Demography of the California Condor: Implications for reestablishment

The remnant wild population of California Condors (Gymnogyps californianus) of the 1980s exhibited a rapid population decline caused by high mortality rates among adult and immature birds. The most prominent mortality factor was lead poisoning resulting from ingestion of bullet fragments in carcasse s. Successful captive breeding has allowed many birds to be released to the wild since 1992, based originally on an assumption that exposure to lead c ould be prevented by food subsidy. The mortality of released birds, however , has generally exceeded levels needed for population stability calculated from simple population models. Collision with overhead wires was the most f requent cause of death in releases before 1994. Lead poisoning again surfac ed as a problem starting in 1997 as older birds began feeding on carcasses outside the subsidy program. Although poisonings have been treated successf ully by chelation therapy in recaptured birds, food subsidy is proving an i neffective solution to lead exposure. The best long-term solution appears t o be either the creation of large reserves where hunting is prohibited or t he restriction of hunting to nontoxic ammunition in release areas. Until so urces of lead contamination are effectively countered, releases cannot be e xpected to result in viable populations. In addition, problems involving hu man-oriented behavior have resulted in the permanent removal of many releas ed birds from the wild. The most promising reduction in human-oriented beha vior has been achieved in one release of aversively conditioned, parent-rea red birds. Rigorous evaluation of the factors reducing attraction to humans and human structures has been hampered by confounding of techniques in rel eases. Behavioral problems could be more quickly overcome by adoption of a comprehensive experimental approach.