Gulls in PA

Between snow flurries I wandered south of the Delaware River to Falls Twp Community Park in/near Levittown PA for some dilettante gull watching. Dilettante means that you can bird from or near your car, and in fact the first Iceland Gull I saw was seen immediately while scanning the big gull flock before even leaving my car.

That particular Iceland Gull was a fairly hefty first winter, with a second paler and more lightly built first winter bird seen after a more thorough scan. Eventually I was able to pick out a second winter immature Iceland toward the back of the flock with a bicolored bill and a pale gray mantle, but still barring in the tertials. I could not see the entire bird - a shame since I don't see many 2nd winter individuals. There were a few Lesser Black-backed Gulls in the mix - as with the last visit in Jan fewer than expected - and then there was a very interesting "Herring" Gull that caught my attention.

At first I thought I'd finally snagged my first ever Thayer's Gull - the gull had tertials of the same color as the back, contrasting darker primaries, and the overall color of the entire back was checkered and pale. Much paler than most immature Herrings:

with wing-spread shots it even had a primary pattern reminiscent of Thayer's, with pale inner webs, but the hook pattern was a little anomalous:

What eliminated Thayer's was the sheer mass of the bird - big heavy bill and a size/bulk range well within the range for Herring.

Quite an anomalous bird. Probably not Thayer's (by size/bill), probably not Nelson's Gull (Glaucous x Herring) unless it was on the smaller/darker end for that hybrid. It's also superficially similar to Herring x Glaucous-winged Gull which while not unknown on the west coast would be quite an exceptional visitor on the east coast. God forbid it's just a pale Herring Gull, because they are variable enough as it is without getting this bad.