Translocation is an increasingly important tool for managing endangered species, but factors influencing the survival of translocated individuals are not well understood. Here we examine intrinsic and extrinsic drivers of survival for critically endangered California condors (Gymnogyps californianus) whose wild population recovery is reliant upon releases of captively bred stock. We used known fate models and information-theoretic methods to compare the ability of hypothesized covariates, most of which serve as proxies for lead exposure risk, to predict survival rates of condors in California. Our best supported model included the following predictors of survival: age of the recovery program, precipitation, proportion of days observed feeding on proffered carcasses, maximum blood lead concentration over the preceding 18 months, and time since release. We found that as flocks have increased in size and age, condors are increasingly likely to range more widely and less likely to be observed feeding on proffered food, and these “wilder” behaviors were associated with lower survival. After accounting for these behaviors, we found a positive survival trend, which we attribute to ongoing improvements in management. Our findings illustrate that the survival of translocated animals, such as highly social California condors, is influenced by behaviors that change through time.
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We thank the United States Fish and Wildlife Service California Condor Recovery Program, The Nature Conservancy, The Zoological Society of London, and field crews associated with Pinnacles National Park, Ventana Wildlife Society, and the Hopper Mountain National Wildlife Refuge Complex. Special thanks to T. Kelly, D. Moen, B. Rideout, S. Scherbinski, and A. Welch for their important contributions to this study. We are also grateful to D. Doak and three anonymous reviewers for providing helpful comments on an earlier manuscript draft. This project was supported by the U.S. Fish and Wildlife Service. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service.
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Bakker, V.J., Smith, D.R., Copeland, H. et al. Effects of Lead Exposure, Flock Behavior, and Management Actions on the Survival of California Condors (Gymnogyps californianus). EcoHealth 14 (Suppl 1), 92–105 (2017). https://doi.org/10.1007/s10393-015-1096-2