HAYWARD -- Every summer day, volunteers and park workers stand guard on a small island in San Francisco Bay. At the first sign of a threat, they race into action -- blowing whistles, clapping hands and blasting horns.
Their goal: to do whatever it takes to chase away flocks of voracious sea gulls trying to eat tiny endangered birds called least terns that lay eggs at Hayward Regional Shoreline Park. Occasionally, the East Bay Regional Park District even calls out sharpshooters.
The unusual showdown is a small part of a larger drama. In an alarming trend that has scientists scrambling for answers, the bay's population of California Gulls -- squawking, flapping white-and-gray birds that most people associate with the beach -- has exploded from 24 birds in 1980 to more than 53,000 today. In the last two years alone, their numbers soared 41 percent, making the Bay Area home to the second-largest population of California Gulls in the world, behind only Utah's Great Salt Lake.
"It's gone gangbusters," said Dave Shuford, a top Marin County gull biologist. "It's been amazing to follow."
Nobody knows how to stop the population boom. And the problems are mounting: The gulls are increasingly colliding with airplanes, even causing several aborted takeoffs and landings at Bay Area airports. They're swarming landfills, divebombing schools and neighborhoods and gobbling up shorebirds that public agencies have worked for years to bring back from near extinction.
Scientists say the gulls have become a serious threat to the largest wetlands restoration on the West Coast, the effort to restore 15,100 acres of former Cargill industrial salt ponds in the South Bay back to tidal marshes. A central goal of that project, which already has cost taxpayers more than $300 million, is to bring back endangered species.
"This is one of the issues I lose sleep over," said John Bourgeois, who heads the South Bay Salt Pond Restoration Project, a consortium of government agencies.
The gulls have formed 10 huge colonies on bay levees off Union City, Fremont, San Jose and Palo Alto, occasionally venturing as far north as Richmond and Alcatraz Island.
Nobody knows why the birds decided to settle in the Bay Area. One theory is that they came from Mono Lake in the Eastern Sierra after Los Angeles pumped down water levels there in the late 1970s and exposed their nests to hungry coyotes. Another is that a few of the birds simply decided decades ago that the levees of San Francisco Bay were a good place to build nests and lay eggs. And thousands more followed.
Landfills and garbage bins, which offer an endless food supply, are now helping them thrive, experts say.
"It's like eucalyptus trees or weeds," said Bob Power, executive director of the Santa Clara Valley Audubon Society. "It's something that was in harmony and all of a sudden is completely out of whack."
Few solutions in sight
Some Bay Area residents say the answer is clear.
"These sea gulls, they need some thinning," said Gilroy retiree Bill Valiquette, a lifelong Bay Area resident who has seen gull problems dramatically worsen. "Just go around and collect the damn eggs and throw them in the garbage. There's too damn many to shoot. You'd have to take 15 guys with double-barrel shotguns and go crazy."
Wildlife experts say government biologists can't simply massacre thousands of gulls. The public outcry would be too great.
That was certainly the case in 1996, when flocks of great black-backed and herring gulls took over islands at Monomoy National Wildlife Refuge off Cape Cod, Mass., prompting the U.S. Fish and Wildlife Service to approve a plan to feed 5,700 of them pieces of bread laced with poison. Lured by expanding landfills and commercial fish waste, the gulls were wiping out endangered piping plovers and roseate terns by eating their nests and chicks.
But the experiment began falling apart after the dying gulls flew over wealthy coastal areas.
"They died in people's pools and yards and on playgrounds," said Libby Herland, manager of the Eastern Massachusetts National Wildlife Refuge Complex. "There was a public uproar."
Now, the refuge chases gulls off sensitive island areas instead. It also destroys gull nests and eggs while occasionally shooting a few of the most aggressive ones each year. Cape Cod shorebirds are returning, in part because nearby garbage dumps have closed.
Biologists could also destroy thousands of gull nests in the Bay Area. But California Gulls lay up to three eggs a year, and each can live to be 25 years old.
