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Commisioned ID Thread #2 Skua / Jaegers (1 Viewer)

Jane Turner

Well-known member
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!
 

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Thanks for posting this! I havent seen any of these yet, but I will bookmark this for my next seawatching trip.
 
Jane, that's the most practical and helpful advice on skua ID that I've seen. And, yes, I've misidentified juvenile Pomarine as a Great Skua before now.
 
Brilliant stuff Jane. I agree with the usefulness of the confusability of Poms with Bonxie (if that makes sense). A typical train of thought for me is 'I think there's a Bonxie, err, no hold on a minute'. Those ones tend to look like Poms when they get closer!
 
I have been seawatching when two skuas were called as 4 species... I thought they was a darkish juv Pom and a small Arctic skua with broken tail streamers!!! They are confusing. It does help that the autumn Poms tend come come through a lot later than the bulk of the Arctics too!
 
I don`t know if its due to the narrower wings but Long-tailed Skuas always look longer winged than Arctics - if thats any help to anyone ;)
 
Today I had 3 Arctic Skuas at Starr Gate. The second of the three intrigued me. It would flap its wings to gain height, and then stopped flapping and hung in the air at the top of the arc. It did this repeatedly. There was little wind at the time. The other two were much more typical in their flight action.

Anyone seen this before?

Stephen.
 
Jane Turner said:
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!

Hi Jane
I agree totally that jizz experiance is the key to identifying Skuas, particuarly juvs.
I Skua watch every autumn from Hound point in Lothian. I am generally rusty on the first few visits but as the autumn progresses I tend to get my eye in.
So much so that in good years birders are able to identify specks in the distance solely from flight action as they fly towards us.
With regards to yourself having never seen LTS chasing seabirds. I have observed them chasing Sandwich Terns on numerous occasions.
Chases however tend to be very half hearted affairs, generally giving up straight away, although I once observered a Juv on a very prolonged and determined chase.
I have on a few occasions even seen the tables being turned with the sandwich Tern turning around and chasing off the LTS.
This never happens with Arctic Skua as basiclly its the boss !
Last autumn I had the privilage to see a Juv Pom chase a Kittiwake, it grabbed it by the wing and threw it into the sea where it dived in after it.
The Kittiwake managed to escape however, but I had no doubt the Pom was trying to kill it.
Two other interesting facts also occur in the upper Forth, firstly it pays to look at migrating Gannets as the flocks sometimes has a Bonxie tagging along with them.
Secondly Skuas either sat on the water or flying low over the sea sometimes begin to rapidly climb skywards, this always results in a flock of Skuas seen migrating at altitude with the aforementioned birds trying to catch them up.
 
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I guess here we have Arctics most of the autumn and they are here specifically to feed off the terns. The other skuas only end up here in strong winds (except the summering poms) and are mostly concerned with getting away again!

One of the goriest things I've seen is a Bonxie wade into a flock of roosting large Gulls, knock a LBBG on its back, put a foot on eat wing and proceed to eat it alive.

I too always associate a suddenly high tern flock with a low skua. Another thing - it seems that Gulls can spot the jizz similarities between Poms and Bonxies since an approacting one will often precipitate panic in a roost. Finally for now, though I've never seen it, the LTSkuas that sometimes end up in the Mersey mouth on big winds are often reported to be eating Leach's Petrels!
 
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