eWestern Birds
The Quarterly Journal of Western Field Ornithologists
Plumage Variation in Bering Sea Plectrophenax Buntings and the Specific Status of McKay’s Bunting
Jack J. Withrow
ABSTRACT: McKay’s Bunting (Plectrophenax hyperboreus) is an enigmatic and little studied passerine that breeds only on one of the most isolated groups of islands in North America. Recent field work on those islands, St. Matthew and Hall, and the nearby Pribilof Islands produced specimens of breeding McKay’s and Snow Buntings (P. nivalis) demonstrating that plumage variation in both taxa is significant, probably not related to age after the first year, and varies continuously between the extremes within a taxon. The extreme of one closely approaches that of the other. McKay’s Buntings are paler overall and levels of black pigmentation of the wings, back, and tail, in conjunction with sex, allow qualitative diagnosability of these taxa by plumage in nearly 100% of individuals if enough of the bird can be seen. Levels of plumage variation are congruent with recent genomic work suggesting their relationship is extremely close. Current information suggests that McKay’s Bunting is not a biological species and should be considered a subspecies of the Snow Bunting.