The adult Scissor-tailed Flycatcher, with its extremely long tail, is only likely to be confused with the stray Fork-tailed Flycatcher but this species has a dark cap. Juvenile Scissor-tailed Flycatchers and molting adults lack the extremely long tail and might be confused with kingbirds. The pale head and lack of yellow underparts should distinguish the Scissor-tailed Flycatcher.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.