It took some time, but I guess I’ve got it.
Almost as soon as I moved here I noticed that the gulls at Firhill Basin didn’t have the dark brown head as the Czech ones did. Ever since I tried to make out what species they were.
They definitely aren’t the Black-headed Gull / faoileag dhubh-cheannach / racek chechtavý / Chroicocephalus ridibundus that I was accustomed to. The RSPB website confused me for some time with its “for much of the year, it has a white head”. (WP says “The hood is lost in winter, leaving just dark vertical streaks.”) Personally, I have never noticed anything such happening. Anyway, I have been in the old country last week, the heads were definitely dark brown, and here they are still definitely white.
For quite a long time I suspected I was confronted with the European Herring Gull / glas-fhaoileag / racek stříbřitý / Larus argentatus. It wasn’t until fairly recently that one of them came near enough for me to be able to recognize both the beak and the legs as being of a yellowish colour – which put paid to herring gull whose legs are supposed to be reddish .
The Common Gull / faoileann / racek bouřní / Larus canus then. I just hope that I won’t some day see one close enough to notice a red spot on its beak – because that’s one thing this particlular species is supposed not to have.
And of course, there’s also the possibility that there are two or more species moving hereabouts. In which case, with my sight, I’m sentenced to being puzzled forever.