By Jimfbleak - Own work, data from Arlott, Norman (2007) Birds of the Palearctic: Non-Passerines, London: Collins, pp. 211 ISBN: 0007147058. , Hume, Rob (1993) The Common Tern, London: Hamlyn, p. 51 ISBN: 0540012661. , Olsen, Klaus Malling; Larsson, Hans (1995) Terns of Europe and North America, London: Christopher Helm, p. 88 ISBN: 0713640561. , Sibley, David (2000) The North American Bird Guide, Robertsbridge: Pica Press, p. 232 ISBN: 1873403784. , Hilty, Steven L (2002) Birds of Venezuela, London: Christopher Helm, p. 310 ISBN: 0713664185. , Raffaele, Herbert A; Raffaele, Janis I; Wiley, James; Garrido, Orlando H; Keith, Allan R (2003) Field Guide to the Birds of the West Indies, London: Christopher Helm, p. 28 ISBN: 0713654198. and Simpson, Ken; Day, Nicolas (2010) Field Guide to the Birds of Australia - 8th Edition, Camberwell: Penguin Books, p. 110 ISBN: 0670072311., CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=18358977