Forster's Tern メリケンアジサシ（メリケン鯵刺）

S. forsteri; Genus: Sterna; Family: Sternidae

The Forster's Tern, Sterna forsteri, is a member of the tern family Sternidae. It breeds inland in North America and winters south to the Caribbean and northern South America.
This species is rare but annual in western Europe, and has wintered in Ireland and Great Britain on a number of occasions. No European tern winters so far north (wikipedia).