Environmentally induced stress affects fitness of bold and shy alike: A long‐term study of personality and feather corticosterone in Arctic‐breeding kittiwakes

Individual repeatable variation in behaviour, that is 'personality', is hypothesised to mediate how animals respond to environmental stress. However, temporal variability in local conditions and spatial constraints across the annual cycle may affect individual responses to environmental change and the subsequent impact on fitness. Here we tested how the relationships among personality, stress exposures and fitness may vary between the breeding and wintering periods in the black-legged kittiwake (Rissa tridactyla), a long-lived migratory seabird inhabiting the rapidly changing Arctic. We conducted a long-term (2013-2021) study to explore how personality, represented by boldness, was related to feather corticosterone (fCORT), an indicator of stress exposure during feather growth. To examine temporal variation in this relationship, we focused on feathers grown during the breeding, post-breeding and pre-breeding stages, three periods when seabirds experience varying spatial constraints. We studied the covariation in fCORT, boldness and two fitness measures (chick survival and adult return rates) while correcting for two major proxies of resource availability: the subpolar gyre and Atlantic water influx (AWI) We observed a season-dependent effect of boldness: 'bolder' individuals had lower fCORT concentrations than 'shyer' conspecifics during breeding and post-breeding but higher levels prior to breeding. Higher fCORT during breeding occurred during years of low AWI and correlated with lower chick survival, while higher fCORT prior to breeding correlated with lower likelihood of return to the colony. Personality did not mediate inter-annual relationships between fCORT and environmental measures or fCORT and fitness. Our results highlight that while the negative effects of environmentally induced stress on fitness appeared to be ubiquitous across personality types, how and when bold and shy individuals experience stress is highly context dependent, reflecting different spatial and temporal constraints during the breeding and wintering stages.