This bizarre South American endemic tern seems to be unrelated to other terns and is thus placed in its own genus. Although normally confined to South America it has wondered north with records from Illinois, Ohio, New Jersey and Nicaragua. Two subspecies are normally recognized. This is the widespread nominate race. It is replaced to the south by a poorly differentiated darker mantled race but some authors consider the differences to be too slight for recognition. Canon PowerShot SX60 HS.
References:
Gochfeld, M., Burger, J., Kirwan, G.M. & Garcia, E.F.J. (2019). Large-billed Tern (Phaetusa simplex). 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/54048 on 3 July 2019).
Large-billed Tern (Phaetusa simplex), In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. retrieved from Neotropical Birds Online: https://neotropical.birds.cornell.edu/Species-Account/nb/species/labter1