GENERAL SUMMARY AND CONCLUDING REMARKS 



the younger as a possible explanation of the art of nest 

 building. Tradition in connection with this particular aspect 

 of behaviour does not appeal to me as a satisfactory solution, 

 for we cannot, as I pointed out when discussing the nest 

 building instinct of the Eeed Warbler, assume that a young 

 male and a young female never mate together ; and even 

 granting that such an assumption were in some cases correct, 

 there is a still greater difficulty to be overcome in the fact 

 that the females of certain species — the Willow Warbler, 

 Wood Warbler and Eeed Warbler for instance — are alone 

 responsible for the work of construction. If then this wonder- 

 ful art is neither begotten of experience nor is the outcome of 

 tradition, how is it to be explained ? I cannot explain how 

 it is done; we seem forced to fall back on inherited instinct. 

 I believe that the young bird is as perfectly equipped with 

 the mechanism necessary to produce these beautiful pieces of 

 architecture as many insects which are provided with the 

 mechanism necessary for the performance of a complicated 

 series of activities once and once only in their lives. 



Regarding as a whole the species whose lives have been 

 dealt with in this work, we find that there is no one rule 

 which summarizes the behaviour of the sexes as to the care 

 of their offspring. The males of one species share the burden 

 equally with their mates, the males of another take little part 

 in the rearing of their family. It is the males of the three 

 smaller species, the Willow Warbler, Wood Warbler and 

 Chiff-chaff, who for some reason are not called upon to work 

 so diligently as their mates, and these three build dome-shaped 

 nests. Can we establish any relation between the behaviour 

 of the male and the specific type of structure that has been 

 evolved ? It is difficult to do so with the life histories of a 

 few species only to draw upon. But if there is one fact that 

 the behaviour of the female, and in some cases of the male, 

 does really seem to show, it is the necessity for constant 

 brooding when the young have just left the egg. We can 

 understand the immense importance of warmth; we need 



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