98 CHILDHOOD OF ANIMALS 



only birds in which they are so fully formed at the time of hatching 

 that they can be used for flight at once, but they appear very quickly 

 in all young birds and can often be counted long before the chicks 

 have left the egg. Quills are usually replaced once a year. Some 

 water-fowl shed them all at once, and in their unhappy flightless 

 period have to hide in the reeds in some sheltered corner of a lake, 

 an easy prey to any foe that discovers them in their day of peril. In 

 most birds they are shed and replaced in pairs, so that at any time 

 there are not more than one pair in the wings and one pair in the tail 

 out of action, and there are always enough for flight to take place. 



Besides the quills, there are two kinds of feathers, more or less 

 corresponding with the fur and the under-fur of mammals. There 

 are the contour feathers which make up the greater part of the 

 covering of the body, giving that not only its shape but most of its 

 colour and pattern, and forming the decorative plumes on head 

 and wings and tail. They are not spread evenly over the surface 

 of the body, but are inserted on special regions, with naked spaces 

 between them in all except a very few birds, and even in some 

 of these, such as the ostrich, they are arranged on definite tracts 

 in the young bird, although they are evenly distributed in the adult. 

 Secondly, there are the softer, more tuft-like down feathers, corre- 

 sponding with the under-fur of mammals, and like that found most 

 abundantly in creatures which require special protection from cold. 

 These may be attached to the interspaces between the contour 

 feathers, or they may be distributed all over the bird, or they may be 

 found only on the feather-tracts, concealed by the other feathers. 

 It seems most probable that these down feathers are a later develop- 

 ment and are degenerate contour feathers, the only purpose of which 

 is to thicken the warm covering of the body. 



There are many reasons why birds should moult, and from time to 

 time renew their outer garment, which is at once an ornament, a 

 protection and a most useful organ. Feathers are fragile and quickly 

 become frayed, broken or worn. In a few cases the wearing of the 

 tips of the feathers at first smartens the plumage. The throat of the 

 sparrow is dingy in winter, mottled with brown and black, but as the 

 tips of the feathers wear off they reveal the brilliant black band 

 which decorates the bird in spring. So also the rosy pink of the 

 linnet's breast in spring appears only when the dull tips of the winter 

 feathers have been worn off. In some birds, this accident has been 

 transformed to a system. Many brightly coloured ducks acquire 

 their brilliant breeding plumage in autumn, and yet in spring, when 



