LOS ANGELES -- Three California condors found in northern Arizona and southern Utah have died of lead poisoning and three others had toxic levels of lead in their bodies, prompting conservationists to urge hunters to use non-lead ammunition and to carefully dispose animal carcasses that condors could feast upon.

Biologists recently captured and tested nearly 30 of the endangered birds in the region after a hiker reported seeing a dead, 11-year-old male condor in the Grand Canyon, the Peregrine Fund, which is dedicated to preserving birds of prey in the wild, said Tuesday.

Of the birds captured, two died in addition to the bird found by the hiker, reducing the overall condor population in the West from 391 to 388, according to the U.S. Fish and Wildlife Service, which oversees condor recovery.

The other three birds were treated and released back into the wild.

X-rays showed one bird had 18 shotgun pellets in its digestive system, another had six pellets and a third contained the remains of a spent bullet, suggesting the condors died after eating carcasses of animals that had been shot with lead ammunition.

Chris Parish, head of the Peregrine Fund's condor recovery program in Arizona, said lead exposure typically occur during the deer hunting season from October to early December. He said it was possible that the recent exposures were the result of illegal hunting activity or somebody putting down their animal by shooting them with lead bullets.

"The potential for scavengers to be exposed is there as long as a carcass is available," Parish said. "We're asking people, if they're going to use lead-based ammunition for any of those purposes, to remove the carcass."

He said that if the hiker hadn't found the dead condor and reported it, biologists wouldn't have tested the condors because the lead exposure occurred outside of hunting season and wouldn't have been able to capture, test and treat the birds.

Lead poisoning is the leading cause of death for condors, the largest flying land bird in North America weighing up to 26 pounds with a wingspan of about 9 feet. Condors are bred in captivity and found in the wilds of California, the Arizona-Utah border, and Baja California. They reach maturity at about 6 years and produce only one egg every other year.