Diet explains red flight feathers in Yellow-shafted Flickers in eastern North America

ABSTRACT Yellow-shafted Flickers (Colaptes auratus auratus subspecies group of the Northern Flicker) occasionally have orange to red flight feathers in eastern North America far from the hybrid zone with the Red-shafted Flicker (C. a. cafer subspecies group). Blocks of feathers of anomalous color tend to show bilateral symmetry and may differ from one year to the next in the same bird. It has been suggested that hybridization with cafer must be the source of the red color and that selection for that color could explain the high incidence of red or orange shafts in eastern flickers in some localities. Complex, though largely unproven, physiological mechanisms have been hypothesized to explain the variegated look. We evaluated a simpler, dietary explanation for the variation: that the pigment rhodoxanthin acquired exogenously at the time of feather molt comes to rest alongside the carotenoids normally present in these feathers. An exogenous source of rhodoxanthin exists in the berries of nonnative bush hone...