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Lead Exposure And Hormonal Stress Response In California Condors


The primary factor inhibiting the recovery of the critically endangered California condor (Gymnogyps californianus) is lead poisoning from ingestion of spent lead ammunition. My dissertation research documents the sources and effects of lead poisoning in condors, and provides the first information on the effects of lead on the hormonal stress response in condors. My first chapter aims to help identify sources of lead to condors by investigating three illegal condor shooting events. I use lead isotope ratios of condor tissues as well as ingested and embedded ammunition to find probable cause to link these shooting events. For my second and third chapters, I provide what are to the best of my knowledge the first data on the hormonal stress response in condors, and how lead exposure impacts this stress response. We know the vast majority of wild California condors are frequently lead poisoned, but we have limited data on how these frequent lead poisoning events affect the birds’ physiology. Lead poisoning has been shown in other organisms to heighten the hormonal stress response, which can lead to suppressed fitness in wild birds. My findings indicate that this dysfunction is occurring in wild condors, as I found a positive association between hormonal stress response outcomes and the amount of time a condor spends at risk for lead poisoning (foraging outside the management area). Interestingly, I also found that the annual frequency of a condor feeding on marine mammals, which contain high levels of hormone-disrupting chemicals such as polychlorinated biphenyls, is also associated with hormonal stress response elevation. My work fills a critical lack in our understanding of how long-term contaminant exposure might impact the California condor recovery effort, and has important implications for other scavenging species exposed to lead and other environmental contaminants worldwide. Future study is needed to investigate whether the altered hormonal stress response is impairing the fitness, survival and reproduction of wild condors.

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