Separated from all other nightjars except nighthawks the pale patch in the wing. Lesser Nighthawk is similar to Common and Antillean nighthawks but tends to have its white patch farther out (2/3 of the way from the bend of the wing) its wing. Female Lesser Nighthawks can be identified with very good views of the spread wing. All three species are easily identified by call.
Length and wingspan from: Robbins, C.S., Bruun, B., Zim, H.S., (1966). Birds of North America. New York: Western Publishing Company, Inc.