Your expert opinion is kindly being sought on a large First Cycle / First-winter gull seen and digiscoped very poorly in the evening at Gangneung, Gangwon Province, Republic of Korea on December 6th 2014. It would be wonderfully helpful to have your thoughts on the identity of this bird (shown below on this closed URL) and whether the bird’s identity can be confirmed one way or another, pure or hybrid, based on the images and the description.
The bird was found by NM at 16:55 and seen on and off for 4-5 minutes at dusk in among a flock of several hundred Slaty-backed and Vega Gulls and a few Common Gulls at a pre-roost by the beach (apparently used by gulls that spend most of the day foraging 2-3km+ offshore). The bird was watched and digiscoped through a tripod-mounted Swarovski scope, as it preened about 100m distant from me, before it took flight, crossing 200-300m to land on a small island; then circling then landing again when it was seen distantly 15 minutes later in increasingly worsening light through NM’s scope by two other observers (Subhojit Chakladar and Jason Loghry).
Conditions were clear, with a moderate wind and temperatures close to freezing, but rapidly-failing light.
The sequence of digiscoped images (all by NM) have been cropped and resized a little but otherwise NOT altered. Therefore all plumage tones and details can be compared directly with other gulls that were adjacent to it.
Click on a thumb: every image is opened enlarged in a new browser window.
Note: Notes were dictated onto a phone during the observation period. All salient points that were noted below are included, along with a few details most apparent from a subsequent review of the series of images.
- Impression: The bird immediately stood out to NM as it looked exceptionally dark, with extensive dark grey (intermediate in tone between adult Vega and adult Slaty-backed Gull) on the mantle and also on the breast sides; contrasting with a plain-looking brown wing; and white coming through in splotches and wide streaks on the neck sides (images 4,11,12).
- Structure: It was similar in size to the adjacent Vega and Slaty-backeds (certainly not obviously larger or smaller), and obviously bigger than Common Gull (image 11). It looked big-headed (recalling Glaucous-winged Gull) but perhaps not as deep-chested or quite as pot-bellied as most of the Slaty-backeds (image 4). It was perhaps a little flatter-backed and deeper-bellied than most of the Vega(image 11). The bill was moderately long and showed a strong gonydeal angle and some droop (image 4). The legs were thin-looking when compared with Slaty-backed. The primary projection looked a little longer than Slaty-backed. It had a strong tertial step.
- Bare Parts: The bill was all dark; the eyes were dark; and the leg colour was greyish-pink or off-pink with darker scutes , appearing darker than other gulls in direct comparison and obviously different from all “typical” Slaty-backed of a similar age (images 3,4,5,12).
- Contrast, at Rest: The strongest plumage contrast was the white on the neck-sides and upper breast contrasting with the dark of the upperparts and belly (images 3, 5).
- Contrast, in Flight: a) Views and the images suggest the underwing was mostly dark mud-brown, with an extensive solid-looking block of dark across the underwing coverts and additional dark “lines”, with paler flight feathers (images 6,9). On these brief views, the underwing therefore appeared much darker and less contrasting than expected in Slaty-backed or Glaucous-winged Gull. B) The upperwing (seen poorly) lacked any obvious (any?) pale blaze on the inner primaries, but perhaps had a pale trail (suggested by image 7). C) the bird had a paler half-collar; and D) most especially the bird had a strongly contrasting whitish rump and uppertail coverts (both weakly patterned, and certainly not spangled or densely barred with brown) with an apparently all-dark, blackish tail and paler area on the vent. The rump and tail created an eye-catching contrast when the bird was seen at about 150m distance through the scope, for only a few seconds however, showing much greater contrast than shown by any similarly-aged Slaty-backed Gull or Glaucous-winged Gull knowingly seen to date by NM. Unfortunately, there is no image showing this feature.
- Plumage Details: Head. At rest, the head showed a full, dark greyish, slightly oily-looking hood (much more extensively dark than in any similarly aged Slaty-backed or Glaucous-winged), with some paling to the rear of and above the eye especially (images 2,4,5).
- Plumage Details: Saddle. Much of the “saddle” on more or less head-on views and less clear side views appeared dark grey, with some (small?) upper scapulars (?) showing spotty or streaky black centres and narrow white edges. The lower scapulars had larger dark centres with broader paler tips (images 1,2,4,5,11).
