More than 100 sick California brown pelicans -- a federal endangered species -- have been treated through SeaWorld's animal rescue and rehabilitation program during the past two weeks, senior staff veterinarian Judy St. Leger said Monday.

That is five to eight times more than the park normally takes in this time of year. St. Leger said experts are investigating whether there is a problem with the supply of fish on which the pelicans feed.

The emaciated and dehydrated birds have been picked up from beaches throughout the county, St. Leger said, including Carlsbad, Encinitas, Cardiff, Solana Beach and Del Mar.

Approximately 15 birds have been rehabilitated and released, while approximately 35 others have died. More than 50 birds are still being treated.

"It's very serious," St. Leger said. "The birds come in extremely debilitated. They're extremely weak."

After arriving at SeaWorld, the birds are injected with vitamins and given oral fluids containing nutrients or ground fish. If ready, St. Leger said, birds are fed a whole fish.

"The idea is to gradually get them back onto their normal diet," St. Leger said.

California brown pelicans feed primarily on mackerel, sardines and anchovies, according to U.S. Fish and Wildlife Service.

The sick birds -- all of them juveniles -- are not able to find food to support themselves, St. Leger said.

If beachgoers come across sick pelicans, St. Leger said, they should contact a lifeguard.

"We don't want people to pick up these birds," she said.

Oceanside Lifeguard Sgt. Cory Thompson said that last week a couple sick pelicans were spotted on Oceanside beaches, while an additional three or four were accidentally hooked by fishermen.

Encinitas Lifeguard Cpt. Larry Giles said two sick pelicans were spotted on the shore between Beacons and Grandview last week. Though one got away, the other was turned over to Wildlife Assist for rehabilitation.

Contact staff writer Ben Frumin at (760) 943-2313 or bfrumin@nctimes.com.