Monday August 11, 2025
SF Gate —
Dozens of rare amphibians boarded a helicopter from the Bay Area last week, unaware of the journey that was ahead: a 250-mile flight to their new home in a national park.
Yellow-legged frogs were once one of the most abundant animals in the alpine habitats of the Sierra Nevada. But for the past decade, the Oakland Zoo has been raising individuals from the now-endangered species and releasing them to the wild as a way to boost their numbers in the aftermath of a deadly disease that has decimated 90% of their population. Known as chytridiomycosis, or the chytrid fungus, the disease leads to “devastating effects” and has contributed to the greatest loss of biodiversity ever caused by a pathogen, the zoo said in a news release.
The fungus attacks the amphibians’ permeable skin and makes it difficult for them to breathe and regulate their salt and water intake, leading to lethargy, loss of appetite and eventual death. The disease is highly contagious and can wipe out populations in a matter of weeks.
But researchers at UC Santa Barbara have been working with the zoo to create an inoculation procedure — essentially a vaccine — against the fungus. For the latest release, zoo staff first collected the frogs as tadpoles in 2023 and took them into their recovery program, where the animals underwent anti-fungal chytrid treatments to protect them against the virus. The frogs were also pit-tagged — a process similar to microchipping a pet — so their whereabouts could be monitored by U.S. Fish and Wildlife staff once they were reintroduced to the wild. After getting swabbed for the disease one last time, they were transported to their final destination: Laurel Lake at Sequoia and Kings National Park.
Known for the distinctive golden hues on their bellies and the undersides of their limbs, yellow-legged frogs are a native species that grow no larger than the size of a golf ball, yet have a surprising range of ecological benefits. They help control insect populations, serve as prey to larger animals, and their skin is easily affected by environmental changes, helping researchers to identify and track broader changes in their habitats.
“Yellow-legged frogs once were a keystone species in high-elevation lakes, but chytrid and other factors reduced their populations significantly,” the zoo said in a news release.
Last week’s release was “a major milestone,” however, marking the thousandth frog the zoo has transported to the wild, Samantha Sammons, wildlife recovery program manager at the Oakland Zoo, said in the news release. The zoo said it plans to expand such efforts through biobanking frog genetics and developing new methods to breed the species for future releases conducted in partnership with Mountain Lakes Research Group and the National Park Service.
“We need to keep this movement going to continue helping native California wildlife and make sure that these frogs don’t disappear,” Sammons said.