It has been over 15 years since Delacour and Mayr (1945) first urged that the mergansers (Mergus)and the goldeneye-Bufflehead group (Bucephala) be merged into a single tribe (Mergini) rather than being maintained in separate subfamilies (Aythyinae and Merginae). Their reasons for this change were several, and included such points as the similarities in the downy young, female color patterns, occurrence of wild hybrids between the two genera, and tracheal structure. Indeed, except for the shape of the bill in these two groups there is no good means of distinguishing the two subfamilies. As Delacour and Mayr pointed out, bill shape and structure is highly adaptive and should not be used for the erection of major taxonomic categories. However, these two subfamilies are still upheld in the fifth edition of the AOU Check-list. Delacour and Mayr described the general similarities in the sexual behavior of Mergus and Bucephala, but no one has yet had the opportunity of critically comparing the behavior of most species in the two groups. Myres (1957,1959a, 1959b) reviewed well the behavior of the Bucephala species, but was not fortunate enough to compare directly copulatory behavior in this genus and Mergus. He has, however, provided detailed descriptions of courtship and copulation in the Common Goldeneye (B. clangula) , Barrow's Goldeneye (B. islandica), and Bufflehead (B. albeola). The behavior of the Common Goldeneye has also recently been described by Dane et al. (1959) and Lind (1960). I have been able to observe closely courtship display in all three species of Bucephala and in four species of Mergus, including the Hooded Merganser (M. cucullatus), Smew (M. albellus), Red-breasted Merganser (M. serrator) and Common Merganser (M. merganser), both in the wild (Johnsgard, 1955) and under captive conditions at the Wildfowl Trust, Slimbridge, England. Here I also have observed copulatory behavior in the Common Goldeneye, Barrow's Goldeneye, Hooded Merganser, Smew, and Common Merganser, and have incomplete observations on the Red-breasted Merganser. Although a major summary of my observations on these species and the rest of the Anatidae will be published later, the following observations on the Hooded Merganser are of special interest and have a direct bearing on Delacour and Mayr's (1945) proposed classification.
Available at: http://works.bepress.com/paul_johnsgard/31/