CHARACTERS AND HABITS OF BIRDS 19 



as many eggs as she can cover. The desired number of eggs 

 having been laid, the process of incubation by the parents begins. 



The incubation of their eggs by birds is one of the most re- 

 markable things in nature. We say that " instinct " leads birds 

 to build their nests and to keep their eggs warm for a period 

 varying from two weeks for small birds, to six weeks for the 

 ostrich ; but " instinct " is only a term to describe the apparently 

 intelligent actions of the lower animals, which we say have not 

 intelligence enough to know 

 the reasons for the things 

 that they do. 



The mother of a young 

 mammal knows that it came 

 from herself, and she can 

 see that it is like her and 

 others of her kind. It at 

 once seeks her care and 



FIG. 3. Sitting hen 

 responds to her attentions. 



The egg which a bird lays is as lifeless to all appearances 

 as the stones which it often so closely resembles. Only after 

 many days or weeks of tiresomely close attention does it produce 

 a creature which can respond to the care lavished upon it. The 

 birds incubating eggs not only give them the most unremitting 

 attention, but those that fill their nests with eggs before begin- 

 ning to incubate methodically turn the eggs and change their 

 position in the nest, this being necessary because otherwise the 

 eggs at the center of the nest would get too much heat and those 

 at the outside would not get enough. A bird appears to know 

 that if she begins to sit before she has finished laying, some 

 of the eggs would be spoiled or would hatch before the others ; 

 and, as noted above, aerial birds seem to know better than to 

 hatch more young than they can rear. But no bird seems to have 

 any idea of the time required to hatch its eggs, or to notice the 

 lapse of time, or to care whether the eggs upon which it sits are 



