Thursday, 26 November 2009

A Port Meadow Caspian Gull

There's not been much to report recently on the bird front. However my local patch, Port Meadow, has finally sprung back into life with the arrival of some decent flood waters from all the rain we've been having and indeed the river now looks close to bursting its banks and turning it back into a lake. This is vital in order to ensure that there is a decent amount of flood water to last ideally at least until spring. I've been making twice daily trips down there as I am determined to find something good before the year end. Since I've been birding there from the Autumn of 2007 onwards there has always been at least one scarcity for each half of the year. The list is as follows 2007 H2: grey phalarope & pectoral sandpiper; 2008 H1: Temmink's stint; 2008 H2 American Golden Plover; 2009 H1 spoonbill. However with there having been such a dry autumn there have been no floods to speak of until recently and so time has been slipping away for me to find a decent bird to keep this list going. There were also a few "good county birds" this spring in the form of an avocet, a bar-tailed godwit and a little tern but these aren't proper scarcities in their own right just in the county so I can't even borrow a spare from the first half to count for the second half. This is all nonsense I know but I have a real soft spot for the Meadow and would very much like it to have the birding recognition that it deserves. This is one of the reasons why I run my Port Meadow Birding blog and I am always touched and surprised by the number of people who come up to me saying how much they like it.

Now that there is a decent amount of flood water there is much more chance of a decent gull roost so I've been going out to check in the afternoons and a couple of days ago I made the pleasant discovery of a lovely Caspian Gull in amongst the roost. Followers of this blog will know that I have in the past been struggling with the whole herring/yellow-legged/Caspian gull complex and have been working diligently at improving my identification skills. In my recent blog entry on finding a 1st winter Caspian at Didcot I mentioned that I now felt more confident on this age group but had yet to master the adult birds. All my staring at Caspian Gull photos must have paid off somehow because as soon as I saw it I thought Caspian Gull: the jizz and shape just looked right. I went through my adult Caspian check list:

  • Long parallel-sided bill of pale or washed out yellow colour (often almost limey in colour)
  • Clean white head with gently sloping forehead, dark "bullet-hole" eyes
  • The Cachinanns facial expression: to me it's a kind, sad and aloof expression. It definitely doesn't look fierce though can sometimes look "imperial"
  • A mantle colour that's a shade darker that argenteus, about the same as argentatus but lighter that michahellis.
  • Legs that are a paler pink that your typical herring gull
  • Moderate amounts of white in the primary for the closed wing (not small amounts as for michahellis)
The gull in question: note the "kind, sadly aloof" expression.
A wider shot allowing comparison of the bill and mantle colour. Note the long parallel-sided and rather washed out bill colour. You can't see it very well but the legs were definitely pink.

All this checked out perfectly. There was just one final test which is the underwing and really requires a videograb so I set about videoing. Ideally one wants a full underwing flap but unfortunately I wasn't able to get this. What one is looking for is a reasonable white tip to P10 with a white underwing primary covert covering the inner web of P10 so that one is left with a small black area and perhaps a black finger extending down the outer web. This didn't seem to match so well and left me slightly wondering though everything else looked so good and I am starting to realised that with gulls there is often so much variation that one can't always get everything to match up. Nevertheless to be on the safe side I sent my shots to Ian Lewington the county recorder and top gull expert to see what he said. He agreed that it did appear to have all the right characteristics of a Caspian Gull and that the amount of black on the underside of P10 was still within the acceptable range for a Caspian though only just.

The best underwing shot that I was able to manage. There is rather a lot of black on this but apparently it's within the acceptable range for a Cachinnans.

An example of what a standard P10 underwing look like. Note the white underwing primary covert on the inner web with the thin finger of black extending down the outer web.

So using the Bird Guides classificaiton of five degrees of rarity: common, local, scarce, rare and mega, it's not a scarcity, being merely a local bird but it's the best bird that I've had on the Meadow so far this autumn and it's enabled me to further my knowledge of the "Way of the Gull Master". I'll carry on going to the roost down on the Meadow to see what else of interest I can find.

No new ticks to report for either the county or national year list.

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