The Sierra Nevada yellow-legged frog (Rana sierrae) is declining in numbers, in large part due to its habit of site fidelity — the tendency to return to and use previously occupied habitats. A report, published this year in the Canadian Journal of Fisheries and Aquatic Sciences, tracked the frogs over a 10-year period and determined that R. sierrae is more than 80 percent likely to return to previously used bodies of water to breed and overwinter.
Sierra Nevada yellow-legged frogs are endemic to the Sierra Nevada and other ranges of California and Nevada, and it's estimated that about 90 percent of its historic habitat has been eliminated. Surveyors report that R. sierrae has been reduced to tiny, widely scattered groups in the wild.
The Canadian Journal researchers followed the site fidelity habits of 1,250 Sierra Nevada yellow-legged frogs in Kings Canyon National Park, Calif., from 1997 to 2006. There they saw the evidence that R. sierrae habitat has been severely damaged by the introduction of nonnative trout into water bodies, pesticide drift from Central California and the drying effects of climate change. The trout prey on R. sierrae, whose habitat has historically been fishless. Tadpoles require three to four years of overwintering, meaning that if a lake dries up or is overrun with trout, several years' worth of tadpoles die.
Site fidelity is seen in many animals and can offer numerous benefits. Animals become familiar with a specific area's prey, predators and unique features, and they learn how to return each year, leading to higher rates of survival and reproductive success. In the face of habitat loss and deterioration, however, it can be a danger. The Sierra Nevada yellow-legged frog does not have a terrestrial phase and its propensity to return to bodies of water that no longer support it could hasten its decline.
Restoration projects that include removing trout from lakes have been started in Kings Canyon and in other areas that the frogs return to year after year. Researchers emphasize that those launching restoration efforts must keep site fidelity in mind.