62 Endangered San Francisco Garter Snakes Released in San Mateo County

Conservation teams released 62 endangered San Francisco garter snakes at sites in San Mateo County this fall, the first release from a program that raises the snakes at the San Francisco Zoo before returning them to the wild. The zoo announced the milestone on Nov. 10. Biologists will monitor the release sites to see how the snakes fare.

The project began with pregnant snakes that U.S. Geological Survey biologists collected from a healthy wild population in 2025. The females gave birth at the zoo and were returned to the wild. Zoo staff raised the young so they could grow larger before encountering predators in the wild.

Teams used genetic testing to help decide where to release the young snakes. About a third went back to the area their mothers came from. The rest went to other populations where the project aimed to increase both numbers and genetic diversity. The partners include the Midpeninsula Regional Open Space District and state and federal wildlife agencies.

The zoo says more than 130 additional snakes were born there in 2026 and are being raised for another release planned for 2027. That group is separate from the 62 snakes already released. Monitoring this fall’s release will help guide the next round.

Why This Matters for Animals

The San Francisco garter snake lives only on the San Francisco Peninsula and into northern Santa Cruz County. It needs freshwater habitat, where it hunts frogs and other prey, and nearby upland areas for cover and shelter. The U.S. Fish and Wildlife Service says development has fragmented the snake’s remaining populations. Drought, declining prey and illegal collection also threaten it.

The release puts young snakes into several wild populations. It is too early to know how many will survive and reproduce. Those outcomes will help biologists judge whether raising young snakes at the zoo can strengthen wild populations over time. The accompanying AI-generated illustration shows a fictional snake at an imagined wetland.

Source: San Francisco Zoo & Gardens — November 10 release announcement