BIRDS 



73 



Nests differ greatly in their complexity and in .the kind of 

 material used. Some birds, for example the gulls and many 

 other sea-birds, usually deposit their eggs on rocky ledges or 

 in slight depressions in the sand along the shore. On the 

 other hand, the Baltimore oriole constructs out of grasses, plant 

 fibers, and strings a marvelous nest hanging high up in the 

 trees, near the outer ends of branches (Fig. 73). Between 

 these two extremes are all gradations of nest complexity. 



The eggs laid by birds vary in number, size, and color. 

 The tiny humming bird, for 

 instance, lays two white 

 eggs, each a third of an inch 

 in diameter (Fig. 56) ; three 

 to five greenish blue eggs, 

 each nearly an inch in 

 diameter, are usually found 

 in a robin's nest, while an 

 ostrich deposits twelve to 

 fourteen eggs, each weigh- 

 ing three to four pounds. 



66. Common methods of 

 classification. — One of the 

 simplest ways of classifying 

 birds is that of dividing them 

 into groups according to the 

 kind of food they eat. For 

 instance, we may speak of fish- 

 eating, seed-eating, and insect- 

 eating birds. This, however, 

 is far from being a scientific 

 classification, since birds that 

 differ considerably in struc- 

 ture, and therefore not closely related, frequently five upon 

 the same kind of food. For example, both the pefican (Fig. 57) 



Fig. 57. — The pelican. (Photo- 

 graphed by E. R. Sanborn.) 



