patagoniasvale Tachycineta leucopyga

Common and familiar swallow of southern South America; found widely from the coast to Andean foothills and from open forests to beaches. Often near water and regularly around towns and villages, associating readily with slightly smaller Blue-and-white Swallow. Identified easily in most of range by clean white underparts and big white rump patch; also note that the tail is less deeply forked than Blue-and-White Swallow. Juvenile is duller above and with a variable dusky breast band.