail eliminating bullfrogs from portions of the refuge and moving leopard frog eggs, tadpoles or small frogs to new sites in the area, said Schwalbe. Livestock tanks will be used to re-establish leopard frogs on the refuge. The techniques from this study will be available to ranchers, such as those in the Malpai Borderlands Group, who are already working successfully to preserve amphibians and other wildlife on their lands.
"This may prove our most effective management tool for conserving pond-dwelling leopard frogs and other closely related species through their current crisis in the American West. We’ll evaluate the success of our efforts by the spread of leopard frogs to sites where we did not introduce them," Schwalbe said.
