One thing that seems to be missing from the discussions on why this Great Black-backed Gull isn't typical, is context:

large, white-headed, pink-legged gulls are variable.

Most first-winter Glaucous-winged Gulls are a fairly uniform muddy brown, but I've seen individuals that had more extensive white tips to the wing coverts and scapulars. As Glaucous-winged Gulls (and their hybrids with Westerns) age, their bill goes from all black to yellow. Usually the second and third-winter birds have pale yellow or pale pink bills, but I've seen individuals that had bright pink bills with a black tip, like that of a first or second-winter Glaucous Gull. When I first noticed this I thought it represented hybridization with the Glaucous, but given that there were no plumage characters to suggest Glaucous genes, I concluded that it was just a regular variant from the norm. I've since observed this to be not uncommon in Glaucous-winged and GWxW Gulls.

Glaucous-winged Gulls have a fairly stout bill, with a pronounced gonydeal angle and a slight bulge at the tip of the bill. However, I've seen individuals that had bills that were more slender than expected, without a pronounced gonydeal angle. Given that there were no plumage characters to suggest anything other than a pure Glaucous-winged, I conclude that this just represents variation in this species. (Note that I have photographs of all these variations I've mentioned so far.)

I'm not as familiar with Great Black-backed Gulls as I am with our local species, but recently I reviewed my photographs taken in North Carolina, Massachusetts and Newfoundland. There is also variation in this species. I have a photograph of a first-winter bird with a bill that would be more typical of a Herring Gull. Again, since there were no plumage characters to suggest anything other than a pure GBB, I conclude that it represents variation within this species.

And I won't even get started on variation in the Thayer's Gull.

I see no reason why the Renton bird is not a Great Black-backed.


Mike Donahue
Seattle