PLUMAGE VARIABILITY FUNCTIONS FOR STATUS SIGNALING IN LEAST AUKLETS

This study investigated whether the variable plumage of the least auklet, Aethia pusilla, a small seabird of the Bering Sea, functions for status signalling. Adult least auklets varied continuously in underpart colour from unmarked white to nearly black. Although there was variability within age groups, adults tended to lighten in plumage as they aged. There were no differences in plumage between the sexes. Observations of natural interactions among adult and immature birds of different plumage indicated that lighter birds usually defeated darker birds in agonistic interactions within each age group. Model presentation experiments were performed to test whether plumage colour alone signals social status. Auklet models presented in white plumage were approached less closely and induced more responding adult and immature birds to flee compared to the same models presented with dark plumage. Furthermore, birds with lighter plumage approached the white model closer than did birds with darker plumage. The results provide evidence for status signalling by plumage in a non-passerine bird and document another species where status signalling works within age (adult versus immature) categories. © 1990 The Association for the Study of Animal Behaviour.