Chap. VII. INSTINCTS OF THE CUCKOO. 209 



ally and justly been ranked by naturalists as the most wonder- 

 ful of all known instincts. 



Instincts of the Cuckoo. — It is supposed by some natu- 

 ralists that the more immediate cause of the instinct of the 

 cuckoo is that she lays her ep^gs, 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 eg'p;s, those first laid would have to be left 

 for some time unincubatcd, or there would be eggs and young 

 birds of different ages in tlie same nest. If this Avere the case, 

 tlie 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 prol:)abl3' have to be fed by 

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

 ment ; 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. Merrcll, 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 fully feath- 

 ered, 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 Euro- 

 pean cuckoo had the habits of the American cuckoo, and that 

 she occasionally laid an e^^ 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 yoimg 

 were made more vigorous by advantage 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 advan- 

 tage. And analogy would lead us to believe that the young 

 thus roared would be apt to follow by inheritance the occasion- 

 al 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 

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

 sits on them and feeds her young ; this rare and strange event 

 evidently is a case of reversion to the long-lost aboriginal in- 

 stinct of nidification. 



