Threatened frogs making a comeback in Yosemite National Park
Federally threatened California red-legged frogs are showing signs of a return to Yosemite Valley in Yosemite National Park after a 50-year absence following their reintroduction as part of a collaborative effort by the National Park Service, Yosemite Conservancy, the San Francisco Zoo & Gardens, U.S. Fish & Wildlife Service, California Department of Fish & Wildlife and NatureBridge.
A new generation of red-legged frogs were discovered this spring in Yosemite Valley when National Park Service ecologists found eggs in ponds and meadows. This is the first documented breeding of red-legged frogs since the release of the species’ adult frogsbegan in 2017. It often takes years to see such a result, according to Yosemite National Park Superintendent Mike Reynolds.
“It’s unusual to find eggs in any location and to find them this soon is a strong indication that red-legged frogs are adapting successfully to the riparian areas where we reintroduced them,” said Reynolds. “This is a major milestone in our work to reestablish a species that contributes to a healthy park ecosystem.”
The red-legged frog had not been seen in Yosemite National Park in a half century. So far, the program, which began in 2016, has reintroduced an estimated 4,000 California red-legged frog eggs and tadpoles and 500 adult frogs. Last week, about 200 more adult frogs were released in Yosemite Valley and another 275 will be released in June. The adults were reared at a special San Francisco Zoo facility. For the first time, this summer 75 red-legged frogs will be fitted with radio transmitters to better understand their behavior and habitats to determine the best locations for future reintroductions.
“Despite Yosemite’s popularity, it is also an important wildlife sanctuary. Protecting vulnerable species like red-legged frogs maintains the park’s biodiversity as nature envisioned,” said Yosemite Conservancy President Frank Dean. “Sustained results on programs like this take patience and a multi-year commitment by donors, the park and partners.”
Over the past three years alone, Yosemite Conservancy donors contributed $570,000 to protect aquatic species in the park. The Conservancy provided $130,000 for Yosemite frog programs in 2019.
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. The release of adult frogs, as opposed to frog eggs or tadpoles, also significantly increases their chances of survival.
A permanent frog rearing facility, known as the San Francisco Zoological Society and Yosemite National Park Conservation and Recovery Facility, opened in 2016 in San Francisco. California red-legged frogs continue to be raised in a quarantined environment to accommodate the specific needs of the animals under the care of specialized staff.
“The program has been a great teaching tool and a scientific success,” said San Francisco Zoo & Gardens CEO and Executive Director Tanya Peterson. “We are honored to work hand-in-hand with the National Park Service, Yosemite Conservancy and federal and state agencies as partnerships like these help us achieve our conservation mission and ensure the environmental health of one of our world’s great natural treasures and the resurgence of a threatened species.”
“Each of the agencies involved played a critical role in the success of reestablishing the species in Yosemite Valley,” said, Jennifer Norris, Ph.D., field supervisor of the Sacramento U.S. Fish & Wildlife Office. “Species recovery is at the core of our mission and we’re looking forward to continued collaboration to ensure that the California red-legged frog thrives.”
This effort would not have been possible without the assistance of private land owner Diane Buchholz of Garden Valley, Calif., who allowed red-legged frog eggs to be collected from her property. NatureBridge, which provides hands-on environmental science programs for children and teens, has participated with the National Park Service in releasing frogs in Yosemite Valley.
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.