In the breeding season, the male McCown's Longspur is easily identified. The female and winter plumages are very similar to other longspurs. Smith's and Lapland have less white in the tail, especially at the base. McCown's has a rusty shoulder and a larger bill. Chestnut-collared often has a hint of chestnut on the nape. Lapland Longspur has rusty wings. McCown's Longspur can be told from Snow Buntings and Horned Larks by its streaked upperparts.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.