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Abstract

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.