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Mystery Gulls from Choshi, Japan (1 Viewer)

jmorlan

Hmmm. That's funny
Opus Editor
United States
9-10 February 2019. Choshi--Choshi Port, Chiba Prefecture, Japan.

I was unable to match these up with expected Vega or Slaty-backed Gulls. The first might be Mongolian, but after seeing real first cycle Mongolian and discussion with locals decided that it was probably just a variation of Vega.

I'm drawing a blank on the second. Maybe another Vega? Any help would be much appreciated.
 

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Hi Joe,

both birds are either Slaty-backed Gulls or perhaps hybrid Slaty-backed x Vega Gulls.
The pattern of the greater coverts does not look entirely typical of Slaty-backed but otherwise the birds match this species pretty well.
 
Thanks. I can see that for bird #1. For bird #2, the black wing-tips and white body with checkered mantle are hard to reconcile. We considered worn Slaty-backed, but it did not look worn in the field. Is Great Black-backed Gull a possibility?
 
Is Great Black-backed Gull a possibility?

Absolutely not.

1w Slaty-backed can show blackish primaries. Upperparts look fine for this species; most of the scapulars are still juvenile and fresh which helps explain the different appearance from more advanced birds like #1.
I do not see a truly white body here, just white head/neck set off from uniform brown flanks - much like bird #1 actually.
 
It is all wrong for Caspian Gull: fresh juvenile plumage in February still (!), barred greater coverts, brown flanks, wrong bill shape, short primary projection, and also too much white on the juvenile scapulars.
 
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