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

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