Hundreds of Mountain Yellow-legged Frogs Leap Back Into the Wild
Birch Aquarium, San Diego Zoo Wildlife Alliance and other partners join forces to help save this endangered amphibian.
Photos and Videos: Alex Feltes, Birch Aquarium
More than 350 Mountain Yellow-legged Frogs have been reintroduced into the wild in Southern California’s San Bernardino Mountains, marking one of the largest releases to date and a significant step in efforts to save this endangered species. The release also represents a milestone for Birch Aquarium at Scripps Institution of Oceanography at UC San Diego — the aquarium’s first-ever species reintroduction and a historic moment in its growing conservation work.
Birch Aquarium, in collaboration with San Diego Zoo Wildlife Alliance (SDZWA), UCLA, Big Bear Alpine Zoo and additional partners, released the frogs into a wildlife preserve managed by The Wildlands Conservancy. This effort is part of a long-running recovery program with partners at the U.S. Fish and Wildlife Service, the U.S. Geological Survey, the California Department of Fish and Wildlife and the U.S. Forest Service.
“It was an incredibly exciting and emotional day for our team, as releasing these frogs into the wild marks a historic first for Birch Aquarium,” said Sean Bruce, Assistant Curator of Fishes and Invertebrates. “We have been raising these frogs for more than a year, and to finally reach this milestone is truly remarkable!”
Of the released frogs, 220 were raised behind the scenes at Birch Aquarium, while the rest were raised at SDZWA and UCLA.
“This release was made possible by the extraordinary dedication of our Husbandry Team and the invaluable collaboration of our partner organizations in this recovery project. Our shared passion and expertise made this success possible, and we hope these frogs thrive here for many years to come,” said Bruce.
From Aquarium to Wild
Each organization carefully transported its frogs in coolers to the mountains. Upon arrival, the team hiked the frogs to three sites along a lake within a protected reserve. At the lake, the frogs were divided into two groups: one for hard release and the other for soft release.
The hard-release frogs were immediately introduced into the lake. The soft-release frogs were temporarily released into a specially designated habitat, where they were closely monitored over the next several days as they gradually acclimated to their new surroundings. This included daily health checks and feeding the frogs a variety of insects. They were then released into the same lake alongside the first group.
The frogs were released in two stages to evaluate which release method is most effective for supporting the long-term survival of Mountain Yellow-legged Frogs. Each frog is also microchipped with a Passive Integrated Transponder tag, allowing researchers to identify individuals during future surveys. This technology will enhance long-term monitoring and inform ongoing conservation efforts.
A Future For Frogs
Successful recovery depends on strong collaboration among partners. This release was especially exciting because it brought together one of the largest groups of people to work side-by-side on a single release of Mountain Yellow-legged Frogs.
It also marked the second introduction of these frogs to the lake within the wildlife preserve managed by The Wildlands Conservancy. More than 70 frogs were first released in 2023, and the recent August release — the largest to date — added even more to the area.
“Thanks to these efforts, Mountain Yellow-legged Frogs are hopping around Bluff Lake for the first time since they were last recorded here in 1951,” said Tim Krantz, Conservation Director for The Wildlands Conservancy.
Going forward, researchers will continue to monitor and track these endangered frogs at the release site multiple times each year, with the overarching goal of supporting the release of more frogs in the future.
The hope is that these efforts help downlist or delist Mountain Yellow-Legged Frogs as an endangered species by enhancing the genetic diversity of both captive and wild populations, optimizing reintroduction efforts, increasing wild frog populations and more!
About Birch Aquarium at Scripps
Birch Aquarium at Scripps is the public exploration center for Scripps Institution of Oceanography at UC San Diego. Perched on a bluff overlooking the Pacific Ocean, Birch Aquarium features the groundbreaking work of Scripps Oceanography and UC San Diego scientists as well as conservation breeding programs and interactive exhibits. Birch Aquarium’s mission is to connect understanding to protecting our ocean planet, which it achieves through engaging hands-on learning opportunities for more than 500,000 guests and 40,000-plus pre-K-12 students each year. Visit aquarium.ucsd.edu for more information.