Even if all of the gulls' eggs were destroyed tomorrow, "because they are such a long-lived species, you wouldn't see results for 20 years," said Cheryl Strong, a biologist with the Don Edwards San Francisco Bay National Wildlife Refuge in Fremont. "And with 53,000 birds, times three eggs per pair, we don't have the staff or the money."
It's not like they're running out of food, either.
California Gulls eat fish, garbage, bugs, even their own eggs and young.
"Gulls are tough. They are persistent," Shuford said. "They'll eat anything. If they were fragile, they wouldn't be causing a problem."
Environmental laws are also blocking a quick solution.
Some people might think of gulls as flying rats. But along with condors, trumpeter swans and other beloved birds, they are protected under one of America's oldest environmental laws: the Migratory Bird Treaty Act of 1918. That's because gulls live in the winter on the Pacific Coast and migrate inland every spring to lay eggs.
The law makes it illegal to kill any California Gull or destroy its eggs without a permit from the U.S. Fish and Wildlife Service.
Gulls vs. planes
As the number of gulls grows, so do the problems.
From 2003 to 2012, gulls collided with airplanes 57 times at Mineta San Jose International Airport, a 50 percent jump from the previous decade.
Many of the incidents caused little or no damage. But some have been eye-opening. In June 2012, gulls struck a Southwest Airlines jet landing in San Jose, causing $50,000 damage to an engine. In 2009, a United Airlines flight carrying 140 passengers was forced to abort a takeoff after it hit 10 gulls, damaging an engine and its radar system while racing down a rainy runway.
Under pressure from the Federal Aviation Administration, the airport is spending $100,000 this year to hire a biologist from the federal Wildlife Services agency to harass and possibly shoot gulls and other birds that could put flights at risk, although so far no gulls have been killed.
Most of the gulls' population boom has been south of the San Mateo Bridge, so neither San Francisco International Airport nor Oakland airport has reported an increase in gull strikes. In April 2012, however, a United Airlines 747 bound for Hong Kong from San Francisco was climbing after takeoff when a gull flew into its engine, causing vibration and stalling. The plane returned to the airport to make an emergency landing.
Smaller planes have also been hit.
"I heard a thunk, and then the gull was physically wrapped around my wing," recalled Robert French, of Woodland, who flew into a group of gulls in July 2012 with his two-seat Cessna 152 while landing at Palo Alto Airport. "I was very lucky. If the bird had hit the windshield, it could have broken it and come into the cockpit, which would have been a real problem."
French, an astronomer at the SETI Institute in Mountain View, said the gull caused $2,000 damage to his plane.
In some cases, birds cause a lot more havoc in the skies.
Capt. Chesley "Sully" Sullenberger famously hit a flock of Canada geese after takeoff from New York City in 2009. After his US Airways jet lost power, he was forced to make a daring landing on the Hudson River.
Bird strikes on planes in the U.S. cause an estimated $718 million damage a year, according to FAA data. Large birds like Canada geese and brown pelicans are among the most dangerous, but gulls are hit the most, followed by pigeons and raptors.
Nearly every major airport has permits to kill birds that threaten aircraft safety. Still, at least 231 people have been killed worldwide in plane crashes caused by birds since 1988.
In some places, the growing gull population isn't a safety threat so much as a major nuisance.
In the fall and winter, huge flocks of gulls descend on San Jose's Pioneer High School, fouling roofs and outdoor areas where students eat. The birds have mobbed the Almaden Winery neighborhood and other schools nearby.
"Until I saw it for myself, I couldn't believe it," said Stefani Garino, Pioneer's principal. "At certain times of the school year, there are literally hundreds and hundreds of birds on the roof of our gym and theater. Something will spook them, and they'll all start flying at once. If it's during a time when kids are out, like during lunch, enough of them have been pooped on that they all go running and screaming for shelter."
Landfills are targets, too.
Newby Island landfill near Milpitas spends $300,000 a year to pay for 15 trained falcons, dogs, propane cannons and other tools to keep gulls from eating trash. "It's a constant battle," said Rick King, the landfill's general manager.
Thousands of gulls are also vexing Guadalupe Landfill in South San Jose, where they may have moved after being chased off Newby Island. Guadalupe spends about $100,000 a year on propane cannons and other hazing tools.
