Because of its unique feeding strategy, the Red-breasted Nuthatch is most likely to confused with other nuthatches. White-breasted Nuthatch lacks a black eyeline and has mostly white underparts. Brown-headed and Pygmy Nuthatches have brown caps, white patches on the nape and lack the eyelines.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.