22 ABOUT BIRDS IX GENERAL. 



birds, and it is the thorough anointing of the feathers 

 which makes water so readily run off a duck's back. 



The breathing capacity of birds is phenomenal; 

 they breathe not only with the lungs but with the 

 whole body, inflating numerous air-sacs under the 

 skin, and also certain bones. Birds breathe much 

 more rapidly than animals. Their wonderful power 

 of flight is explained by the lightness of the air-filled 

 body, and by their great muscular strength ; the breast 

 muscles which move the wrings are enormous, some- 

 times weighing one-sixth of the whole bird. 



There is the greatest variety in the structure and 

 consequently in the habits of dilTferent birds, some 

 being especially adapted to life in the water, and 

 others to aerial life, while the Ostrich and its rela- 

 tives can neither swim nor fly. By far the greater 

 number of birds, however, are at home on earth or in 

 the air, and can range the wide world over, the most 

 free and independent of all creatures. 



Aerial birds have great expanse of wdng in pro- 

 portion to the size of body, and their wings are long 

 and pointed, while birds that spend most of their time 

 perching or on the ground, like the Sparrows, have 

 short round wings. Between the two extremes of 

 shape and use there is every possible variety, adapted 

 to the habits of all species. 



The bill of a bird is its hand, and is wonderfully 

 varied to suit different habits of feeding and nest 

 building. It may be long or short, slender or stout, 

 straight or hooked at the end, curved up or down, 

 wide and flat or high and narrow, but is always ad- 

 mirably adapted to its special use. In its varied 

 forms it is used as forceps, chisel, hammer, trowel, 

 shovel, probe, hook or needle. 



