This counterpart of the Arctic Tern does not undertake long migrations like its northern cousin, but usually stays close to breeding areas. It is similar to Arctic Tern, but has longer legs and bill and less black in it wings. Also wintering Arctic Terns lack the full black cap of breeding Antarctic Terns. Separation from the similar South American Tern (S. hirundinacea) even more difficult but that species not known from New Zealand. Five or six subspecies usually recognized, but differences slight with much overlap and the validity of some are questionable. New Zealand birds are ascribed to S. v. bethunei which is intermediate in size within the larger paler nominate group. Canon PowerShot SX50 HS.
References:
Gochfeld, M., Burger, J. & Garcia, E.F.J. (2017). Antarctic Tern (Sterna vittata). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/54027 on 5 March 2017).
Higgins, P.J.; Davies, S.J.J.F. (Eds.) 1996. Handbook of Australian, New Zealand and Antarctic birds. Vol. 3. Snipe to Pigeons. Oxford University Press: Melbourne
Sagar, P.M. 2013. Antarctic tern. In Miskelly, C.M. (ed.) New Zealand Birds Online. www.nzbirdsonline.org.nz
Shirihai, H. (2002) A Complete Guide to Antarctic Wildlife. The Birds and Marine Mammals of the Antarctic Continent and the Southern Ocean. Princeton University Press: Princeton & Oxford.