Gull ID, Czech republic (1 Viewer)

I took this video on 3rd March 2018: https://vimeo.com/262673072


I believe it's not Chroicocephalus ridibundus because they were around too and these were bigger and their flight was different (they didn't wave their wings as frequently). I have a problem recognising Larus canus from L. cachinnans. Given to the voice and flight I think this one should be L. canus. There was hundreds of them and it is on a place where both species may occur (but I believe it was just one of them because they were all the same size). The river is quite close to a dump where also L. argentatus, L. fuscus, L. michahellis, L. marinus and L. tridactyla were seen but I thought it's too late for them (they are there during December and January).

Nothing like L.canus which is considerably smaller, different structure + much darker mantle. One of the larger white headed gulls- I would go for L. cachinnans.

Thank you! If you know some book or web that could help me learn to recognise gulls, I would appreciate it a lot (currently I have Svensson's Collins Bird Guide Second edition). Also I found some pictures of some of the gulls in flight if that might help? But since there was hundreds of them in flocks I can't tell if they are all the same species.

All you need is here: http://www.gull-research.org

Pic #2 (in post #3) is a 2nd winter/3rd calendar year Caspian Gull, and I suspect that the others are too

Okay, thanks a lot!