Male preference for female foot colour in the socially monogamous blue-footed booby, Sula nebouxii

Female ornaments are expected to evolve through sexual selection when male parental investment is high. Blue-footed boobies are socially monogamous seabirds with a long period of biparental care. Males and females have colourful feet that are displayed ostentatiously during courtship, both before and after pairing, and extrapair copulations are frequent. We manipulated the foot colour of paired females to test whether this trait influences male courting behaviour, used here as an index of male preferences. There were no differences in time spent at the courting site, frequency of female courtship or frequency of copulations of 11 control and 15 experimental pairs. Experimental females, which had duller feet, received less intra- and extrapair courtship, suggesting that foot colour influences female attractiveness and opportunities for extrapair interactions. Our results support the idea that female foot colour in the blue-footed booby is favoured by sexual selection through male preference.