CONCERNING THE CUCKOO 121 



selection it may be said has acted thus far, but how 

 comes it that a particular cuckoo lays a certain type 

 of egg in a particular nest ? The answer is very 

 interesting. It has been noted by several observers 

 that the same cuckoo always lays eggs of the same 

 type, and recent observations also establish a strong 

 probability that each cuckoo generally lays in the 

 nest of the same species of bird. Now both these 

 peculiarities would in all probability be hereditary. 

 The cuckoo, in fact, deposits her egg in a suitable 

 nest, not from any extraordinary or mysterious 

 instinct, but because the descendant of a bird reared, 

 for instance, in a skylark's, from an egg resembling 

 those of the foster-parent, would herself probably 

 lay in a skylark's nest, and produce an egg of similar 

 appearance. We appear to have here an exceedingly 

 interesting state of things. Natural selection has, 

 as it were, developed in individuals of the cuckoo 

 tribe the tendency to produce certain varying types 

 of eggs, and at one and the same time has also 

 developed the tendency to deposit these eggs in 

 the nest of the suitable species of bird. The great 

 variation in size and appearance in the cuckoo eggs, 

 therefore, simply corresponds roughly to the variation 

 among the eggs of the numerous species of foster- 

 parents made use of by the bird. 



If the facts have justified us in regarding the cuckoo 

 as a bird which experiences great difficulty in obtain- 

 ing sufficient food, we have found, therefore, in the 

 operation of natural selection alone a sufficient 

 explanation of the extraordinary series of habits 

 and instincts which have rendered the bird remark- 

 able from time immemorial. That the difficulty 

 has been an increasing one from some distant time 



