166 THE BIOLOGY OF THE SEASONS 



handless a sacrifice involved in the turning of arms into 

 wings the bulk of the work is done with the bill and with 

 the feet, and the body is used to mould the framework, the 

 bird turning round and round inside the growing nest, making 

 it fitter at every turn with a poke of the bill and a thrust of 

 the foot. The busy bird suggests at times an extremely 

 energetic and somewhat fussy sculptor, working on his clay, 

 dabbing here and dabbing there, smoothing down and 

 ruffling up, and pausing every now and then to look at it 

 with critical appreciation. But when we look at the finished 

 product, such as the nest of a chaffinch, we must stand 

 amazed at the artistic achievement. It may be safely said 

 that the wonder grows upon us as we probe deeper into the 

 details of the nest. 



SUBJECTIVE ASPECT 



It is not difficult to observe how a bird uses its bill and 

 feet in fashioning the nest, but it is very difficult to get near 

 the inward spirit. The only course is to select the interpre- 

 tation that fits the facts best and makes fewest assumptions. 

 Is the art of nest-building instinctive ? That is to say, has 

 the bird an inborn power of fashioning a nest of a par- 

 ticular type without education or experience? Does it 

 require only what the Germans call an Auslosungsreiz 

 a liberating stimulus to pull the trigger of an innate 

 capacity ? And is this innate capacity the outcome of 

 an age-long selection which favoured those individuals 

 whose brain varied in the direction of useful constructive 

 art? 



In support of this way of looking at the nest, there are a 

 few observations, e.g. that canaries that had never seen more 

 than a shop-made felt nest have been known to make an 

 effective nest of moss and hair ; or that a greenfinch, 

 incubated by a canary in a canary's nest, made, in the course 



