This beautiful Caspian Gull in almost complete juvenile plumage is all classical when it comes to plumage pattern and proportions. As seen in the video is has rather unmarked white underwings and central belly. It has relative long legs with longer tibia; the bill is relative long and without pronounced gonys angle. It has a good cachinnans jizz with high push up breast, flat belly slightly dropped behind legs and long elongated slim rear.
Note that left of the Caspian Gull stands a juvenile Baltic Gull (Larus fuscus fuscus) which is also a rather uncommon gull in Denmark.