BIRDS loi 



pelicans; hard ivory-tipped bills for the wood-boring wood- 

 peckers, etc. 



The technical classification of birds is based more upon the 

 structure of feet and bills and internal structure than upon 

 color, size, or habit, although, of course, these are also used. 



Feathers are skin modifications, as are scales and hair. 

 They serve a variety of purposes. The downy under- 

 feathers are the warm underwear. We utilize them for 

 pillows and warm feather-beds. Feathers are non-conductors 

 of heat, and thus keep in the heat of the body; but the air 

 included between the feathers also acts as a non-conductor. 

 On cold days the birds may be seen ruffling up their feathers 

 so as to include more air, thus utihzing the principle of the 

 "dead air space" which we employ in our storm-windows. 

 Birds that hve in the water have their bodies more thickly 

 covered with down than other birds. Nestlings and pre- 

 cocial birds, like young chickens, have another kind of down. 

 This is pushed out as the real feathers develop. There are 

 also slender hair-like feathers, called pin-feathers, which the 

 cook singes off the fowl. These are rudimentary feathers 

 with only a shaft. 



The plumage feathers cover the down feathers and add to 

 the warmth. In some birds, as in the owls, the plumage 

 feathers are very soft and render the flight noiseless. But 

 in most birds the chief function of plumage feathers seems 

 to be to give the coloration — for beauty or for protection. 

 These feathers in nearly all kinds of birds do not cover the 

 whole body, but grow in distinct tracts, yet overlapping the 

 bare areas. 



On the tail and wings are long stiff feathers, called quills, 

 which are used in flying. These may be taken as typical. 



