Seagulls swarm a percolation pond in the Almaden neighborhood of San Jose, California

SAN JOSE, Calif. — Thomas and Stephanie Andersen bought a house in the suburbs last April, with a manicured lawn, a porch and a patio out back.

Everything was going well for the 30-something couple and their two young daughters on the quiet cul-de-sac in San Jose’s Almaden Valley neighborhood.

Then the seagulls showed up.

Like a scene from an Alfred Hitchcock film, thousands of the squawking, flapping, marauding white birds descended on a pair of ponds about 30 feet from the Andersens’ house on Bergamo Court. That was last November.

Not only are the birds still there, no one is exactly sure where they came from or how to get rid of them.

“It sounds like you’re at the beach,” says Stephanie. “They squawk all day. They get in fights. And it’s a sanitation issue.”

The gulls show up every morning shortly after 8 a.m., cover the sports fields at nearby Dartmouth Middle School, then swarm the ponds. They flap. They circle. They drop copious amounts of waste. Gratefully they leave at sunset, but the next morning, they come back.

“I clean up the deck every day,” says Thomas, with a sigh.

The ponds are percolation ponds, owned by the Santa Clara Valley Water District and used to recharge local underground aquifers. Their banks this week were littered with chicken bones, scraps of plastic and prodigious puddles of goopy white guano.

Increasing numbers

“I have seen them in increasing numbers,” said Nina Merrill, a wildlife biologist with the water district. “I’ve seen them at Dartmouth Middle School too. They seem to be blanketing the athletic fields. My guess is they are coming from the bay.”

For the past eight years, Merrill has used border collies to chase away resident Canada geese, whose numbers can also become problematic around the waste district’s several dozen ponds. The mysterious seagulls present a different problem.

“What can we do about it? That’s a good question,” she said. “We need these ponds for groundwater replenishment. If it’s a long-term problem, we’ll have to study it. It’s not something we can ignore.”

One thing is for certain: The population of gulls, mostly California gulls, in South San Francisco Bay has exploded in the past 30 years — turning it into the largest gull nesting area in the state. And biologists say unwelcome visits to other Silicon Valley neighborhoods may become more common in the years ahead.

In the early 1980s, researchers counted only a few hundred gulls in the South Bay. Last year, there were 46,000. Historically, the gulls flew every summer to Mono Lake, in the Eastern Sierra, to breed. But as Los Angeles drained the lake to supply its drinking water demands, its level dropped. By 1979, land bridges emerged that allowed coyotes to eat thousands of the gulls’ eggs. The next year, the birds began nesting in San Francisco Bay.

Over time, the flying scavengers raided garbage dumps, laid lots of eggs, and flourished. Recent studies show the gulls are eating the eggs and offspring of shorebirds, including endangered snowy plovers, American avocets, Forester’s terns and black-necked stilts — threatening the success of multimillion-dollar efforts to bring back the bay’s wetlands.

Hindering wetland restoration projects

“Everyone is really concerned,” said Caitlin Robinson-Nilsen, waterbird program director for the San Francisco Bay Bird Observatory in Alviso.

“We have such amazing diversity of nesting and wintering birds in the bay, we don’t want this one species to out-compete all the others.”

The Andersens remain puzzled by their predicament. They wonder if recent work to restore former industrial salt ponds might have sent the gulls looking for new turf — their neighborhood.

In December, crews working for the federal and state government breached a levee on a former Cargill Salt pond known as A6 where more than 10,000 gulls had been nesting. The project is part of the effort to convert the salt ponds back into wetlands for birds, fish and other wildlife, restoring San Francisco Bay’s natural conditions.

But Cheryl Strong, a biologist with the U.S. Fish and Wildlife Service in Newark, said that project does not explain the presence of Almaden Valley’s super flock. Gulls only nest there between March and August, she said. When the pond was flooded three months ago, the gulls weren’t there. They were wintering in other parts of the bay, or along the coast.

This summer, nobody knows where those gulls will lay their eggs, she said, adding more than 1,000 birds have been fitted with leg bands to track them.

“Gulls are hard. They are relatively intelligent,” said Strong. “They don’t mind being around people. We consider them a nuisance species.”

And shooting them is illegal under the 1916 Migratory Bird Treaty.

Strong said biologists are considering oiling their eggs to stop them from hatching. But gulls can live 20 years or more, and oiling thousands of eggs is expensive.

Another theory for the unexplained Almaden Valley invasion: As South Bay landfills have chased gulls away more aggressively, the birds headed for neighborhoods. At the request of the U.S. Fish and Wildlife Service, Newby Island landfill in North San Jose has spent hundreds of thousands of dollars in the past two years shooting whistling bottle rockets, running herding dogs, and even hiring a falconer to send out falcons every day to scare away gulls.

“It’s been enormously successful,” said Rick King, general manager of Newby Island landfill. “Five years ago, there were probably 10,000 gulls a day at the landfill trying to forage. Today, on the average, there are probably less than 1,000, and on some days there are none.”

Asked where the birds went, he paused.

“I don’t know,” he said. “My whole job is to keep them off my facility.”

The Guadalupe Landfill, operated by Waste Management, is two miles south of the Andersens’ home. Calls intended to inquire about its gull management activities were not returned.

Questions of control

“The issue is how do you control the landfill operations so that it discourages the gulls?” said Bob Power, executive director of the Santa Clara Valley Audubon Society. “How do you control parking lot (trash bins) in fast food locations? I don’t have an answer to that.”

That leaves the Andersens, and their neighbors, with lots of birds.

They’ve contacted the water district and City Hall, and had no luck so far. Some biologists said the birds might leave in the summer to breed in the bay or at Mono Lake. But they could easily be back next fall.

“They are out of control. It’s beautiful when they go away,” said Stephanie Andersen. “They should live by the ocean. Seagulls don’t live in San Jose!”