Coping with novelty and stress in free-living house sparrows

Individuals respond differently to stressors and it has been suggested that stress responses are related to coping styles (consistent individual differences in behavior and physiology). We studied behavioral responses to a novel object and corticosterone response to stress during chick rearing in free-living female house sparrows (Passer domesticus). To prevent mates from influencing each others' behavior, we removed the males temporarily from nests and tested the females the following day either with a novel object placed on the nest box or as control. The two groups differed only in behaviors that were a priori defined as responses to the novel object (latency to first feeding, time spent near the nest, and inspecting the novel object by hovering in front of it) indicating that mate-removal per se had no effect on female behavior. Based on these variables, females' coping behaviors were categorized as 'bold', 'inquisitive' or 'shy' by discriminant analysis. Baseline corticosterone, measured on the day following the novel-object or control test, was not related to any measure of coping. Stress-induced corticosterone, however, was negatively related to number of hoverings in front of the nest (a measure of explorativeness) and accordingly differed between the behavioral coping categories, with 'inquisitive' birds having the lowest stress response. We propose that the relationship between physiological stress response and behavioral response to novelty (a component of personality or coping style) may be more complex than previously suggested, and individuals cannot always be unambiguously categorized along a single personality axis.