Great- a big 1st-cycle gull. What the heck is it?
It can be pretty flummoxing to get crippling looks at a bird that just doesn’t look like anything in your field guides. While hawks can wipe out literalists searching for a perfect match (does any Red-tailed Hawk really look just like the ones illustrated?), young large gulls really run the gambit of intra-species diversity. Even when accounting for individual variation, some still feel like square pegs trying to fit into the round holes provided by the guides at hand. One such bird has been making the rounds in Broomfield and Boulder Counties in Colorado’s northern Front Range this winter. On the one hand it shows traits of a 1st-winter Glaucous Gull- very large overall size, flattish head, beady little dark eyes, pink legs, crisply demarked wide black tip on an otherwise pink bill, and paler than most young Herring Gulls nearby for comparison. But the bird would certainly be pretty far out on the dark end of the Glaucous Gull spectrum and the wingtips are darker yet, not concolorous as would be expected on a Glock.
The bird’s wing projection is a bit long for Glaucous Gull as well, and perhaps the Frankengull appearance typical of that species is softened just a bit. Keeping in mind that large gulls are notoriously lax in their mate selection, hybridism should always be considered when all of the pieces don’t quite add up. While general field guides have disappointingly few gull hybrid examples provided, Howell & Dunn’s Gulls of the Americas has an extensive section of photos and discussions of about any mixed-up gull possibility to be found in the ABA area. Here we find a really solid match for the mystery gull- a hybrid 1st-winter Glaucous x Herring Gull, AKA Nelson’s Gull. Thanks to Steve Mlodinow and Christian Nunes for putting me on this interesting beast!
1st-winter Nelson’s Gull (Glaucous x Herring), Broomfield County, Colorado, 15 Jan 2012.