Evaluating Brandt’s Cormorant (Phalacrocorax penicillatus) reproductive success: Effects of parental care behaviors and estimating individual chick survival

Variation in reproductive success is widely measured in seabird biology in an effort to indicate changes in the marine environment, or understand basic questions about ecology or conservation of seabirds. When variation in seabird reproductive success is suggested to indicate changes in the marine environment without identifying the proximate causes of such variation, inference is limited to association, and the proximate causes themselves could prove more effective as indicators. My study informs this problem by examining and quantifying proximate causes of variation in reproductive success, at the level of nests and individual chicks. I used video of Brandt’s Cormorant (Phalacrocorax penicillatus) nests on Castle Rock National Wildlife Refuge (NWR) to monitor parental care behaviors and test their influence on reproductive success in 2015. I also estimated annual variation in survival of both nests and individual eggs and chicks from 2011-2015 on Castle Rock NWR. Lastly, I compared nest survival to individual egg and chick survival to evaluate and improve upon how seabird reproductive success is traditionally measured. Parental care behaviors had no statistical influence on survival in 2015, but nest and individual egg and chick survival varied dramatically from 2011-2015 (nest survival range: 0.083-0.942; individual survival range: 0.037-0.719). Derived estimates of nest survival from egg and chick survival demonstrated validity of measuring individual survival. My results demonstrated that inclusion of proximate causal factors that influence reproductive success and contemporary parameter estimation methods help inform seabird biology and current monitoring techniques