Sunday 3 January 2010

Slaty-backed Gulls, Choshi, Japan (1-3 January 2010).

First winter. This is a very typical bird. The general plumage tones are rather uniform and the tail is wholly dark.
First winter. There is a huge amount of individual variation in 1 w birds, from very pale birds through to ones like this. All birds however (or at least the ones that I confidently identified as SBG) seem to share some basic plumage features, including the unform greater coverts, simply patterned tertials (brown with paler tip, lacking strong patterns), darkish eye mask and wholly or virtually all dark tail (i.e. very like smithsonianus).

Second winter. Second winter birds varied from largely brown individuals to ones with white bodies, grey mantle and pale, bleached looking creamy wings. This is a medium bird; its dark smudgey face is not typical - most have a darker eye mask but lack such sooty areas on the lores and chin of this bird.

Second winter. An example of a paler bird; note the very typical pale brown primaries.

Third winter. Some more advanced 2w birds look like this, but the 3rd generation primaries (blackish with small white tips) can be used to age it confidently as a 3rd w.

Adult. Unfortunately, strong sunlight made getting the correct/true-looking grey tones in this and the subsequent photo very difficult. In life, in neutral light they appear about the same grey tone as an intermedius LBB. There is some individual variability in upperpart grey tone of the birds at Choshi, with the palest birds appearing, to my eye, to be paler than intermedius but a fraction darker than graellsii. On a couple of occasions, paler and more typical individuals were seen side-by-side and the difference was quite clear.

Another adult

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