Caspian gull ?

[benoit.nabholz]

Hello

I would like to use your expertise on this gull (two attached pictures).

I have taken these two pictures in Stockholm today. The pro caspian gull features are the small dark eye and the dark line on the bill despite the fact that the rest of the plumage indicate an adult. The bad points are the quite big gonydeal angle and the not so long bill.

Unfortunately it never spread its wing during my observation so I can say nothing on the P5 or on possible black tongue.

Do you think that this is just an Herring gull ssp argentatus or could it be a Caspian?

Benoit

[JanJ]

Hi Benoit.

Even if an open wing shot is the better thing in cases like this, I´m afraid your gull is a Herring Gull. The small looking eye and the dark line on the bill as you call it is not a full proof feature for Caspian Gull, although I´ll grant you that the small eye usually is a rather good indication of Caspian. On your gull the eye is not dark but slightly yellowish-white and even if the orbital ring seems to have some reddish in it on the pictures, it seems to be mixed with yellow and also looks quite narrow, especially in front of and behind the eye as oposed to slightly broader in these parts in Caspian, but there are exceptions to that! The bill- as you say, has a rather prominent gonys-angle, which alone doe´s not exclude some big male Caspians though. However, the expansion near the tip compared to the base doesn´t refflect the more so called pencil shaped of Caspian, equally wide throughout. A dark mark on the bill in winter is not nessecarily a sign of a non-adult, since adult can have it, or lack it. However, some brownish feathers on the lower scapulars would be a better sign of a non-adult bird in this case. Many Herrings are at this time of year white-headed, some with a reddish orbital ring and small looking eyes inviting to confusion with Caspian (or Yellow-legged Gull). Notable, some Caspian have pale eyes.

White head:

http://www.pbase.com/slisch/image/108806277

White head and reddish orbital ring orund a smallis looking eye:

http://www.pbase.com/slisch/image/91502557

again with another Herring:

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

Dark-eyed individual:

http://www.pbase.com/slisch/image/82149662

A classic looking Caspian:

http://www.pbase.com/slisch/image/92103087

Even if this example shows the extrem differences between the two, some are not that strikingly different:

http://www.pbase.com/slisch/image/91501903

Check further on Svalan and here:

http://www.truthjalpen.blogspot.com/

JanJ

[John Bell]

hi Benoit et al,

As JanJ says this is a Herring Gull. I wouldn't claim an adult Caspian in Scotland without seeing a stretched wing. I'm guessing the status of Caspian in Scotland is similiar to that in Sweden (ie rare). Still it is good to ask. Best way to learn!

All the best,
John

[benoit.nabholz]

Thank-you very much for the comments and link.

I agree that it's a Herring gull, Caspian is indeed rare in Stockholm but seem more regular in the south Sweden (e.g. Skane).

For information, this bird had some black pigmentation (spot) on the iris. From the 200-300 adult argentatus observed at the same time in Stockholm, 1-5% had a white head.

Benoit

[John Bell]

hi Benoit et al,

The black pigmentation on the iris can be caused by 'bruising' I'm told. Particularly by birds feeding on rubbish tips that are sticking their faces into anything and everything. Stuff pokes into the eyes and bruises it. I believe that is one reason why you sometimes see gulls with asymmetric pigmentation in their eyes.

I guess Caspian Gull is more prone to feeding at night time than most other gulls? I think that is the case with Audouin's.

cheers,
John

Thank-you very much for the comments and link.

I agree that it's a Herring gull, Caspian is indeed rare in Stockholm but seem more regular in the south Sweden (e.g. Skane).

For information, this bird had some black pigmentation (spot) on the iris. From the 200-300 adult argentatus observed at the same time in Stockholm, 1-5% had a white head.

Benoit