Very small swift with stiff, quick wingbeats. Grayish overall with paler throat and brownish rump. Relatively short-winged and short-tailed compared with other similar swifts. Often in small flocks. Listen for its high-pitched chips and trills. Feeds on aerial insects over a variety of habitats, including forests, fields, towns, and bodies of water. Multiple populations are surely distinct species. Migratory population breeds extensively in the western U.S. and Canada, wintering to Central America. Resident “Richmond’s Swift” occurs through much of Mexico and Central America, and is darker overall than migratory Vaux’s with a more contrasting pale throat and browner rump. There are also resident populations on the Yucatan peninsula and in western Venezuela, for which identification criteria are not well-defined. Range overlaps with several other similar swifts in Mexico and Central America. Vaux’s is smaller with quicker wingbeats than Chimney Swift or Gray-rumped Swift, with higher-pitched calls.