After 10 years of work, Yosemite marks return of California red‑legged frog with 10,000th release
Yosemite National Park marked a major conservation milestone with the reintroduction of the federally threatened California red‑legged frog after a decade of work, releasing its 10,000th frog and restoring multiple generations after a 50‑year absence.
Key takeaways
- 10,000th release: The program symbolically released its 10,000th frog, nicknamed “Twain,” on May 7 in Yosemite Valley (CDFW, NPS).
- Multi‑agency effort: Recovery was led by the National Park Service with partners including the U.S. Fish and Wildlife Service, California Department of Fish and Wildlife, Yosemite Conservancy and San Francisco Zoo & Gardens.
- Methods: Actions included invasive bullfrog removal, habitat restoration under the Merced River Plan, and captive rearing of frogs from wild eggs to 1‑ and 2‑year juveniles.
- Ongoing work: Roughly 830 juveniles released so far this year and about 600 eggs are being reared for future releases (NPS).
Main content
Background: how a native frog vanished and why it matters
The California red‑legged frog (Rana draytonii) is the largest native frog in the western United States. Once found across parts of California, it vanished from Yosemite Valley around the 1970s and had been absent for roughly 50 years. Invasive American bullfrogs introduced to the park were the main driver of the decline, preying on or outcompeting native frogs. Elevated raccoon numbers—tied to decades of open refuse sites in and near the park—also increased predation on eggs and juveniles. Removing those threats was critical to recovery. (See the CDFW news release for details.)
Rob Grasso, aquatic ecologist at Yosemite National Park: “After invasive bullfrogs eliminated red‑legged frogs from the area decades ago, we removed those threats and created conditions for recovery. Today, multiple generations of frogs are established in Yosemite Valley.”
Partners and methods: a decade of coordinated work
Collaboration: The recovery effort is a multi‑agency collaboration. The National Park Service led onsite work in Yosemite, coordinating invasive species control and habitat restoration. The U.S. Fish and Wildlife Service provided oversight and support; Sacramento field office acting supervisor Kim Turner praised cross‑agency cooperation and emphasized partner roles.
Funding and restoration: The California Department of Fish and Wildlife helped secure grants and funding for habitat restoration projects approved by California voters. Laura Patterson, CDFW’s amphibian and reptile conservation coordinator, noted that these grants were key to restoring wetlands and stream banks needed for frog survival.
Support from nonprofits and zoos: Yosemite Conservancy supplied donor funding for research and restoration. The San Francisco Zoo & Gardens and the San Francisco Zoological Society operate a dedicated rearing facility opened in 2016 that raises frogs from wild‑collected eggs to juveniles for release.
Rearing facility and releases: building frog generations
The rearing facility in San Francisco began operations in 2016 as a partnership between the National Park Service and the San Francisco Zoological Society. Staff collect eggs from nearby wild populations and rear them to one‑ and two‑year‑old juveniles in controlled conditions, improving survival odds after release while park habitats recover.
Dr. Rochelle Stiles, director of field conservation at the San Francisco Zoo: “When the program began in 2016, no California red‑legged frogs remained in Yosemite Valley. Today, every frog in the valley traces back to this effort.”
Production and scheduling: The program has released roughly 830 juveniles so far this year and is rearing about 600 eggs for future releases (NPS). Raising frogs to larger juvenile stages before release increases post‑release survival while invasive predators and habitat conditions are managed.
Event in Yosemite Valley: the 10,000th frog and community outreach
On May 7 partners and visitors gathered near Yosemite Falls for remarks and the symbolic release of several zoo‑reared frogs, including the program’s 10,000th frog, nicknamed Twain. The ceremony featured agency remarks and local elementary students participating in outreach that connects youth to conservation work.
Video coverage and reporting of the ceremony are available from local outlets: ABC30 and a short video from CBS47/YourCentralValley. A YouTube short also captured moments from the release: YouTube short. The National Park Service posted event details online (NPS event details).
Challenges faced and lessons learned
The recovery was not a quick fix. Park staff spent decades removing invasive bullfrogs and managing raccoon pressures. Habitat work tied to the Merced River Plan restored wetlands, streambanks and connected river systems that frogs need for breeding and juvenile refuge. Those habitat improvements, funded in part by CDFW grants, helped ensure that released frogs could survive and reproduce.
Scientific innovation: Yosemite aquatic wildlife biologists, in partnership with UC Santa Barbara and zoo partners, developed rearing and release techniques that strengthened survival outcomes. Despite droughts, severe winters and floods, multiple generations are now established — a sign that combined strategies of invasive removal, habitat restoration and captive rearing can work.
Sources and media coverage
Public information and reporting on the program and milestone include the CDFW news release, the National Park Service event details, local coverage from ABC30 and video from CBS47/YourCentralValley and a YouTube short.
Implications for San Diego, California
Funding and policy: Yosemite’s success shows how voter‑approved state funding and interagency grants (via CDFW and partners) can deliver measurable habitat restoration outcomes. San Diego agencies that rely on CDFW grants may view this as a model to fund targeted restoration and invasive control.
Regional ecology and recovery playbook: Threats in San Diego—including invasive species, urban runoff and fragmentation—mirror drivers elsewhere. The Yosemite model suggests a playbook: remove invasive predators, restore wetlands and stream habitat, and use captive rearing when wild populations are too small to recover unaided.
Public engagement and visitor management: Yosemite’s outreach—schoolchildren involvement and public ceremonies—helped build community support. San Diego parks, nature centers and zoos can adapt similar strategies, along with improved refuse control to reduce raccoon attraction and targeted visitor education to protect sensitive habitats.
Research and collaboration: The rearing facility model and data showing resilience through droughts and floods offer research opportunities for San Diego institutions. Partnerships among zoos, universities and agencies can expand captive rearing, monitoring and post‑release survival studies across the state.
For more information
Read the CDFW news release, view NPS event details, and see local coverage from ABC30 and CBS47/YourCentralValley.
