Clark, A. 1974. The status of the whistling ducks in South Africa. Ostrich 45:1-4. Since the 1920's the status ofDendrocygna viduataandD. bicolorhas changed from that of an irregular to that of a regular species in the Transvaal, Zululand, Natal and Orange Free State. In more recent years their numbers have shown a steady increase and breeding has been established.D. viduatanumbers built up more quickly thanD. bicolorand it has become an established resident whereasD. bicoloris primarily a summer visitor.