Gull ID - Stubber's Green, UK (2 Viewers)

Could be a hybrid Caspian x Herring as suggested but a pure Herring - perhaps not -although structurally it would fit one. However, I don´t see a pure Caspian structurally (good fit on plumage for 2cy type Caspian), large head, wrong bill structure, especially to short-billed if a male, short primary projection and rather short legs, although some Caspian looks shorter-legged - both in the field and in images. 'Bump' behind the legs Caspian feature alright.

http://www.xs4all.nl/~daarruud/cachinnans3b.html

http://waarneming.nl/foto/view/572763

http://www.iesmeulmeester.nl/fotos.php?actie=subcat&cat=1&subcat=2&kj=2

Harry - I can´t say anything about the number of 2-3cy Caspians lacking the mirroron p10, but it is a variable character, most of which I have seen have had a mirror, from very small - hardly noticeable, to quite large, clearly visible.
No mirror on this one:

http://www.xs4all.nl/~calidris/caspian3w2.htm

Note similarities on this one to the subject gull, but also note structurally differences, as mentioned above.

http://www.xs4all.nl/~calidris/caspian5w2.htm

JanJ

Harry Hussey said:

Hi there,
I would like to know what proportion of 2nd-w Caspian Gulls lack a small white mirror on P10?

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About 50%, in my experience.

smiths said:

I realize that a hybrid can never be fully excluded, but I actually see little wrong for this to be a 2w Caspian Gull. The bill could easily fit a (large) male and the underwing is well within the variation.
It is definitely not a Herring Gull.
The thumbnail posted above (message #3) shows two American Herring Gulls, so is not really relevant here.

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smithsonianus on the blackish based tertials in the older individual?

JanJ

Yes; and, importantly, solid black tail spots apparently lacking the jagged edges and/or thin, dirty barring usually seen in 3w European Herring Gull. Add to this the very pale iris and the extensively brown-washed hindneck and belly.

smiths said:

About 50%, in my experience.

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If it was a 3rd winter Herring, isn't it more likely that it would show a mirror in P10?

For that matter, if it is a 2nd winter Herring, it could also show a mirror in P10 so it's difficult to use this as an ID feature, perhaps.

Odd bird this one.

smiths said:

Yes; and, importantly, solid black tail spots apparently lacking the jagged edges and/or thin, dirty barring usually seen in 3w European Herring Gull. Add to this the very pale iris and the extensively brown-washed hindneck and belly.

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Agree to all those features mentioned by smitshs, which of course is good for smithsonianus.
The solid markings on the tertials without vermiculation (some with vermiculation), together with the tail pattern, and the extensive markings on the hindneck (also shown by some argentatus/argenteus).
Lots of variation in both smithsonianus and argentatus/argenteus, but a set of smithsonianus features on the same individual in W. Europe would probably be a good catch.

http://cyberbirding.uib.no/gull/hg/3w_02.php

Came to think of this one (some of the links doesn´t work)

http://www.birdforum.net/showthread.php?t=76476&highlight=american+herring+gull

JanJ

Alan Dean has now done an article on this bird (see below):

http://www.deanar.btinternet.co.uk/wmgulls/misc/uncertain/2W201208.htm

I agree on the comments made by Alan.
Mixed characters.

We often speak of the huge variation in LWHG, which of course is correct. However there are some consistent features I belive, by which we are able to identify - with a certain confidence - typical characters belonging to a certain species or ssp.
Caspian Gull is one of those species that has certain characters which make up for the more or less typical appearance of that species.
The Caspian Gull below shows characters that are well associated with that species on jizz and plumage. Only the bill would seem to contradict this. Doe´s that mean that it´s not a Caspian? We would accept a Herring Gull with a somehowe different than expected bill shape but by no means a Caspian, or a Yellow_legged for that matter.
One of the reasons for that is probably that we are much more familiar with Herring Gull.

http://waarneming.nl/foto/view/103129

http://waarneming.nl/foto/view/103128

JanJ

what's unusual with that bill shape here: http://waarneming.nl/foto/view/103129 ? too short?

the attached i would call a bit more unexpected (sorry to bore you with the same pic again)

Whooops, wrong images attached in post 28! Didn´t check. Find the right ones later.

JanJ

JANJ said:

Whooops, wrong images attached in post 28! Didn´t check. Find the right ones later.

