104 A PHILOSOPHER WITH NATURE 



natural history, it has been for long supported by 

 observations numerous and authentic enough to 

 satisfy the most exacting. Where the cuckoo is 

 plentiful almost any painstaking observer will be 

 able to find for himself the intruder's egg in the 

 nest of one or other of the species of birds commonly 

 made use of. The mother has been caught by 

 many observers in the very act of foisting her 

 offspring on her neighbours, and the young bird 

 has been followed in every step of its adventurous 

 career from the egg to the adult. Nothing in fact 

 has been left undone necessary to satisfy the utmost 

 scruples of anyone gifted with that sceptical bias 

 in these matters which the pursuit of science is 

 supposed to demand. 



The eggs of the cuckoo have been found in the 

 nests of nearly every species of bird in Great Britain 

 and the Continent suitable for its purpose. The 

 nests principally made use of in England are those 

 of the meadow-pipit, hedge-sparrow, and pied-wag- 

 tail. In certain districts where the reed-warbler 

 is common the nest of this bird is a great favourite, 

 and the same may be said of the redstart. Although 

 the range of choice which the cuckoo exercises is very 

 wide it is a noteworthy fact that the bird nearly 

 always chooses a nest belonging to a species the 

 natural food of which is suitable to her own young. 

 The foster-parent is thus nearly always insectivorous, 

 the nests of birds which feed on vegetable substances 

 being rarely used. Even the best regulated instinct, 

 of course, sometimes errs, and the cuckoo's is no 

 exception to the rule, the unnatural parent sometimes 

 providing foster-parents equally unnatural for her 

 young by occasionally depositing her eggs in nests 



