May 



all or a portion of the eggs found in the foster nest. 

 The destruction of all would, in many cases, lead to 

 the desertion of the nest altogether ; the supposed 

 motive in destroying a portion only involves too 

 fine a discrimination in a bird capable of placing its 

 pale-coloured egg in an open nest by the side of the 

 bright-blue eggs of the hedge-sparrow. I regard 

 the action as one of simple offence committed upon 

 eggs not its own in the presence of an egg which is 

 its own, and as comparable in the impulse prompt- 

 ing it with those acts of defence to which nesting 

 birds are impelled when their eggs are threatened. 

 Both sets of actions regard the present, not the 

 future. 



I would explain in a similar manner the fact if 

 it be a fact that the cuckoo deposits its egg in an 

 empty nest, or in one containing only the earlier 

 eggs of a brood. Such a course involves the recog- 

 nition of a present fact, that there is more room for 

 the introduction of an extra egg in a nest containing 

 one or two eggs than in one containing four or five, 

 and has not, I am convinced, any reference to the 

 advantages accruing to the young cuckoo through 

 being early hatched or having fewer competitors in 

 the nest. 



- The presence of the singular depression in the 

 back of the young cuckoo might be accepted as being 

 correlated with the impulse to eject if it were shown 

 conclusively that this impulse lasted as long as the 

 depression ; but it would appear that the hollow 



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