Los Angeles - A mystery disease is striking California's huge flocks of pelicans, which are being found disoriented far from their usual habitat, and displaying extreme fatigue and bruising inside their beaks, the Los Angeles Times reported Wednesday.

Bird rescuers suspect that fatal algae toxins may be responsible for the scourge, but the birds do not display many of the symptoms associated with those toxins, which normally occur in the summer.

Another suspect is run-off from the fire retardant that was used in huge amounts to battle wildfires along the coast last summer.

The birds are usually seen flying in formation along the Pacific Coast or diving into the ocean to catch fish in their large beaks. But in recent weeks many have been found deep inland and far away from their usual routes.

Adding to the consternation is that many of the dead pelicans are adults, while it is usually the younger birds that are the most frequent victims to disease.

"We've ruled out starvation because there are plenty of fish in coastal waters right now," said Jay Holcomb, executive director of the northern California-based International Bird Rescue Research Centre. "We're seeking answers from all the experts we can find."