California condors have got it rough. Not only are they an endangered species, but the free-flying birds are chock full of lead. For two decades scientists and hunting advocates have argued over the source of the heavy metal. Meanwhile, more than two dozen condors have undergone chelation therapy to remove lead, and at least four birds have died from lead poisoning.

Now scientists have irrefutably pinpointed the poison source: hunting ammunition. Condors ingest ammo when they feed on the carcasses of animals killed but not retrieved by hunters, or the gut piles left behind. The lead from 20 of the 26 live condors sampled matched that from ammo sold locally, report the authors in the current issue of Environmental Science & Technology.

Lead exposure may already be hurting the condor’s recovery:

In addition to mortalities from lead poisoning, it is likely that elevated lead exposures have a widespread effect on condor morbidity, based on the well-documented effects of lead on the peripheral and central nervous, renal, immune, reproductive, and hematopoietic systems in humans, laboratory animal models, and wildlife at blood lead levels as low as 100 ng/mL or lower.

But the authors are hopeful that their study will help to spur efforts to limit lead ammo in California—something that’s failed repeatedly in recent years.

Revealing sources of lead exposure for the California Condor will aid in the remediation and prevention of elevated exposures to this endangered species and other wildlife.

Sounds great. Any chance of hunters lining up to trade in their traditional ammo for a more expensive lead-free alternative? Guess it’s worth a shot.

Story by Alisa Opar. This article originally appeared in Plenty in October 2006. The story was added to MNN.com in July 2009.

Copyright Environ Press 2006.