the chimney swift looks very much like the closely related vaux's swift, but is slightly larger, with relatively longer wings and tail, slower wingbeats and a greater tendency to soar. it tends to be darker on the breast and rump than the vaux's swift, though there is some overlap in plumage coloring. it can be as much as 30 percent heavier than vaux's swift, and its wings, which are proportionately narrower, show a pronounced bulge in the inner secondaries. the chimney swift is smaller, paler and shorter tailed than the black swift. in central america, it is most similar to chapman's swift, but it is paler (matte olive rather than glossy black) and has a stronger contrast between its pale throat and the rest of its underparts than does its more uniformly colored relative.