Chaetura vauxi are the smallest swifts in North America. The length of their body is generally 11 cm. Size cannot be used to determine gender. Vaux's swifts are designed for speed; they posses an aerodynamic shape with long, pointed wings, short and blunt humeri, and a small body. These swifts have short legs and small feet. The bill is short and stout. (Bull, Collins 1993)
Both sexes have very similar plumage, plain grayish brown appearance sometimes highlighted by a slight green iridescence. "Rump and upper tail coverts range from a pale brownish gray to a duller shade like that of the back" (Wetmore 1957). The upper breast and throat area are paler than the rest of their underbelly. (Bull, Collins 1993)
Range mass: 15 to 22 g.