Mountain Yellow-Legged Frogs are loaded into a helicopter/Oakland Zoo

Call it "frog lift."

Tadpoles were emergency-airlifted from remote locations in Sequoia and Kings Canyon national parks, transported to Oakland Zoo and San Francisco Zoo to be cleared of disease, raised into frogs, immunized, and then released back into their natal lakes with hopes of restoring their dwindling populations in the wild.

The project is a partnership between the Oakland Zoo, San Francisco Zoo, Sequoia and Kings Canyon national parks, and the U.S. Fish and Wildlife Service. The goal is to recover endangered mountain yellow-legged frog populations in the wild.

Mountain yellow-legged frogs are threatened by non-native predators and disease (chytridiomycosis), which is caused by amphibian chytrid fungus and is responsible for the decline or extinction of more than 200 amphibian species worldwide. The mountain yellow-legged frog has been listed as endangered by the U.S. Fish and Wildlife Service since 2014.

The frogs that recently were released in the parks were raised from tadpoles in quarantine at both the Oakland Zoo and San Francisco Zoo, as part of a “head-start” program to increase their chance of survival in the wild. The program involves collecting diseased tadpoles from wild populations, clearing them of disease upon arrival at zoos, growing them into healthy juvenile frogs, and inoculating the frogs to boost their immune response to the fungus before reintroducing them to their population sites.

Park Service staff release mountain yellow-legged frogs into the wilderness/Oakland Zoo

Amphibian chytrid fungus has been present in Asia, South America, and Africa for approximately a century, but has spread to almost every continent in recent decades, likely due to the worldwide exportation of amphibians. 

Of the 215 healthy young frogs that were transported by helicopter and released into lakes in Sequoia and Kings Canyon national parks over the past two weeks, Oakland Zoo raised 99 of them and San Francisco Zoo raised 116 of them.

“Our collaboration with biologists and several government agencies has given us the opportunity to inoculate these frogs against the deadly disease that has already wiped out 90 percent of this species in the wild,” said Margaret Rousser, zoological manager at Oakland Zoo. “We are honored to be able to make a real difference in the conservation of this species.”

The release indicates the success of the program, now in its third year and ongoing. The program looks to continue and succeed as other groups of tadpoles are salvaged and brought to zoos for more head-starting.

“This partnership has been critical to the recovery of the mountain yellow-legged frog,” said Sacramento Fish and Wildlife Office Field Supervisor Jennifer Norris, Ph.D. “We’ve been able to maximize the expertise of each partner to successfully recover and relocate over 400 frogs over the past couple years alone.”

“These frog reintroductions are the result of close collaboration and effort by many partners,” added Danny Boiano, aquatic ecologist at Sequoia and Kings Canyon national parks. “However, the expertise provided by the zoos has been instrumental to the success of being able to return so many frogs to the wild.”

The move to immunize the frogs is something new, according to Jessie Bushell, Director of Conservation at the San Francisco Zoo.

“Just like vaccinating people, we are jump-starting their disease fighting immune systems. When released, these frogs will be better able to fight future chytrid infections. It might seem like a lot to go through, but letting populations completely die out is not a good option.”