The Northern Gannet is by far the most common booby from Canada to the Gulf of Mexico. It is identifiable at great distances by its plunge-diving behavior and large size. The adults are easy to separate from other white boobies by the lack of black on the inner wings. Immatures can be confused with other immature boobies but typically lack white patches on the rump or upper back until they also have white heads.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.