Tuesday 17 February 2015

Mystery Bird

This gull was photographed on the river Otter back in June 2006. I personally think that it has the look and feel of a first-summer caspian gull but with 'all wrong' wing coverts that could perhaps be explained by extreme wear and abrasion, but it's hard to be sure from this single image. The photograph is taken from my original glossy print, and is obviously poor quality, but you can see the following:
  • Sloping forehead, smoothly contoured nape and tiny eye set high in head to give friendly expression and subtle jizz that characterises caspian gull. Compare head shape and heavy brow on adjacent herring gull.
  • Tapered bill, lacking pronounced gonydeal angle. This is lost somewhat in the above photo but easier to see on my original. The bill is blackish with a paler base and tiny yellow tip, just visible in the photo. The gape is long and pronounced.
  • The breast is high and smoothly contoured in this relaxed posture. Look closely and you can see a distinct bulge behind the legs - the oft quoted 'hanging belly'.
  • The nape is lightly marked to give the necklace effect that you'd expect to see, although it is faded, presumably due to wear.
  • The grey mantle is lightly marked with small dark 'diamonds', lacking the heavy anchor marks/barring more typical of herring gull.
  • The tertials, though heavily worn, appear to show brown centres and neat cream fringes, though again, heavy wear means you probably can't read too much in to this.
  • You can't get much from the tail but it does look very blackish, arguably more so than you might expect on a herring gull at this time of year.
Now to the real problem feature - the wing coverts. These look all wrong for caspian gull and all right for herring gull, but they are extremely worn, faded and abraded, with just the shafts of most of the greater coverts and inner median coverts remaining. The outer greater coverts are partially obscured by the overlying flank feathers. These wing covert feathers will be almost a year old and were the reason the identification was dismissed back in 2006, and why it should probably be dismissed now. Of course, as with any bird you ideally need to see all the features well, so without underwing detail and tail detail the identification wouldn't be concrete anyway.
As always, thoughts appreciated.

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