8 



FAMILY ANATIDAE 



(e) Neck, thick in appearance, with curiously enlarged air-sac in 

 the upper neck of the males. 



(f) Eggs, usually numerous and relatively large in size. 



TREE DUCKS 



Subfamily Dendrocygninae 



There are, distributed throughout the 

 world, ten forms of Tree Ducks, of which two 

 are found regularly in North America. 

 Though a sharply differentiated group, these 

 ducks seem to form a link between the Swans 

 and Geese and the true Ducks, exhibiting 

 characters found in all three groups. 



This Subfamily is characterized by the 

 following features: 



(a) These are freshwater ducks of the in- 

 terior; as in the Swans and Geese the sexes are 

 alike in colour; feed by reaching down in shal- 

 low places (tipping) as do the Surface-feeding 

 Ducks, but more generally by grazing on land 

 as do the Geese; feed chiefly on vegetable mat- 

 ter ^ are very desirable table birds. 



(b) Neck long, having 17 vertebrae. 



(c) Legs and feet very long; as in the 

 Swans and Geese, tarsi are reticulate all 

 around, i.e., uniformly covered with small 

 hexagonal scales (scutellate in Ducks); 

 hind toe without lobe, as in the Surface- 

 feeding Ducks and Geese; claws, long. 



(d) As in the Ducks, the lower end of 

 the windpipe in the male is modified to 

 form a voice-box (fig. 32). 



(e) Some species nest in trees, others 

 on the ground. 



OTHER SURFAMILIES 



FIG. 14.-Typical Tree Duck 



FIG. 15.- Typical foot and 

 bill of Tree Duck 



Not Found in North America 



Plectropterinae. Consists of three Geese, (a) a semipalmated (hal: 

 webbed) Goose, with hind toe on level with other toes, found in Aus 

 tralia and New Guinea, and (b) two varieties of Geese with high fronta 

 knob on bill, and spur on bend of wing, found in Africa. 



Gereopsinae. Consists of one semipalmated Goose found in Aus 

 tralia. 



Merganettinae. Consists of seven forms, all races of the same species 

 which represents a link between the Mergansers and the Diving Ducks 

 they have no serrated bill as in the former, and possess a spur on th< 

 bend of the wing. All found in South America. 



