Breeds patchily, islands and coasts of Azores, British Isles, and western France, Somalia to southern Africa, also coastal southeastern Canada and northeastern USA, Florida Keys, Belize cays, islands off n Honduras, West Indies and islands north of Venezuela.
arideensis
Seychelles to Madagascar and Rodrigues I.
korustes
Sri Lanka, Andaman Islands, and Mergui Archipelago (southwestern Myanmar).
bangsi
Arabian Sea; eastern China and Ryukyu Islands (southern Japan) eastward to New Guinea and Vanuatu.
gracilis
Moluccan islets and western and northern Australia (southwestern Australia to southeastern Queensland).
