The Tree Swallow is most similar to the Violet-green Swallow. The Violet-green Swallow has white patches that extend further onto the sides of the rump, a white area that extends behind and over the eye and greener upperparts. Bank and Northern Rough-winged Swallows look similar, especially in Fall. Bank Swallow is smaller, this feature is especially noticeable as mixed flocks of swallows often sit on telephone wires. Bank has a dark breast band that is lacking or indistinct in the Tree. From above, Bank Swallow has a paler rump that contrasts with the darker back and tail where the Tree Swallow is uniformly-colored. Northern Rough-winged Swallow has a dusky throat and warmer brown upperparts than the Tree Swallow. Swallows often call in flight and these calls are excellent clues to identification.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.