REPRODUCTION— NIDIFICATION 193 



tion to this aspect of nest-building among birds. Whether we 

 shall ever learn anything of the factors which have brought about 

 these departures depends entirely upon the observations, of those 

 fortunate enough to be able to study the facts in the field. 



This chapter would be incomplete without a brief comment 

 on the question raised by Dr. Alfred Russel Wallace, years ago, 

 as to whether birds build by instinct or by imitation. Without 

 doubt he did much to confuse the issues at stake by com- 

 paring the nest-building of birds with the house-building of 

 man : an obviously false analogy. In spite of the dogmatic 

 assertions of this eminent naturalist, there is absolutely not 

 only no evidence in support of his contention that birds build 

 by imitation, but all the known facts are directly against him. 

 He first argued that the art of nest-building was acquired by 

 the young bird while in the nest. That is to say, between the 

 intervals of sleep and feeding it takes mental notes of the 

 construction of its cradle, against the day when these notes may 

 be useful ! Relinquishing this, he next suggests that the young 

 bird, just before building its first nest, makes a survey of the 

 cradles of others of its own species; and finally, that young 

 birds must pair with old birds and so learn the secret from 

 their more experienced mates ! But it is all very well to talk 

 of imitation, but who set the fashion of each type of nest 

 originally? No, there can be no question of imitation. Nest- 

 building is a product of selection and is instinctive. This is 

 shown by the fact that wild birds taken from the nest before 

 they can see, and kept in captivity under suitable conditions, 

 will, at the appropriate time, build a nest typical of their species. 

 That a bird's first nest is less perfect than succeeding nests has 

 often been urged, and this is probable ; for practice necessarily 

 leads to perfection. There is nothing remarkable, indeed, about 

 the part played by instinct in this matter. Young spiders yet 

 but an hour old will at once proceed to spin a web as perfect 

 as that of an adult, and there can be no question of imitation 

 here. A caterpillar when full-grown will spin for itself a most 

 elaborate cocoon, or suspend itself by the tail, and place a 

 girdle round its body to bear its weight in the chrysalis stage, 

 yet there can be no factor other than " instinct " at work to guide 

 it. For this act is performed but once in its life, and is carried 

 out in isolation. 

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