THE NATURAL HISTORY OF NESTS 167 



of time, a true greenfinch nest of fibrous roots, moss, wool, 

 and horse-hair. 



There is also an indirect argument in support of the view 

 that the fashioning of the nest is instinctive ; it is based on 

 the fact that the nature of the nest is usually specific. That 

 each bird keeps, as a rule, to its own type of nest does not 

 exactly prove that the whole business is instinctive ; but it 

 points in that direction, and it seems to us to rule out the 

 view that each nest is the expression of independent and un- 

 prejudiced artistic skill. It must be noted, however, that so 

 great an authority as Dr. Alfred Russel Wallace refuses 

 altogether to admit this argument. According to his view, 

 " each species uses the materials it can most readily obtain, 

 and builds in situations most congenial to its habits. . . . 

 The materials of birds' nests, like those used by savage man 

 for his house, are, then, those which come first to hand ; and 

 it certainly requires no more special instinct to select them 

 in one case than in the other." Similarly, he interprets the 

 characteristic architecture of the nest in terms of the general 

 habits of the species, the nature of the tools (bill and feet) 

 they have to work with, and the material they can most 

 easily obtain. 



The non-instinctive theory, supported by Dr. Wallace, 

 lays emphasis on imitation and tradition. While a bird may 

 inherit an indefinite tendency to build a nest at the proper 

 time, the manner of its building depends on the extra- 

 organic tradition of the species. From generation to genera- 

 tion there is a " tradition " registered in the nest itself, which 

 is, in a sense, a " permanent product," and including all the 

 possibilities of imitation and suggestion from previous and 

 contemporary nest-builders. Even with human mothers, 

 where there is intelligent awareness rather than vague 

 instinctive prevision, how important is the social tradition 

 of what is fit and proper in the way of provision for the future 



