Gull with 'thayeri' P10 pattern

[heuglini]

Hi guys!

yesterday I had a very interesting gull flying overhead while I was gullwatching in a little lake in northern Italy.
It had a very pale underwing pattern with a lot of white in the hand. I already had some Caspian Gulls in the same place last year with a similar P10 pattern, but something about this gull still scares me: the head looks a bit too rounded in some shots (even if I would not trust this too much as they are flight shots), the eye looks a bit big and the eye-ring seems to be not deep red. Maybe the black on P5 too is not the solid black band I'm more used too, but I see from other's pictures it's not that rare.

I would really like to know what do you think of this gull.

Thanks and happy new year to all
Michele

[lou bertalan]

hi michele,

i see a female type cachinnans (edit: that gonys angle looks better for a male!), with some untypical features like pale iris, bright yellow legs and, well, thayeri pattern is there in about 10-15% of ponticus birds. broken p5 band in 5-10% of them.
with that pattern (extensive white halfcircle towards black in primaries) this cannot be anything else than caspian gull. or a F2 hybrid perhaps, some hybrids look identic to one of their parents unfortunately...

cheers and happy new year!

lou

[Theo Muusse]

The fresh article in Br Birds are accurate on the colour of the tongue on p10: as it looks grey here, hybrid origin may well be the case.

Theo Muusse

[adriaens]

I am not sure if I fully understand that feature from Br Birds, but my interpretation after reading the paper is that it refers specifically to the colour at the end of the tongue ?
If so, that would make it an in-hand character mostly, sometimes visible in the field or on photographs when the bird fully outstretches its wing.
Here, in this bird, we can see a little bit of the base of the tongue on P10, and yes, it looks as grey as the primary coverts, but surely that is perfectly normal ?
If that alone is enough to suspect a hybrid, I fear that I have never seen a 'good' adult Caspian Gull in my life!

[lou bertalan]

Here, in this bird, we can see a little bit of the base of the tongue on P10, and yes, it looks as grey as the primary coverts, but surely that is perfectly normal ?
If that alone is enough to suspect a hybrid, I fear that I have never seen a 'good' adult Caspian Gull in my life!

errrr!? so are you talking about the dorsal p10 tongue? they are grey in adult caspian gulls...or not?

[adriaens]

Yes, dorsally. The tongue often looks slightly paler than the primary coverts, and this is typical for pure birds, according to the article.

CaspianGullAd_Liege_7Dec08_0346.JPG (487.03KiB)Viewed 5858 times

[lou bertalan]

that's indeed a more or less in-hand character then...

is that BB article available online already?

[JanJ]

Dorsally as mentioned. The article doesn´t mention (as far as I can see), specifically that the whitish tounge in p10 is restricted to a certain part in it´s lenght. From p9 inwards the whitish is restricted to the end of the tounge. Certainly this feature is slightly varaible since some individuals (as mentioned in the article), shows pale greyish tounge, less contrasting with the primary coverts. However, all the Caspians in the sample (article), the p10 tounge where paler than the mantle. Often impossible to see in th field and also in a vast majority of pic. according to light and angle - which this pic might be an example of:
http://www.artportalen.se/birds/gallery ... eID=179065

Peter´s bird here is a nice exeption. In combination with the tounge colour the black to white ratio plays an important role and also according to the article there should be less black than white in a so called true Caspian. More to come on this topic in the future I´m sure!
Intresstingly the pattern of p5 in Michele´s bird which shows a broader marking on the inner web, usually the oposite.

Just a few birds here:

http://www.iesmeulmeester.nl/fotos.php? ... catsub=410
http://www.artportalen.se/birds/gallery ... eid=267028

JanJ

[heuglini]

Very interesting comments! I ordered the two issues of British Birds regarding Caspian Gull ID just a few days ago and I'm still waiting for them.
I agree that this feature could be very hard to discern in the field and pictures: after looking in my archive, I was able to find just a single bird showing P10 well enough to asses its colour...maybe it's not pure white, but surely it's a paler grey than the coverts.
Interestingly this bird is another 'thayeri' Caspian!







Regarding the initial bird, here is a crop of the picture where P10 is best shown
Unfortunatly P9 outer web seems to run very close to the shaft and leaves just a liiiitle piece of P10 visible.



thank you all for your comments!
Michele