SURROUNDINGS OF THE HOME 277 



vane of the feather. The hollow quill is both light and 

 strong. 



The legs and necks of wading birds, such as the heron, are 

 greatly lengthened; the feet of swimming birds, such as 

 ducks and geese, have the toes joined by a web. Birds that 

 perch have one toe of the four opposite to the other three 

 even as the thumb is opposite the four fingers of the human 

 hand. With some birds that climb, two of the toes are 

 opposite the other two. 



Birds have no teeth. The food when swallowed may 

 lodge and remain for a time in an enlarged portion of the 

 food passage known as the "crop", where it becomes more 

 or less softened. It then passes on into what corresponds 

 to the stomach ("the gizzard") where by action of the 

 strong muscular walls it is subjected to a grinding process. 

 Sand, gravel, and other like material is swallowed by fowls 

 and birds to aid in this. 



The horn-like bills (beaks) of birds are of varied shapes 

 and degrees of strength, and are adapted to the kind of food 

 upon which the birds live. 



In the humming bird the bill is slender and much elon- 

 gated; in ducks and geese broad and much flattened; and in 

 hawks and eagles it is powerful enough to tear the flesh of 

 their prey when once their claws (talons) have grasped it. 

 The bill is an important means of identification of species of 

 birds. 



Failure in food supply is probably one of the reasons why 

 birds migrate on the approach of winter. Their return to 

 more northerly latitudes in the spring doubtless involves 

 other causes. In preparation for these migrations, even as 

 in nest building, birds exhibit an instinct that occasions 

 wonder. Some kinds gather in flocks numbering thousands, 

 taking their journey only after days of seeming preparation. 

 With some kinds of birds these migrations are made at night, 



