California Red-Legged Frog

A California red-legged frog after just being released in Cook's Meadows on May 3, 2019.

Al Golub

 

The California red-legged frog was made famous by Mark Twain in his story the “Celebrated Jumping Frog of Calaveras Country.” It is 2-5 inches long and is the largest native frog in the western United States. It is reddish in color on the underside of the legs and belly, and communicates with a series of short soft grunts. It is found in ponds, pools and streams and wet meadows.

But for fifty years, the California red-legged frog was absent from Yosemite National Park. The disappearance of the red-legged frog from Yosemite is the result of a variety of decisions made over nearly a century. The introduction of non-native, highly invasive and predatory American bullfrogs is the most definitive cause of the red-legged frog decline. Artificially high populations of raccoons, which are predators of frogs, resulted from open refuse sites in the 1970s and severely impacted populations. Over decades, those conditions were reversed. The health of the Yosemite Valley ecosystem improved with a variety of efforts that increased the frog’s chances of survival. The invasive bullfrogs have been eradicated, open refuse sites closed, and naturally occurring river and stream bank habitat restored to allow for a successful reintroduction of the native frogs.

With these improved conditions, a collaborative effort was inititiated in 2016. So far, the program has reintroduced an estimated 4,000 California red-legged frog eggs and tadpoles and 700 adult frogs with future release dates set.The adults were reared at a special San Francisco Zoo facility. For the first time, during the summer of 2019, 75 red-legged frogs were fitted with radio transmitters to better understand their behavior and habitats to determine the best locations for future reintroductions. The release of adult frogs, as opposed to frog eggs or tadpoles, also significantly increases their chances of survival.

A new generation of red-legged frogs were discovered in spring 2019 in Yosemite Valley when park ecologists found eggs in ponds and meadows. This was the first documented breeding of red-legged frogs since the release of the species’ adult frogs began in 2017. It often takes years to see such a result. This important milesone shows great potential for this frog species to thrive in the park.