Dead and dying California brown pelicans are littering the state’s coastline and nearby inland areas, and wildlife experts aren’t sure why.

An unusual number of ill or dead adult birds have been reported from southern Oregon to Baja California. While it’s common for up to 80 percent of young California brown pelicans to die each year from starvation, adults aren’t typically affected, according to the International Bird Rescue Research Center in Fairfield, Calif.

Rescuers have brought more than 75 ailing birds to the center over the past 10 days, and it's received hundreds of calls about pelicans that are either dead or are sick and confused, according to executive director Jay Holcomb. The birds are exhausted, and their pouches and feet are discolored, the Los Angeles Times notes. They're also disoriented, Holcomb says, with many landing inland on highways, roads and runways instead of sticking to the coastline as they typically do.

"The ones that are captured are very thin, emaciated birds — these are animals who know how to care for themselves that don’t know where they are," Holcomb says. "The starvation is secondary, so something is going on that's making them not able to hunt."
State and federal wildlife authorities are analyzing blood samples from the sick and dead birds. Holcomb says the results should be in within a week or two.

Holcomb speculates that domoic acid, a neurotoxin produced by algae, may be a culprit. Birds ingest the chemical, which can cause permanent short-term memory loss, if they eat fish and shellfish that have consumed algae. But the birds aren't suffering seizures (and falling from the sky while flying), a hallmark of domoic acid poisoning. (Birds and humans that are poisoned by domoic acid may also experience vomiting, nausea, diarrhea, abdominal cramps, headache, dizziness, confusion, motor weakness, irregular heartbeats and coma.)

Another possible cause: a virus peculiar to pelicans or some other unknown toxin in the fish they're eating, Holcomb says, noting that if domoic acid poisioning were to blame, sea lions, seals and possibly whales and dolphins would likely have been affected. "There are a lot of big question marks," he says. "Right now everything is in the air."

California brown pelicans are an endangered species that almost died out in the late 1960s after exposure to the insecticide DDT (banned in 1972 because of its probable carcinogenic effects) and its byproduct DDE caused their eggshells to thin. Worldwide, there are an estimated 650,000 brown pelicans, the majority of them in Peru.

Image of Brown Pelican/National Park Service