Seasonal Changes of Sexual and Territorial Behaviour and Plasma Testosterone Levels in Male Lesser Sheathbills (Chionis minor)

Abstract

Lesser sheathbills C. minor (Aves: Charadriiformes) have a brief annual breeding season but under certain circumstances territoriality persists outside the breeding season. Seasonal increases in plasma testosterone levels in free-living adult males coincided with increases in the mass of testes, the seasonal peak in mutual pair displays and the occurrence of nest-building and copulation. Territorial aggression outside the breeding season was not dependent on high testosterone levels.