PECULIAR INTERRELATIONS 129 



when, raising the wings to keep its burden in position, it climbs 

 up the nest backwards. Little by little, with widely spread 

 legs, and the use of the beak as a lever, the journey to the top 

 of the nest is made, when, with a supreme effort the helpless 

 little Robin or Hedge-sparrow, as the case may be, is sent sprawl- 

 ing, to die very shortly after of exposure. Not until the last 

 is ejected does this extraordinary little criminal relax its 

 efforts ; but so soon as all is over it settles down contentedly to 

 enjoy life, developing a most ravenous appetite, and making the 

 most exacting demands upon its foster-parents. 



Without for the present discussing the factors which have 

 resulted in this most successful fraud on the part of the Cuckoo, 

 we may refer next to another very remarkable phase of this 

 life-history, and this concerns the coloration of the Cuckoo's egg, 

 which, as a rule, bears a very close resemblance to those of the 

 nest in which it is laid. In other words, the eggs of the Cuckoo 

 show a very remarkable range of variation, or rather of colora- 

 tion, corresponding, roughly, with the number of species which 

 are used as dupes. 



Evidence has now accumulated to show, however, that this 

 range of colours becomes manifest only when the eggs of a 

 large series of Cuckoos are examined. In other words, the 

 eggs of any particular Cuckoo are all of the same type, both in 

 colour and markings ; and this is true when all the eggs laid by a 

 single female throughout each season for a number of years are 

 examined — and such series have been found, by reason of 

 certain peculiarities of colour and pattern. Further, it is now 

 almost conclusively established that the colour and pattern of 

 any given egg bears a more or less close resemblance to the 

 eggs of the host in whose nest they are placed. Where this 

 rule is broken it is more than probable that the disparity is due 

 to untoward circumstances, to the fact that the Cuckoo at the 

 time she deposited her egg was unable to find a suitable nest, 

 and so dropped the egg into the nearest likely nest available 

 to take its chance. How this curious resemblance came about 

 it is not easy to see at first ; for it is certain that the bird 

 cannot in any way voluntarily influence the colour of her egg, 

 nor can we suppose that she carries her egg in her mouth while 

 she makes the round of nests in the neighbourhood for the 

 purpose of selecting that as a nursery which contains eggs most 

 9 



