Saunders’s Gull is rare in Hokkaido, this was only the 5th time I’ve seen one (and the 3rd at Yakumo). 4 of them have been in the same fortnight over the years (the last week of April or the first week of May). And 4 of them have been immature birds like this one…
It was tiny and very easy to pick out due to it tern-like flight.