Beak color dynamically signals changes in fasting status and parasite loads in king penguins

Dynamic ornamental signals that vary over minutes, hours or weeks can yield continuous information on individual condition (e.g., energy reserves or immune status), and may therefore be under strong social and/or sexual selection. In vertebrates, the coloration of the integument is often viewed as a dynamic ornament, which in birds can be apparent in the beak. King penguins (Aptenodytes patagonicus) are monomorphic seabirds that possess conspicuous yellow–orange (YO) and ultraviolet (UV) beak spots that are used by both males and females in mate choice. We studied the dynamicity of beak spot sexual traits, and to what extent they reflected changes in individual condition in fasting king penguins and in penguins treated with an anti-parasitic drug. We also describe the maturation of this colorful ornament during the yearly catastrophic moult. On a time-scale of days to weeks, beak spot coloration changed in response to fasting and experimental changes in parasite load. Beak spot UV brigh...