Demography of the California Condor: Implications for Reestablishment

Authors

  • Vicky J. Meretsky,

    1. *School of Public and Environmental Affairs, Indiana University, 1315 East 10 th Street, Bloomington, IN
      47405–1701, U.S.A., email meretsky@indiana.eduWildlife Preservation Trust International, P.O. Box 16426, Portal, AZ 85632, U.S.A. Department of Environmental Science, Policy & Management, 151 Hilgard Hall, University of California, Berkeley, CA 94720–3114, U.S.A. §Wind Wolves Preserve, P.O. Box 189, Maricopa, CA 93252, U.S.A. **Grambling Cooperative Wildlife Project, Grambling State University, P.O. Box 841, Grambling, LA 71245, U.S.A.
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  • Noel F. R. Snyder,

    1. *School of Public and Environmental Affairs, Indiana University, 1315 East 10 th Street, Bloomington, IN
      47405–1701, U.S.A., email meretsky@indiana.eduWildlife Preservation Trust International, P.O. Box 16426, Portal, AZ 85632, U.S.A. Department of Environmental Science, Policy & Management, 151 Hilgard Hall, University of California, Berkeley, CA 94720–3114, U.S.A. §Wind Wolves Preserve, P.O. Box 189, Maricopa, CA 93252, U.S.A. **Grambling Cooperative Wildlife Project, Grambling State University, P.O. Box 841, Grambling, LA 71245, U.S.A.
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  • Steven R. Beissinger,

    1. *School of Public and Environmental Affairs, Indiana University, 1315 East 10 th Street, Bloomington, IN
      47405–1701, U.S.A., email meretsky@indiana.eduWildlife Preservation Trust International, P.O. Box 16426, Portal, AZ 85632, U.S.A. Department of Environmental Science, Policy & Management, 151 Hilgard Hall, University of California, Berkeley, CA 94720–3114, U.S.A. §Wind Wolves Preserve, P.O. Box 189, Maricopa, CA 93252, U.S.A. **Grambling Cooperative Wildlife Project, Grambling State University, P.O. Box 841, Grambling, LA 71245, U.S.A.
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  • David A. Clendenen,

    1. *School of Public and Environmental Affairs, Indiana University, 1315 East 10 th Street, Bloomington, IN
      47405–1701, U.S.A., email meretsky@indiana.eduWildlife Preservation Trust International, P.O. Box 16426, Portal, AZ 85632, U.S.A. Department of Environmental Science, Policy & Management, 151 Hilgard Hall, University of California, Berkeley, CA 94720–3114, U.S.A. §Wind Wolves Preserve, P.O. Box 189, Maricopa, CA 93252, U.S.A. **Grambling Cooperative Wildlife Project, Grambling State University, P.O. Box 841, Grambling, LA 71245, U.S.A.
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  • James W. Wiley

    1. *School of Public and Environmental Affairs, Indiana University, 1315 East 10 th Street, Bloomington, IN
      47405–1701, U.S.A., email meretsky@indiana.eduWildlife Preservation Trust International, P.O. Box 16426, Portal, AZ 85632, U.S.A. Department of Environmental Science, Policy & Management, 151 Hilgard Hall, University of California, Berkeley, CA 94720–3114, U.S.A. §Wind Wolves Preserve, P.O. Box 189, Maricopa, CA 93252, U.S.A. **Grambling Cooperative Wildlife Project, Grambling State University, P.O. Box 841, Grambling, LA 71245, U.S.A.
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Abstract

Abstract: 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 carcasses. Successful captive breeding has allowed many birds to be released to the wild since 1992, based originally on an assumption that exposure to lead could 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 frequent cause of death in releases before 1994. Lead poisoning again surfaced as a problem starting in 1997 as older birds began feeding on carcasses outside the subsidy program. Although poisonings have been treated successfully by chelation therapy in recaptured birds, food subsidy is proving an ineffective solution to lead exposure. The best long-term solution appears to be either the creation of large reserves where hunting is prohibited or the restriction of hunting to nontoxic ammunition in release areas. Until sources of lead contamination are effectively countered, releases cannot be expected to result in viable populations. In addition, problems involving human-oriented behavior have resulted in the permanent removal of many released birds from the wild. The most promising reduction in human-oriented behavior has been achieved in one release of aversively conditioned, parent-reared birds. Rigorous evaluation of the factors reducing attraction to humans and human structures has been hampered by confounding of techniques in releases. Behavioral problems could be more quickly overcome by adoption of a comprehensive experimental approach.

Abstract

Resumen: Las poblaciones silvestres remanentes del cóndor de California (Gymnogyps californianus) de los anõs 80 exhibieron una disminución poblacional rápida debido a altas tasas de mortalidad de individuos adultos e inmaduros. El factor de mortalidad más prominente fue el envenenamiento por plomo ocasionado por la ingestión de fragmentos de municiones en cadáveres. La reproducción exitosa en cautiverio ha permitido muchas liberaciones en ambientes silvestres desde 1992, bajo el argumento de que la exposición al plomo puede ser prevenida mediante el subsidio de alimento. Sin embargo, la mortalidad de aves liberadas ha excedido generalmente los niveles necesarios para alcanzar una estabilidad poblacional calculada a partir de modelos poblacionales simples. Las colisiones con alambres en lo alto fueron la causa más frecuente de las muertes en liberaciones anteriores a 1994. A partir de 1997, el envenenamiento con plomo surgió una vez más como un problema, puesto que las aves de edad avanzada comenzaron a alimentarse de cadáveres fuera del programa de subsidio. A pesar de que el envenenamiento ha sido tratado exitosamente mediante terapia de quelación de las aves recapturadas, el subsidio de alimento ha probado ser una solución ineficaz contra la exposición al plomo. Las mejores soluciones de largo plazo aparentan ser la creación de reservas grandes donde la caza sea prohibida o se restrinja la caza a municiones no tóxicas en las áreas de liberación. Solo una vez que la contaminación por plomo sea contrarrestada efectivamente, no se podrá esperar que las liberaciones resulten en poblaciones viables. Además, los problemas de conductas orientadas hacia humanos ha resultado en la remoción permanente de muchas aves liberadas de zonas silvestres. La reducción más prometedora de conductas orientadas hacia humanos ha sido obtenida en una liberación de aves criadas por sus padres y condicionadas adversamente. La evaluación rigurosa de los factores que reducen la atracción hacia humanos y estructuras de humanos ha sido obstaculizada por la confusión de técnicas en las liberaciones. Los problemas de conducta podrían ser superados más rápidamente mediante la adopción de una estrategia experimental comprensiva.

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