Drawn into the vortex: The facing-past encounter and combat in lekking male greater sage-grouse (Centrocercus urophasianus)

摘要

Lekking male greater sage-grouse (Centrocercus urophasianus) compete with neighbours not only by strutting to attract females but also by directly challenging other males. These challenges include approaching another male and adopting an anti-parallel orientation at close quarters ('facing past encounter') and fighting, in which the birds strike one another with their wings. Facing past encounters and facing past encounters that led to fights in free-living sage-grouse were videotaped and analysed to test predictions arising from two sets of hypotheses to account for the features of such encounters. They could be used to assess or threaten opponents (index signal or threat signal hypotheses) or they may be the result of a stalemate in which one bird's attempts to gain an vantage point for attack are neutralised by counter moves by the other bird (combat hypothesis). Frame-by-frame analyses of both facing past encounters and fights were used to extract data to test specific predictions arising from the three hypotheses. The results, overall, support the hypothesis that the facing past orientation arises from combat. However, the results also suggest that, once in the anti-parallel orientation, opportunities emerge for communication to take place.