40 WATER FOWL OF INDIA AND ASIA. 
the species, though occasionally less developed in 
females and young. 
In habits, as above observed, Ducks vary exceedingly ; 
in addition to their varying attachment to the water, 
and the corresponding difference in their powers of 
locomotion there and on land, there is much diversity 
in their nesting-habits, most breeding on the ground, 
while some select trees ; and these usually perch freely, 
though from the formation of their feet they cannot 
move about among the boughs so easily as do most 
perching birds. Most breed out of India, to the north, 
but, except the Goosander, all the few resident Indian 
water fowl belong to this sub-family. 
In diet Ducks are omnivorous, though some species 
are more vegetarian and others more carnivorous than 
others ; grain and shell-fish find especial favour with 
them. The ridging of the bill enables this organ to be 
used very effectively for straining small items in their 
dietary from mud or water. Some feed below the 
surface, plunging for their food, while others only tilt 
up their tails and reach down, maintaining their 
position by padding with the feet. 
As there are no less than twenty-nine species in this 
sub-family, their discrimination is a matter of more 
difficulty than that of the others. I shall, however, 
divide them for convenience into manageable groups 
separated by easily appreciable characters. And in the 
descriptions of the species I shall avoid as far as possible 
describing the often complicated colouring of the 
plumage in too much detail, while laying stress on the 
salient points of the species. 
According to their build and (more or less) corres- 
ponding habits, we may divide the true Ducks into 
diving Ducks, Goose-like Ducks, and ordinary surface- 
feeding Ducks, groups easily recognizable. 
The diving Ducks are at once marked off by their 
large feet, which have the outer toe as long as or even 
