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Today me and Frank Majoor observed a pair of most likely argentatus Herrings on the dump of Barneveld. The male was wearing a clipring at the left tarsus. We were not able to read it due to the distance.
While approaching the birds, they flew off.

Interestingly, the male was showing a tayeri-patter in p9-10. Does anybody have any idea about its origin. Any project with cliprings in the Baltic?

Hi Albert,
I cannot help with the clip ring, but maybe with the species:
I feel sure that the bird is a Caspian Gull, rather than argentatus. A few show such a "thayeri pattern".
Note that the underside of P10 shows almost no black on the inside of the shaft, which is typical for Caspian Gull.
Also, Herring Gulls with this little black in the primaries do not normally show a black band on P5.

Agree with Peter.
The clipring appears darkish which reminds me of the polish type...
Matsalu would, I feel, appear higher and less dark.
Frank didn't have a clue?

Theo

Thanks Peter and Theo.
Our first impression was cachinnans either. But I only had my binoculars and camera, since my scoop is in repair. I dind't know the p5 thing and was confused by the pattern.
I guess it must have been Poland again.
Nevertheless, it was the first time I saw a pair of cachinnans in the Netherlands...

One more vote for Caspian.

JanJ

Today, at my village Voorhout, adult Herring with thayeri on P9-P10.