276 GENERAL SCIENCE 



birds need to be fed and brooded by the parents. Chickens 

 and the young of other domestic fowls, however, are able to 

 walk and get food for themselves in a very short time. The 

 rapid growth of their feathers is soon sufficient as a protec- 

 tive covering to keep them warm. 



Like the hair or fur upon animals generally, feathers are 

 an outgrowth of the skin. They serve to retain heat within 

 the body of the bird. The body temperature in birds is 

 much higher than it is in man (110 F.). This involves 

 special provisions for respiration quite unlike those in the 

 human body. The amount of energy developed within the 

 bodies of birds is seen strikingly manifested in the long- 

 sustained flights of homing pigeons which are estimated to 

 exceed at times eighty miles per hour. 



The shedding of feathers at certain seasons is called 

 " molting.' 7 The growth of a new coat of feathers is rapid. 

 There is more or less of a change of coloring as the plumage 

 of birds is renewed with "live" feathers. The colorings of 

 the male and female birds are usually different, and the 

 characteristic colorings of the same species is maintained so 

 fully in each successive generation as to be a ready means of 

 identification. 



The variety of colors in plumage is largely a matter of the 

 deposition of color materials (pigments) in different portions 

 of the plumage. The change in colors as viewed from differ- 

 ent positions is a phenomenon that in Physics is called light 

 dispersion. It is due to the fact that the barbs and barbules 

 of the feathers have surfaces marked by very fine lines so 

 close together as to break up the light that falls upon them 

 into its color elements. 



The feathers of the tail and wings of a bird furnish an 

 excellent illustration of "adaptation" in their use for flight. 

 Two rows of interlocking barbs and barbules are arranged 

 along opposite sides of a stiff mid-rib, the whole forming the 



