Jets roar to a takeoff and scream over the Oakland Bay Bridge, making the Alameda Naval Air Station runway seem one of the most unlikely places for a nature preserve.
But each summer the air station is transformed into a sort of maximum-security bird sanctuary when nesting pairs of California least terns begin to breed in a fenced-in some 75 yards from a runway flanked by land-based cannons and armed warships.
The California least tern, an endangered species more commonly found in the southern part of the state, has no other fertile nesting grounds in Northern California. About 100 nesting pairs--a local record, up from 72 in 1989--are breeding at the base this year, making the military installation home to more than 90% of the least tern population in the north.
"It is critical to keeping them breeding in Northern California," said Laura Collins, caretaker at the four-acre Alameda breeding area. "We really don't have any big success stories anywhere else."
The California least tern has bounced back fairly well since the bird--a cousin to the sea gull, about nine inches from tail to bill--was included 20 years ago on the first federal list of endangered species. From a low of about 300 breeding pairs 30 years ago, the least tern population had increased to 1,250 pairs by 1989, Collins said.
In part because of open spaces and fenced-off beaches on military bases, more than half of the least tern population heads to one of the installations at breeding time, said Barbara Massey, an ornithologist who studies a least tern breeding colony program in Los Angeles.
Most of the state's least terns nest on beaches in Southern California--about 350 pairs at Camp Pendleton, near Oceanside, another 250 pairs at Venice Beach, and about 250 more at Bolsa Chica State Park in Huntington Beach.
But the Alameda Naval Air Station least terns are not the only ones with a penchant for airports. Although the birds naturally seek beach nesting spots, they have been known to look elsewhere. About 10 pairs of the birds make their nests at the Metropolitan Oakland International Airport, and another small group nests between two runways at a San Diego airfield, Massey said.
The sharing of Tarmac and airspace by 200 birds and two reserve squadrons of attack jet aircraft--not to mention four squadrons of helicopters and other military planes--requires some adjustments. For example, Collins sets a period in late summer when the Navy shuts down its 3,000-foot main runway and directs traffic to another airstrip at the base.
During this period, a Navy spokesman said, fledglings' first short flights often land them in the middle of the runway.
"At a certain time during the growing process . . . these least terns have a tendency to run out on the runways, and they try to hide on the white and yellow paint strips," said Bill Valente, the base's assistant public affairs officer.
The Navy has taken other steps to protect the birds. Navy builders surrounded the breeding area with an electrified fence, capable of jolting predators with a harmless but discouraging shock from six-volt batteries. This year, the base hired federal animal control workers to come in and catch cats and rival birds that threaten the least terns and their eggs, Navy spokesman David Kashimba said.
For breeding birds, the problems associated with airstrip nesting don't end there. At especially noisy times--when jet pilots practice touch-and-go landings, for example--the birds sometimes do fly away. But they keep coming back. Theoretically, steady high noise levels could pose problems for the birds, which bring food only to chicks that recognize and return their call.
"I don't know how they manage to teach their chicks their calls when there's the roar of jets everywhere all the time," Massey said.
But the birds manage so well that some of the people who help protect them say the air station colony could anchor a Northern California comeback that could eventually link up with the southern colonies and spread the birds throughout the state.
"The least tern is one of the success stories, in terms of managing endangered species," Collins said.