Environmental contaminants in California condors

Five wild California condors (Gymnogyps californianus) that died in 1980-86 were necropsied and tissues were analyzed for environmental contaminants. Three died of lead (Pb) poisoning, 1 presumably of cyanide (CN) poisoning, and 1 nestling of handling shock. Organochlorine concentrations were low in 4 condors that were analyzed for these contaminants. Blood samples from 14 wild and 14 captive condors were analyzed primarily for Pb. Five of 14 wild condors sampled had elevated (>0.70 ppm) concentrations of Pb in blood whereas Pb concentrations in all captive condors were low. Lead levels in individual birds often fluctuated over time. Lead exposure, especially poisoning, was a major factor affecting the wild California condor population during 1982-86. The probable source of Pb was bullet fragments in carrion on which condors were feeding. J. WILDL. MANAGE. 52(2):238-247 The wild population of California condors has been declining for many years (Koford 1953, Wilbur 1978, Snyder and Johnson 1985). In the winter of 1984-85 it declined from 15 to 9 individuals and 4 of 5 known breeding pairs were lost. Since 1985 1 wild California condor has died and the remaining 8 were placed in captivity to enhance the captive flock. Many causes have contributed to the decline of the condor although most are poorly documented (Wilbur 1978, Ogden 1983, Harlow et al. 1984). Some causes that appear to have contributed to the decline are shooting, loss of habitat, disturbance, inadequate food supply, and environmental contaminants. The role of contaminants in the decline of California condors has only been partially assessed (Kiff et al. 1979, Wiemeyer et al. 1983, 1986b). Contaminants such as 1,1-dichloro-2,2-bis(pchlorophenyl)ethylene (DDE); strychnine; sodium monofluoroacetate (Compound 1080); and Pb have been implicated in the condor decline but little corroborative evidence has been provided. The contaminant levels in potential condor food and in the tissues of turkey vultures (Cathartes aura) and common ravens (Corvus corax) that occur within the condor range were assessed in 1980-81 (Wiemeyer et al. 1986b). Wiemeyer et al. (1986b) determined that, in some cases, Pb concentrations in bones of turkey vultures and feathers of California condors were elevated above normal background levels. Elevated levels of organochlorines were also found in turkey vultures, but not in potential condor food. These findings prompted us to sample tissues and determine causes of mortality of all dead condors, and obtain blood samples from all condors captured for telemetry studies during 198286 or for use in captive flocks. Our objective was to identify contaminants that may have been involved in the decline of the condor population. For field assistance we gratefully acknowledge L. Andaloro, D. B. Barbour, D. A. Clendenen, J. Grantham, J. A. Hamber, S. B. Kimple, D. B. Ledig, V. J. Meretsky, J. C. Ogden, L. A. Riopelle, G. D. Sanders, H. A. Snyder, N. F. R. Snyder, and J. J. Woods of the Condor Research Center and veterinarians B. Gonzales of the Los Angeles Zoo; J. L. Allen, D. L. Janssen, and J. E. Oosterhuis of the San Diego Wild Animal Park; P. K. Ensley of the San Diego Zoo; and P. A. Gullett of the National Wildlife Health Center. N. J. Thomas provided analytical methods used at the National Wildlife Health Center. We thank S. H. Fritts, R. M. Jurek, H. R. Perry, J. E. Semberski, and M. G. Holmes for administrative support. We owe special thanks to the ranchers of Kern County who allowed us to trap California condors on their property. We thank J. Grantham, C. E. Grue, L. F. Kiff, O. H. Pattee, and S. R. Wilbur for reviewing the manuscript. The Idaho Cooperative Fish and Wildlife Research unit is funded and supported by Idaho Department of Fish and Game, University of Idaho, U.S. Fish and Wildlife Service, and the 1 Present address: Idaho Cooperative Fish and Wildlife Research Unit, College of Forestry, University of Idaho, Moscow, ID 83843.