Sunday, 11 February 2018

Choshi (2): Glaucous-winged Gulls

Despite being over the moon at having successfully nailed Thayer's Gull Larus thayeri at Choshi, at the outset this had not been my chief target. That, in fact, had been something substantially easier: Glaucous-winged Gull Larus glaucescens. I had anticipated that getting one of these would present no problems whatsoever, but also that they might prove to be rather thin on the ground, at least in comparison to numbers of other big gulls. Both expectations proved to be correct, and I never saw more than a dozen or so per day despite covering much of the (extensive) harbour complex. I was completely overjoyed when I encountered my first, about ten minutes walk out of Choshi centre in the direction of the harbour. This was a wonderfully large and aggressive fourth-winter (or similar such near-adult on account of black in the bill), which landed in a bunch of gulls I was watching only twenty metres or so in front of me. It just simply barged all the other gulls out of the way and threw down the fish they were all squabbling over before moving on!

My second individual was similarly aggressive and also quite raucous, though sadly I didn't think on to fish out my tape recorder and record its (distinctive honking) call. I had read somewhere that first-winters have a distinctly 'oily-blue' cast to much of their plumage, which this one certainly had. It was otherwise rather plain- and dark-looking, with short primary projection, faded 'Venetian blind' effect through its outer primaries, clean white under-primaries, and closely and densely barred upper- and undertail coverts. This one was also rather large and very territorial!

Another kind of first-winter had me struggling with it for a while, but I decided in the end that this too had to be Glaucous-winged Gull (just more extensively bleached than those I had seen already). This seemed correct as an explanation as both the upper- and undertail coverts were dark (with paler tips worn off) and the greater coverts pale unmarked brownish throughout. If these were Slaty-backed Gulls Larus schistisagus (which can look very similar indeed), one would expect either uniform white in these areas or perhaps some brownish bars, and Slaty-backed Gull, too, should also have a more strongly contrasting secondary bar than was present in these birds.

There were also a number of second-winters around, and some of these looked quite advanced for a big gull of that age. These had saddles and many upperwing coverts already adult-like, much as in Slaty-backed Gull (to which I guess this taxon must be closely related) of the same age.

By far the most frequently encountered age class of Glaucous-winged Gull, though, was first-winter, and the vast majority of these were still quite dark-looking (not bleached) with 'oily-blue' sheens throughout. A few more typical individuals are shown below.

Together with Thayer's Gull, Glaucous-winged Gull meant two lifer gulls for me from this trip to Choshi. Just as with the Thayer's Gulls, Choshi came up trumps in providing me with a number of individuals and a selection of age classes to look at and photograph. I was optimistic at the outset that this would be the case, but was nevertheless delighted to leave with so many photographed so nicely and at such incredibly close range to boot! Above photos taken at Choshi Harbour, Chiba Prefecture 6-9/2/18.

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