Ruud invited me to take part in this forum - so I will try...
Today I have found this gull at my local site in Wörth near river Donau/Danube, central Austria.
Fleshy long leg (it had a healthy 2nd one), bill coloration and bill proportions seem to fit for Caspian, but primaries and head with pale eye and slightly dark mask around eye looks well for YLG.
![Question :?:](./images/smilies/icon_question.gif)
Maybe a hybrid?
![Image](http://web.utanet.at/schwei76/hybrid.jpg)
Wolfgang