Date of this Version
Without doubt, waterfowl of the family Anatidae have provided the greatest number and variety of bird hybrids originating from both natural and captive conditions. The recent compilation by Gray (1958) has listed approximately 400 interspecies hybrid combinations in this group, which are far more than have occurred in any other single bird family. Such a remarkable propensity for hybridization in this group provides a great many possibilities for studying the genetics of speciation and the genetics of plumage and behavior, and it also provides a valuable tool for judging species relationships. It may generally be said that the more closely two species are related the more readily these species will hybridize and the more likely they are to produce fertile offspring. In waterfowl, chromosomal imcompatibility and sterility factors are thought to be infrequent, a circumstance which would favor the large number of hybrids encountered in this group. In addition to this, however, it can probably be safely concluded that the Anatidae are extremely close-knit in an evolutionary sense, for their behavior, anatomy, and other characteristics all indicate a monophyletic origin. It was for these reasons that Delacour and Mayr (1945), in their revision of the group, sensibly broadened the species, generic, and subfamilial categories, and in so doing greatly clarified natural relationships.