Nelson's Gull

Today, Sandy Hook was shrouded in dense fog, which gave me a day off from hawk counting and provided me with an opportunity to scour the Hook in the mist for birds. The northern tip of the Hook is never so wildly beautiful and mysterious (and devoid of people) as in dense fog.

At the very tip (the "False Hook") I found this unusual-looking gull. At first I thought it was a Glaucous Gull, but I quickly realized the wingtips were too dark for that species. Somehow the bird seemed too light to be a Herring Gull. Not knowing what I was looking at, I decided to try for some photos.

I now believe it to be a first cycle 'Nelson's Gull', i.e. a hybrid between Glaucous Gull and American Herring Gull. It shows a mix of characters from both species, and Howell & Dunn's authoritative Gulls of the Americas (2007) lists that combination under the header "widespread hybrids". Confirmed interbreeding occurs in the Mackenzie Delta, Northern Territories, Canada (Howell & Dunn 2007), a potential source for this individual.

I also considered first cycle Slaty-backed Gull and first cycle Thayer's Gull, but Glaucous Gull x American Herring Gull seems a better fit. Especially the crisply bicolored 'Glaucous type' bill does not fit first cycle birds of either species, but is good for 'Nelson's Gull'. There's other disqualifying field marks. I do confess I am not a larophile, so I welcome discussion of the finer ID points from the initiated.

Cited literature:
Howell, Steve N.G. & Dunn, Jon (2007) Gulls of the Americas. Peterson Reference Series, Houghton Mifflin Company, New York.