The very dark upperparts and white underparts of the adult Sooty Tern are also found in the Bridled Tern but note that the Bridled Tern has a white collar, paler upperparts, and paler undersurfaces to the flight feathers. The mostly dark plumage of the juvenile Sooty Tern is somewhat similar to alternate-plumaged Black Terns. Sooties are much larger and browner than Black Terns. Brown Noddies are similar to juvenile Sooty Terns but have pale caps, wedge-shaped tails and dark bellies.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.