This is a breeding plumage (alternate) adult on top and an immature on the bottom. Non-breeding (basic) plumage is similar but has a dark hood. This distinctive gull is endemic to the coasts of Patagonia in southern South America. It is primarily a scavenger. Some authors (e.g. Burger et. al 2018) place this species with other gulls in the genus Larus. Historically it was placed in its own genus, Gabianus. See: SACCprop250 for details on current classification. in Leucophaeus. Formerly called Scoresby's Gull. Canon PowerShot SX50 HS
References:
Burger, J., Gochfeld, M., Garcia, E.F.J. & Boesman, P. (2018). Dolphin Gull (Larus scoresbii). 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 https://www.hbw.com/node/53961 on 29 April 2018).
Dolphin Gull (Leucophaeus scoresbii), In Neotropical Birds Online (, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. retrieved from Neotropical Birds Online: https://neotropical.birds.cornell.edu/Species-Account/nb/species/dolgul2