320 THE WONDER OF LIFE 



erythrophthalmics), which nests and broods. It also has a 

 tendency to produce eggs at irregular intervals (one to three 

 days), so that there are eggs and young in the nest for a longer 

 time than usual. Any disadvantage which might arise 

 from this has been met by the fact that the young ones 

 leave the nest in succession on the seventh day after birth, 

 and thereafter spend a couple of weeks in a ' climbing 

 stage ' preparatory for flight. In this climbing the young 

 bird, which has clambered or even jumped from the nest, 

 moves about very effectively among the twigs. It grips 

 the twigs very firmly with its feet and can hang head 

 downwards fastened by two toes ! ' It profits by the 

 strength with which it was born endowed, and the exercise 

 which it has received through the grasping reflex, for it 

 is a perfect acrobat, and there seems to be no necessary 

 feat of climbing of which it is incapable '. Herrick goes 

 on to compare it to the young of the old-fashioned Hoatzin 

 of the Amazons, which is also an adept climber ; both use 

 the bill to help the toes, but the Hoatzin has the advantage 

 of having a clawed thumb and first finger. 



Now the interest of this is that the American black- 

 billed cuckoo shows something of the irregularity in egg- 

 laying which the European cuckoo shows, and that it 

 obviates a possible disadvantage by the peculiarity 

 that the young bird leaves the nest very early, and has a 

 remarkable climbing period during which it has a strong 

 sense of fear. Prof. Herrick notes two other points : 

 ' When disturbed in its nest-activities, the black-bill has 

 been known to transfer its eggs to a new nest of its own, 

 an action which strongly suggests the practice of the Euro- 

 pean cuckoo of carrying its laid egg to the nest of a nurse.' 



' The American species occasionally " exchange " eggs, 



