As constituted here, the tribe Mergini includes all the species which Delacour and Mayr (1945) originally placed in the group.
Delacour later (1959) removed the four species of eiders and placed them in a separate tribe, Somateriini, between the dabbling ducks and
pochards. This was done apparently as a result of Humphrey's anatomical studies (1955, 1958), which suggested that the eiders might
be more closely related to Anus than to the other "sea ducks." I have discussed this problem elsewhere (Johnsgard, 1960f, 1964) and concluded that the original inclusion of the eiders in the Mergini seems to fit the facts more adequately. Woolfenden (1961) has reached the
same conclusion using anatomical evidence.