Small dark swift. Look for the contrasting whitish band across the rump. Plenty of geographic variation across its disjunct range, with some populations showing a less contrasting rump band. Very similar to Gray-rumped Swift, which can sometimes be separated by the lack of a whitish band across the rump, but often best left unidentified as not all Band-rumps clearly show the whitish band. Usually seen in flocks, sometimes quite large, feeding over forests, clearings, open fields, and lakes.