Dietary carotenoid supplementation affects orange beak but not foot coloration in Gentoo Penguins Pygoscelis papua

Red, orage, and yellow carotenoid-based coloration abounds in birds, with over half of all avian orders known to display it in some form. Penguins (Order Sphenisciformes), however, are one order of birds for which the proximal causation of ornaments is unclear, i.e., whether such colors in plumage or bare-parts are carotenoid-based. We experimentally supplemented the diet of captive Gentoo Penguins Pygoscelis papua for two months with extracts of krill, a common carotenoid-rich food source for these animals in the wild, to determine whether orange coloration in the beak and feet is influenced by carotenoid content of the diet. We found using UV-Vis reflectance spectrophotometry that dietary carotenoid enrichment elevated beak but not foot brightness. This suggests that the crustacean part of the diet is at least in part responsible for orange beak coloration but not feet in Gentoo Penguins and that, like other carotenoid signals, these traits have the potential to reveal important aspects of mate quality (e.g., nutrition, health).