JanJ

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hi all,

I'm guessing that Jan is looking for this one, even if he was looking for a different bird it still illustrates his point.

http://waarneming.nl/foto/view/570755

It was ringed as a full grown first winter in the Netherlands.

cheers, pim

Yes Pim - that´s the one.
Good thinking.

JanJ

variation in caspian bills

yepp, that's what i'd call an untypical caspian bill

talking about variation in caspian bills - attached some pics i shot in the danube delta, may 2007 (same day, same place), sorry reg to hijack your thread.

first 2 birds (pics 1-4) have similarly short stubby bills, but not with a bulging gonys. most males however have 'albatros snouts' like the one shown before, here in a more wary pose (pic 5)

bird in pic 6 has one how we'd like to have a caspian bill - long, thin and pointed.

this is a link to a short one (but thin, female type): http://www.netfugl.dk/pictures/birds_user_uploads/19014_UU_5074_KM1k3nov-5.jpg

pics 7-9 are the same (male) bird, just to see how different head shape can look in different poses.

as addition a bird with a really pale iris (pic 10) just to scare you a bit more :-O

notice variation in leg colour also: from dull yellow, fleshy with yellowish tinge to grey/'colourless'.

note also that bird 1 (pics 1-2) has very extensive white mirrors (not only the typical large p10 tip but also a huge p9 mirror with just a very thin subterminal mark separating it from the white tip) and on underside of p10 the white tongue is merged with the mirror.

for another anomaly in primary pattern, a rudimentary p5 mark (usually strong on both webs as in michahellis) see latest posts in "gulls": http://www.birdforum.net/showthread.php?t=100197&page=34

i'd like to add some thoughts on the stubbers green gull: structure as well as plumage looks good for a male caspian. i consider only 2 points as relevant for a reasoning towards a hybrid: short primary projection (main point) and lack of p10 mirror, not even a hint of it. i disagree with smiths that only about 50 % show such. male ponticus i guess have them in 80-90% of cases! i suspect that hybridisation between cachinnans and argentatus is more frequent and extended than we think. it probably occures in a large area from poland, belarus to rusia. hybrids seem to be fertile and many of the western european winterers seem to come from this zone of "intergradation" like panov/monzikov have called it: http://www.gull-research.org/papers/25panov.pdf

Simply looking at my collection of photos of 2nd-cycle Caspian Gulls (from Belgium mostly, but also Finland, Poland, Ukraine and Switzerland) in which P10 can be properly judged (26 birds in total), reveals 14 birds with a mirror and 12 without -- 54 and 46% respectively. Of those 12 without, 11 look like typical Caspian in all other respects, while one shows a browner underwing than usual.
The point is: it is not unusual to come across a 2nd-cycle gull that looks like a Caspian, but lacks a mirror on P10.
In addition, it is well known that some 2nd-cycle argentatus also show a white mirror on P10 already, so I am not sure if the presence or absence of this feature would prove much in the case of a potential hybrid.

The Panov & Monzikov paper perhaps could be relativated to some extent. Especially their ideas on 'omissus' have been contradicted by more recent studies (e.g., Crochet et al 2002 and Gay et al 2007). The article by Gay et al (2007) deals with hybridization between Caspian and Herring Gulls. The conclusions are that:
a) Hybridization indeed occurs between these two species and, yes, F1 hybrids are fertile;
b) The zone of secondary contact between the species is actually quite narrow, and may be limited to Central Poland. As often the case in large gulls though, offspring (including hybrids and backcrosses) may disperse far from their natal colony and start breeding hundreds of miles further;
c) Gene flow between the two species may be asymmetric, i.e. male cachinnans seems to be more likely to pair with female argentatus than female cachinnans with male argentatus (though this needs further testing);
d) While there appear to be no barriers to neutral gene flow between the two species in the area of secondary contact, there does seem to be selection on the colouration of bare parts, which reduces introgression. More precisely, birds with light-coloured irises and eye-rings (like argentatus) may be reproductively isolated from birds with dark irises and eye-rings (like cachinnans). Again, this needs further testing, but "introgression of these phenotypic traits seems nevertheless slower compared to neutral markers".
This suggests that there is a premating barrier to introgression, be it incomplete, and that hybridization might not be as widespread as suggested by Panov & Monzikov.

