Tuesday, 5 April 2011

2nd winter argentatus Herring Gull?

Heard my first Willow Warbler of the year singing this morning - probably my favourite Scottish songster. To me that seems earlier than normal, but I think that lots of migrants are coming through early this year. There is a big westerly in the offing though, so that'll soon sort them out! A Chiffchaff was in the back garden momentarily this evening but the main action then was a passage of 125 Meadow Pipits NW overhead in an hour. From records elsewhere there seems to have been a major coastal movement of that species today. This seemed quite a big passage here so late in the day - I wonder whether poor weather earlier in the day had held them up.

Looking over some photos taken at Musselburgh yesterday just now I had forgotten about this Herring Gull that failed to cooperate fully with the camera. I would tentatively age this bird as a 3 calendar year (2nd winter) and think that it could be an example of a far northern argentatus individual?

This first shot gives an idea of how pale the bird was compared to other Herring Gulls.

Unfortunately the skies then greyed considerably and the wind whipped up... This next shot shows its upperparts and bill pattern which were reminiscent of a Glaucous Gull, though the headshape looks like Herring Gull.

As the bird preened it showed almost snow-white underparts as well as head and neck. Careful scrutiny showed that this plumage was not adult type, but instead had much reduced dark markings - possibly showing leucism or extreme bleaching - or are possibly consistent with northern argentatus.
The outer primaries were as dark as a typical young Herring Gull, but the secondaries showed little sign of a dark subterminal band. The tertials had reduced brown markings yet the tail had a reasonably strong narrow subterminal band. These features can be seen in the open-wing shots below in which the bird in question is uppermost in both.

Here is a final shot of the bird as it headed inland towards Musselburgh looking like a strange pale hybrid. While it could be that this bird has some Glaucous Gull genes mixed in, I think it more likely that it is a pale northern argentatus Herring Gull. Of course, adult northern argentatus birds end up darker backed and paler wing-tipped than our local argenteus Herring Gulls, so it is slightly unintuitive that they should be the other way around as younger birds...

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