CONDITION-DEPENDENCE AND SEX TRAITS IN THE MALE GREAT BUSTARD

Secondary sex traits involved in the courtship display of the male gre at bustard (Otis tarda) are analyzed in the light of condition-depende nce theory. Heaviest males at the start of the mating period further g ained about 30 % in body mass. Both display performance and developmen t of morphological traits involved are mainly determined by body mass. Males who developed sex traits were among those in good physical cond ition, although not the current physical condition but weight of the m ale correlates with the development of sex traits. We discuss the idea that weight may be a good indicator of overall physical condition dur ing development up to maturity, rather than just the current condition at a given season. Our results show a discontinuity both in display p erformance and in the development of morphological traits - i.e. birds of weight below a certain threshold neither performed the display nor fully developed the secondary sex traits. This constitutes evidence o f cost reduction by males when expected benefits from mating are low, and is consistent with the viability-conditioned expression of the tra its.