Nest defense, personality, and fitness of a locally endangered island passerine

摘要

Abstract Personality, or repeatable variation in behavior, may impact an animal's survival or reproduction. Parental aggression is one such personality trait with potentially direct implications for fitness, as it can improve offspring survival during vulnerable early life stages. We took advantage of a long‐term nest box and fledgling survival monitoring project to explore the potential fitness consequences of both repeatability and variation in parental aggression in breeding pairs of a locally endangered passerine species (Såli: Micronesian starling, Aplonis opaca) in the presence of an invasive predator, the brown treesnake (Boiga irregularis), on the island of Guam. To do so, we tested for associations between aggressive offspring defense throughout the nesting cycle and three fitness measures: hatching success, fledging success, and post‐fledging survival. Aggression varied greatly among breeding pairs and was repeatable within pairs (R = .47), providing evidence of a personality trait. Consistent with parental investment theory, nest stage was the best predictor of parental aggression, which increased with offspring age. Aggression was positively correlated with hatching success during the egg stage, but not nestling or post‐fledging survival. We propose that parental aggression was decoupled from nestling and fledgling survival because parents were unable to defend young from nocturnal, invasive brown treesnakes. More broadly, our findings demonstrate that repeatable variation in personality traits may not necessarily confer fitness benefits, particularly in the presence of invasive predators.