Once Thought Extinct, Pacific Pocket Mouse Reintroduced to SoCal's Coastal Canyons
With its cheecks full of seeds, one of the captive bred Pacific pocket mice in the San Diego Zoo breeding facility. Credit: San Diego Zoo
For more than 20 years, the Pacific pocket mouse was thought to be extinct from the marine terraces of the southern California coast.
It was surprising then, when in 1993, the first mice were found at the Dana Point Headlands in Orange County.
Will Miller, biomonitor at the Calsbad Fish and Wildlife
Office, monitors the status of the recently released
Pacific pocket mice at Laguna Coast Wildnerness Park,
in Orange County, Calif. Credit: Mike Long/USFWS
“The rediscovery came at a time when the Service thought the animal was gone,” said Will Miller, a biomonitor with the Carlsbad Fish and Wildlife Service Office. “It is the only known remaining site for the Pacific pocket mouse on private lands.”
The nocturnal Pacific pocket mouse is the smallest mouse species in North America, with adults typically weighing between 6 and 7 grams (about the same as three pennies).
The other two populations known to exist are on the Marine Corps Base, Camp Pendleton in San Diego County, where they were discovered in 1995.
Since that time, no other populations have been found.
Fast forward another 26 years.
A group of 50 endangered Pacific pocket mice were adjusting to their new homes within the rugged hills above Laguna Beach, California, in early June.
Their man-made underground burrows, constructed by the biologists from the San Diego Zoo and their partners, built from biodegradable materials, were covered by acclimation cages, and placed inside the Laguna Coast Wilderness Park, part of Orange County Parks.
Biologist Debra Shier, of San Diego Zoo Global, removes the acclimation cage from Pacific pocket mouse burrow, releasing the animal to the wild. Credit: Ken Bohn, San Diego Zoo
Then, a week later, as the sun was setting, a team of seven biologists removed the acclimation cages. The animals were free to forage on their own.
This simple act of removing the cages marked a significant historic moment: the Pacific pocket mouse was now back in its historic range, establishing what the biologists hope will be a successful wild population of this critically endangered animal.
“Saving the Pacific pocket mouse from extinction has been accomplished through collaboration with numerous federal, state and local partners,” said Michael Long, chief of listing and recovery for the U.S. Fish and Wildlife Service’s Pacific Southwest Region. “Across Southern California, the service is working with its partners to conserve our native species and their habitats.”
Burrows for the Pacific pocket mouse are marked with yellow flags in the closed off area with Laguna Coast Wilderness Park. The park lies within some of the last remaining coastal canyons in Southern California. Forty miles of trails lead visitors through oak and sycamore woodlands and up onto ridges with expansive scenic vistas where rocky bluffs tower above the canyon trails. Credit: Ken Bohn, San Diego Zoo
Shortly after its rediscovery, the Service federally listed the Pacific pocket mouse as endangered in 1994. Following the listing, partnerships were formed with the landowners of the Dana Point Headlands, the Center for Natural Lands Management, California Department of Fish and Wildlife (CDFW), and other individuals to help recover the mouse.
Conservation efforts began in 1996 when the Service and the CDFW entered into a conservation agreement with the private landowners of Dana Point Headlands. The agreement established an eight-year, 22-acre temporary preserve on the 121-acre Dana Point Headlands site while allowing the owners to conduct compatible development activities.
Meanwhile, in June 2012, 22 adult Pacific pocket mice were taken from the three remaining wild populations along the California coast to participate in a breeding program at an off-exhibit area at the San Diego Zoo Safari Park. Eight more mice were collected from the wild populations by 2014. The Pacific pocket mouse breeding facility currently cares for more than 100 animals.
A recently released Pacific pocket mouse. Credit: Ken Bohn, San Diego Zoo
The released Pacific pocket mice have a small microchip under their skin that allows staff to identify each animal. Biologists expect to return to the site for observations and trappings, and they will be able to scan the microchips to identify the mice and track health information, including weight and size—and, perhaps, whether they are pregnant.
In the wild, the three Pacific pocket mouse habitats are separated by human development, so there was no chance for these populations to interbreed.
“We are honored to welcome the Pacific pocket mouse back into its historic range, in the Laguna Coast Wilderness Park,” said Barbara Norton, supervising park ranger, OC Parks. “We’re so proud of our amazing OC Parks system, and it’s exciting to know that this species will contribute to the health of the ecosystems within the parks.”
Pacific pocket mice improve ecosystem function, because they are seedeaters that disperse the seeds of native plants throughout their habitat. They also dig burrows that hydrate and increase nutrient cycling in the soil, which encourages growth of native plants.
The Pacific pocket mouse release team: (L to R) Nancy Frost, CDFW, Shauna King, San Diego Zoo Global, Debra Shier, San Diego Zoo Global, JP Montagne, San Diego Zoo Global, Mike Long, USFWS, Thea Wang, San Diego Zoo Global, Jamie Chang, San Diego Zoo Global, Samantha Leivers, San Diego Zoo Global, William B. Miller, USFWS, Asako Navarro, San Diego Zoo Global. Credit: Ken Bohn, San Diego Zoo
Jon Myatt, digital communications manager for the Pacific Southwest Region based in Sacramento,and Jenny Mehlow, senior public relations representative for San Diego Zoo Global, contributed to this article.
