This pale immature gull was at Lake Loveland (in Loveland, Larimer County, northern Colorado, USA) on 14 December 2006, at dusk (4:00 pm). Is it a rare Thayer's Gull (Larus thayeri, dozens of reports each winter) or a megarare Iceland (Kumlien's) Gull (L. glaucoides kumlieni- only a handful of previous reports for Colorado).

The first row of images are untouched. The second row are the same photos altered in an attempt to improve the clarity or lighting of the image. Click on thumbnail for a larger image.

The lack of extensive gray on the mantle, and overall dark coloration, indicate a 1st cycle bird, probably 6 months old. The bill structure with a pronounced gonydeal angle, and the relatively large body size (images 5-6) compared to accompanying Ring-billed (L. delawarensis), California (L. californicus), and Lesser Black-backed (L. fuscus) are all suggestive of Thayer's. The apparent small size (images 1-4) relative to Herring Gull (L. argentatus smithsonianus), small round head and short bill with developing paleness at the base (image 5), pale concolorous wings, extensive white edges to primary feathers, strong white barring of tertials and greater coverts (images 1,2,4) and molted 1st basic mantle and scapular feathers favor Kumlien's (Kumlien's begins this molt in Dec; Thayer's in March). Is it Thayer's? Or Kumlien's? Or a Hybrid? After much deliberation (and discussion with other larophiles), I now believe this is a Kumlien's Gull.

Why do I believe it is Kumlien's? Numerous eastern birders told me that it would be identified as Kumlien's in the East (albeit a dark one). Therefore it seems to be well within the range of variation for Kumlien's, whereas it would be anomolous for Thayer's. However, what most influenced me was the occurrence of 2 other almost identical individuals photographed in Utah on Dec 27 ( http://timaverybirding.com/icgu/icgu.html ) and in southern Colorado on Jan 14 2007 ( http://www.cam.cornell.edu/~pauljh/ ). If only the one bird had occurred, I would have considered it an anomaly, and left it as unidentified. But three in one region makes a pattern, perhaps indicating a southern wave of darker Kumlien's Gulls from the western part of its breeding range where more introgression from the Thayer's Gull population would have occurred. Interestingly, 2 other paler Kumlien's Gulls were reported from even further south this winter (East Texas and southern New Mexico), further suggestive of an unusual pattern of southwestward vagrancy for Kumlien's Gulls this winter. [More Iceland Gulls showed up in April 2007 during the post-winter staging of gulls along the Colorado Front Range -- see the 2007 gallery]