Bird experts suspect that California Brown Pelicans that have been mysteriously dying and turning up ill may have become sick and disoriented in a severe winter storm last month off the coast of Oregon that forced them to fly south in search of food and warmth.

Since last month, some 460 of the birds have shown up thin and confused – or dead — in Oregon and California, far from the coast where they typically feed. Domoic acid, a poison in algae that causes brain damage if ingested, was an early suspect. 

But Dan Anderson, an avian ecologist at the University of California, says the birds were probably disoriented because they’d flown 1,000 miles (1,609 kilometers) after getting cold and wet when temperatures dipped below freezing and 60 mile-per-hour (97 kilometer-per-hour) winds slammed into East Sand Island in the Columbia River, where the Pelicans were roosting. “They just flew a thousand miles and had their tails frozen off,” Anderson tells the New York Times. “They probably weren’t feeling so well.”

David Jessup, a senior veterinarian for the California Department of Fish and Game, also believes weather was the culprit. “Quite a few have severe frostbite injuries: frozen toes and foot webs, and nasty lesions on their pouches,” he told the Los Angeles Times. “They're in pretty good body condition otherwise. Even confused and depressed pelicans were not showing signs of brain damage."

The illnesses are a concern for California, where the bird is an endangered species after nearly being wiped out by the pesticide DDT and its byproduct DDE in the 1960s. But the case isn’t closed. Low levels of domoic acid were found in blood samples of 19 sick birds, according to the L.A. Times.

"Until complete test results are available, we're not prepared to say what is to blame for the constellation of symptoms we've been seeing in these birds," Laurie Pyne, development director for the Fairfield, Calif. International Bird Rescue Research Center,  told the L.A. Times. "We're still trying to put the puzzle pieces together."

Image of Brown Pelican by Calibas via Wikimedia Commons