SAN CLEMENTE ISLAND, Calif. — The sign leaves no doubt about the risk of entering the steep seaside hills that North America’s rarest bird calls home: ‘‘Danger. Boom. Explosives. Unexploded Ordnance and Laser Range in Use. Keep Out.’’
But despite the weekly explosions that rock this Navy-owned island off the Southern California coast — the military’s only ship-to-shore bombardment range — the San Clemente Island loggerhead shrike has been rebounding from the brink of extinction.
The black, gray, and white songbird, whose population has gone from a low of 13 in the 1990s to 140 today, is among scores of endangered species thriving on military lands during the past decade.
For many, it’s a surprising contrast, with troops preparing for war, yet taking precautions to not disturb animals such as the red-cockaded woodpecker and thumb-size Pacific pocket mouse. But military officials downplay the relationship, saying they’re concerned primarily with national security.
Defense spending on threatened and endangered species jumped nearly 45 percent over the past decade, from about $50 million a year in 2003 to about $73 million in 2012. The military protects roughly 420 federally listed species on some 28 million acres, according to the Pentagon.
The Defense Department is increasingly partnering with environmental groups to buy critical habitats that can act as buffer zones around bases, including a deal announced in June near the Army’s Joint Base Lewis-McChord in Washington state that will restore prairie habitat.
‘‘I’ve seen entire convoys with dozens of soldiers come to a screeching halt because a desert tortoise was crossing the road,’’ Pentagon spokesman Mark Wright said.
Environmentalists say there has been an attitude shift by the Pentagon, which has a history of seeking exemptions from environmental laws in the name of national security.
Generals shudder at being considered tree-huggers. But the military’s top brass also realizes that protecting wildlife can, in turn, protect training ranges. The more wildlife thrives, the fewer the restrictions. If endangered species populations decline further, the military could face being told to move training out of areas.
Defense Department properties have the highest density of threatened and endangered species of any federal land management agency, according to a group that tracks wildlife.
On average, military lands boast 15 threatened and endangered species per acre — nearly seven times more per acre than the US Forest Service, according to the Pentagon.
Security keeps huge swaths of terrain off-limits to humans, turning training grounds into de facto wildlife refuges.Bases have inadvertently preserved wetlands, old-growth forests, and tall-grass prairies by halting urban sprawl. The Marine Corps’ 125,000-acre Camp Pendleton is the largest undeveloped coastal stretch between Los Angeles and San Diego, with about 15 federally listed wildlife species.
In some areas, native plants that thrive from a natural cycle of wildfires have benefited from the artillery exercises, according to environmentalists. Troops also often use only a limited area for training, including on San Clemente.
Defense Department biologists have helped military branches boost wildlife numbers, according to environmentalists.
The endangered perch-like fish called the Okaloosa Darter was downgraded in 2011 to “threatened” after Eglin Air Force base restored its watershed with erosion control projects, according to the US Fish and Wildlife Service.
The threatened San Clemente Island lizard, which now numbers more than 20 million, is also being considered for removal from federal listing.