Endangered Birds Nest in New Habitat : Environment: Officials are cheered by the nesting of least Bell’s vireos in man-made surroundings along the San Luis Rey River in Oceanside.

Sometime in April, a small, gray, male songbird from Mexico laid claim to a patch of willow forest along the San Luis Rey River in Oceanside and let loose its long, warbling song.

The sound attracted a female, and the birds mated and built a nest in the thick brush. Two months later, the nest was full of chicks.

That seemingly common event has caused excitement and cautious optimism among city, federal, and state officials, as well as wildlife biologists.

For the biologists it means that just maybe the birds, known as least Bell’s vireos, can be saved from extinction.

For government construction agencies, success in creating the bird’s habitat from scratch means that multimillion-dollar construction projects might be able to proceed on time.

The bird, which winters in Mexico but returns to California each spring to nest, was once common throughout the state. But, by 1986, when it was officially declared an endangered species, its numbers had dwindled to 300 pairs concentrated in Southern California, said wildlife biologist Larry Salata of the U.S. Fish and Wildlife Service’s Carlsbad office.

More than 40% of those were found on the huge, 126,000-acre Camp Pendleton Marine base north of Oceanside. There, biologists working for the Marines in 1976 launched one of the earliest programs to preserve the bird.

Salata and other biologists say wildlife habitat protection efforts since 1986, plus this year’s spring rains, have helped return the population to anywhere from 500 to 600 pairs statewide. That’s still a long way from the 5,000 needed by some estimates for complete recovery. But it is at least enough to inspire hope.

“We’ve got a long way to go, but we are heading in the right direction,” Salata said.

“It has been wonderful,” said Barbara Kus, adjunct professor of biology at San Diego State University. She has been studying the least Bell’s vireo since 1986 and is a volunteer member of a group of scientists who are working with Fish and Wildlife on plans for the recovery of the species.

For other government agencies, especially the city, Army Corps of Engineers and the California Department of Transportation, the nesting on the San Luis Rey River means they’ve got a chance of launching or completing on time two major construction projects near the river.

One project is the $63-million Corps of Engineers flood control plan begun two years ago along 7 miles of river from the ocean to Douglas Bridge. Oceanside Assistant City Manager Dana Whitson said that, if the levees aren’t built, a 100-year flood such as the one that hit Oceanside in 1916 could wipe out at least $100-million worth of commercial and residential property and endanger hundreds of lives.

The other is Caltrans’ $25-million California 76 project, aimed at creating a 3-mile-long expressway from Interstate 5 to the San Luis Rey River Valley, allowing drivers to bypass crowded Mission Avenue.

Both projects will destroy nesting habitat needed by the vireo, and Caltrans and the corps are required by federal environmental laws to replace every acre torn out with new forests.

The corps must create 42 acres of habitat before the Department of Fish and Wildlife will allow the levees to be completed. Work was scheduled to be finished in 1994.

Caltrans must create 7 acres before work begins on the highway. The project is scheduled to start in 1993.

Another 21 acres may have to be bought and planted, said Caltrans project manager Gary Klein, to settle a lawsuit filed by the Sierra Club against the highway project.

The two birds that took up residence in the river valley are considered evidence that efforts to replace the willow forest may work. The 12-acre home of that pair, situated in the heart of Oceanside, is man-made, created literally from the ground up by the Corps of Engineers beginning in 1989.

Since April, the birds have been joined by a second nesting pair, along with a lone, singing male that officials hope will find a mate and nest.

“We’re pleased with that, very pleased, very excited,” said Jim Crum, corps project manager for the flood control project. “From what I understand, it is the most successful site that the U.S. Fish and Wildlife is aware of for the least Bell’s vireo.”

Three other sites, scattered downriver from the 12-acre patch, have been failures to various degrees. In one, the soil proved too salty to support the vegetation, said Crum. Another has been invaded by a bamboo-like plant known as the giant reed.

First imported from Europe as an ornamental yard plant, the reeds spread rapidly through Southern California rivers and choke out native vegetation.

The less successful sites will have to be cleared of reed or moved entirely, said Crum.

But the success at the one site, dubbed Whelan I after nearby Whelan Ranch, has made agency officials hopeful. “Whelan is our first success . . . so we are hoping that, by the end of 1994, the rest will be on line,” Crum said.

Lessons learned about creating riverside forests on the San Luis Rey River may prove vital if the vireo is to ever recover completely, biologists said.

To reach the point where it can survive on its own, wetlands habitat will have to be restored, created and protected throughout the state, because 90% of the natural habitat has been destroyed by man, Salata said.

Besides habitat protection and replacement, also contributing to early success, said Salata, are programs by various agencies to trap and kill an aggressive competitor of the least Bell’s vireo known as the brown-headed cowbird.

An invader from the eastern United States--virtually unknown in California until about 100 years ago--the cowbird does not build its own nests or raise its own young.

Instead, it lays its eggs in the nests of others--such as the least Bell’s vireo--and lets them raise baby cowbirds instead of vireos, said Kus of San Diego State.

Even with this spring’s success story, biologists warn that there is a long way to go before anyone can claim a victory.

“It’s going to take a lot more focus, management and money toward the problem, which is more than just the vireo, but the protection, maintenance and recovery of wetlands” throughout the state, Salata said.

“At least in the short term, it has been demonstrated (on the San Luis Rey) that vireo habitat can be created,” he said. But what still has to be proven is whether those new, man-made forests will survive and thrive on their own without sprinklers or replanting.

“But it’s encouraging,” Salata said.

“We’ve learned we can grow riparian trees and shrubs, if they are planted under the proper conditions,” said Kus. “And this year, we’ve finally learned that vireos will forage and nest in restoration areas.”

But, say biologists, the huge costs of restoration and replacement of habitat, together with the uncertainty of success, should be a warning that it is better not to destroy natural habitat to begin with.

Crum of the corps said his agency spent at least $1 million initially, and has paid out hundreds of thousands of dollars since in an effort to grow new river forests.

Caltrans officials say they’ve spent much more, about $2.4 million on the San Luis Rey River alone. That includes $1.5 million on their 7-acre Oceanside site near the city airport for the highway bypass project. It also includes $900,000 on a 5-acre site in Bonsall, a requirement before wildlife agencies would allow construction of the new California 76 Bonsall Bridge in 1990.

“The money and time it takes to do all this,” said Salata, “would still lead us to avoid and minimize impact to the greatest degree possible . . . not to place a lot of reliance on artificial habitat because it can be very costly and can take time.”

“To me, restoration is not an alternative to preservation,” said Kus. “Every time we destroy habitat and think we can replace it, we are gambling. So I don’t see it as a panacea.”