Possible Hybrid Caspian x Herring Gull

[gabrieljamie]

I was at Dungeness in late December 2007. Whilst I was there I saw this bird on the beach at the Patch. It certainly did not look like any of the other Caspian Gulls I had seen at Dungeness earlier that morning and earlier in the week.
A photo of the bird can be found at the following link: http://www.flickr.com/photos/23555819@N07/2246999769/
I have also have a link to a more typical Caspian Gull seen a day or two earlier
http://www.flickr.com/photos/23555819@N07/2247035109/
I thought it might be a hybrid due to it seemingly showing features of both Caspian and Herring. The bill was long (appears shorter in photo due to the bird looking slightly towards me), and there was hardly any gonydeal angle.

Structurally, the bird seems to show the protruding breast of Caspian, and rounded head. However, the bird seems to show a prominent "hanging belly" behind the legs (which I thought was more of a feature of Herring Gull). The bird also has the small black eye of Caspian Gull. The streaking on the head also seems intermediate between Caspian and Herring. It shows slightly more concentrated streaking on the nape (like Caspian should) but instead of showing a nearly all white head (as in all the other adult Caspians I have seen) it shows faint dark markings over much of the head (perhaps revealing the slight Herring Gull influence). Another feature this bird shows which I have noticed on Caspian are the white "eyelids". The legs are long and thin, however (and this is one of my main problems with it being a Caspian) the legs are a bubblegum pink colour, very reminiscent of Herring and not at all like any Caspians I have seen. Also the bird does not seem to have a pronounced tertial step (Does this support Caspian?).

The mantle colour is lighter than most of the Caspians I have seen in real life, but from photos I have seen it looks within the range of Caspian. The colour is certainly greyer than the presumed argentatus Herring on its right and lacks the bluish tones of that species.

Unfortunately this is the only photo I got of the bird and I did not manage to see it in flight. I have never seen a Caspian hybrid in the field before so if any of the above features I have used to reach my conclusion are wrong or there are other features that I have overlooked, I would very much like to hear about them.

Gabriel

[Harry Hussey]

Hi Gabriel,
I'm not really the person to advise you here, seeing as how my Caspian Gull experience is limited to a 1st-w here in Co.Cork last February, though I would share your concerns about the initial bird on this thread: in particular, I don't recall seeing pics of adult Caspians with such bright pink legs...grey-pink, flesh or dull yellowish, yes, but not 'bubblegum' pink, as you put it.
Of course, it's possible that 'pure' Caspians could show odd bare parts colours, but, given the existence of not insubstantial numbers of hybrid young and backcrosses from the Polish colonies, which, I think, have been proven to stray as far west as the UK(??), surely limiting ourselves to birds within the currently accepted range of variability of Caspian is the best course of action for now...given your own caution with this bird, I am sure that you will agree.
(It is also true that we cannot be 100% sure of the genetic 'purity' of even classic birds, but surely it makes sense to treat such birds as Caspian where no anomalous features are noted)
I am sure that someone who actually knows what they are on about, like Brian or Jan, will post here soon!
Regards,
Harry

[Brian S]

I have seen just one adult-like gull here at Southwold that I suspected might have been a cachinnans hybrid. It shared a number of structural characters with your bird, notably around the head, but the mantle was a little dark and the legs more yellow than pink - so perhaps had some michahellis influence (not like the pinks legs of your gull).

It first appeared as a third-winter, then returned for its fourth winter intrinsically in adult plumage. The outermost primary had a white tongue (often greyer on michahellis, though eastern birds tend to be whiter, just to confuse things) on its inner web, but it did not extend down as far towards the tip as on cachinnans. The head structure was more angular than cachinnans and much more like michahellis, but the bill was especially pale like yours.

Your gull may have cachinnans influence, but from the pictures I am not sure. Can you give any information on the primary pattern? Based on the tone of the mantle, the structure of the head, the colour of the legs, I just can't really say too much.

As an aside, over the last ten years of watching gulls in Suffolk, I would suspect that Herring Gulls are attaining white heads earlier in the winter than they used to. I have no actual data to back this up, but it just feels like it. Those that have a white head early can confuse the unwary - though I am not suggesting that here.

Brian S

[gabrieljamie]

Brian and Harry

Thanks a lot for your comments. Unfortunately I only saw the gull briefly as, soon after I took the photo, it flew up with a large number of Herring Gulls (frustratingly at a point when I was not looking at it through the scope) and despite a lot of searching I was unable to relocate it. In hindsight I should have perphaps spent more time studying the bird rather than focusing on getting photos.

Is it possible for some Herring Gulls to show extensive white tongues as in cachinnans?

Brian, I would be interested to know if you have noticed both argentatus and argenteus attaining white heads earlier in winter or whether this is peculiar to one or the other. Are there any populations of Herring Gull in Europe which generally attain their white heads earlier in the winter?

Gabriel

[JanJ]

As Brian mentioned, the white headed can confuse the unwary, and they do!
Here in Southern Sweden some Herring Gulls (argentatus) can show all white heads as early as late Dec. onwards. Late winter early spring hormones starts to flow making bare parts more intensely coloured together with the loss of head streaking. Many such early white-headed Herring Gulls I see usually have brightly coloured bare parts, simply ataining breeding plumage. The head streaking is variable, many are well streaked, even more intense than this one from begining Nov.

http://www.pbase.com/slisch/image/88852276

This Finnish Herring in the background is all white-headed begining Jan. Note the redd orbital ting and to a certain extent the difference in iris colour:

http://www.pbase.com/slisch/image/91502331

A Caspian like individual:

http://www.pbase.com/slisch/image/88852719

Another Finnish Herring with Caspian characters such as bill size/colour and somehow leg colour:

http://www.pbase.com/slisch/image/91601918

Dramatic difference - note the extremlythin bill of the Caspian:

http://www.pbase.com/slisch/image/88349620

A classic!

http://www.pbase.com/slisch/image/91719918

As for your gull Gabriel - might have Caspian influence, it certainly looks that way. But as Brian say´s a primary view would be good to see.

JanJ