NEWPORT BEACH, Calif. (AP) — A dozen of the hundreds of brown pelicans found starving on the Southern California coast were released Friday after rehabilitation at a wildlife center.

The pelicans were returned to the wild at Corona del Mar State Beach after treatment at the Wetlands and Wildlife Care Center in Huntington Beach. They were among about 70 that have been brought to the center since mid-May, said Dr. Elizabeth Wood, the facility's veterinarian.

“They were all brought in in a state of emaciation,” Wood said. “They were basically starving.”

The birds were not showing any signs of obvious disease and they tested negative for disease, she said.

“So basically it just seems like a mass starvation event. They were found all over the beaches — emaciated, anemic, dehydrated and with the feathers not waterproofed anymore,” Wood said.

The birds, however, responded well to basic care, including fluids and large amounts of fish, she said.

“We don't have a clear answer as to what caused this,” Wood said.

The California Department of Fish and Wildlife said last month that hundreds of starving pelicans had been admitted to wildlife rehabilitation facilities since about May 13, and many died shortly after their arrival at facilities. The department similarly found no indications of disease or unusual parasites.

It's not known if the starvation event is over, but Wood said the intake of birds has declined dramatically over the last week or so.

The 12 birds released Friday will serve as a “sentinel group” to see how they fare before additional birds are released. All were banded so that wildlife experts can identify them if they end up on beaches in distress again.

Rehabilitating each pelican costs about $45 a day, Wood said.

Brown pelicans are an important part of the Pacific Coast ecosystem, feeding on northern anchovy, Pacific sardine and mackerel.

The impact of the pesticide DDT, which caused eggshell thinning, led to the listing of California brown pelicans as endangered under the federal Endangered Species Act in 1970. After DDT was banned, the species recovered and was removed from the U.S. endangered list in 2009. It remains protected under state law.

Wood said anyone encountering a sick pelican should call wildlife experts and not touch it.