BRITISH WARBLERS 



the departure of a parent from the nest and its arrival with a 

 fresh supply of insects varies considerably. Sometimes it 

 appears to be in no great hurry and may not return for twenty 

 minutes or more, whilst at other times it seems to be equally 

 anxious that there should be no delay, and consequently 

 returns in from five to six minutes. The parents as a rule 

 approach the nest separately, but occasionally they arrive 

 together, and when this occurs the same offspring may be 

 fed by both of them. Defascation usually ensues a few 

 moments after the young one has been fed, and the parent 

 w r aits for this to happen, and then carries the fceces away 

 or swallows them. The routine of feeding is very similar to 

 that which occurs in the case of the Eeed Warbler ; the bird, 

 that is to say, which is the more hungry, is the more vigorous 

 in stretching out its neck, and the more liable consequently to 

 receive ' food. We can therefore explain the behaviour of the 

 parents at the nest without imputing to them any intelligent 

 control. There still remains, however, one point in connection 

 with the care of the offspring, which, though appearing to be 

 purposeful, may nevertheless be one of those beautiful adjust- 

 ments of Nature, the development of which can be referred to 

 selection. It is this : defsecation usually ensues after food has 

 been supplied by the parent, who then carries the fcsces away 

 and thus prevents the contamination of the nest. Now it 

 often happens that the parent divides each supply of food that 

 it brings between two of the young, and no doubt economy is 

 thus effected in the time and energy which it is compelled to 

 devote to securing the necessary food. But it is clear that 

 if both the young were to eject the fceces forthwith the parent 

 could not conveniently remove them and Nature's object would 

 not thereby be attained. If, however, the methods adopted 

 by the parents be closely observed, it will be noticed that the 

 various insects are not divided equally between the two 

 offspring, but that one receives a larger proportion than the 

 other. It may well therefore be that there is some relation 

 between the method thus adopted and the ejection of the 



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