This bird is also known as Parasitic Skua or Parasitic Jaeger.
The Arctic Skua is mostly a passage migrant in Scotland but in the north of Scotland and in the Scottish Northern Isles it is a locally common breeder. It winters in the Southern Atlantic ocean. It resembles a dark gull with pointed wings with a fast swooping flight. It will relentlessly chase gulls and terns until they are forced to disgorge their food which the Skua catches in mid-air. There are two plumage morphs called pale phase and dark phase.
These photographs were taken at Tyningham Bay in East Lothian of an autumn passage migrant and on Handa Island which is a nature reserve in the far north west of Scotland where both dark and pale phase Arctic Skuas and Great Skuas nest.