Thayer's/Iceland Gull Taxonomy
The traditional view is that Iceland Gull is a species composed of two subspecies: nominate glaucoides and kumlieni. The latter birds are sometimes called Kumlien's Gull. Birds that appear intermediate between Kumlien's and Thayer's (and they occur regularly) are called "intergrades" or, more correctly, hybrids.
These webpages are organized according to a different perspective, which is supported in the latest literature. In this view, Iceland Gull has no subspecies; only nominate glaucoides is considered Iceland Gull. The old kumlieni is merely one point on the spectrum between Thayer's and pure Iceland. "Kumlien's Gull" is thus a term that may be applied to any of the birds within that hybrid swarm.
See Weir, D.N., A.C. Kitchener, and R.Y. McGowan. 2000. Hybridization and changes in the distribution of Iceland gulls (Larus glaucoides/kumlieni/thayeri). J. Zool., Lond. 252: 517-530.
