Shane Blodgett has helpfully pointed out that the tertials of my Thursday
and Friday birds have different patterns. In my opinion that leaves the
Friday bird as a pretty good Thayer’s and the Thursday bird as an
intriguing mystery for which I still need open wing shots. Others may
disagree with the call for the Friday bird.
Thanks, all!
On Sat, Feb 6, 2021 at 12:31 AM Joshua Malbin
wrote:
> On Thursday I was gulling in Prospect Park when I noticed an unusually
> light first-winter gull fly in among the many first-winter Herring Gulls on
> the lake. I thought it was a dark Kumlien’s Iceland Gull, possibly even a
> Thayer’s, and posted a few photos to a gull forum. People looking at those
> commented that it had a potbellied look and wondered whether it could even
> be a Slaty-backed Gull. Open-winged photos were absolutely necessary for
> that determination, they said, so I went back to Prospect on Friday and
> eventually a bird showed up that I am pretty sure was the same one from the
> day before. This time I was able to get some photos of the open wing and
> the tail, though I was only able to get it bathing and flying. Since I
> could not get it standing on the ice again in the same posture I can’t be
> completely sure that Friday’s bird is the same as Thursday’s, but the bill
> and head shape and pattern look the same to me. I have posted Thursday and
> Friday’s photos in an album here:
>
>
> https://flic.kr/s/aHsmU8fiKa
>
>
> Assuming that they are the same, the bird does show many features that
> appear to my inexpert eye to be consistent with first-winter Slaty-backed.
>
>
> First the standing pictures: It has the potbellied, short-winged look that
> first caught many people’s eyes. The primaries are soft brown, not as dark
> as Herring, and the tertials are even lighter brown with pale edging. The
> greater and median coverts appear plain and relatively unmarked. The
> undertail is quite light, nearly unmarked.
>
>
> The open wing and flight pictures: There is a strong secondary bar and a
> distinct inner primary window. The outer primaries show a pattern with pale
> tongues on the inner part of the feathers. The tail seems quite dark, all
> the way to the outermost feathers.
>
>
> I am aware that this is a very difficult identification to make, and West
> Coast birders have a particularly hard time ruling out Herring x
> Glaucous-winged Gull (Cook Inlet Gull) as a potential confusion taxon at
> this age stage. Either Cook Inlet or Slaty-backed would be pretty rare for
> the northeast. It could also still be a Thayer’s or even a very dark
> Kumlien’s, as I originally pegged it. It appears smallish for either
> Slaty-backed or Cook Inlet based on the photos of those I have reviewed,
> for example, with a bill that may be too delicate.
>
>
> If others with more expertise would be willing to review these photos and
> let me know what they think, I would greatly appreciate it. If you are
> interested in looking for the bird, gulls tend to start congregating on
> Prospect Park Lake in midmorning. They come in to drink and bathe, and then
> rest on the ice awhile and then leave. I had to wait nearly three hours on
> Friday before this bird reappeared, which it finally did at around 12:30
> p.m. On Thursday I think I had it about an hour earlier.
>
>
> Good luck if you try.
>
>
> Joshua Malbin
>
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