The Rising Threat of Lead: Trends in Fatalities of California Condors

ABSTRACT Endangered species face threats that change over time, and understanding variation in the importance of threats is valuable for guiding species recovery. The reintroduced population of critically endangered California condors has faced a number of threats over the three decades since the species was first released back to the wild. We modeled interannual and interseasonal trends in the leading causes of death for wild condors. Our analysis showed strong evidence ( P = 0.971) that the estimated annual probability of death from lead toxicosis has increased since reintroduction started. This increase was most pronounced in the central California subpopulation. Adults were disproportionately affected by lead toxicosis, a trend that may be explained by increased exposure associated with age‐related changes in foraging behavior that lead to decreased reliance on clean proffered food sources. Population‐level mortality from trauma showed a temporary increase in 2012, and fire‐related mortality was higher during the summer months. Pattens also varied across subpopulations, with the southern California subpopulation of condors showing distinct temporal peaks in deaths from trauma (in 2012) and predation (in 2010). Our analysis suggests that threats to condors have not been static over space and time. Managers can therefore use this information to adaptively manage and target mitigation efforts when and where they are the most effective.