THE FOOD OF THE OTHER LAND ANIMALS 



89 



seeds; but if they see another bird, as a cardinal, eating them 

 they will promptly follow suit. 



The flight of birds gives them a very great advantage in the 

 search for food. As birds cannot hibernate and require a very 

 large amount of food 

 in proportion to 

 their weight on ac- 

 count of their great 

 activity and high tem- 

 perature, which is 

 normally as much as 

 110.2° in some, the 

 colder regions would 

 be almost birdless 

 were it not that the 

 birds are able, when 

 the waters freeze and 

 the land life passes 

 into the winter con- 

 ditions, to fly south- 

 ward to regions where 

 they can still find 

 abundant food. Trop- 

 ical birds of many 

 kinds also wander 

 about over more or 

 less definite tracks at 

 different seasons. 



There are various 

 types of parasitic 

 birds which live by 

 robbing other birds. IMost, but not all, of the Old World 

 cuckoos, though only one of the American so far as known, 

 lay their eggs, or rather place them, in the nests of other 

 smaller birds; the young cuckoo, shoving the other young 

 birds out of the nest, is reared by the foster parents. The 



Figs. 99-104. ]Moths. 

 For explanations of the figures see p. xiv. 



