Stress associated with group living in a long-lived bird

Abstract

Many long-lived avian species adopt life strat- egies that involve a gregarious way of life at juvenile and sub-adult stages and territoriality during adulthood. However, the potential associ- ated costs of these life styles, such as stress, are poorly understood. We examined the effects of group living, sex and parasite load on the base- line concentration of faecal stress hormone (corticosterone) metabolites in a wild population of common ravens (Corvus corax). Corticoster- one concentrations were significantly higher in non-breeding gregarious ravens than in territor- ial adults. Among territorial birds, males showed higher stress levels than their mates. Parasite burdens did not affect hormone levels. Our results suggest a key role of the social context in the stress profiles of the two population fractions, and that group living may be more energetically demanding than maintaining a territory. These findings have implications for understanding hormonal mechanisms under different life styles and may inspire further research on the link between hormone levels and selective pres- sures modulating gregarious and territorial strategies in long-lived birds.