INSTINCTS OF THE CUCKOO. 235 



INSTINCTS OF THE CUCKOO. 



It is supposed by some naturalists that the more imme- 

 diate cause of the instinct of the cuckoo 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 unincu- 

 bated, 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 migrates 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 succes- 

 sively hatched, all at the same time. It has been both 

 asserted and denied that the American cuckoo occasionally 

 lays her eggs in other birds' nests ; but I have lately heard 

 from Dr. Merrill, of Iowa, that he once found in Illinois a 

 young cuckoo, together with a young jay, in the nest of a 

 blue jay (Garrulus cristatus) ; and as both were nearly full 

 feathered, there could be no mistake in their identification. 

 I could also 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, 

 and that she occasionally laid an egg in another bird's nest. 

 If the old bird profited by this occasional habit through 

 being enabled to emigrate earlier or through any other 

 cause ; or if the young were made more vigorous by advan- 

 tage being taken of the mistaken instinct of another species 

 than when reared by their own mother, encumbered as she 

 could 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 

 us 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 more successful in rearing 

 their young. By a continued process of this nature, I believe 

 that the strange instinct of our cuckoo has been generated. 

 It has, also, recently been ascertained on sufficient evidence, 

 by Adolf Mtiller, that the cuckoo occasionally lays her eggs 

 gn the bare ground^ sits on them and feeds her young, Thi? 



