Papers in the Biological Sciences


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Published in American Birds (1976) 30(5): 905-908. Copyright 1976, American Birding Association. Used by permission.


One of the most spectacular shifts in waterfowl dIstnbution patterns in North America is the degree to which Mallards (Anas platyrhynchos) have come to replace Black Ducks (Anas rubripes) as the dominant breeding and wintering species in the eastern half of the United States and Canada over the past several decades. The reasons for these changes in the actual and relative numbers of Mallards and Black Ducks are doubtless many and probably include such factors as man-induced habitat changes, game management practices such as artificial stocking programs and changing hunting regulations, and possibly even climatic trends, but there can be no doubt that the Mallard has successfully colonized many areas which once were almost entirely occupied by Black Ducks, and In some areas has completely replaced that species. The evolutionary consequences of increased contact between the two forms in terms of ecological competition and genetic interchange resulting from hybridization, have yet to be fully understood, but are obviously substantial.

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