Investment in eggs is influenced by male coloration in the ostrich, Struthio camelus

Life history theory predicts that females should modify their investment in a particular breeding attempt according to the likelihood of its success, as the investment of females in reproduction is typically higher than that of males. The ostrich mating system is promiscuous, and is thus a particularly interesting one in which to investigate differential investment by the sexes. To date, there has been no evidence that female ostriches discriminate between males as potential mates, but the degree of dimorphism in this promiscuous species and the variation in chick size within clutches suggest that differential maternal investment is likely. We investigated the relationship between egg mass and coloration of the feathers, bill, neck and legs of 15 male ostriches, maintained in a breeding flock at an ostrich farm in South Africa. Paternity was determined using microsatellite markers. We found that the colour of the neck, white and black body feathers, and the brightness of black feathers, predicted egg mass. These traits are exposed during the male courtship display, so we suggest that these visual cues influence the degree of maternal investment in eggs through their influence on female perception of mate quality.