Great Dusky Swift forages over forested and riverine habitats in eastern South America. in Bolivia, Brazil, Paraguay, and Argentina. It is well-known to birders for flying around the incredible torrents of Iguazu Falls. It is one of few species of swift that is regularly observed perched when it clings to exposed rock faces. Great Dusky Swift is dark grayish brown with a silvery head, and is fairly large in size.