The role of age, sex, subspecies, body size and fuel load in determining the social status of a migratory passerine during the non-breeding period

Abstract

The social status is seen determined by sex and/or age, body size and body condition. However, knowing which of these factors play a more relevant role to determine social dominance is often difficult since studies of competition under field conditions are com-monly affected by several confounding factors that cannot be controlled or are even un-known. We studied experimentally which factors determine the dominance in captive Northern Wheatears, Oenanthe oenanthe during the non-breeding season, i.e., autumn and winter. We subjected two individuals at a time to experimental conditions with food provided at a feeder; these individuals differed in sex, age, body size, fuel load and sub-species. Social status appeared to be determined by age and sex during the autumn migra-tion period, but not in winter. In particular, adults and males displaced first-year birds and females from the feeding site. Other traits such as body size, fuel load and subspecies, did not have significant effects on the social status.