NAVY STEPS UP EFFORTS TO SAVE ENDANGERED BIRD : SHRIKE TO BE BRED IN CAPTIVITY.

Byline: Les Line The New York Times

The San Clemente loggerhead shrike, possibly the most endangered bird in North America, may have a better chance to survive because its landlord, the Navy, is moving to protect the wild population and to breed the shrike in captivity, conservationists say.

The bird, found only on San Clemente Island in the Pacific Ocean 75 miles northwest of San Diego, is a subspecies of the loggerhead shrike, a predatory songbird that ranges widely but sparsely across the United States and southern Canada. A survey of the island by biologists in November turned up only 15 shrikes; another 10 are in a breeding facility recently opened by the Navy on the island.

The Navy has owned the 56-square-mile island since 1933, using it mainly for ship-to-shore bombardment training and for practicing simulated landings on an aircraft carrier. The shrike was added to the Federal Endangered Species list in 1977, and last summer the American Bird Conservancy threatened to sue under the Endangered Species Act to force the Navy to take steps to save the bird from extinction.

The loggerhead shrike is a robin-size bird with striking gray, black and white plumage, a black mask and a strong hooked bill. Shrikes hunt small birds, mice, lizards and large insects, but since they lack the sharp talons of hawks and owls, they have to impale prey on thorns or barbed wire to tear the animals into eatable pieces.

The San Clemente loggerhead shrike is smaller and lighter in color than shrikes on the California mainland, and scientists recognized the bird as a distinct subspecies in 1903. Ornithologists visiting the island around that time found the shrike ``tolerably common'' and ``well distributed.'' But by the mid-1980s, minimum estimates of the bird's breeding population ranged from 11 pairs to 5 pairs. Moreover, most of the shrikes were concentrated in canyons at the southwest end of the island, near the Navy's bombardment targets, where wildfires started by exploding shells threatened their nesting sites.

In a 1990 report on the ``Natural History and Management of the San Clemente Loggerhead Shrike,'' published by the Western Foundation of Vertebrate Zoology, two researchers, Thomas A. Scott and Dr. Michael Morrison, wrote: ``Biogeographic factors shaped the distribution of this subspecies, but human actions, specifically the introduction of exotic species, have altered the ecosystem of San Clemente Island and subsequently jeopardized the shrike's existence.''

Goats were introduced to San Clemente Island around 1875 by a ranch worker and their numbers exploded ``through neglect'' after the Navy took control of the island, the scientists reported. By 1976, when the Navy began killing and trapping goats, much of the island's native vegetation and shrike nesting habitat had been destroyed, they said.

A population of feral domestic cats has existed since the turn of the century, and black rats are believed to have arrived aboard Navy ships in the 1930s. Predation on incubating adult shrikes, nestlings and newly fledged young, particularly by cats and a small native fox, ``is a critical factor in the decline of shrikes on the island,'' the authors concluded. During the five-year study, predators raided 49 percent of the shrike nests, and 45 percent of the surviving fledglings died before they became independent of their parents. The Navy removed the last of more than 27,000 goats from San Clemente Island in 1992, and Sandy Vissman, an endangered species biologist at the Fish and Wildlife Service's field office in Carlsbad, Calif., said vegetation on the badly eroded island had begun to recover. But for years, conservationists have chafed over what Gerald Winegrad, a staff lawyer for the American Bird Conservancy, called the Navy's ``heel dragging'' in carrying out a recovery plan for the shrike.

In a letter to Interior Secretary Bruce Babbitt and Defense Secretary William Perry in July, Winegrad said the Navy, despite repeated warnings from the Fish and Wildlife Service, ``continues to conduct military operations that have placed the species in jeopardy of extinction.'' He said the Navy had refused to consult with the wildlife agency and had failed to carry out measures to increase the shrike population.

In response, the Navy has agreed to introduce a program to control the rats and feral cats; to develop a plan to control fires using tanker planes in partnership with the Forest Service, and to restrict shore bombardment in shrike habitats.

``We're not doing anything different,'' said Jan Larson, the Navy's natural resources manager at North Island in San Diego. ``We were forced to do it a little more quickly when the American Bird Conservancy came into the picture.''

Five pairs of San Clemente loggerhead shrikes have been moved from quarantine at the San Diego Zoo to the island's new captive breeding building. Dr. Nancy Harvey of the zoo's Center for the Reproduction of Endangered Species, which will operate the breeding program, says she hopes to raise and release 40 juvenile shrikes this year and to add another dozen birds to the captive population. ``This is the first attempt to restore an endangered songbird through captive breeding, and we need to grind out as many young as we can because of the heavy losses to predators,'' she said.