Behavioral Specializations for River Life in the African Black Duck (Anas sparsa Eyton)1

Field studies on individually marked birds near Stellenbosch, South Africa support the view that Anas sparsa is a river specialist derived from a pond‐dwelling mallard‐like ancestor. The key river adaptation is year‐round territoriality and only established pairs breed. Mates cooperate in territory defense and both sexes engage in damaging fighting (using wing‐spurs) over mates and territories. Changes in social behavior interpreted as consequences of river specialization include elimination of raping, strong development of mate‐testing, mate‐stealing and mate‐holding tactics, and reduction of social courtship to a vestigial condition.