Fox in the Tern House : Marauders Destroy Most of Nests, Endangering the Sanctuary’s Future

A red fox and a sparrow hawk have raided more than two-thirds of the nests of least terns at the Bolsa Chica wetlands, jeopardizing the colony of the endangered species at the reserve, authorities said.

The ecological reserve is home to about 10% of the state’s population of the rare bird.

The problem began last month when a lone red fox attacked 60 of the bird colony’s 90 breeding nests, destroying about two-thirds of its eggs. Troy Kelly, a biologist with the California Department of Fish and Game, said it was the most devastating attack by a predator since the breeding area was established in the late 1970s.

And in recent days, he said, a marauding American kestrel, commonly known as a sparrow hawk, has carried off more than a dozen of the terns’ surviving chicks, raising grave concerns about the colony’s future.

“There’s a potential of losing the entire nesting effort for this year at Bolsa Chica,” Kelly said. If that happens, the birds could abandon the area and never come back. “The situation is pretty critical,” Kelly said. “I’m very concerned.”

Attacks by foxes are not uncommon, Kelly said. A red fox preyed on the birds in Bolsa Chica two years ago, but the damage was not so extensive, he said. The most recent attacks, Kelly said, left about 90 to 120 eggs in the nests, most of which have hatched.

This year, the alarm was first sounded early last month when a volunteer visiting a half-acre breeding island noticed the destroyed tern nests.

A small bird with a black cap and yellow bill, the California least tern numbers about 2,000 mating pairs statewide and is on state and federal endangered species lists. The bird generally spends the winter in South America. About mid-April, Kelly said, the birds migrate north to various California locations, including Bolsa Chica, where they build nests in the sand and lay eggs that hatch in late May or early June.

Until 1978, Kelly said, the wetlands attracted an annual least tern population of only about 25 mating pairs. But a renovation project resulted in the construction of a breeding island, complete with open stretches of sand and tile shelters for older chicks. Today, he said, the area is visited annually by about 200 mating pairs.

Kelly--who oversees six wetland areas in Southern California--was attending a meeting in Sacramento when he heard of the volunteer’s discovery that a fox had raided nests. He rushed home, he said, and for three nights slept in his car near the breeding grounds, armed with a spotlight and shotgun, hoping that the fox would return. Then, at a cost of about $5,000, the state hired a professional trapper who stalked the fox for 10 days.

All to no avail. “He was probably just passing through,” Kelly said of the fox. “He could return.”

That would spell major trouble, according to the biologist. No more money is available to hire another trapper. And with his staff thinned by budget cuts, Kelly said, all he can do is patrol the area regularly with shotgun at hand.

It was during a patrol this week, in fact, that the biologist encountered evidence of the second major threat to the area’s least tern population: a foraging sparrow hawk, perhaps from a nearby park, preying on the tern’s newly hatched chicks. Under normal circumstances, Kelly said, the birds could defend against such attacks by mobbing an intruder en masse. With their numbers decreased, however, they now are easily overcome.

“The hawk worries me,” Kelly said. “If I don’t do something about it quickly, he could do more damage than the fox.”

The biologist said he plans to spend the next several days armed with his shotgun, waiting for the animal. “It’s a constant battle,” he said. “We don’t like shooting birds, but you have to weigh the various factors, and right now the least tern weighs more heavily than the hawk.”