Skuas an interesting note from the County recorder
Recent sightings of a group of light and dark morph Skuas in Berkshire lead to some discussion about identification features. This is not the first time as some difficulty arose last year at Queen Mother Reservoir about identifying these species. The discussion was about birds found by Paul Cropper and a contribution from Marek Walford.
Chris Heard recently put this note on the BerksBirds Yahoo Group which may be of interest:
Dark morph juvenile Long-tailed Skuas are, of course, quite frequent but - as Marek said - dark morph adults may not actually exist. 'Skuas and Jaegars' (by Olsen & Larsson) states that adult Long-tailed Skua "occurs only as a pale morph (i.e no intermediate morph either).... and the existence of a dark morph adult is still to be proven".
To put this in context, Dave Davenport (author of several papers on Long-tailed Skua occurrence) has seen over 4,000 adult Long-tailed Skuas in the UK (!!) and has never seen anything resembling a dark morph adult.
So Paul's dark morph adult (as clearly indicated by the pronounced tail streamers) must surely have been an Arctic Skua. And, in the absence of any structural differences, the likelehood is that pale morph adult was also this species. Some adult Arctics do show remarkably long tail streamers and can take you by surprise even after prolonged seawatching.
But this does raise the issue of whether inland skua flocks are ever composed of more than one species. Different skua species do mingle when collecting, for instance, at the mouth of the Swale (N.Kent) but Dave Davenport reports that they invariably separate into single- species groups when they head inland. In autumn, flocks of Arctic Skuas are occasionally recorded over inland counties and in autumn 1985 there were several inland groups of Poms (see Bit Birds 80:404- 421) - but DD says that they too were all single-species flocks. I cannot recall ever hearing of an inland Long-tailed associating with another skua species.
Last year, during eight days seawatching at Bridges of Ross* (Co Clare), I saw a total of 24 Long-taileds (singly or in groups of 3- 4) and my impression was that passing Arctic and Long-tailed Skuas may coincide but that cohesive flocks were generally of single species; they even seem to travel at different speeds and Long-tails often loiter and feed on the surface - which Arctics and Poms rarely do. In the same period this year I saw just two Long-tails but, remarkably, they went past separately at the same moment in time (perhaps - by remaining in sight of one another - they were actually together).
It has become axiomatic to state on this group that skua identification is often not straightforward - but perhaps that is part of their attraction. [Even their genetic make-up is confusing... several studies indicate that Pomarine is closer to Bonxie than the smaller skuas - somewhat at odds with their morphology]
Chris Heard
* The October issue of Birdwatch magazine includes a feature on August's seawatching at Bridges of Ross - which was written by Niall Keogh - one of the sharpest of the new generation of Irish seawatchers.
Colin Wilson - 22 September 2005