Tests are being conducted on two rare condors found dead in water tanks in Southern California, officials say. The decayed carcasses of the two birds were found about two weeks apart last month in open-air water tanks used by Kern County firefighters, the Los Angeles Times reported Saturday. The remains were sent to a forensics laboratory in Oregon to determine how the birds died. There are only about 100 condors living in the wild in the state and the deaths of three of them this year are considered a blow to decades-long efforts to bring the species back from the brink of extinction, said Kim Delfino, director of Defenders of Wildlife California Program. The county fire department is working with officials from the condor program to look at ways to prevent further deaths during the next wildfire season when the tanks are refilled with water, the Times said. "A lot of time and effort goes into each individual bird and it's never a good thing to hear about another dead condor," Steve Kirkland of the U.S. Fish and Wildlife Service told the newspaper in an email. "While the loss of the two birds to the recent drownings is a setback, the larger cause of mortality, and the primary threat to the recovery, of the species is lead poisoning." The Times reported recently that the Los Angeles Zoo and Botanical Gardens had treated 21 condors for lead poisoning in October, about half the number seen in a typical year. Adam Keats, senior counsel and urban wildlands program director for the Center for Biological Diversity, said the high amount of lead poisoning being seen in condors is likely linked to hunting. "There's a wide use of lead ammunition in condor habitats. The availability of lead needs to be reduced by sale and stocking," Keats said. Lead poisoning is the leading cause of death among juvenile and adult condors, said Curtis Eng, chief veterinarian at the zoo, noting at least one bird died of lead toxicity this year.