For three decades, the California condor has been inching away from the brink of extinction with the help of a lot of human intervention. An intensive wildlife management program, which includes captive breeding and medical monitoring of wild birds, costs an estimated $5 million per year. From a low of 22 birds in 1982 to today's population of around 400, California condors have made a modest recovery. But a recent study published in the Proceedings of the National Academies of Science shows chronic lead poisoning is a persistent problem, and the species will continue to require extensive support in order to survive in the wild if the problem is unmitigated.
The California condor is a majestic bird with wings that span more than nine feet. They are considered New World vultures and can travel 150 miles a day searching for carcasses. The trouble arises when they eat animal carcasses shot with lead-based ammunition. Myra Finkelstein, a toxicologist at UC Santa Cruz and lead author on the study, found that despite a recent ban on lead bullets, the carcasses left by hunters are the smoking gun in the case of condor lead poisoning.
From 1997 to 2010, twenty percent of the wild condors sampled suffered from lead poisoning serious enough to need chelation therapy, a metal detoxification process also used for humans with lead poisoning. Over this time period, the annual prevalence of potentially serious but nonlethal lead exposure ranged from 55 to 88 percent of the California condors in the wild.
Finkelstein and her co-authors confirmed that lead from ammunition was the primary source of the birds' contamination by isotopic analysis, which compares the specific type of lead found in samples from the birds to lead from many possible sources. A partial ban on the use of lead-based ammunition in condor habitats, enacted in California in 2008, appears to have had no effect on the incidence of lead exposure or poisoning. Some hunters could be ignoring the ban, but it's also probable that condors are scavenging outside of this protected area, where there are no constraints on the use of lead ammunition in hunting land-based species. (The U.S. Fish and Wildlife Service banned the use of lead-based ammunition in hunting waterfowl in 1991, but there is no comparable federal action regarding the use of the same ammunition on any other species).
Condors need to eat 75-150 carcasses every year to maintain a healthy weight. Finkelstein and her colleagues determined that even if fewer than 2% of the carcasses contain lead, there is a 50% chance that a condor will eat contaminated meat. At this rate, the hope for a self-sustaining wild condor population is unrealistic. The current efforts to help the species are too resource-intensive and expensive to continue in perpetuity. Unless hunters change their practices, experts fear the wild population will again slip toward extinction in a few decades.