SUBFAMILY FULIGULINM 



The most obvious external character distinguishing the ducks of this subfamily is 

 the expanded, flap-like membrane forming the lower part of the hind toe. This is in 

 correlation with the slightly greater development of the other swimming membranes 

 of the foot for use in diving, for as compared with the Anatinse, the feet are notably 

 larger in proportion. The toes are relatively longer with broader webs, the outer toe 

 scarcely, or not, shorter than the middle one. The tarsi, on the other hand, are 

 usually shorter in comparison, but agree with those of the Anatinse in being scutel- 

 late in front. The sexes are differently colored, and while the males have a large os- 

 seous bulla at the lower end of the windpipe, as in the surface-feeding ducks, it gen- 

 erally differs in having the bony walls perforated by irregular openings covered by 

 membrane. 



The ducks of this group are often known as the diving ducks or sea ducks in dis- 

 tinction from the surface-feeding or river ducks (Anatinse), for much of their food 

 consists of animal or vegetable matter which they obtain by diving in moderate 

 depths. For this, their feet with enlarged swimming membranes are especially 

 adapted, while in general form they appear more stoutly built, less slender, than the 

 surface-feeders. In winter they are prone to frequent the seacoasts along whose open 

 waters food is usually obtainable without great difficulty. 



The following key, based on that of Salvadori (1895) indicates the external char- 

 acters of the genera here recognized. 



A. Bill rather broad and flattened; primaries partly whitish with the tip and outer web of the first 

 three or four brown. 



a. Upper mandible with prominent indentations; head of male crested Netta 



b. Upper mandible with indentations not prominent; head not crested. 



1. Bill convex at base; outline of loral feathering straight and inclined backward. 



Metopiana 



2. Bill smooth, not convex or rounded at base Nyroca 



B. Primaries uniform dark brown or blackish. 



a. Central tail-feathers narrow, short, curled; wings very short; bill very strong Tachyeres 



b. Central tail-feathers not curled up; no short, stiff feathers on head of adult male. 



1. General plumage of males not black. 



aa. Head crested; bill strong and thick. 



Tail-feathers somewhat rounded at the tip; edges of upper mandible not bent in; 



males with glossy head Bucephala 



Central tail-feathers of male very long and pointed; edges of upper mandible 

 partly bent inward Harelda 



bb. Head not distinctly crested; bill conical, tapering Histrionicus 



2. General plumage of males black, of females grayish brown, not barred Oidemia 



c. Central tail-feathers not curled up; some patches of shorter stiff feathers on the head of males. 



