Experiments on colour ornaments and mate choice in king penguins

Research on animal ornaments used in mate choice has largely focused on males, particularly for bird species with sexually dimorphic coloured patches of feathers and integument. Relatively less information is available for coloured ornaments of sexually monomorphic species and the use of these ornaments during mate choice. The king penguin, Aptenodytes patagonicus, is a monogamous marine bird in which both sexes show very similar coloured ornaments (UV and yellow–orange colours on the beak, yellow–orange auricular feathers, and yellow to rusty-brown breast feathers). These ornaments have previously been implicated in mate choice. We used manipulative experiments to test the role of coloured feather patches in the choice of partners that occurs during pair formation. Experimental reduction of auricular patch size delayed pairing, and alteration of auricular and breast patch colour from yellow to white caused an even stronger delay (white treatments gave adults the appearance of immature birds). Surprisingly, we found that time to pairing did not differ between treatments for females, but males showed significant delays in pairing in general and especially when treated. Thus, females seemed to be more selective in mate choice than males, a phenomenon that might be explained by a male-biased sex ratio in the colony. Nevertheless, our results indicate that choice of mate may be much stronger in one of the sexes in what appears to be a sexually monomorphic species, for which we expected sexual selection to favour mutually strong male and female mate choice.