Effects of Lead Exposure, Flock Behavior, and Management Actions on the Survival of California Condors ( Gymnogyps californianus )

Translocation is an increasingly important tool for managing endangered species, but factors influencing the survivalof translocated individuals are not well understood. Here we examine intrinsic and extrinsic drivers of survivalfor critically endangeredCalifornia 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 survivalrates 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 profferedcarcasses, 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 profferedfood, and these “ wilder” behaviors were associated with lower survival. After accounting for these behaviors, we found a positive survivaltrend, which we attribute to ongoing improvements in management. Our findings illustrate that the survivalof translocated animals, such as highly social California condors, is influenced by behaviors that change through time.