California banned the use of lead bullets to kill game in 2008, but apparently not all hunters have switched to copper. Like still-buried mines long after the war has ended, the bodies of carcasses killed with lead bullets are poisoning scavenging birds such as the California condor.
The great condor, owner of the widest wingspan in North America, had dropped to 22 birds throughout the United States in 1982—a long way from its heyday, when the nine-foot-wingspan birds flew freely in a habitat that stretched from British Columbia to Mexico, the San Jose Mercury News reported.
Condors have made a notable comeback, the study in Proceedings of the National Academy of Sciences noted, but mainly because of human intervention.
Comparing feathers and blood samples from trapped condors both before and after the 2008 law, researchers found no difference in lead levels, the study reported. Lead poisoning can damage the nervous systems of the birds as well as impair liver and kidney function and cause death, an article about the findings in the journal Nature said. Moreover, at least 20 percent of condors living in the wild carried high enough lead levels that they needed expensive treatment to remove it.
“By any measure, the lead poisoning rates in condors are of epidemic proportions,” said Myra Finkelstein, a toxicologist at the University of California at Santa Cruz, who led the research, to Nature.
The condor population is up to about 400 birds from about 22 in 1982, Nature said, but many of them live and are born in captive breeding centers. In other words, those birds are not in the wild. Just 24 chicks were born in the wild, Nature said, a rate that would take 1,800 years to reach the goal of 150 wild birds outlined in California’s recovery plan.
“Condors must consume 75–150 carcasses every year to maintain a healthy weight,” Nature noted. “The study found that even if fewer than two percent of the carcasses contain lead, there is a 50 percent chance that a condor will eat contaminated meat.”
The Mercury News said that 30 percent of the condors captured annually have lead levels high enough to block reproduction and cause immune system problems, even if it doesn’t kill the birds.
The birds need constant human monitoring if they are to survive, which is not optimal for full recovery of the species, the researchers said.
“Lead poisoning is preventing the recovery of California condors,” Finkelstein told the Mercury News. “The population is not self-sustaining.”