Chap. VII. OF THE CUCKOO. 217 



she lays her eggs, not daily, but at intervals of two or 

 three days ; so that, if she were to make her own nest 

 and sit on her own eggs, those first laid would have 

 to be left for some time unincubated, or there would be 

 eggs and young birds of different ages in the same nest. 

 If this were the case, the process of laying and hatching 

 might be inconveniently long, more especially as she 

 has to migrate at a very early period; and the first 

 hatched young would probably have to be fed by the 

 male alone. But the American cuckoo is in this pre- 

 dicament; for she makes her own nest and has eggs 

 and young successively hatched, all at the same time. 

 It has been asserted that the American cuckoo occa- 

 sionally lays her eggs in other birds' nests ; but I hear 

 on the high authority of Dr. Brewer, that this is a mis- 

 take. Nevertheless, I could give several instances of 

 various birds which have been known occasionally to 

 lay their eggs in other birds' nests. Now let us sup- 

 pose that the ancient progenitor of our European 

 cuckoo had the habits of the American cuckoo ; but 

 that occasionally she laid an egg in another bird's 

 nest. If the old bird profited by this occasional habit, 

 or if the young were made more vigorous by advantage 

 having been taken of the mistaken maternal instinct of 

 another bird, than by their own mother's care, encum- 

 bered as she can hardly fail to be by having eggs and 

 young of different ages at the same time ; then the old 

 birds or the fostered young would gain an advantage. 

 And analogy would lead me to believe, that the young 

 thus reared would be apt to follow by inheritance the 

 occasional and aberrant habit of their mother, and in 

 their turn would be apt to lay their eggs in other birds' 

 nests, and thus be successful in rearing their young. 

 By a continued process of this nature, I believe that the 

 strange instinct of our cuckoo could be, and has been, 



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