Abstract

The reintroduction of California condors (Gymnogyps californianus) to the wild began in 1992 after the last wild bird was brought into captivity in 1987. A successful captive breeding program produced a first chick in 1988 and has increased the size of the California condor population from a low of only 22 birds in 1982, to 63 birds in 1992, and 197 birds in 2002. Currently, there are 90 birds in the wild: 44 in California, 41 in Arizona (this includes the first successfully wild-hatched and fledged chick), and five in Baja California, Mexico.

To date, 174 birds have been released, with an overall mortality rate of 33%. Carcasses of most dead condors (85%) have been recovered and necropsied by the Department of Pathology at the San Diego Zoo (the exception being carcasses serving as evidence in legal proceedings, which go to the U.S. Fish and Wildlife Service for necropsy). Causes of mortality of condors that have died during the first 10 years of the program from 1992–2002 have been analyzed: 17% of all mortalities have been due to power line collisions; 13% due to lead toxicity or suspected lead toxicity; 11% due to predation; and 6% have been due to emaciation. Causes of mortality have not been determined in 21% of the mortalities because of advanced autolysis or scavenging of the carcass. Other causes of mortality have included wildfires, shooting, propylene glycol poisoning, drowning, and neoplasia.

In the first 2 years after releases began in 1992, five of eight released birds were killed in power line collisions, so in 1994 we began a power line aversion program for all pre-release birds, which appears to have successfully reduced power line collisions as a significant cause of mortality, with only four power line deaths documented in the last 10 years. Currently, lead toxicity ranks as the largest threat to California condors. Birds appear to be at increased risk for lead poisoning once they reach sexual maturity at approximately 6 years of age and begin foraging for food on their own. From 1999–2002, lead toxicity was the cause of death in 21% of recovered carcasses, and we suspect that the cause of mortality in a significant percentage of the unrecovered carcasses was likely due to lead toxicity, given the social feeding habits of this species, as well as the numbers of birds known to be mature and foraging for food on their own at the time they died. Lead toxicity is not a new threat—it is thought to have been a significant contributing factor to the demise of the California condor in the wild, with three cases reported in the early 1980s.¹ A comprehensive monitoring, screening and treatment program for lead toxicity was instituted for wild condors, and a multiagency task force and the U.S. Fish and Wildlife Service (USFWS) are proceeding with hunter awareness programs to educate the public about ways to eliminate this threat by retrieving or burying carcasses or gut piles and using lead-free ammunition.

Acknowledgments

The authors wish to recognize the field biologists of the USFWS, Peregrine Fund and Ventana Wilderness Society who work hard in difficult conditions to monitor and care for these birds in the wild, and who perform the often-difficult task of immediately recovering dead birds for pathology. We thank the pathologists at the San Diego Zoo for their contributions to this data, and Ron Jurek at the California Department of Fish and Game for keeping meticulous track of population size and distribution. We wish to thank the veterinary and animal care staff of the breeding facilities at the Los Angeles Zoo, San Diego Wild Animal Park and World Center for Birds of Prey for their efforts in providing healthy and behaviorally well-prepared birds for reintroduction to the wild. Special thanks to the members of the California Condor Recovery Team and its contributors who continue to actively and tenaciously manage this endangered species.

Literature Cited

1.  Janssen, D.L., J.E. Oosterhuis, J.L. Allen, M.P. Anderson, K.G. Kelts, S.N. Wiemeyer. 1986. Lead poisoning in free-ranging California condors. J Am Vet Med Assoc. 198 (9): 1115–1116.