Social status signalling in white-crowned sparrows: an experimental test of the social control hypothesis

Abstract

Abstract. Some winter flocking passerines possess variable plumage that functions to signal social status. The social control hypothesis has been proposed to explain why subordinate birds do not cheat by displaying the brighter signal of dominant birds. This hypothesis assumes like-versus-like aggression between dominants and suggests that cheating is prevented by an increase in the number of interactions that cheaters encounter with legitimately dominant birds. The presence of like-versus-like aggression in white-crowned sparrows, Zonotrichia leucophrys, was assessed by simultaneously introducing an adult and immature male, members of the highest and next to lowest ranking age-sex classes, respectively, into four aviaries containing resident adult and immature males. Contrary to the social control hypothesis there was no difference in the amount of aggression resident adults directed against introduced adults and immatures. Furthermore, resident adult males did not initiate aggression against other resident adult males more often than against resident immature males. Adult residents behaved the same regardless of whether they were the more or less common age class among residents. Social control is unlikely to be responsible for the evolutionary stability of social status signalling in white-crowned sparrows, and a review of other studies reveals little evidence that it controls cheating in any species.