338 THE STRUCTURE AND LIFE OF BIRDS chap. 



believe, at intervals of several days, so that if she were 

 herself to undertake the incubation, she would have 

 to leave one for some time unsat upon, or else have 

 eggs and young in the nest together at the same time. 

 A German naturalist, Karl Eimer, gives a rather 

 different account ; the Cuckoo lays two eggs in a clutch ; 

 that is, if she made a nest herself, she would lay only 

 two eggs in it. And as she generally migrates 

 before August, she would not, if she herself nested, 

 get many young ones reared in the course of the 

 summer. In favour of the former view it may be 

 urged that the American Cuckoo, who almost always 

 builds a nest for herself, does have young birds and 

 eggs in process of hatching in the nest at the same 

 time. In any case we must look to the bird's great 

 laying powers for the explanation of the cuckoo 

 instinct. The egg of the Cuckoo is wonderfully small 

 considering the size of the bird. It is less than an 

 inch long, and J inch broad. A Hedge Sparrow's egg 

 is about i inch long and a little more than J inch 

 broad. Thus there is no very great difference in bulk. 

 But the Cuckoo is 12 inches long and the Hedge 

 Sparrow only 5 J, a monstrous disparity even when wc 

 allow for the length of the Cuckoo's tail. The dimin- 

 utive size of the interloper's egg no doubt deceives 

 the toster mother, and is necessary if it is to hatch as 

 early as those of the rightful owner. Moreover, if it 

 were not so small, how would the bird after laying it 

 be able to take it in her beak and deposit it in the 

 nest where it is to be left ? The egg sometimes varies, 

 approaching in colour those in the particular nest 

 chosen, so that it is bluish when laid in a Hedge 



