From the Brink of Extinction: Oakland Zoo Releases Critically Endangered Frogs into the Wild

Aug 2, 2016>
Oakland, CA –Oakland Zoo, along with the National Forestry Service and US and CA Fish and Wildlife Service, has released 53 critically endangered mountain yellow-legged frogs into lakes in Sequoia and Kings Canyon National Parks in the high Sierras following a severe population die-off last summer. The precious cargo, emergency evacuated as tadpoles last summer, was again airlifted back into their natal lakes as healthy adult frogs in hopes of restoring their population in the region.

The frogs, victim to non-native predators and the deadly chytrid fungus, were raised at the Zoo in quarantine from tadpoles as part of a "head-start" program. The program involves growing the tadpoles into healthy juveniles and inoculating them to boost their immune response to a deadly fungal disease called chytridiomycosis (chytrid). The highly infectious Batrachochytrium dendrobatidis fungus has caused more than one third of the world's amphibian species become extinct within the last fifteen years.

Oakland Zoo Zoological Manager, Margaret Rousser, made the four-hour drive to meet the helicopter in Three Rivers, California where the frogs raised at Oakland Zoo were flown and then trekked 15 miles over 12,000' passes before being released into the waters. "It's absolutely heartbreaking how many amphibians have succumbed to chytridiomycosis. These are species that we will never be able to bring back. We are, however honored to be trusted with such important work by the biologists and governmental agencies in charge. We take our responsibility to the natural world and our environment very seriously," said Margaret Rousser, Zoological Manager at Oakland Zoo.>
The release marks the success of the program, now in its second year and ongoing, and on August 10 another 'tadpole evacuation' will be conducted in the Big Pine area of Inyo National Forest. After collection, the tadpoles will be hiked down to the base of the mountain by environmental scientists from CA Department of Fish and Wildlife and handed off to Zoo staff to be transported to Oakland Zoo where they will be raised, treated for chytrid by zookeepers, grown to a healthy size, inoculated, and then returned to their natal lakes in 1-2 years.

The rapid and severe decline of the Northern Distinct Population Segment of mountain yellow-legged frogs led the US Fish and Wildlife Service to list them for protection under the Endangered Species Act in 2014.

The conservation collaboration between the National Park Service, the US and CA Fish and Wildlife Service, and Oakland Zoo is helping to save a native California species and give it legs to thrive and repopulate in the wild. Seeing flourishing frogs in healthy habitats is the ultimate goal of the rescue for recovery, so future generations are able to see and experience these animals first-hand, rather than reading about their demise in textbooks.


The mountain yellow-legged frog complex in the Sierra Nevada is comprised of two species (Rana muscosa and Rana sierrae) that inhabit high elevation aquatic habitats. Although historically abundant, these frogs have been extirpated from more than 92 percent of their geographic ranges, with many of the remaining populations depleted. Declines were first recognized during the 1970s and have accelerated markedly since the 1990s. The realization that these patterns would rapidly place these species at risk of extinction led to Endangered listings for both species under the U.S. Endangered Species Act. Mountain yellow-legged frogs in the Sierra Nevada occur between the headwaters of the Feather River and the headwaters of the Kern River. Rana sierrae occupies the northern and central Sierra Nevada south to the vicinity of Mather Pass (Fresno County), whereas Rana muscosa occupies the Sierra Nevada south of this area.

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