San Diego – October 06, 2026 -- San Diego Zoo Wildlife Alliance has established a third reintroduced population of endangered Pacific pocket mice at North San Mateo, a training area within Marine Corps Base Camp Pendleton.
The milestone marks 20 years since the Alliance launched its Pacific Pocket Mouse Conservation Program in 2006. Since then, the organization has released more than 500 Pacific pocket mice into new and existing populations across the species' native range in Southern California.
The mouse weighs about as much as three pennies
The Pacific pocket mouse is the smallest and one of the most endangered mammals in North America, roughly the size of a human thumb. Once believed extinct, it was rediscovered in 1993 when a small remnant population turned up in Orange County, prompting an emergency listing under the federal Endangered Species Act. Only three original wild populations survive today.
Reintroduced mice act as ecosystem engineers
Debra Shier, Brown Endowed Associate Director of Recovery Ecology at San Diego Zoo Wildlife Alliance, said establishing the Camp Pendleton population is a key step toward recovery. She noted that the mice's burrowing improves soil hydrology and nutrient cycling while creating shelter used by other species.
Breeding program began adding genetically diverse mice in 2012
In 2012, the conservation program added a captive breeding effort to produce genetically diverse, behaviorally competent mice for release into native habitat. The first reintroduced population was established at Laguna Coast Wilderness Park in Orange County in 2016, followed by a second population at Camp Pendleton in 2024.
Five organizations share the recovery effort
The program is a partnership among San Diego Zoo Wildlife Alliance, the U.S. Fish and Wildlife Service, the California Department of Fish and Wildlife, the U.S. Geological Survey, and Marine Corps Base Camp Pendleton. The groups work together on habitat protection, population growth, and scientific research to support the species' long-term survival.