North American Birds

VOLUME 68 NO4 2015

A Quarterly Journal of Ornithological Record Published by the American Birding Association. The mission of the journal is to provide a complete overview of the changing panorama of our continent’s birdlife.

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452 n o r t h a m e r i c a n b i r d s c o m m o n s c ot e r i n n o r t h a m e r i c a twentieth century, when the two were considered conspecific, combined as subspecies under nigra (e.g., Phillips 1926, Peters 1931). The American Ornithologists' Union (1944) followed these authorities un- til 2010, when analyses of bill morphology and vocalizations (Sangster 2009) prompted a review that led to their classifcation as full species (Chesser et al. 2010). Published pear to lack yellow tones in the orbital skin; at least some of these individuals appeared to be slightly subadult. So yellow orbital skin appears to be supportive, if present, for an identifcation of adult male Common Scoter, but more investigation of this aspect is desirable. Ornithologists considered nigra and amer- icana to be distinct species until the early et al. 2008, Bradbury 2011). Such structural differences would likely be most discernible with both spe- cies under observation together (and ideally well photographed). Differences in orbital skin color in adult male Common and Black are illustrated in both Madge and Burn (1988) and Svensson et al. (2002) but are not mentioned in the text of either book; these il- lustrations show Common with yellowish orbital skin, Black with orbital skin near enough in tone to the plumage and iris color that it is not discernible. Garner et al. (2008) indicate explicitly that adult male nigra has orbital skin that tends to be yellow, whereas that skin tends to be "bluish grey" in adult male americana. Palmer (1976) and Bordage and Savard (2011) indicate that "eyelid" color in adult male Black Scoter is yel- low. However, a search of photographs online reveals numerous Common Scoters with yellow orbital skin and only a very few individual Black Scoters with discernibly pale orbital skin (none with yellow). (The indication of yellow "eyelids" could refer to the color of the interior eyelid skin rather than the visible orbital ring.) Some closely photographed male Common Scoters ap- Figure 4. Common Scoter, Crescent City, California, 1 February 2015. Under sunny conditions, the bird's head and neck appeared blackish (sometimes glossy black) and contrasted with the back and especially the body plumage, which showed brownish cast. In direct sunlight, the bill tended to look more dark gray than black. At close range and in optimal lighting, the orange-yellow orbital ring was usually evident (compare Figure 5). Photograph by Robert C. Fowler, Jr. Figure 3. Common Scoter, Crescent City, California, 1 February 2015. The orange patch in the culmen extends into a narrow groove in the center of the osseous knob at the base of the bill. Black Scoter has no such groove in this knob. This photograph was taken during overcast conditions, which made the bird's plumage and bill appear uniformly blackish. Photograph by Robert C. Fowler, Jr.

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