THE EUROPEAN CUCKOO sGl 



While the young cuckoo is still blind and mute, at the tender age 

 of about ten hours, it develops a sudden and powerful impulse to 

 eHminate all the other inmates of the nest. The touch of any object, 

 whether it is an egg or a nestling, seems to cause it intense discomfort, 

 possibly even pain, and it forthwith attempts to rid itself of the intoler- 

 able presence. There is a small highly sensitive cavity on its back in the 

 region of the synsacrum into which it attempts to roll the offending egg 

 or nestling. Eventually, at the cost of a protracted, exhausting and hide- 

 ous struggle, it succeeds in hoisting its burden to the side of the nest and 

 ejecting it over the side. This is repeated until the young cuckoo remains 

 as the sole occupant of the nest. Three and a half to four days after 

 hatching when the plumage begins to grow, it becomes less sensitive 

 and the all-powerful desire for solitude fades away. The dorsal cavity, 

 which now no longer serves any useful purpose, is gradually obliterated. 



It is a curious fact that the parent birds do not become agitated by 

 the disappearance of the rest of the clutch and do not appear to notice 

 the absence of their own young. They never attempt to feed them if 

 they lie starving on the ground and sometimes will even remove one 

 from the edge of the nest if the cuckoo has failed to heave it well over 

 the side — as if it were a piece of unwanted rubbish. It appears that 

 small passerine birds entirely fail to recognise their own young at this 

 stage of development if they are not in their proper place — i.e. well and 

 truly in the bottom of their nest. 



Not all species behave like the young European cuckoo and eject 

 the eggs and young from the nest. In some cases, for example, in the 

 genus Eudynamis, the young brood-parasite is reared together with the 

 nestlings of the foster parents. The general colouring of the young 

 cuckoo's plumage somewhat resembles that of the fosterers' young — 

 black when crows and starlings are the host and brown if the other 

 nestlings are brown, too. They are consequently less conspicuous and 

 tone in with the rest of the brood. In another group of parasitic birds, 

 the African widow-birds {Vidua), this resemblance to the fosterers' 

 young is developed to an amazing degree — even down to such details 

 as the distinctive specific markings inside the gape. 



When it is about twenty-one days old the young of the European 

 cuckoo leaves the nest, which has often, by this time, become too small 

 for it. Cuckoos which are reared in wrens' nests, for example, present a 

 most extraordinary sight bulging out of the entrance hole — often back- 

 side foremost. Before the young cuckoo starts on the long migration to 



