148 ODD HOURS WITH NATURE 



pleted structure looks a less fine piece of crafts- 

 manship than the nest of the thrush, but, to human 

 eyes, a more comfortable cradle for nestlings. 

 The point is, that it contains a stage in the work- 

 manship which is absolutely concealed. Neither 

 by inspection while in the nest nor by inspection 

 after leaving it could the blackbird's young dis- 

 cover the existence of the intermediate cup of 

 mud. So far as the blackbird is concerned, we 

 are therefore pushed back to the old theory of 

 instinct. The idea, that instruction enters into 

 the work of nest -building is not, however, ex- 

 cluded by excluding teaching of the young. Both 

 birds take part in the work, and, unless they are 

 both birds of a, year, one of them, has already 

 learnt the way. If it could be assumed that one 

 of a pair is always older than the other, we should 

 have a manner of transmission. Unfortunately 

 for that theory, there are cases not a few in which 

 the male takes no part in the building. 



