These small terns were fairly common around sand-bars in the Amazon. This close relative of the Least Tern is primarily confined to the interior of tropical South America east of the Andes. It differs from Least Tern by its slightly larger size, larger bill without black tip, longer legs and more extensive black on its outer wing. Its flight style is similar to Least Tern, often hovering over the water before dipping to the surface. Canon PowerShot SX60 HS.
References:
Gochfeld, M., Burger, J., Garcia, E.F.J. & Boesman, P. (2019). Yellow-billed Tern (Sternula superciliaris). 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/54034 on 30 June 2019).
Yellow-billed Tern (Sternula superciliaris), 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/yebter2