Range map of Kumlien's Gull (L.g. kumlieni); Red: breeding, Blue: nonbreeding
The question we need to ask in the United States is not whether glaucoides can stray into the lower 48 states, but rather, can it be distinguished from the regularly occuring Kumlien's? Most adults are easily distinguished since the majority of Kumlien's show some darker gray tones to the outer webs of the outer primaries. The confusion arises in what Steve Howell has called "stage zero" Kumlien's Iceland Gulls. These are adult individuals with pure white wingtips that mimic the appearance of nominate glaucoides.
The distinguishing features of glaucoides include a paler-mantle (Glaucous Gull coloration) and a pale lemon-yellow iris in all adult stages. It should be noted that mantle shade is difficult to ascertain without side-by-side comparisons of benchmark species; this is another reason why North American observers must be cautious when considering the nominate race. Other supporting features on glaucoides include a rounder and more gentle look to the head with a bill that is typically smaller than Kumlien's - but there are varying degrees of overlap.
Here is an adult Kumlien's Gull (front) shown with an adult American Herring Gull. Could you think of at least 2 reasons why this isn't a nominate glaucoides?
Chicago, IL; 26 Dec 2010 |
In my opinion, Iceland Gull (L.g. glaucoides) is one of the most beautiful gulls of the Holarctic. Any report of this race in North America should be scrutinized with care; sightings should be well documented with photographs, preferably next to other species that can be used for comparison.
Resources
Charles, D. 'Identification challenges presented by 2nd winter Kumlien's Gull'. IRBC Gallery Notes.
Dunn, J. & Howell, S.N.G. 2007. Gulls of the Americas: 462-470.
Howell, S.N.G. & Mactavish, B. 2003. Identification and Variation of Winter Adult Kumlien's Gulls. Alula 9(1): 2-15
Olsen, K.M. & Larsson, H. 2004. Gulls of North America, Europe, and Asia (reprint).
Zimmer, K.J. 1991. Plumage Variation in Kumlien's Iceland Gull. Birding XXIII(5): 254-269