Frogs Signal Earth-Watch Warning
Scientists study world's declining amphibian population as a key environmental indicator
BIOLOGIST Richard Wyman looks concerned as he stares out from a cabin porch at the Edmund Niles Huyck Preserve and Biological Research Station here. Within the nightly symphony of bullfrogs and peepers, he hears a warning signal."They [amphibians] are crying out," says Dr. Wyman, executive director of the Huyck Preserve. "In fact, they are more than crying out, they are screaming. It's time to listen to what they are saying." For 17 years he has watched frog, toad, and salamander populations decline in the northeastern United States. And worldwide, amphibian numbers are also on a mysterious downward slide. Some researchers say these water and woodland inhabitants are town criers warning of larger environmental problems: global warming, acid rain, and pollution. Frogs and other amphibians are "great indicators of what is going on in the ponds, forests, soil, and even the air, because they are very susceptible to changes in the environment," according to Wyman. Many amphibians are aquatic as well as terrestrial, and their thin skins absorb pollutants from both the soil and water. As adults, they sit at the top of their food chain [see diagram], where they ingest pollutants in concentrated quantities from their prey. Since they do not migrate much, they can signal problems of contamination in their region. "Amphibians are the canaries in the global coal mine of ecology," says George Rabb, director of the Brookfield Zoo in Chicago. (Canaries were used to warn of poison gases or lack of oxygen. If the canary died, miners knew they had to get out.) Last February, the World Conservation Union, which is headquartered in Switzerland, assigned one of its branches, the Species Survival Commission (SSC) in Chicago, to organize a task force to investigate the problem. The SSC includes 3,000 scientists worldwide and more than 100 specialized groups whose aim is to provide solutions for saving endangered species. From this request, the Declining Amphibian Population Task Force (DAP) was born. "This is a SWAT team response to the problem," says Dr. Rabb, also the chairman of the SSC. "Get in, find out what is going on, and get the information out as fast as possible." The task force, coordinated by James Vial of the University of Tulsa in Oklahoma, is an international organization of scientists who will monitor the amphibians in their region and gather data. "The whole world will be divided into working groups based on biodiversity [similar ecological conditions and habitat requirements]. There will be 13 work groups in the United States alone." Dr. Vial says. "The Panama-Costa Rica group is already up and running." Each work group is responsible for assessing the problem in its region, setting goals, and conducting experiments necessary to achieve them. The results will be entered into a worldwide network database, called the "Froglog," then analyzed by scientists. The Northeast US work group, headed by Wyman, is up and running, and the Huyck Preserve is acting as an outdoor frog laboratory. An 18-inch high aluminum amphibian trap forces frogs into buried paint cans where they are counted and released by research assistants, helping Wyman monitor the movements, types, and number of amphibians in the forest - a frog census. South of the trap, corners of white mesh bags filled with known amounts of tree litter poke through the forest floor and test the effects of acid rain on decomposition. Four similar stations are set up - one in each forest type on the preserve. The global decline of amphibians initially received serious attention in 1989 at the First World Congress of Herpetologists in Canterbury, England. "I went to the meeting expecting to hear the usual research papers," Wyman says. "What I heard instead was scientist after scientist standing up, noting declines, disappearances, and even extinctions of amphibians in their area." But the problem has been noticed by individual herpetologists much earlier. In 1973, a new amphibian species named the gastric brooding frog was discovered in a small area in the Australian rain forest. "It converts its stomach to a womb and gives birth through its mouth," says Michael Tyler, professor of zoology at the University of Adelaide, Australia. "This was so unusual that we did a lot of work on it. National Geographic even came down and filmed them. But by 1980, they had disappeared completely." "I was horrified by the extent of the decline," Dr. Tyler says. Another example is the Golden Toad of Costa Rica. Jay Savage, professor of biology at the University of Miami, Fla., discovered it in 1963, hidden in a remote region of the Monteverde Forest Preserve in Costa Rica. "This was a beautiful little toad," says Dr. Savage. "When I discovered them in 1963, there were thousands.... In 1988 there were none. I've been studying amphibians for 30 years in this region, and that's unusual no matter how you look at it." STEVEN TILLEY, a professor of biology at Smith College in Northhampton, Mass., says that while a few species are declining for unexplained reasons, the numbers are not great enough to convince him that the decline is an environmental warning signal. "This may only be a natural fluctuation," Dr. Tilley says. "Yes, a lot of species are declining, but because of loss of habitat, pollution, etc. This is nothing new. Very few [disappearances] are spooky ... and we just don't know enough to decide if it is natural or not." Reasons for their disappearance are not clear, though several theories are being studied, including global climate change, acidification of habitat due to acid rain, increase in ultraviolet (UV) radiation due to thinning of the ozone layer, and habitat fragmentation that occurs when an animal is restricted in its range because of habitat destruction. Tyler is not convinced that the decline in Australia is the result of any one of these theories alone. "It's not the greenhouse effect, because frogs in Australia do well in hot temperatures," he says. It's not acid rain, because there is virtually no acid rain here [in Australia]. And it's not UV because frogs are disappearing in rain forests, where there is a canopy over the amphibians and UV light can't get through. "It may be some holistic effect, and we are getting a combination of all of these," he says. Destruction of habitat, the most common reason for any species' decline, is not being extensively studied, however, because frogs and salamanders are disappearing from areas supposedly unaffected by habitat loss. HE work group in Australia, though not yet officially organized under the DAP task force, has already started gathering information in its region. In order to investigate the problem, Tyler sent out government-funded questionnaires to see if people had noticed a decline in the amphibian population. The response has been overwhelming. Hundreds of letters poured in from farmers with ponds that once echoed with a symphony of frogs but now are silent. "One lady in the outback, 80 years old, has been living in the same house since she was a child," Tyler says. "She wrote that when she was little, the frogs in her pond used to keep her awake at night. Now it's all quiet." The Australian state governments are even getting children involved. "The governments in Victoria and South Australia are organizing a 'Frog Watch' where children can go look for frogs or count tadpoles," Tyler says. Much of the international data today have been based only on anecdotal evidence - stories and citings from people. Amphibian populations have been heavily studied only within the last 20 to 25 years. So the decline could be a natural population fluctuation in nature, Wyman says. It is hard to compare recent findings with population numbers from 100 years ago and know if this decline is cyclic, because population records aren't that old. "This whole issue does have a certain Chicken Little attitude to it. The sky isn't falling - yet," Wyman says. "But it's happening worldwide so it would be silly not to pay attention to it [the decline]."