California's brown pelicans are headed east to feast.

Known for hanging out along the Pacific Coast, a growing number of the young long-billed birds are finding their way to inland cities such as Stockton, Davis and Antioch -- one even ventured to Yosemite National Park.

Changes in the Pacific Ocean's environment have likely caused a ripple effect by pushing schools of sardines and anchovies away from the coastline, forcing the fledglings, which are distinct from adults by their brown heads, to look elsewhere for food, said Jay Holcomb, director emeritus of International Bird Rescue in Fairfield. The warming of ocean waters and change in coastal currents have likely pushed the fish from the shore, he said.

"It doesn't take much to throw off the balance," Holcomb said.

The young brown pelicans leave the nest around May and June to follow the adults and learn to find food. Adults know to go farther out to sea to hunt for fish.

"(The young pelicans) are desperately trying to figure things out. Through trial and error they find it, though sometimes it is in unusual places," Holcomb said.

"They're opportunistic feeders," said Rebecca Dmytryk, director of WildRescue, a Moss Landing-based animal rescue group.

The birds tend to seek out water sources, particularly those that are connected to the ocean.

"The Delta is the easy water to follow. They just keep following it along and then hit Antioch and beyond," said Susan Heckly, wildlife rehabilitation director for Walnut Creek's Lindsay Wildlife Museum.

The pelicans have never been reported at inland locations to the same extent they are now, she said.

In the past couple of weeks four brown pelicans have made their home at the waterfront near Antioch's Riverview Lodge restaurant and municipal pier, several local fishermen said Friday.

A longtime fisherman said he saw a brown pelican there a couple of years ago, but sightings have been rare.

Mike Moran, a naturalist with the East Bay Regional Park District, agrees. He said the birds have even been found at Antioch's Contra Loma Reservoir and Oakley's Big Break Regional Shoreline lately.

"You have to be careful. They'll steal your bait if you aren't careful, or lunge at the fish you have on the line," said Carl Hill, of Antioch. "They're a nuisance."

Earlier, one fisherman was gutting his morning catch when a pelican tried to take the fish. A friend had to shoo away the bird and stand guard.

"They can really be flustering and make tempers flare," Dmytryk said.

It is common to see white pelicans in the Delta area, but not brown ones, Moran said. Aside from their color, the white pelicans tend to fish from the surface, while the brown pelicans dive into the water to catch fish.

"It's kind of an oddball thing," Moran said. "They're a type of bird that is normally pretty faithful to their habitat."

Part of the reason for the brown pelican proliferation could be that the population has rebounded since being considered an endangered species in the early 1970s. Because there are now more pelicans in the wild, there is a larger number of stranded and malnourished birds, Holcomb said.

Animal rescue groups throughout the state are finding that to be the case.

The Peninsula Humane Society in San Mateo County has taken in more than 30 emaciated and hypothermic brown pelicans in need of urgent care in the past two weeks. In a typical year it normally sees 20 to 25 malnourished pelicans.

Signs that brown pelicans are in need of urgent care include when they are lying on their sides, approachable to humans, or are overly aggressive with fisherman, said Scott Delucchi, a humane society spokesman.

"It's never been this concentrated," he said.

Holcomb said sickly young pelicans have been found in areas as diverse as the rural farming land of Davis to the mountains of Yosemite.

Though it is normal for some fledglings to die in the summer because of natural causes, the increase in pelicans on beaches and piers led the state Department of Fish and Game to issue a news release last week advising the public not to feed them.

"Although the pelicans may exhibit begging behavior and some may appear weak, the birds need to remain wild and forage naturally," Fish and Game officials said.

Hill said he notices people feeding the brown pelicans at the Antioch pier.

"They aren't going to learn to hunt or fend for themselves hanging out around here," he said.

Mike White, of Oakley, sees the same thing about five miles farther inland at the Antioch-Oakley regional shoreline.

"There are a lot around here on the weekends when it's more crowded," he said. "They're smart. If there's a great meal to be had, they're going to hit it."

Pelican feeding can also lead to the birds becoming entangled in fishing lines around piers, which can damage the throat pouch and intestinal tract, according to Fish and Game.

Runoff oil from fish-cleaning stations -- usually found at boat ramps and piers -- is also falling on the birds as they try to grab fish scraps, Dmytryk said. The fish juice messes up a pelican's feathers, making it become hypothermic -- even unable to float or fly.

Holcomb characterized the movement of pelicans inland as a "natural occurrence" and not a trend, adding that if the fish swim back to the shoreline, the birds will likely follow.

"It's all about the fish and where they can find food to eat," he said.

Contact Paul Burgarino at 925-779-7164. Follow him at Twitter.com/paulburgarino.