THE KOEL AND ITS ALLIES 311 



erows and may thus help to limit their 

 numbers to some extent". 



All the Cuckoos under review shirk 

 parental duties and get other members 



of the bird-world to bring up 

 Nests and ^j^^-^, children. Parasitic Cuckoos 



are therefore regarded as social 

 pests by other birds which, though fully 

 conscious of the stratagem played on 

 them, are yet helpless and become unwi- 

 lling dupes at the hands of the Cuckoos. 

 Birds are strangely lacking in a sense of 

 proportion and, unable to discriminate 

 between their own eggs and those of 

 their deceivers, unconsciously rear up the 

 children of the latter. Nesting operations 

 and the nursing of the young are a 

 blind instinct with birds. They are im- 

 pelled to these actions by Nature, and 

 engrossed in them, they never stop to 

 see whom they are bringing up. Other- 

 wise, how can the crow which is otherwise 

 a very clever and cunning bird fail to 

 notice its mistake and feed the young 



