David M. Larson
Northern Flickers (Colaptes auratus) occur in two distinctively colored subspecies groups—Yellow-shafted (C. a. auratus) and Red-shafted (C. a. cafer). In each case, the subspecies groups contain multiple populations. The names come from the coloration of the shafts and undersides of the flight and tail feathers, a genetically determined distinction caused by the yellow carotenoid pigments in auratus and red 4-keto derivatives of the same carotenoid pigments in cafer. The largely eastern Yellow-shafted and western Red-shafted subspecies groups interbreed in the midwestern states, often giving rise to offspring with intermediate coloration. While the overlap zone is far from the East Coast, it is not uncommon to see Northern Flickers with a few red primaries in New England. So how does that happen? Some researchers have suggested that the multicolored birds are hybrids with periodic shifts in the types of pigments deposited. However, no one has come up with a plausible genetic control mechanism for coloring some feathers and not others, changing coloration patterns in the same individual birds from year to year, and changing the color part way through feather growth.
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