Most birders, including the American Ornithologists’ Union, accept Kumlien’s Gull as a subspecies of Iceland Gull. Others say that Kumlien’s Gull is a subspecies of Thayer’s Gull.  Still others say that Thayer’s Gull, Iceland Gull, and Kumlien’s Gull are all a single species and we all are kidding ourselves by pretending otherwise. What the heck is going on here?

Kumlien’s Gull Larus glaucoides kumlieni

First of all, how does one identify Larus (glaucoides) kumlieni? Wikipedia is a little bit less than helpful in this regard, though pretty much every resource I have checked agrees with the sentiment of Wikipedia’s Kumlien’s Gull page:

The taxon is pale in all plumages, with a remarkably variable amount of pigment in the primaries. Individuals range from completely white-winged (indistinguishable from nominate glaucoides Iceland Gull) to so much dark in the wings as to be indistinguishable from Thayer’s Gull. Eye color is also variable, from pale yellow to dark brown. Such remarkable variation seems to lend credence to the belief that Kumlien’s Gull is in fact a hybrid swarm.

Where does that leave the average birder? Confused, of course.  Essentially, if you have an Iceland Gull that seems a bit dark in the wings or a Thayer’s Gull that seems a bit light in the wings you might have a Kumlien’s Gull. Peter Harrison, in his Seabirds: an Identification Guide, insists that “[Thayer’s Gull] is separable in the field from Iceland Gull.”

How does Harrison do it?  He says that Kumlien’s Gull “Differs from Iceland Gull in variable slate of brown outer web and subterminal bar on outer 5 primaries.”  Harrison apparently never dealt with the more white-winged varieties of Kumlien’s Gulls.  He does, however, mention in his description of Thayer’s Gulls that “Experienced birders will know that it is not possible to identify all gulls specifically” before he goes on to let birders know how to differentiate a Kumlien’s Gull from a Thayer’s Gull:

Kumlien’s Gull also has whitish underside to primaries and a proportionately smaller bill than Herring Gull, but differs from Thayer’s in yellow iris, paler mantle and more silvery primaries usually with inconspicious dark grey or blackish outer webs and subterminal bars confined to outer 3-4 primaries; moreover, tips of outer 2 primaries are extensively white.

Clare Kines shared a link with me that I found particularly interesting. It is the “Taxonomic History of Thayer’s Gulls” by Ron Pittaway, which was published in Ontario Birds.  His conclusion is that Thayer’s Gull, Kumlien’s Gull, and the nominate subspecies of Iceland Gull are all one species, an interpretation that I, with my limited knowledge, find compelling:

The published and specimen evidence clearly indicate that Thayer’s Gull is not a distinct biological species. The ’new school’ of taxonomists, such as Richard Snell, treats Thayer’s as part of the Iceland Gull complex, but would not give it subspecies ranking because its clinal characters vary geographically at different rates and in different directions. I recommend following the traditional treatment of Godfrey (1986) that lists three subspecies of the Iceland Gull: nominate L. g. glaucoides, L. g. kumlieni, and L. g. thayeri. The two approaches used by Snell and Godfrey are not incompatible. We could classify Iceland Gulls as Type I (glaucoides-like), Type II (kumlieni-like) and Type III (thayeri-like). Regardless of how we classify them, they are no more or less identifiable in the field. The AOU is bound to change its position as more authors independently adopt a taxonomy recognizing that Thayer’s is a form of the Iceland Gull.

Does your head hurt yet?  Yeah, me too.  Here, let’s look at some more images of a Kumlien’s Gull and pretend that it is just a pretty birdy that won’t make us think too much.

Much better, right?  And as to what a Kumlien’s Gull actually is, well, hey, look over there!  It’s an Ivory-billed Woodpecker riding a Great Auk!

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Written by Corey
Corey is a New Yorker who lived most of his life in upstate New York but has lived in Queens since 2008. He's only been birding since 2005 but has garnered a respectable life list by birding whenever he wasn't working as a union representative or spending time with his family. He lives in Forest Hills with Daisy, their son, Desmond Shearwater, and their indoor cat, B.B. His bird photographs have appeared on the Today Show, in Birding, Living Bird Magazine, Bird Watcher's Digest, and many other fine publications. He is also the author of the American Birding Association Field Guide to the Birds of New York.