INSTINCTS OF THE CUCKOO. 251 



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 (G-ar- 

 rulus oristatus); 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 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 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' nest, 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 prob- 

 ably a case of reversion to the long-lost, aboriginal instinct 

 of nidification. 



It has been objected that I have not noticed other re- 

 lated instincts and adaptations of structure in the cuckoo, 

 which are spoken of as necessarily co-ordinated. But in 

 all cases, speculation on an instinct known to us only in a 

 single species, is useless, for we have hitherto had no 

 facts to guide us. Until recently the instincts of the 

 European and of the non-parasitic American cuckoo alone 

 were known; now, owing to Mr. Eamsay's observations,_we 

 have learned something about three Australian species, 

 which lay their eggs in other birds' nests. The chief 

 points to be referred to are three: first, that the common 