- Plumage Details: Closed wing. The wing coverts were dark brown, with some paler spangling on e.g. the median coverts. The greater coverts showed a strong panel of dark brown, all spangled paler distally, though with this spangling much more extensive distally on the inner than the outer greater coverts (images 1,2,4). The primaries were blackish, with paler tips (2, 11). The pale v’s (?) on the tip were confined to the tip and did not extend down the feather edges as is typical in Slaty-backed or Glaucous-winged (image 2,12).
- Plumage Details: Tail. At rest, the tail appeared black (image 3); in flight the upperside of the tail appeared all dark with no obvious pale at the base of any rectrices (no image). If present, any such pale had to be very limited as it was specifically looked for and not seen.
- Plumage Details: Underparts. On the underparts, white was emerging on the chin, behind the mask and on the breast. Most of the breast sides were infused with dark grey that merged into a plainer dark brown or dark-grey brown belly (images 2,4,5). The vent was white with some random dark marks or weak bars (?) (images 2,4,11).
In closing, just to add that during the past 25 years of gulling in East Asia, NM has never knowingly seen a similar tone of dark grey on the underparts of a Slaty-backed Gull or such extensive dark grey in the upperparts of any Slaty-backed Gull either in December or in its first cycle. NM has never seen such dark grey tones in any Glaucous-winged Gull in Asia or in any of the brief visits to North America. Neither the structure nor the plumage fit any regularly-occurring Korean gull.
The general look of the bird and many of the details therefore immediately reminded NM strongly of Western Gull, seen on three different visits to North America (though never in December).
How appropriate was such an impression? If others think that this bird has Western genes, can hybrid influence be reasonably ruled out? And in order to understand how much encouragement should be given to others to look for this gull or to make any effort with any gull that might look like this (!), how unlikely is Western Gull as a vagrant to Asia? How rare is it north to Alaska or out of range?
Thanks again for any input and advice you can share!
The following comments have been received (on December 8th and 9th) in response to the URL sent to several expert gullers on the west coast of the USA.
“Good points” for Western Gull, “almost everything you mentioned. I can't imagine what else this bird could be …Not as good: the bill looks a bit thin at the base, but certainly not outside the range of Western variation...the streaky look on the breast is not a typical Western thing, but I think that has more to do with the arrangement of feathers than actual feather pattern in this case. In some shots I am seeing some cross-barring on the breast too, which IS very characteristic of Western / Glaucous-winged.
Due to its restricted range and habitat, Western is extremely unlikely to hybridize with anything other than Glaucous-winged. In California, we say it has hybrid influence if the upperside of the primaries or tail are anything paler than very dark brown, or sometimes if the bill looks longer.
This bird would certainly be called a pure Western in California, with only that extremely blurred shot showing the undersides of the primaries suggesting that they may be on the pale side (can't really tell though)… the only thing that sounds odd to me is the whiteness of the rump--I would expect considerable brown barring on a first-cycle bird. But the rump does stand out as having a whitish background, which can blur out fine bars in bright light.”
“Steve Hampton responded that it felt like a first-cycle Western but better photos would be desirable (no further details). Ken Burton said he thought it may have some Glaucous-winged influence (but mostly Western).”
“Well, I wouldn't say that it is not a Western Gull, though a few things might not lead up to it being a classic first-cycle individual.
First, it is very dark, even for a Western. Where I live in Central California the first-cycle birds are paler than this. However, we do get darker individuals like this from the southern California and northern Baja California breeding populations (subspecies weymani). These would seem less likely to turn up in Korea than the nominate northern population, but one never knows.
It looks like the newer formative feathers on the back are entirely dark, without pale fringing. Most Westerns have these feathers with more-obvious pale fringing, but perhaps some can have feathers that come in this dark.
The white streaking on the head and breast is normal, just caused by wet / dishevelled feathers. I think it stands out more on these dark birds simply because of greater contrast.
The bill seems on the thin side for Western, though is probably matched by some females. Your description of the bird's size seems better for female than for male, if a Western.
My greatest concern for Western is the apparent pale under-primaries visible on the shot with half of the bird in flight. Normally the outer primaries on Western are darker than this, among the darkest juvenile primaries one encounters among gulls. They typically grade from dark gray in the inner panel to blackish in the outer primaries, and usually also show even darker/black tips to the outer primaries, which should be apparent in a shot like this. This wing would seem to be more uniformly paler like in some Glaucous-winged x Western hybrids, but I've never seen a bird this dark that I presumed had any Glaucous-winged genes in it…
The closest contending species might be American Herring Gull, some of which have very dark plumage in their first year (these are more common in eastern than in western North America). The under-primary pattern might be a better fit for one of these dark Herrings, but I would certainly not expect the formative feathers to be this dark and to lack pale fringing.”