'Caspian' Gull at Sean Walsh Park - 24th & 29th Dec

For the last 3 years a Caspian Gull has been reported hanging around Sean Walsh Park in Tallaght. I only found out about it recently from irishbirding.com, so have spent quite a bit of time over the last week looking for it. I caught up with it briefly on Christmas Eve, and again for a prolonged period yesterday, thanks to meeting up with an Irish birder (Dave Fox).

First seen as a juvenile, this 4 year gull is now in adult winter plumage for the first time, and the most striking thing initially is the darker shade of the mantle. It really stands out from the argenteus Herring Gulls it is most similar in size to, looking quite a lot like a Scandanavian argentatus Herring Gull. This isn't a normal feature of Caspian, but is within the range of variation. Note the long primary projection, a feature of Caspian.

It has a nice upright stance most of the time, and is relatively easy to pick out at some distance in profile when with other large gulls.

The legs are greyish which fits Caspian, not pink as would be expected in a Herring Gull

It has dark olive-coloured eyes, and only light streaking on the hind-neck. The gonys is also quite small, though the bill seems shorter and deeper than I expect from Caspian.

All in all, a smart bird with all the features you'd expect from a Caspian Gull...

...until it takes off, and the wing pattern is completely wrong. While the white mirror on the final primary (P10) is present, there's nothing at all on P9...

...and now it looks like an argenteus Herring Gull. A strange bird to be sure. Currently several local birders are carrying around little plastic bottles to try and collect a fecal sample so a definitive ID can be made. The wonders of modern birding techniques...