Web Release Date: August 30,
Ammunition is the Principal Source of Lead Accumulated by California Condors Re-Introduced to the Wild
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Department of Environmental Toxicology, University of California, Santa Cruz, California 95064, Bodega Bay Institute, 2711 Piedmont Avenue, Berkeley, California 94705, Ventana Wildlife Society, 19045 Portola Drive, Suite F-1, Salinas, California 93924, Department of Geological and Environmental Science, Stanford University, Stanford, California 94305, The Peregrine Fund, World Center for Birds of Prey, 5668 W. Flying Hawk Lane, Boise, Idaho 83709, and Zoological Society of San Diego, P.O. Box 120551, San Diego, California 92112
Received for review March 30, 2006
Revised manuscript received July 19, 2006
Accepted July 20, 2006
Abstract:
The endangered California Condor (Gymnogyps californianus) was reduced to a total population of 22 birds by the end of 1982. Their captive-bred descendants are now being released back into the wild in California, Arizona, and Baja California, where monitoring indicates they may accumulate lead to toxic levels. Fragments of ammunition in the carcasses of game animals such as deer, elk, and feral pigs not retrieved by hunters or in gut piles left in the field have been considered a plausible source of the lead, though little direct evidence is available to support this hypothesis. Here, we measured lead concentrations and isotope ratios in blood from 18 condors living in the wild in central California, in 8 pre-release birds, and in diet and ammunition samples to determine the importance of ammunition as a source of exposure. Blood lead levels in pre-release condors were low (average 27.7 ng/mL, SD 4.9 ng/mL) and isotopically similar to dietary and background environmental lead in California. In contrast, blood lead levels in free-flying condors were substantially higher (average 246 ng/mL, SD 229 ng/mL) with lead isotopic compositions that approached or matched those of the lead ammunition. A two-endmember mixing model defined by the background 207Pb/206Pb ratio of representative condor diet samples (0.8346) and the upper 207Pb/206Pb ratio of the ammunition samples (0.8184) was able to account for the blood lead isotopic compositions in 20 out of the 26 live condors sampled in this study (i.e., 77%). Finally, lead in tissues and in a serially sampled growing feather recovered post-mortem from a lead-poisoned condor in Arizona evidence acute exposure from an isotopically distinct lead source. Together, these data indicate that incidental ingestion of ammunition in carcasses of animals killed by hunters is the principal source of elevated lead exposure that threatens the recovery in the wild of this endangered species.
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