When flushed, the white outer tail feathers of the Vesper Sparrow are easy to observe. Other birds with this field mark are American Pipit, Horned Lark, Lark Sparrow and longspurs. All lack the heavily streaked breast of the Vesper Sparrow. When perched, the Vesper Sparrow looks similar to several other species of sparrows. Savannah has a yellow supercilium, pale central crown stripe, shorter tail and lacks rusty shoulder and eye ring. Song has rounded tail, breast spot, and lacks rusty shoulder and eye ring. Lincoln's has a buffy breast. Baird's and juvenile Grasshopper are larger-headed and shorter-tailed.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.