Monday 6 February 2012

Fermanagh Thayer's-type revisited

So, here are my best (although still incredibly ropey) shots of the Co. Fermanagh Thayer's Gull, taken on 6th January of this year at Lower Lough MacNean. They are unaltered, just cropped.

Although thayeri was considered at the time, I naively came to the conclusion in the field that it was probably just a dark Kumlien's Gull (albeit a Thayer's lookalike). This was based on my distant views and interpretation of the bird's features (with the recent Dunbeg bird, to which I thought it showed many similarities, niggling at the back of my mind). A combination of features that suggested identification away from a typical Thayer's Gull were:

  • predominately pale scapulars (i.e. dark tips only)
  • reasonably pale and well-marked tertials
  • tail a milky dark brown rather than black
  • primaries look a 'diluted' dark brown rather than black/near-black
  • extensive pale in greater coverts as well as upperparts in general
  • obvious pale base to bill
  • relatively delicate structure

This bird was relocated, perhaps not unsurprisingly, some 10km or so to the east at Enniskillen Dump during late January, where much better views have since been obtained. And, judging from Derek Charles' photos as well as this youtube video, it looks an altogether more promising candidate. However, the features mentioned above still apply and, as such, it is not a unequivocal, dark juvenile Thayer's. Having said that, it does look OK for one.

Problem is, is looking OK good enough in a Western European context? While this bird may look alright on the west coast of the USA, in vagrant context (where Kumlien's Gull is a much more likely occurrence) the situation is perhaps somewhat different. It was my impression that a classic would show a combination of darker primaries, secondaries and tertials, more extensively dark coverts and scapulars, and perhaps a more robust structure - many Thayer's just look bulkier than Iceland/Kumlien's, more akin to Herring Gulls (although don't get me wrong, this bird is within range; it looks bulkier than your average glaucoides). Even if you take a holistic approach to studying this bird, I just thought it seemed to show a bit too much pale in it to confidently identify as an obvious thayeri at the time - particularly on the upperparts. That's not to say it isn't one, though, and think the dull light conditions (and dark green fields) made it appear paler than it really is. Plus it didn't help I was viewing at around 400 metres' range! In hindsight I should have tried harder to get closer, or at least hung around longer to obtain better views in better light.

To me, this is still one of the better candidates we've had in recent years - better than the Dunbeg bird, the Oxon/Derbys bird a few years back, and also the Rossaveel 'thing' last winter. However, it clearly isn't a dark juvenile Thayer's such as that in Denmark in 2002. Obvious moult and wear aside, it doesn't actually look too dissimilar to the 2005 Barnatra bird.

So, to sum up... it's a dark member of the glaucoides/kumlieni/thayeri complex. Great looking gull. Do I think this bird is a classic, unequivocal Thayer's Gull? No. Could it be one? Probably.

One thing is for sure - if it isn't thayeri, then my goodness can kumlieni come close!

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