Behavioral and Ecological Factors Contributing to American Black Duck-Mallard Hybridization

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Abstract
Investigation of courtship and pair formation of a wintering population of American black ducks (Anas rubripes) and mallards (A. platyrhynchos) near Ottawa, Ontario [Canada], indicated that initially drakes of both species exclusively courted and paired intraspecifically. After all female mallards had paired, the remaining mallard drakes joined black duck courtship groups. Of the 33 unpaired black duck females remaining at this time, only 27% formed intraspecific pairs; 73% selected mallard drakes as mates, despite there being an excess of black duck drakes. A scenario for black duck-mallard hybridization is proposed. It involves ecological factors including the male-biased sex ratio in northern wintering populations, artificial feeding and roost-site limitation. Other behavioral aspects, such as the earlier pair formation in mallards and the superiority exhibited by mallard drakes when competing for black duck females are discussed.