INTRODUCTORY 21 



kind — each, be it understood, have to be learnt. Now 

 a bird's intellectual powers advance to maturity much 

 more quickly than in the human race. A young bird 

 three or four days old is capable of considerable 

 powers of memory and observation, and during the 

 time that elapses in which it is in the nest it has 

 ample opportunity of gaining an insight into the 

 architecture peculiar to its species. It sees the posi- 

 tion of the nest, it notes the materials, and when it 

 requires one for itself, is it so very extraordinary that, 

 profiting by such experience, it builds one on the 

 same plan ? Again, birds often return to the place 

 of their birth the following season, and possibly see 

 the old home many times ere they want one for them- 

 selves. This aided by the strong hereditary impulse 

 to build a nest similar to the one in which they first 

 saw the light, and aptitude to work up certain special 

 materials, the collective and inherited or transmitted 

 result of many generations, aid them in their task. 

 Further, we know that some birds do not breed for 

 several seasons after they are hatched, and conse- 

 quently must often see older birds at work and profit 

 by the experience. Then, again, many birds breed in 

 companies, and the young may watch and imitate the 

 work of older and more experienced nest-builders 

 around them. Young birds may also often pair with 

 older and more experienced mates. The nests these 

 young birds build may, and often do vary from the 

 original type in many slight particulars ; and it is by 



