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FLEAS, FLUKES AND CUCKOOS 



weaver birds, cow-birds and cuckoos. Deliberate destruction of the eggs 

 or nestlings of the fosterer by the young of the brood-parasite is known 

 among cuckoos and honey guides. The former heave them out of the 

 nest and the latter are thought to peck them to death. Parasitic cow- 

 birds achieve the same object by a more subtle method. They manage 

 by importuning the foster parents to get most of the food for themselves 

 and the rightful young eventually die of under-nourishment and 

 debility. 



Successful brood-parasitism, like successful ecto-parasitism, seems to 

 impose development and specialisation along certain lines. Therefore, 

 in widely separated groups of birds, located in opposite sides of the 

 globe we find these striking examples of parallel development. 



