Habitat urbanization and stress response are primary predictors of personality variation in northern cardinals (Cardinalis cardinalis)

Behavioral traits that vary consistently among individuals across different contexts are often termed as ‘personality traits,’ while the correlated suite formed by those traits is called a ‘behavioral syndrome’. Both personality trait and behavioral syndrome are potentially responsive to animal ‘states’, defined as strategically relevant individual features affecting the cost-and-benefit trade-offs of behavioral actions. Both extrinsic ‘states’ (e.g. urban versus rural habitats), and intrinsic ‘states’ (e.g. sex), may shape among-individual variation in personality traits, as well as behavioral syndromes. Here, we used northern cardinals sampled from four locations to examine the effect of habitat type (urban versus rural, an extrinsic state), stress hormone corticosterone (CORT) parameters, body weight and sex (intrinsic states) on personality traits and behavioral syndrome variation. We used behavioral trials to measure five personality traits. Using principal component analysis to quantify personality traits first, followed by general linear mixed models, we found that habitat type, CORT at capture and 2-day CORT response affected some personality traits, while body weight and sex did not. Cardinals inhabiting more urbanized areas had lower CORT metabolite levels at capture and were more neophilic, less neophobic and also less aggressive than their rural conspecifics. Using structural equation modeling to construct behavioral syndromes formed by our selected personality traits, we found that urban and rural cardinals varied in the models representing syndrome structure. When utilizing the shared syndrome structural model to examine the effects of states, habitat type and 2-day CORT response appear to affect syndrome variation in a coordinated, not hierarchical, manner.