HELP'S ON WAY FOR RARE SONGBIRD; TRAPPING OF COWBIRDS MAY HELP SAVE SPECIES.

Byline: Patricia Farrell Aidem Daily News Staff Writer

Man alone isn't driving a tiny songbird found in Santa Clarita's river beds to the brink of extinction. Fellow birds are helping.

Blamed in part for the severe decline of the rare least Bell's vireo is the brown-headed cowbird, the target of a three-year trapping effort to begin this week in two usually dry rivers - the Santa Clara and San Francisquito Creek, where they meet in Valencia.

Where bulldozers and pesticides have failed, the cowbird is annihilating the vireo by taking over the songbirds' nests, destroying its eggs and laying its own, said Sherry Teresa, executive director of the nonprofit Centers for Land Management, which is overseeing the trapping.

``These poor little guys are getting whacked from all sides,'' Teresa said.

``The cowbird is a nest parasite - they won't build their own nest, they will go around and take over the native birds' nests. They push out the eggs or lay their eggs on top of them.''

And the vireo, in a nurturing mode, doesn't figure things out.

``They will raise the cowbird chicks,'' Teresa said.

The trapping, covering a mile-long stretch of the two waterways, was ordered by the U.S. Department of Fish and Wildlife. It is a condition of the approval of The Newhall Land and Farming Company's development along the two rivers, particularly the Bridgeport residential project, Newhall Land spokeswoman Marlee Lauffer said.

The program is being done in concert with another effort to save the endangered vireo. Speakers that sound an unsettling chirping have been placed in the riverbed to discourage the songbirds from nesting - and risking the destruction of those nests by construction equipment, Lauffer said.

The trapping program raises some complex questions - primarily man's effort to control what appears to be the natural order.

Teresa sees the conundrum.

``It is natural selection in action, but the problem isn't entirely nature. We've had a big hand in it,'' she said.

More than 90 percent of Southern California's riparian habitat has been wiped out by development, she said. And the same is happening to coastal scrub lands, habitat for another cowbird victim, the endangered gnatcatcher songbird.

Over the decades, nonnative cowbirds have migrated from east of the Mississippi River. They feed on cow and horse droppings and especially proliferate around dairy operations, thus their name, Teresa said.

To trap the birds, five wire mesh cages, each 10 feet by 10 feet, will be placed in the rivers this week, said Pete Bloom, a research biologist consulting for the Camarillo-based Western Foundation of Vertebrate Zoology.

The hope is that the cowbirds will be drawn to ``humane'' traps stocked with grain, water and a lure bird. Once inside, the trap will close then be checked twice daily by Bloom's crew members.

The captive cowbirds will be taken to an Orange County rehabilitation center as food for hawks, falcons, owls and other birds of prey, Bloom and Teresa said.

``That's a very sensitive issue,'' Teresa said. ``We can't release them or they will come back. The best thing we can do is use them to help wildlife birds.

``It's sad, but it has to be done to protect the natives,'' she said.

This program is a first for Bloom, who said the federal government initiated cowbird trapping about 10 years ago in Southern California.

Cowbirds can be recognized from a distance by the harsh rattle and squeaky whistle that is their call. They measure about 7-1/2 inches long. The male has a brown head and metallic green and black body. The female is grayish-brown with lighter coloring.

The vireo is gray and under 4-3/4 inches long, and noted for its melodic whistle. Its numbers have severely declined in the past 20 years.