A rash of brown pelican deaths and illnesses was probably caused by a severe mid-December storm in the Pacific Northwest, state wildlife officials believe.

An estimated 400 birds turned up dead, injured or sick along the California coast beginning about Dec. 19. The episode has largely faded, state officials said.

"It doesn't appear severe (poisoning) or disease appears to be doing this. It appears to be more weather-injury and nutrition-related," said David Jessup, senior wildlife veterinarian for the California Department of Fish and Game.

Sick and dead birds began showing up in the Bay Area and Monterey a week before Christmas, and days later brown pelicans with the same symptoms - sickly, malnourished and apparently confused - began turning up in the Los Angeles area.

The birds were taken to the International Bird Rescue Research Center in Fairfield for emergency care.

At first, wildlife rescue officials and others feared the problem might be an outbreak of domoic acid, a toxic product of algae in the ocean, or disease.

Jessup said testing of birds and carcasses will continue but that for now it appears the problem was the weather.

Brown pelicans, though still an endangered species, have recovered since the pesticide DDT was banned in the early 1970s. They have been showing up farther north in recent years, and this year some of the birds stayed too late in the season.

For instance, hundreds of brown pelicans remained on East Sand Island in the Columbia River near Portland, Oregon, in mid-December, three months after a record 12,000 brown pelicans were counted on the island.

They were caught in a severe storm in which temperatures dropped to 3 degrees and snow fell on the beach, Jessup said.

The cold weather apparently prompted the laggard birds to begin migrating south.