Hundreds of brown pelicans (Pelecanus occidentalis) have been found sick or dead off the California coast in the past month, the victims of a mysterious ailment that has scientists baffled.

When found alive, the birds appear hungry and disoriented. But necropsies performed on dead pelicans found that they had been eating, so the casualties don't appear to be from lack of prey. But their stomachs did contain unusual prey, like squid—not the sardines and anchovies they normally dine on.

Many of the pelicans also appear to have some sort of unidentified residue on their feathers, which may affect the feathers' insulating ability. "When we wash them, you can tell something is coming off. The water is discolored, like when you wash really dirty clothes," Jay Holcomb, director of the International Bird Rescue Research Center (IBRRC) in Cordelia, Calif., told The Mercury News. "That's not normal."

Scientists don't know where this residue is coming from or what it is exactly, but so far theories include side effects from red tide or pollution runoff into the ocean.

Many of the birds coming into the center suffer from hypothermia. Holcomb told the newspaper that if the birds are cleaned soon enough, they regain their health within two weeks. So far, afflicted pelicans brought to rescue centers have had about a 60 percent survival rate.

Right now, rescue centers are inundated with sick pelicans. Another IBRRC site in San Pedro has 200 birds, and the San Francisco Oiled Wildlife Care and Education Center (also run by the IBRRC) is treating another 100. The IBRRC alone is spending $1,000 a day to feed and care for the birds. Another group called Pacific Wildlife Care estimates it costs $500 to care for and rehabilitate a sick pelican.

The California Department of Fish and Game announced it is helping to investigate the deaths, but it has no actual money to spend, thanks to the state's current budget crisis.

A similar, also unexplained pelican die-off occurred in January 2009.

Brown pelicans are a rare endangered species success story. Once ravaged by the effects of DDT, the brown pelican was formerly protected under the U.S. Endangered Species Act. But decades after DDT was banned in the U.S., pelican populations have rebounded, and the bird was removed from the endangered list last November. The current population is estimated at around 650,000.

Image: Brown pelican, via Wikimedia Commons