www.gull-research.org

We have a Caspian lookalike with some argentatus-jizz in Aarhus Harbor. This is the third winter that we see this adult gull in the harbor and there is a completely match between years. All three years is has had the almost complete white summer head from November when arriving at the site.

It has only black on outer edge of p5, but also on left wing a little black spot on p4, extensive grey tongues on the five outer most primaries, all white tips to p10, darker upperparts than argentatus, when seen on water it gives a classic cachinnans jizz with rather small head, slender elongated rear and flat back, but when seen standing on ground it gains some argentatus appearance due to head profile and body.

Could it be a pure cachinnans or is most likely a hybrid cachinnans x argentatus or even just an aberrant argentatus in advanced moult?


November 2009

in flight: http://2.bp.blogspot.com/_PYB8xNHlQmw/S ... llage2.jpg

standing with argentatus: http://3.bp.blogspot.com/_PYB8xNHlQmw/S ... llage1.jpg

swimming and standing with argentatus: http://3.bp.blogspot.com/_PYB8xNHlQmw/S ... llage3.jpg

standing with argentatus: http://2.bp.blogspot.com/_PYB8xNHlQmw/S ... -11-09.jpg

swimming with argentatus: http://2.bp.blogspot.com/_PYB8xNHlQmw/S ... -11-09.jpg

standing alone: http://3.bp.blogspot.com/_PYB8xNHlQmw/S ... -11-09.jpg


December 2007

open wing: http://2.bp.blogspot.com/_PYB8xNHlQmw/S ... G_1685.jpg

open wing: http://1.bp.blogspot.com/_PYB8xNHlQmw/S ... G_1686.jpg

standing with argentatus: http://bp3.blogger.com/_PYB8xNHlQmw/R5P ... 23_red.jpg


November 2007

standing with argentatus: http://bp2.blogger.com/_PYB8xNHlQmw/R5P ... 57_red.jpg


Thanks in advance

Regards

Kent
http://gulldk.blogspot.com/

For me, it is a cach.

To me, the head shape, the shortish wing, the primary pattern give me too much of Herring influence to make it a pure cachinnans.
It may be a pure argentatus to me.

Theo

I can´t decide whether it´s a pure Caspian or a possible Caspian x Herring. The primary pattern looks quite good for Caspian - there´s a certain degree of variation in the pattern of each primary, lenght of the dark on the outer web, lenght of grey tongue. So a lack of, or a thin complete or not, or just a spot on the outer web on p5 is seen in some - http://1.bp.blogspot.com/_JXeDixaPw40/S ... 9K8206.JPG (Chris Gibbins). However, if it´s within the variation of Caspian is to be considered, but probably so. A primary pattern like the one in Kent's gull here, linked below, I have once seen in a straightforward Caspian, except the dark mark on p5 was in p4 and the dark spot on the outer web of p4 was on p3!
A set of the wellknown structurall features for Caspian probably allows for a certain degree of 'not so typical features'

http://2.bp.blogspot.com/_PYB8xNHlQmw/S ... G_1685.jpg

Here:

http://4.bp.blogspot.com/_PYB8xNHlQmw/R ... 23_red.jpg

it shows it´s best side for a Caspian. Blow the pic. up to at least 400% and you will see a quite pronaunced gonys angle and a slight blob tipped impression. Then again bill proportions vary to in gulls - apart from the sexual differences.

This one is interesting for the discussion in question:

http://www.iesmeulmeester.nl/fotos.php? ... catsub=203

Jan

kent, jan, ...

as we have seen variation in primary pattern and bill shape in breeding birds from the black sea is much larger than we are used to accept for western european winter guests. for example a pronounced or hanging gonys is shown by rel. many birds in the dobrogea/danube delta. (see the attached examples)

slow by slow i think these criteria (for winter guests) are weakening but there is the problem that we don't actually know how many caspians wintering between sweden and italy actually are hybrids or backcrosses. to me about half of the polish caspians e.g. somehow look like they may at least be influenced by its relatives breeding in the same colonies and this process might go on with the years producing more and more such birds (i think this is seen in the holland and british birds also). and there are mixed colonies producing hybrids further east, in belorussia and russia (i get nightmares when seeing pics of those iwanowo oblast birds).
so in many of such cases it might be safe to say it is probably a caspian but with certain off-typical features or to just accept that we don't know how "pure" these cachinnans are.

lou

In the discussion bird, I think the fore-head streaking and streaking on top of its head, that is what rules out a pure caspian to me..

Theo