I've come across a couple of requests for id features for skuas. I'll start the ball rolling with a jizz-based post. Anyone fancy doing plumage?
How I identify Stercorarius Skuas on build and flight! (Based on Irish Sea observations in strong winds)
The first thing to appreciate is that Long-tailed Skua is a rare bird. I make an effort to seawatch in any good weather and I can go years without seeing one. I may be a bit negligent in recording all the Arctic Skuas I see and still they out-number Long-tailed by 300 to one and Pomarine by 100 to one in my records. The trouble with skuas is that they are probably the most “jizz”-dependant of all birds. Many guidebooks still concentrate somewhat misleadingly on plumage features which can vary surprisingly between individuals of different ages and in typical viewing (think lashing NW gales and squalls) can be amazingly hard to see! It takes a lot of practice to get tuned into the jizz of skuas, but once you do they suddenly become quite easy.
Flight pattern of birds that are moving in strong winds;
• Arctic Skuas usually fly in dramatic high arcs (careening) outstripping even Kittiwakes in their ability to fly into high winds. Typically they rise on stiff wings angled back sharply at the carpal joint.
• Pomarine Skuas are more likely to fly without careening. Instead they keep rather low and employ deep regular gull-like wings beats and often disappear down wave troughs.
• Long-tailed Skuas to me look just like Sandwich Terns in flight. I almost never think they are skuas at first and have never seen one careen. They usually fly about 10 feet above the water in a straight line with extremely bouncy wing-beats. Speaking to Harry this afternoon he described them as like a Nightjar…. Which is right!
I’ve never seen a Long-tailed Skua chasing other seabirds and my only sightings of Pomarine skua chasing (e.g. Lesser Black-backed Gulls) have been non-breeding birds which summered. Autumn Poms around here are most often seen feeding on carrion!
Build – body shape
• Arctic Skuas look very chesty – the point at which the curvature on the underside changes is just about level with the leading edge of the wing, like a Peregrine and the base of the wings is a little less than the length from the rear edge of the wing to the end of the tail (minus streamers).
• Pomarine Skuas have a much deeper centre of gravity, the point at which the curvature changes is right in the middle of the wings. They lead with their belly – like a Glaucous or Great Black-backed Gull. The base of the wing tends to look a little broader than distance between the hind edge of the wing and the tail end. I find they have a longer arm to hand ratio than Arctic
• Long-tailed Skua has point of inflexion similar to Arctic Skua, level with the leading edge of the wing, but it’s a lighter bird, if you like more of a Hobby than a Peregrine. The wing base is a probably a little narrower than Arctic Skua though a lot of that might be due the longer rump and tail on this species. I find they looks to have a shorter arm to hand ratio than Arctic.
There is surprisingly little difference in actual size between these species, but Pomarine is a much more robust bird. I operate a policy that all distant (incoming) skuas are either Arctic or Great till proved otherwise and I have (briefly) mistaken Pomarine for Great Skua on build and flight too many times for it to be a coincidence.
This picture is an exaggerated caricature of the silhouette of the three smaller skuas handicapped by being drawn in Paintbrush! A couple of my avatar are skuas - I'll put them up too.....just looking for a pom! Found one!
How I identify Stercorarius Skuas on build and flight! (Based on Irish Sea observations in strong winds)
The first thing to appreciate is that Long-tailed Skua is a rare bird. I make an effort to seawatch in any good weather and I can go years without seeing one. I may be a bit negligent in recording all the Arctic Skuas I see and still they out-number Long-tailed by 300 to one and Pomarine by 100 to one in my records. The trouble with skuas is that they are probably the most “jizz”-dependant of all birds. Many guidebooks still concentrate somewhat misleadingly on plumage features which can vary surprisingly between individuals of different ages and in typical viewing (think lashing NW gales and squalls) can be amazingly hard to see! It takes a lot of practice to get tuned into the jizz of skuas, but once you do they suddenly become quite easy.
Flight pattern of birds that are moving in strong winds;
• Arctic Skuas usually fly in dramatic high arcs (careening) outstripping even Kittiwakes in their ability to fly into high winds. Typically they rise on stiff wings angled back sharply at the carpal joint.
• Pomarine Skuas are more likely to fly without careening. Instead they keep rather low and employ deep regular gull-like wings beats and often disappear down wave troughs.
• Long-tailed Skuas to me look just like Sandwich Terns in flight. I almost never think they are skuas at first and have never seen one careen. They usually fly about 10 feet above the water in a straight line with extremely bouncy wing-beats. Speaking to Harry this afternoon he described them as like a Nightjar…. Which is right!
I’ve never seen a Long-tailed Skua chasing other seabirds and my only sightings of Pomarine skua chasing (e.g. Lesser Black-backed Gulls) have been non-breeding birds which summered. Autumn Poms around here are most often seen feeding on carrion!
Build – body shape
• Arctic Skuas look very chesty – the point at which the curvature on the underside changes is just about level with the leading edge of the wing, like a Peregrine and the base of the wings is a little less than the length from the rear edge of the wing to the end of the tail (minus streamers).
• Pomarine Skuas have a much deeper centre of gravity, the point at which the curvature changes is right in the middle of the wings. They lead with their belly – like a Glaucous or Great Black-backed Gull. The base of the wing tends to look a little broader than distance between the hind edge of the wing and the tail end. I find they have a longer arm to hand ratio than Arctic
• Long-tailed Skua has point of inflexion similar to Arctic Skua, level with the leading edge of the wing, but it’s a lighter bird, if you like more of a Hobby than a Peregrine. The wing base is a probably a little narrower than Arctic Skua though a lot of that might be due the longer rump and tail on this species. I find they looks to have a shorter arm to hand ratio than Arctic.
There is surprisingly little difference in actual size between these species, but Pomarine is a much more robust bird. I operate a policy that all distant (incoming) skuas are either Arctic or Great till proved otherwise and I have (briefly) mistaken Pomarine for Great Skua on build and flight too many times for it to be a coincidence.
This picture is an exaggerated caricature of the silhouette of the three smaller skuas handicapped by being drawn in Paintbrush! A couple of my avatar are skuas - I'll put them up too.....just looking for a pom! Found one!
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