Endangered Mountain Yellow-legged Frogs Reintroduced

Large Group of Endangered Mountain Yellow-legged Frogs Reintroduced in the San Bernardino Mountains

More than 100 local mountain yellow-legged frogs (MYLF) will be making the San Bernardino Mountains their home after San Diego Zoo Global and the U.S. Geological Survey (USGS) reintroduced the large group into the mountainous habitat—increasing the wild population of an endangered species that, in some areas, is on the brink of being extirpated.

This release is part of a captive breeding program started by San Diego Zoo Global in partnership with the U.S. Fish and Wildlife Service, USGS, the California Department of Fish and Wildlife, San Bernardino National Forest, and other zoological institutions, including the Oakland Zoo and the Los Angeles Zoo. The program, now in its 10th year, began when scientists from USGS rescued 80 tadpoles from a drying creek bed in the San Jacinto Mountains and brought them to the San Diego Zoo Institute for Conservation Research. Since then, thousands of frogs have been bred and released back into the region, with almost 1,200 released in 2016.

“Our goal is to enhance the remaining wild population with captive-bred frogs and manage an efficient reintroduction program,” said Natalie Calatayud, Ph.D., a postdoctoral associate in reproductive physiology at the San Diego Zoo Institute for Conservation Research. “After reintroduction, we monitor release success, growth, health and survival of particular individuals, giving us a better understanding of their life in the wild. Our captive MYLF breeding program will continue to supplement the wild populations in the region.”

Approximately 41 percent of amphibian species are at risk of extinction, making them the world’s most threatened taxonomic group. The MYLF is just one of many amphibians in peril, and like others, it is essential for maintaining the natural balance of the ecosystem in which it lives.

Over the past 40 years, this frog’s population steadily declined due to multiple factors, including habitat loss, drought, introduced predators (trout), pollution and the deadly amphibian disease chytridiomycosis, caused by the chytrid fungus. Their numbers fell so dramatically that the mountain yellow-legged frog was listed as “endangered” under the Endangered Species Act and on the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. One population of the species in City Creek was at critically low levels at the time of listing and may currently be extirpated.

However, as evidence of the breeding program’s success continues to grow, researchers have begun “headstarting” tadpoles from the City Creek population, with a plan to reintroduce individuals to that area next year (2017). When that happens, these released froglets will be the first group to be returned to an area where their population once flourished.