Communication By Agonistic Displays: Ii. Perceived Information and the Definition of Agonistic Displays

Abstract

Abstract1) Great skua (Stercorarius skua) interactions were studied in the club areas of colonies on Hoy and Fair Isle. Attention was centred on reactor response to postures given by actors which did not attack or escape after displaying. 2) The regression of the reactor's escape probability on distance from the actor was analysed for Facing and Not Facing orientations of the actor. 3) Responses shown to the postures Oblique/Long Call/Wing-raising (Facing and Not Facing), Neck Straight/Bill Straight (Not Facing) and Neck Straight/Bill Straight/Long Call (Not Facing) were similar, and depended on distance, rather than the posture. This rules out the possibility that these postures constitute distinct threat signals. However, Neck Straight/Bill Straight (and Neck Straight/Bill Straight/Long Call) Facing showed a distinct pattern of response which indicated that they formed a (single) threat signal. 4) This pattern was consistent across the different colony-year samples. 5) It was concluded that the great skua behaviour patterns analysed here acted to define different situations rather than providing information about signaller intentions.