Bird expert says the mysterious illness is very worrying
Wildlife experts in California, US, are concerned about a mysterious illness affecting brown pelicans from San Diego to San Francisco.
Dozens of the birds - bruised and disoriented - have been landing on highways, airport runways, farm fields and house backyards.
The pelicans have been coming down many kilometres from their normal habitats.
The International Bird Rescue Research Center, which is dealing with the sick animals, says the cause is unknown.
"Typically this time of year we would see a significant die-off of young brown pelicans. We are seeing a larger than normal die-off of adults," it said in a release.
Sometimes this behaviour has been associated with domoic acid, a neurotoxin produced by marine algae (phytoplankton). The birds would take in the acid by eating fish and shellfish that have themselves ingested the algae.
But the pelicans were not exhibiting the other symptoms typical of this problem, the centre added.
Blood samples and carcasses have been sent to laboratories for investigation, the LA Times has reported.
"We just became aware of this problem a few days ago," David Caron, a professor of biological sciences at the University of Southern California, told the paper.
"By the end of the week, we'll have information that should tell us whether or not these animals test positive for phytoplankton toxins."
One theory is that the birds may have ingested chemicals from fire retardants used widely by emergency services recently to tackle severe blazes that ravaged the state.
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