I think that a colour-ringing programme of Caspian Gulls in single-species colonies in the core range could be of great assistance in enabling the degree of variation in the species, free of (recent) genetic input from other taxa, especially when it comes to subadult plumages (using the term to cover all plumages between juvenile and adult summer): variation in the appearance of breeding adults could be ascertained from visits to these colonies, without recourse to colour-ringing, but, as the likes of 1st-summer birds, say, could be expected not to visit these colonies, and may winter (and summer) relatively far from their natal area, it would really help to be able to start from the knowledge that a given bird was a Caspian Gull, allowing one then to study the various features and compare them with the commonly accepted 'gold standard'.
Of course, it is still likely that some birds will still remain unidentifiable, what with hybrids and backcrosses often looking very similar (perhaps indistinguishably so) to either parent species, but at least we would have a better idea of which 'anomalous' features would point towards a likely hybrid, and which could just be due to variation within Caspian Gull.

A couple of years ago I was taken to a 'Caspian Gull' colony in Poland. Although viewing was not brilliant I was amazed how they were so unlike the Caspians I had seen in England and the eastern Med, and clearly this was due to the many of the Polish birds being hybrids with Herring Gulls.
Birds with mixed characters must turn up quite commonly in Britain but could easily be taken as odd looking Herring Gulls.

Steve

smiths said:

Simply looking at my collection of photos of 2nd-cycle Caspian Gulls (from Belgium mostly, but also Finland, Poland, Ukraine and Switzerland) in which P10 can be properly judged (26 birds in total), reveals 14 birds with a mirror and 12 without -- 54 and 46% respectively. Of those 12 without, 11 look like typical Caspian in all other respects, while one shows a browner underwing than usual.
The point is: it is not unusual to come across a 2nd-cycle gull that looks like a Caspian, but lacks a mirror on P10.
In addition, it is well known that some 2nd-cycle argentatus also show a white mirror on P10 already, so I am not sure if the presence or absence of this feature would prove much in the case of a potential hybrid.

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Hi Smiths (Peter?) & all,

on my own pics/descriptions of 2cy cachinnans taken in the Netherlands the percentage of birds showing a white mirror on p10 is 71% (10 out of 14). That could just mean that I use a different set of characters that a gull has to show before I call it a cachinnans. The only pics I have pics of a 2cy from the breeding range (with a Ukrainian ring) does have a clear white mirror on p10. As Harry wrote, high time for a colour-ring programme in the core breeding range. I know Norman van Swelm made a start a few years back but as far as i know only metal rings are used nowadays. Not too hard to organize, but someone has got to go out and do it. Things being as they are in Ukraïne, it's not very likely that they will start such a programme themselves.

On the subject of 2nd cycle L.a. argentatus with a mirror on p10, the ones I have seen all looked like far northern argentatus, i.e. the ones least likely to come into contact with cachinnans. Did you see any 2cy in Finland/Poland with mirrors on p10?

groeten, pim wolf

p wolf said:

On the subject of 2nd cycle L.a. argentatus with a mirror on p10, the ones I have seen all looked like far northern argentatus, i.e. the ones least likely to come into contact with cachinnans. Did you see any 2cy in Finland/Poland with mirrors on p10?

groeten, pim wolf

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Good point, but yes, 2nd-cycle argentatus in Finland/Poland can show a white mirror too.
I have not documented any good examples myself (was more focused on adults), but in a small sample of photos taken by Visa Rauste at Tampere, Finland in late November 2003, 4 out of 8 birds show a mirror on P10. It could be argued that these could include birds from further north or west (though many of the adults in the photos from the same dates look like typical local birds, i.e. with yellowish legs and a significant amount of black in the primaries), but there are other examples on the internet:

Tampere, 27 September
http://www.helsinki.fi/~rauste/gulls/hannu43.html

Tampere, 12 October (two birds: one left, and one in the middle, out of focus!)
http://www.helsinki.fi/~rauste/g/data/pics/C_20081012_IMG_0395.jpg

Finland, March
http://www.tarsiger.com/images/Jniemi/lararg326copy72.jpg

Lithuania, July
http://www.birdpix.lt/albums/userpics/10014/sidabkirasIMG_1240.jpg

Hi all, I've been away over xmas so only just catching up with all of this.

Just to confirm the bird on the Chasewater Website was indeed the gull I observed at Stubber's with Reg and his Dad on the 13th December.

I'm really glad that others have now had the chance to observe and photograph this gull. We were confused with this gull at the time - interesting to see what a difficult bird it has been, even for the experienced gull watchers.

We weren't really happy with Herring Gull as it didn't look like one in the field and there were notable Caspian features.

I notice it's being reported on Birdguides and Chasewater as 2nd-winter Caspian now?