198 INSTINCTS OF THE CUCKOO. [CHAP. YIIL 



nature have become modified by selection, by considering a few 

 cases. I will select only three, namely, the instinct which leads 

 the cuckoo to lay her eggs in other birds' nests ; the slave-making 

 instinct of certain ants ; and the cell-making power of the hive- 

 bee. These two latter instincts have generally and justly been 

 ranked by naturalists as the most wonderful of all known 

 instincts. 



Instincts of the Cuckoo. It is supposed by some naturalists that 

 the more immediate 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 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 

 migrates at^tl 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 both asserted and denied that the American 

 cuckoo occasionally lays her eggs in other birds' nests ; but I have 

 lately heard from Dr. Merrell, 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 migrate earlier or 

 through any other cause; or if the young were made more 

 vigorous by advantage being taken of the mistaken instinct of 

 another species than when reared by their own mother, encum- 

 bered 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 Miiller, that 

 the cuckoo occasionally lays her eggs on the bare ground, sits on 

 them, and feeds her young, This rare event is probably a 



