Yosemite had lost its red-legged frogs; in 2016, teams began restoring the population, and 10 years later, the program reached 10,000 releases as recovery continues

Yosemite is known for granite rock faces, towering waterfalls, and dramatic sunsets, not frogs. But after a decade-long collaboration between multiple parties, a federally threatened frog species that had been missing from the park for decades is now back, according to the California Department of Fish and Wildlife.

Sometimes we can overlook positive news, but this is an amazing example of how wildlife can be brought back. While this may not sound exciting, it can involve a lot of patience and hard work. This is a behind-the-scenes look. The star of this story is the California red-legged frog. It is the largest frog native to the west of the US at two to five inches in size and became famous nationally thanks to a story by Mark Twain titled “The Celebrated Jumping Frog of Calaveras County.”

Ten thousand frogs later


A symbolic release marked the program’s 10,000th frog, nicknamed “Twain,” in Yosemite Valley, as per the California Department of Fish and Wildlife. The National Park Service led this effort with support from the U.S. Fish and Wildlife Service, the state wildlife department, Yosemite Conservancy, and San Francisco Zoo & Gardens. There were no California red-legged frogs in Yosemite Valley when the program began in 2016. All frogs currently in Yosemite Valley stem from this effort, according to the zoo’s Field Conservation Director.

Why the frog disappeared

The disappearance of the frog from Yosemite wasn’t due to one event and was due to many decisions over the past century. Research by the National Park Service points most consistently to the introduction of non-native American bullfrogs as the primary driver. Artificially high numbers of raccoons were also a problem due to open rubbish sites in the 1970s.

A 1999 study titled “Effects of introduced mosquitofish and bullfrogs on the threatened California red-legged frog,” by Sharon Lawler et al., published in the journal Conservation Biology, showed that in ponds with both bullfrog and red-legged frog tadpoles, less than 5% of red-legged frog tadpoles survived compared to 34% in ponds without bullfrogs. Researchers ran this experiment in controlled test ponds, and found mosquitofish weren’t a significant factor.

Frog nursery in San Francisco

A specialist nursery opened in San Francisco in 2016 through a partnership between the National Park Service and San Francisco Zoological Society. Frogs are raised from wild-caught eggs (collected with permission from a private landowner in Garden Valley, California), into one- and two-year-old frogs. Releasing them at this older stage, rather than as tadpoles, gives them a much higher chance of survival, according to the National Park Service.

Positive signs and what’s next

In spring 2019, ecologists in the park found frog eggs in ponds and meadows. This marked the first documented breeding since adult frogs were released in 2017. Milestones like this can take many years to reach. Now multiple generations of frogs have become established in the valley, as noted by the California Department of Fish and Wildlife, quoting Yosemite’s aquatic ecologist. The population has survived droughts, harsh winters, and flooding, according to the zoo.

This year, the zoo released roughly 830 juvenile frogs into Yosemite and is now raising about 600 eggs for future rounds. The species remains federally threatened. It is continuing the work alongside the National Park Service, ten years and 10,000 frogs into one of the park’s quieter conservation success stories.