Landfill operators are sensitive about the issue. Not only are they required by state law to keep nuisance animals away from trash, they also know their facilities can be a major source of food for the gulls, which makes the landfills a target of angry neighbors or biologists trying to solve gull problems.
The landfills don't have federal permits to kill gulls. But increasingly Bay Area biologists do.
In September, scientists at the Don Edwards National Wildlife Refuge in Fremont applied for a "depredation permit" that allows them to destroy eggs and kill problem gulls and other birds that kill endangered terns and snowy plovers in bay wetlands. But the permit, issued in March by the U.S. Fish and Wildlife Service, caps the number of California Gulls the refuge can kill at 40 per year.
Wildlife officials acknowledge that the permit won't reduce the overall number of gulls.
"Philosophically, it's not the role of the Fish and Wildlife Service to control populations of wildlife," said John McCamman, the agency's acting assistant regional director. "We're here to protect and ensure their livelihood, not kill them."
The permit also says the birds can't be killed unless biologists have exhausted other remedies first, such as trying to scare them away with whistles, or using protective fencing. The idea is to take out the "bad actors" -- gulls that do a disproportionate amount of harm to endangered shorebirds.
Promising research from the East Bay shows it actually might work.
When 150 California Gulls descended on a colony of endangered least terns at Hayward Regional Shoreline Park in 2005 and 2006 to feast on their eggs, the terns abandoned their nests. But East Bay parks officials fought back, securing a permit to kill up to 45 gulls a year.
Wildlife Services officials used shotguns to kill 20 of the most aggressive gulls a year on average from 2007 to 2011. And now the park is home to the second-largest least tern colony in the bay.
"Individual birds have a learned behavior. They become specialist predators -- Charles Manson gulls," said Dave Riensche, a biologist with the East Bay Regional Park District. "If you remove them, problem solved. It's like in the schoolyard, if you remove the bully, the other kids don't learn that behavior."
With the worst gulls gone, he said, last year the park district only needed to kill two gulls.
But the Don Edwards refuge is much larger. It has only one intern who searches 30,000 acres -- an area the size of San Francisco -- every few days for gulls killing endangered species. And with federal budget cuts, the refuge received no new funding for gull control this year.
So far, not a single gull has been killed under the refuge's permit, Strong said.
The gulls greatly outnumber endangered species. Most recent counts show only 202 Western snowy plovers and 509 breeding pairs of California least terns living in the bay.
"We are trying to save the species that can be wiped out at any point," said Eric Mruz, manager of the Don Edwards refuge. "When you have 50,000 gulls and a few dozen plovers, we have to focus on the plovers."
Bay Area environmentalists largely support the refuge's plan.
"It's not about going out and just killing things," said Catherine Burns, executive director of the San Francisco Bay Bird Observatory, which has used whistles and other tactics to scare gulls from shorebird nesting areas.
"It's about using the least harmful methods, then escalating strategies if they don't work."
The only long-term solution, says one of the nation's top wildlife experts, is to constantly chase the gulls away, disrupt their nests, better manage landfills and occasionally shoot a few of the most aggressive gulls.
For 40 years, Steve Kress has worked to restore puffins and other birds on rocky islands off the Maine coast. He said that shooting large numbers of gulls doesn't work.
"Gulls are very smart," said Kress, a vice president of the National Audubon Society. "They learn the distance a rifleman can shoot. They stay just out of range, from watching others."
Another option if things worsen in the Bay Area, said McCamman of the Fish and Wildlife Service, would be for his agency to issue a "general depredation order" to allow anyone to destroy gull nests and eggs on their property. The agency has had success with a similar program it put in place in 2006 to control Canada geese.
For now, however, officials at the Don Edwards refuge are doing what they can, hoping the gull population slows.
"It's got to plateau at some point," Strong said. "Could it double again in the next few years? I don't want to think about that."
Paul Rogers covers environmental issues and resources. Contact him at 408-920-5045. Follow him at Twitter.com/PaulRogersSJMN.