INSTINCT 195 



mediate and final cause of the cuckoo's instinct is, that 

 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 

 predicament ; 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 oc- 

 casionally lays her eggs in other birds' nests ; but I 

 hear on the high authority of Dr. Brewer, that this is 

 a mistake. 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 suppose 

 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, en- 

 cumbered 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 ad- 

 vantage. 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, generated. I may add that, according 

 to Dr. Gray and to some other observers, the European 

 cuckoo has not utterly lost all maternal love and care 

 for her own offspring. 



