BRITISH WARBLERS 



This in outline is what seems to be the normal routine. There 

 are plenty of deviations from the rule and plenty of variations 

 of procedure ; the same bird may be fed by both parents in 

 quick succession, or by one parent again and again until well- 

 nigh exhausted by the abundance of food showered upon it. 



Numerous references have been made to the method which 

 has been evolved for ensuring the complete removal of the 

 excrement and thereby the cleanliness of the nest. The 

 importance of cleanliness is alluded to in the life of the 

 Whitethroat and it is unnecessary to discuss the matter 

 further ; attention may nevertheless be directed to the method 

 by which this end is secured. 



We must remember that cleanliness is only brought about 

 by correlated behaviour on the part of parent and offspring. 

 The usual procedure is as follows : the parent delivers food 

 to one of the nestlings and then waits for it to eject the faces ; 

 if it fails 'to do so the parent sometimes touches the anus with 

 its bill, which seems to have the effect of stimulating the 

 nerves which control defaecation ; the fceces are then carried 

 away and dropped some distance from the nest or swallowed. 

 Yet this correlated behaviour on the part of parent and 

 offspring, wonderful though it is, would not be sufficient to 

 ensure complete cleanliness without the contributory physio- 

 logical factor, i.e., the membranous sac or envelope in which 

 the fceces are enclosed and which facilitates the act of removal. 

 But is ease of removal alone sufficient to account for this 

 wonderful contrivance ? Ease of removal implies economy in 

 time, and time is everything. That the young in the early 

 stages of growth should sleep as much as possible, should be 

 kept as warm as possible, and should run no risk of prolonged 

 exposure is imperative if the species is to maintain its position. 

 This biological end is furthered by the specialized activities of 

 the parents, whose behaviour shows how admirably racial pre- 

 paration has fitted them for the task. All their movements, or 

 all her movements as the case may be, are delicately adapted 

 to contribute to the main parental function of supplying 



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