when carl linnaeus first described the chimney swift in 1758, he named it , believing it to be a swallow. this misconception continued well into the 1800s, with ornithologists calling it "american swallow" (e.g. mark catesby) or "chimney swallow" (e.g. john james audubon). in 1825, james francis stephens moved this and other small, short-tailed new world swifts to the genus "chaetura", where it has since remained, although some authorities in the 1800s assigned it to a variety of now obsolete genera. it has no subspecies. the chimney swift's closest relative is vaux's swift. scientists believe that the two species evolved from a common ancestor that was forced to north america's southeastern and southwestern corners by glacial advances. separated for millennia by vast ice sheets, the survivors evolved into two species which are still separated by a wide gap across the continent's midsection. it is also closely related to the chapman's swift; in the past, the three were sometimes treated as a single species.