474 BRITISH BIRDS. 



Family ANATIDiE, or DUCKS. 



The Ducks and their allies form a large and well-defined family, though 

 possibly allied to the Pelargidse through the Flamingoes, and to the 

 Rallidse through the Screamers {Palamedea) . Sclatcr elevates them to 

 the rank of an order, which he places on the one hand next to the 

 Screamers, through Avhich he connects them, by means of the Flamingoes, 

 with the Storks ; but on the other his system breaks down, and he begins 

 a new series with the Pigeons. Forbes associated the Ducks Avith the 

 Grebes and the Divers. Gadow regards the Ducks and their allies as the 

 comparatively slightly modified descendants of the same group of which 

 the Penguins, the Pelicans, the Divers^ and the Grebes are highly specia- 

 lized forms. 



The arrangement of the palatal bones of the Anatidae induced Huxley 

 to place them at the head of his Desmognathous series^ followed by the 

 Flamingoes, the Herons and their allies, and the Pelicans and their allies. 

 The rest of the desmognathous birds, the Birds of Prey, the Owls^ the 

 Parrots, and most of the Picarian birds appear to belong to a different 

 series. Nitzsch states that the form of the feather-tracts in this family 

 follows a very definite type. There is only one notch on each side of the 

 posterior margin of the sternum. As might be expected from the 

 similarity of their habits, the Ducks and their allies in their myology 

 present points of resemblance to the Grebes and the Divers. 



The most important external characters of the Anatidae ai'e their short 

 legs, webbed feet, and laminated bill. 



This family includes about 160 species, and may be subdivided into 

 about a dozen genera, though some of the latter are of very doubtful 

 validity. It may be regarded as almost cosmopolitan in its range, though 

 it is almost solely represented in the tropics by winter migrants. 



The following key to tbe British genera may be useful : — 



a. Sexes alike or nearly so. One moult only, in autumn. 



Lores naked Cygnus . . I Tarsus not scutellated in front, but roti- 



Tarsus longer than middle toe .. Anser.... i culated all round. 



Tadorna. 



b. Sexes generally differently coloured. In addition to annual autumnal moult, 



the males moult in summer almost into female plumage. 



Anas. 



,t. 1 • , 11 , 1 1 i fuligula. 



Umd toe with a well-developed 1 ^ 



membrane | *^^'^'^^'"^'^- . Bill narrow. Lamellaj developed into 



^ Mergcs . . ^ pi-oiuineut teeth. 



