The U.S. Marines at Camp Pendleton care most about two things: keeping America safe and saving a thumb-sized mouse from extinction.
In rugged terrain used in a training exercise known as the Crucible, for instance, food- and sleep-deprived Marine Corps recruits push themselves through simulated combat stress scenarios — and try to avoid disturbing the Pacific pocket mouse, a critically endangered animal that clings to existence by its tiny, sharp claws.
During a recent tour of the area's green hills and wind-swept beaches, Marine environmental officials said the corps is working with federal agencies to create formal safeguards for the mouse.
"A comprehensive management plan would be much broader in scope and depth than simply telling Marines to watch out for the mouse while they are training," said Maj. David Roen, head of environmental compliance for Marine Corp installations in the Southwest. Environmental laws hold military commanders accountable for activities on their bases.
Historically, the range of the mouse scientists know as Perognathus longimembris pacificus extended along the coast from Los Angeles County to Mexico. By the 1990s, it was feared wiped out by coastal development.
In 1993, however, a small population was discovered in the Dana Point headlands. The species, listed as endangered by the federal government in 1994, was later discovered at Camp Pendleton, whose 17 miles of northern San Diego County coastline make it the Marine Corps' premier amphibious assault training center.
Today, the largest known population of the mice inhabits a portion of the Crucible training grounds adjacent to a firing range and bivouacking area.
That is not necessarily bad for the mouse.
Habitat restoration efforts combined with environmental training and intense monitoring by biologists have resulted in strong comebacks for several of the 16 threatened or endangered species that share the base.
"As Southern California has continued to develop, the value of Camp Pendleton as habitat for endangered species has soared," Roen said.
The base hosts one-fourth of the state's endangered California least terns. The number of endangered least Bell's vireos has risen over the last two decades from a few dozen to more than 2,500. One of the last known nesting areas of the endangered Southwestern willow flycatcher lies just south of Camp Pendleton's air station.
"Our Marines know about every species on base, be it a bird, mouse or plant," said Dan Felkin, environmental training section head at Camp Pendleton. Every operation on the base that touches on the environment takes those species into account, he said.
With an annual budget of $6 million, a staff of 100 biologists, geographers, hazardous waste experts and statisticians devise and launch campaigns to rid streams of invasive plants, steer tanks and troops away from wildlife corridors and protect endangered species on the 125,000-acre base.
Commanders and recruits attend lectures on ecology and study maps pinpointing known populations of rare species. They learn to watch for endangered snowy plovers, which like to hunker down in the tracks of amphibious assault vehicles, and California least tern nests, which are mere depressions in the sand. Helicopters are prohibited from flying lower than 300 feet over nesting terns. The lush Santa Margarita River channel is off limits to troops and equipment.
The Pacific pocket mouse is on especially shaky ground, with a population in the wild in the hundreds.
A month ago, the Marine Corps and U.S. Fish and Wildlife Service joined forces with the San Diego Zoo Institute for Conservation Research to establish a captive breeding program with 22 pocket mice captured at Dana Point and Camp Pendleton. The mice, which feature a fur-lined pouch on each cheek and weigh no more than a silver quarter, are currently being held in quarantine at the institute's veterinary center.
Institute biologist Maryke Swartz said the mice are doing well. Cradling one in the palm of her hand and admiring its silky gray fur, she said biologists hope to expand the population to 200 and release 50 into the wild each year.
If all goes according to plan, the first batch of captive-bred pocket mice will be released into the kind of habitat it prefers — a peaceful stretch of sand and sage at Torrey Pines State Natural Reserve in San Diego.