86 SPRING 



seems most probable that they are strays dropped by hen 

 cuckoos which usually frequent the nests of sedge-warblers or 

 other birds nesting in the same thicket. 



When two cuckoo's eggs are found in the same nest, 

 they have probably not been laid by the same bird. There 

 is plenty of room for two cuckoo's eggs and four or five 

 other eggs in a nest, but none for more than one young 

 cuckoo. Being so small when hatched, it has to grow very 

 rapidly, and therefore needs much food ; it can afford to 

 tolerate no rivals, and has a very short way with them. When 

 still blind and naked, and usually before it is forty-eight 

 hours old, it works itself under the other young birds, one 

 by one, scrambles up the side of the nest with its stumps 

 of wings raised to keep the victim in place, and empties it 

 over the edge. Its back is unusually flat and hollow, which 

 appears to be a special adaptation for this bloodthirsty 

 performance. It does not always accomplish its blindfold 

 task the first time. The other little bird sometimes falls 

 down inside the nest ; then the cuckoo rests a little, and sets 

 itself savagely to work again. It is not long before it 

 reigns alone, and before it is fledged it fills the whole nest, 

 and pecks savagely at the hand which attempts to touch it. 



Unnatural as the acquiescence of the foster-parents may 

 appear, they are only acting according to their lights. 

 Their instinct bids them find young birds hatched in their 

 nest ; and they obey their nursing instinct implicitly, indif- 

 ferent to the fact that there is only one young bird left, and that 

 a completely naked and copper-coloured little creature un- 

 like any chick of their own. This active co-operation of the 

 foster-parents in a process which can only lead to the reduction 

 of the numbers of their species is an illustration of the fact 

 that not every acquired habit in nature is necessarily 

 beneficial, as some extreme supporters of the theory of 



