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Wednesday, 12 August 2015

All 4 skuas on Ed's Pelagic

All four species of skua were seen on the annual 'Ed's Pelagic' out of Dingle yesterday, when 12 hardy souls set sail west from Dingle to open ocean, 3-4 kms west of the Blasket Islands. Along with the skuas, several Sooty Shearwaters, lots of Manx Shearwaters, Storm Petrels, Puffins and 4-5 Minke Whales were seen, with Bottle-nose Dolphins, Common Dolphins and Porpoise all making appearances.

Stars of the show were the skuas, with several coming close to the boat and offering fantastic views.

One nearly got away however, when this bird (below) appeared as soon as the 'chum' started going overboard. It was called as an Arctic Skua, but was to prove a valuable lesson in the unexpectedly tricky ID of second year skuas.

'Arctic Skua', the first skua of the day, which appeared at the chum slick within minutes and stayed around the boat for up to half an hour (M.O'Clery).

With a prominent breast band, apparently dark bill, and the 'classic' two short central tail projections, it certainly gave the appearance of an Arctic Skua. Perhaps because it was our first skua of the day, and also because it was close to the boat, the impression of size was difficult to judge subjectively. And, as other birds started to appear at the chum, the 'Arctic' got pushed aside from centre stage, especially when a beautiful adult Pomarine Skua appeared at point blank range, diving into the slick just off the back of the boat, and a few Bonxies made appearances. 

Thank goodness for digital cameras, and no doubt, hundreds of photos of the 'Arctic' were already taken by the range of high-quality cameras and lenses on board, but it was only later, at home, that Eric Dempsey and myself had a chance to go through the photos from the day and realised that this might actually be a Long-tailed Skua. Not a 'forehead-slapping' moment of realisation but rather, ever-growing suspicion with each photo, we were looking at a Long-tailed rather than an Arctic Skua.

Size-wise, we could only be dealing with Arctic or Long-tailed Skua. Checking images against field guides generally showed only adult or first-year birds and scouring for images online threw up all sorts of mis-captioned and/or mis-identified second years. One such skua image was even captioned, 'Glossy Ibis'. 

Despite the superficial resemblance to a second summer (i.e., a third calendar-year) Arctic Skua, there were quite a few contradictory ID features. This photo, below, shows how 'dainty' the overall structure of the bird was while on the water, with a shortish bill and slight proportions.

Other features in favour of Long-tailed Skua were:

• Although upper- and under-tail coverts had mostly been moulted into adult-type coverts, the few still in place were very coarsely barred. It was easy to imagine that, had they not yet been moulted, that the overall appearance would be of a heavily barred upper- and under-tail, more like Long-tailed Skua. See the photo below.

• There were no warm tones to any of the plumage, especially the remaining immature feathers, whereas Arctic Skua would usually show some warm brown or ginger tones to at least some of the immature plumage features.

• Also, in the photo below, note the contrast between black secondaries and brown greater coverts, a pro-Long-tailed feature.

• And, also in the photo below, only the two outer primary shafts show white, again a pro-Long-tailed feature.

• On the underwing, there was virtually no white primary flash usually associated with immature Arctic Skuas (and most Long-tailed Skuas), as in the photo below.

• The prominent breast band can be shown by darker juvenile Long-tailed Skuas, so is not unique to Arctic and Pomarine Skuas.

• The above features, while not necessarily diagnostic of a Long-tailed, in combination were certainly pointing that direction. The clinchers were the shape of the dark cap, which didn't extend below the line of the gape (Arctic and Pomarine Skuas show a dark wedge of black below this gape line) and the shape and structure of the bill. In Long-tailed, the gonys angle occurs almost half way along the lower profile of the bill, while on Arctic, with a proportionally longer bill, this angle occurs about a third of the way along the underside profile of the bill (thanks to K. Mullarney and A. McGeehan for pointers on these features).

(you can click on any of the images for a closer view)

Second summer (third calendar-year) Long-tailed Skua, 4km W of Inishtearaght, 12th August 2015 (M.O'Clery).
Note the gonydeal angle on the underside of the bill, and the black of the 'cap' not extending below the gape line. Interesting also to note the 'dipped in black ink' feet of this bird. Is this pattern distinctive in Long-tailed as opposed to other second year skuas?

So, a second summer (i.e., a third calendar-year) Long-tailed Skua after all. Lots to be learned from this bird. In retrospect of course, we can all say, "Of course it is!", but this was a tricky ID. There were other clues which went missed at the time of the sighting which should have rung alarm bells. The bird fed on the chum slick and showed no aggressive behaviour to other birds, sitting on the water for some time, all behaviours more like Long-tailed rather than the much more aggressive Arctic Skua. Also, although this was the first skua of the day, the small size and proportions should have been evident later, especially once a Pomarine and a Bonxie appeared by the boat, dwarfing the apparent 'Arctic Skua'. 

Second summer (third calendar-year) Long-tailed Skua, 4km W of Inishtearaght, 12th August 2015 (M.O'Clery).

Above all, perhaps the message should be, question everything! Although called as an Arctic Skua, it was photos which proved it to be Long-tailed. Without cameras to hand, it would have slipped under the radar. The clues were there at the time, and of course, we are all now a little wiser. Let's raise a glass to Canon and Nikon...

Adult Great Skua, 4km W of Inishtearaght, 12th August 2015 (M.O'Clery).

Adult Pomarine Skua, 4km W of Inishtearaght, 12th August 2015 (M.O'Clery).

A truly impressive bird, with full 'tail spoons'.