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What happened to the frogs? 1950s research highlights precipitous decline of Yellowstone Park's amphibians By MICHAEL MILSTEIN Gazette Wyoming Bureau YELLOWSTONE NATIONAL PARK - Spotted frogs were so numerous when Frederick Turner worked as a ranger-naturalist at Yellowstone's Fishing Bridge from 1953 to 1955 that he captured almost 1,700 of the small amphibians for research that would lead to his doctorate.
 Gazette photo by Bob Zellar "Forty years ago, these things were quite common and easy to find," he said. But when Turner revisited his former study site in 1991 at the request of researchers from Idaho State University, he could hardly believe what he saw - or didn't see. Frogs, he realized immediately, were scarce. "I was ultimately stunned by the magnitude of the changes," he said. "I was vastly disappointed and very sad." New research at Turner's site near the park's Lake Village complex has since confirmed what Turner saw - that frog populations there have declined by anywhere from four to 10 times, depending on which figures scientists compare. The reasons behind the declines remain unclear, although development has played some part. And there are signs that frogs and toads have also declined elsewhere in the Yellowstone region, mirroring worldwide trends, although there's less information to substantiate those more widespread dropoffs. "They could be missing in some places or many places, but there's just no historic information to tell us where they used to be," said Debra Patla, who conducted the recent research while in graduate school at Idaho State. The one place where there is good historical information is at the Lake area, where from 1953 to 1955 Turner, then a graduate student at University of California-Berkeley, documented the local numbers and habits of what are now known as Columbia spotted frogs living within 70 acres around Lodge Creek. He found that the frogs hibernated along the creek in winter and then migrated in May and June to lay eggs in three pools, where eggs hatched into tadpoles two to three weeks later and, in about 60 days, turned into frogs. Because the frogs lived within a clearly defined area, Turner said, "it was a made-to-order study situation." Probably because of the short summers in Yellowstone, the frogs matured slowly, reaching breeding age after four to six years and living as long as 13 years, Turner concluded. Females grew as large as three inches from head to tail, while males grew to about 2.5 inches. Turner captured nearly 1,700 different frogs during his study, marking them by clipping certain toes, and recaptured 900 at least once. Some frogs traveled as far as 2,000 feet in the course of a summer and Turner mapped home ranges for 86 frogs that ranged in size from 2,500 to 36,000 square feet (a football field covers 48,000 square feet). He estimated the total spotted frog population at between 1,200 to 1,850 frogs. Female spotted frogs lay a single clutch of 200 to 800 eggs every two to three years, so the number of egg clutches each year represents the number of female frogs breeding that year. During the 1950s, Turner counted from 50 to 62 egg clutches in his study area. When Turner returned to the area in 1991, he found far fewer frogs. And without the perspective his historical records provided, researchers working in the park today might not have known anything was amiss, raising the alarming notion that amphibian numbers may also have declined elsewhere in Yellowstone and the region without anyone noticing. "If we hadn't had that data, we would have thought everything was OK," said Charles Peterson, a professor of zoology at Idaho State who supervised Patla's work. "It looked like a great site to us, but it's really a ghost of what it once was." Beginning in 1993, Patla began retracing Turner's steps and repeating his research to compare the spotted frogs today with those of Turner's time and to try to find out where all the frogs had gone. They called on modern tools that Turner never had available, such as tiny radio transmitters that Patla attached to about 15 frogs in 1993 to track them and computerized maps that allowed the researchers to outline the frogs' movements in detail. Frogs sometimes lingered in a small area for few days and then took off, traveling 100 meters over two to three days. A few frogs roamed much farther, traveling as much as a full kilometer over the course of a summer. After three years of work, Patla and Peterson concluded that the overall frog population had dropped to about 225 to 400 frogs, less than a quarter of the numbers Turner saw, and in 1995 they counted just four egg clutches, less than a tenth of the 62 clutches Turner documented 40 years earlier. Based on the number of egg clutches in the 1990s, there were probably no more than about 25 reproducing female frogs in the study area, they said. From 1995 to 1997, they found almost no juvenile frogs, suggesting that reproduction was poor to nonexistent. Frog numbers rebounded slightly during the wet and warm summer of 1997 after park officials fenced horses away from one of the pools that served as a nursery for young frogs, but it's unlikely the population will ever recover to anywhere near the numbers of the 1950s, Patla said. Changes in human use of the area probably drove the changes in the frog population, the researchers found. In the 1970s, park officials had rerouted the main park road away from Yellowstone Lake and directly through the route the frogs had followed from their hibernating sites along Lodge Creek to their breeding pools. And a new pumping system drew water out of a spring at the headwaters of Lodge Creek, eliminating a breeding pond, shrinking the frogs' habitat and reducing the stream's flow enough to strand hibernating frogs and expose them to freezing during the winter. Laws requiring environmental review of such projects were not in place at the time and park officials apparently never weighed the potential impacts on the frog population. Yellowstone managers may not have even known much about the frogs: Turner said they never contacted him during planning for the work. The frogs adapted to the development by retreating to a portion of their former habitat and not traveling as much. "The way the frogs use that area has really changed," Patla said. "They're all clumped up in one corner now." She said other factors could have also played a part. "We know humans have changed things, but they've changed things in so many ways," Patla said. "There may be some effects we haven't even recognized yet." Some similar combination of factors - habitat loss, thinning of the ozone layer, exotic predators, climate changes, pesticides and more - may be responsible for the decline of amphibians worldwide, biologists believe. The mystery surrounding it all reflects a general lack of knowledge about amphibian populations, the same lack of knowledge that bedevils work in Yellowstone. "Most people don't even know those animals are there - and this is a big, well-known national park," Peterson said. Based on Turner's notes, Patla and Peterson concluded that populations of at least two of Yellowstone's other amphibian residents - chorus frogs and boreal toads - had declined around Lake Village, too. Although they found only scattered reports of the historical abundance of park amphibians in general, they believe boreal toads have probably declined throughout the park. Other biologists believe boreal toad populations have also declined in Colorado and southern Wyoming, making them candidates for listing under the Endangered Species Act. Boreal toads in Yellowstone seem to prefer breeding in streams warmed slightly by hot springs, but researchers still are not sure why, Peterson said. There are also historical reports of leopard frogs in nearby Grand Teton National Park, but none are known in the park today. "It's very difficult to draw any broad conclusions about what's happening out there," Peterson said. "You need case studies, in depth, and you need to know what existed before - that's the only way to figure out what's really going on."
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