SANTA CRUZ, CA--A study led by environmental toxicologists at the University of California, Santa Cruz, has confirmed what wildlife biologists have long suspected: Bullet fragments and shotgun pellets in the carcasses of animals killed by hunters are the principal sources of lead poisoning in California condors that have been reintroduced to the wild.
Lead poisoning is a major factor limiting the success of efforts to rebuild populations of the endangered California condor. Since the mid-1980s, condors have been bred in captivity and released back into the wild in California, Arizona, and Baja California. The birds, which feed on carrion, can ingest lead from ammunition in animal carcasses or gut piles left behind by hunters.
The UCSC researchers used a "fingerprinting" technique based on the unique isotope ratios found in different sources of lead. The technique enabled them to match the lead in blood samples from condors to the lead in ammunition. Their findings were published online today by the journal Environmental Science & Technology.
"There had been anecdotal reports for years about condors being exposed to lead from ammunition, but there was never enough clear evidence to document the extent of the problem. We knew that we could probably identify the sources of the lead using isotopic signatures," said Donald Smith, professor and chair of environmental toxicology at UCSC and a coauthor of the paper.
The study was spearheaded by Smith's graduate student, Molly Church, who is now at the University of Pennsylvania's School of Veterinary Medicine and is first author of the paper. Church worked with researchers at several institutions and organizations, including the Ventana Wildlife Society and the U.S. Fish and Wildlife Service, to collect and analyze blood and tissue samples from California condors. She also analyzed ammunition obtained from a variety of sources throughout central California.