Why does dominance decline with age in wintering snow buntings?

Abstract

The influence of sex and age on success in contests over access to food was studied in a wintering population of snow buntings,Plectrophenax nivalisin northeast Scotland over a 5-year period. Males won 87% of dyadic interactions with females, but, in contrast to many other studies, first-winter birds won a majority (60–70%) of intra-sexual interactions with same-sex adults. First-winter males continued to have greater success than adult males even after controlling for an individual's role within a contest, the degree to which the contest escalated, and the severity of the weather. Contests won by adult males were more likely to have escalated, perhaps indicating a greater cost, than those won by first-winter males. Dominance status dropped from an individual's first to its second winter of life, but not thereafter. It is argued that winning winter food fights is of more immediate benefit to first-winter birds, and that reversal of the usual age-related dominance pattern may be due to the species’ itinerant nature in winter combined with a lack of long-term pair-bonds or individual recognition. Assertion of dominance therefore carries only short-term benefits which may not override the costs of aggressive behaviour.