IDENTIFICATION CONUNDRUMS

A small skua species was present at the end of last week on a tiny private lake in Surrey (UK). Sadly it was in poor health but was retrieved and taken into care. A number of photographs were taken at close range and I present them here - http://bbabirding.blogspot.co.uk/p/identification-conundrums.html - but opinions were divided as to which species it was - ARCTIC or LONG-TAILED. Although not visible here, the bird had pale tips to the primaries and pointed tail tips, so does that conclusively identify it as an ARCTIC SKUA (PARASITIC JAEGER)? I welcome any constructive comments

As soon as I saw these images, this shouted 'Long-tailed Skua' at me, but other equally experienced observers said 'Arctic'. Therefore I decided to solicit expert opinion -:

PETER ADRIAENS commented 'The short, stubby bill, the Common Gull-like head, the dark cap (on a juvenile skua), cold plumage tones (especially nape) and the black and white undertail coverts should be enough to clinch the identification. It is a Long-tailed Skua. They can show (slight) pale tips to all primaries'' whilst DANI VELASCO LOPEZ added ''The lack of pale tips to the primaries on juvenile LTS (Long-tailed Skua) is a common misconception amongst birders. Some juvenile LTS can, in fact, show noticeable pale tips to the primaries, although of course usually smaller, less obvious and with a different shape than those of Arctic Skua. There´s also considerable variation in the shape of juvenile centrail tail feathers, with some LTS showing relatively pointed and short, Arctic-like, feathers, and some juv Arctics showing longer, more rounded centrail tail feathers,  thus suggesting LTS. This bird is in my opinion certainly a juvenile Long-tailed.  General structure, bill size and shape, unstreaked nape, profuse barring on the undertail coverts, etc.. indicate so''

The bird remains in care and David Harris has very kindly provided me with a follow-up image showing the upperparts and rump

Hans Larsson commented ''Hi Lee & all, Apart from that the upper tail-coverts do look fine for an Arctic, even more important in my view is the head and bill wich also looks good for an Arctic. Actually a picture of the head would be enough to clinch this bird IMO. I´d like to point out especially the wide and diffuse pale eye crescents, which I think is a very good indication of Arctic along with the heavily streaked face, creating a kind of "unwashed" look that I don´t really see in the more smoothly patterned Long-tailed. Compare with this Arctic:

http://www.netfugl.dk/pictures.php?id=showpicture&picture_id=4220
Also, the bill looks a bit to long for a Long-tailed and critically, the amount of black in the lower mandible is rather small, again matching Arctic (see the linked pic above). Compare with this Long-tailed:
http://www.netfugl.dk/pictures.php?id=showpicture&picture_id=43254

With best regards,

Hans''

Much earlier, Kevin Karlson had very kindly emailed me this -:

Lee,

We recently had a juvenile Long-tailed Skua and a juvenile Arctic Skua on the beaches of Cape May, and I got to photograph both of them. I have processed the LTS shots, but only shot the Parasitic (Arctic) the other day, so they are still raw files that I have not processed. But having seen and studied both species, your bird looks very much like the Arctic Skua that was in ill health as well the other day, and not like the juvenile Long-tailed. The flat head and somewhat substantial bill on your bird is not like the more rounded head and more delicate bill on the Long-tailed, which is a smaller, more petite bird overall. I have attached a few shots of the Long-tailed and will send you a shot of the Arctic tomorrow. The Arctic did have pale tips to the primaries, and the tail feathers were not pointed on the Long-tailed (see flight shot). My feeling on your bird is Arctic. Kevin Karlson

Ps - the ground shot is affected heavily by heat waves, and it is a miracle that I was able to get what you see from the heat wave original file. I did not get  flight shot of the Arctic, since it was sitting on the beach and did not look to be in good health, so I left after a half hour. The bird did fly away about four hours later, but I would be surprised if it survived.

Long-tailed Skua, Cape May, 6 September 2013 (Kevin Karlson)

Juvenile Arctic Skua, Cape May, 29 September 2013 (Kevin Karlson)

Jan Jorgensen from Sweden added ''Interesting views here.

I am in complete agreement with Hans on this one being an Arctic Skua for the
reasons he made above, especially the bill dimensions and pattern.
One more Arctic here showing these features:

http://www.netfugl.dk/pictures.php?id=showpicture&picture_id=13908 -

and one more Long-tailed for comparison, with pale-tipped primaries:

http://www.netfugl.dk/pictures.php?id=showpicture&picture_id=30729

And after reading Hans' reasoning behind his identification, both Peter and Dani changed their minds and ran with Arctic. Andy Holden added ''Hi Lee, Just checked out your shots on the blog. The relatively small nail vrs. medium and pretty straight bill and even more reduced black on lower mandible, swarthy almost ‘water – combed’ pattern of the face and pattern of the primary tips – rather solid terminal white blocks on both webs rather than even terminal tip of some LtS( think juv Red – throated Diver mantle vrs. Juv Black – throated Diver mantle ) all favour this being an Arctic Skua for me. The shot in the cage shows the central tail tip as pointed and dark, eliminating the possibility of any pale tips having worn off. I’d agree it looks rather small and meek in the field ( perhaps due to being so close / unwell ? ) and its vent is rather boldly barred, but otherwise it’a an Arctic for me''

Sadly, the bird died today at the rehabilitation Centre in Surrey. I am hoping to get more photographs of the salient features and critical measurements (LGRE)

Caleb Putnam also kindly emailed me details of a small skua recently present in Michigan, USA - ''We just experienced a small skua in Michigan which some of us felt was likely Long-tailed, but turned out to be Parasitic. It looks quite a bit like your bird (but had only slightly pointed R1). Haven't had much time with your photos but I believe yours is likely a Parasitic. A detailed analysis of our bird is at my blog here, which may be of interest: http://aviantendencies.blogspot.com/

Arizona birder Pete Moulton also quipped ''you can sign me up with the Arctic camp, based mainly on the pointed central rectrices, whitish edging on the primary tips, generally warmish-appearing upperparts, bill shape and coloration (Blackish only on distal 30% or so, and--especially--on the streaked face and neck. Despite my residence in an area where skuas of all types are quite rare, I'm deeply fond of the family, and will be watching with great interest as others chime in''

David Harris retrieved the corpse this afternoon and very kindly emailed me these photographs -: