This is one of the strangest of all terns and is placed in its own unique monotypic genus. The name "Larosterna" is a mash-up of "Larus" (gull) and "Sterna" (tern). Its large size and plumage suggest intermediacy between gulls and terns. This photo shows the bizarre white plumes starting at the bill and curling down around its neck. Although locally common, it is classified as "Near Threatened" by IUCN because of population declines. Threats include over-fishing and disruption of nesting from guano harvesting. Canon PowerShot SX50 HS.
References:
BirdLife International. 2016. Larosterna inca. The IUCN Red List of Threatened Species 2016: e.T22694834A93471847. http://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T22694834A93471847.en. Downloaded on 18 January 2018.
Gochfeld, M. & Burger, J. (2018). Inca Tern (Larosterna inca). 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/54055 on 18 January 2018).
Inca Tern (Larosterna inca), In Neotropical Birds Online (T. S. Schulenberg, editor). Cornell Lab of Ornithology, Ithaca, New York, USA. retrieved from Neotropical Birds Online: https://neotropical.birds.cornell.edu/Species-Account/nb/species/incter1