BIRDS AS AUTOMATA 107 



ment. Upon one occasion I took a robin's egg that was 

 quite cold and placed it among the warm ones in a 

 blackbird's nest. The hen came and brooded the egg 

 along with her own without appearing to notice the 

 addition, although it was much smaller than her eggs 

 and of a totally different colour. 



In the same way, if a set of nestlings of another species 

 be substituted for those already in the nest, the parent 

 birds will usually feed the new family without noticing 

 the change. Instinct teaches a bird to brood all in- 

 animate objects it sees in the nest and to feed all living 

 things, whether they be its own offspring or not, and 

 many birds blindly obey this instinct. It is, of course, 

 to the advantage of the species that this should be so. 

 For it is only on very rare occasions that foreign objects 

 get into a nest, and nature cannot provide for such 

 remote contingencies. 



Similarly, instinct will not allow a bird to pay any 

 attention to objects outside the nest, even though these 

 objects be the bird's own offspring. 



As everybody knows, the common cuckoo nestling 

 ejects its foster-brethren from the nest, and if the true 

 parents were able to appreciate what had happened, 

 how much sorrow among its victims would the cuckoo 

 cause ! As a matter of fact, no sorrow at all is caused. 

 Incredible as it may seem, the parent birds do not miss 

 the young ones, nor do they appear to see them as they 

 lie outside the nest. In this connection I cannot do 

 better than quote Mr. W. H. Hudson, who was able to 

 closely observe what happened when a young cuckoo 

 had turned a baby robin out of the nest. " Here," 



