The Black-necked Swan is the only species of true swan (Cygnus) that breeds in the Neotropics. The plumage is mostly white, apart from the black neck and head; this swan also has a prominent red knob at the base of the bill. The juvenile is similar in pattern to the adult, but the body plumage is grayish, not white, and the head and neck are dusky gray, not black. This swan breeds in emergent vegetation fringing freshwater lakes, but at other times of the year occurs on both freshwater and brackish lakes, as well as in bays and fjords. This species usually is gregarious, and often is in small flocks, although sometimes occurring in aggregations of up to several thousand. The Black-necked Swan is resident throughout much of its range, but some of the southernmost populations are migratory.