The Curve-billed Thrasher is most likely to be confused with the very similar Bendire's Thrasher. Bendire's can be told from adult Curve-billed by its smaller size and straighter bill with a yellow base to the lower mandible. Juvenile Curve-billed is very similar to Bendire's. Other thrashers lack spotting below.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.