No Silver Bullet

The California condor seems well on the path to recovery: the population has rebounded from 22 to about 400 birds, and half are flying in the wild. But these positive results are deceptive, scientists say. The condors are still suffering from chronic lead poisoning, and the population is unlikely to recover fully on its own.

The species “has been a symbol of environmental tragedy and triumph for over 30 years,” the authors write. In 1982, the California condor (Gymnogyps californianus) was nearly extinct, due partly to lead poisoning. Thanks to breeding programs, the population has bounced back. But the birds are getting a lot of outside help: managers monitor their movements, supply them with food, vaccinate them, clean their nesting sites, and perform regular health check-ups.

In a study published in Proceedings of the National Academy of Sciences, researchers measured lead levels in the blood of free-flying California condors from 1997 to 2010. About a fifth of the birds sampled each year had lead poisoning, the team found. Over that time period, nearly half the condors had lead levels high enough to require treatment. 

Scientists believe that most of the lead comes from bullets left in animals that the condors eat. The study authors provided further evidence: 79 percent of California condors released into the wild had lead isotope ratios in their blood similar to those of bullets.

If managers keep helping the birds, the California condor population will remain stable, the researchers predict. But without intervention, the number of birds will quickly dwindle. The management efforts “conceal the lack of true recovery of a critically endangered species,” the authors write. “[T]his species is not on a trajectory to a self-sustaining wild population.” Roberta Kwok | 25 June 2012

Source: Finkelstein, M.E. et al. 2012. Lead poisoning and the deceptive recovery of the critically endangered California condor. Proceedings of the National Academy of Sciences doi: 10.1073/pnas.1203141109.

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