The Condor 97:233-255 The Cooper Ornithological Society 1995
Abstract. Phylogenetic relationships of modem seaducks (Me&i) were investigated
using a cladistic analysis of 137 morphological characters. The analysis produced a single
tree (consistency index = 0.692, excluding autapomorphies) with complete resolution of the
relationships among the 25 taxa recognized. Phylogenetic inferences include: (1) the eiders
(Polysticta and Somateria) constitute a monophyletic group and are the sister-group of other
Mergini; (2) the remaining generic groups of Mergini, sequenced in order of increasingly
close relationship, are Histrionicus,M elanitta + CamptorhynchusC, langula, Bucephala +
Mergellus.L ophodytesa, nd Mergus;( 3) Somateria is monophyletic with S. jischerit he sistergroup
of its congeners; (4) the black scoters (Melanitta nigra-group) are the sister-group of
other scoters; (5) the Bufflehead (Bucephala albeola) is the sister-group of the goldeneyes
(B. clangufa and B. islandica); and (6) relationships among mergansers are as presented by
Livezey (1989). Bootstrapping revealed that the placement of the Smew as the sister-group
of the goldeneyes is only weakly supported, and ancillary analyses revealed that this placement
is only one step shorter than its reduction to a trichotomy with the goldeneyes and
mergansers (including Lophodytes). A phylogenetic classification of modem seaducks is
presented. The Harlequin Duck (H. histrionicus), Long-tailed Duck (Ctangtda hyemalis),
and Steller’s Eider (Polysticta stellerz) are highly autapomorphic. Evolutionary patterns of
selected ecomorphological characteristics-including body mass, sexual size dimorphism,
clutch size, relative clutch mass, nest site, diet, diving method, formation of creches, and
biogeography-are examined with respect to the phylogenetic hypothesis.