Formerly considered a subspecies of the Brown Pelican (P. occidentalis), SACC elevated this bird to full species status in 2007. When perched or swimming, it looks much like an oversized Brown Pelican, but in flight from above it looks strikingly different. This photo taken from the veranda of our cruise ship of an adult in breeding plumage clearly shows large contrasting white patches on its wings and scapulars and its blue gular pouch. Canon PowerShot SX50 HS.
References:
del Hoyo, J., Collar, N., Garcia, E.F.J. & Kirwan, G.M. (2018). Peruvian Pelican (Pelecanus thagus). 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/467293 on 28 January 2018).
Peruvian Pelican (Pelecanus thagus), 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/perpel1
SACC (2007) Proposal (#271) to South American Classification Committee. Separate Pelecanus thagus from P. occidentalis. URL: http://www.museum.lsu.edu/~Remsen/SACCprop271.htm Canon PowerShot SX50 HS