104 Instinct. 



its nest as it does, or that the Chipping-sparrow 

 should hne its nest with hair, and so on of the pe- 

 cuhar characteristics of the nests of hundreds of 

 birds, are things which cannot be satisfactorily ac- 

 counted for, by any appeal to the force of habit or any 

 thing connected with the physical nature of the bird. 



It has been noticed by Mr. Wallace, in his val- 

 uable contribution to Natural History,"^ that birds 

 generally build with the materials most convenient 

 for them ; and this is undoubtedly true as a gener- 

 al proposition, as it is true that they eat the food 

 most convenient for them. And they select for 

 their breeding-places regions where the conditions 

 of building and feeding are best for them. This 

 selection of localities by long journeys even, is a 

 part of their instinctive work. 



But it is not true that birds select the most 

 convenient material for building to any such ex- 

 tent as to lead us to infer that they learned to 

 build with any particular materials simply because 

 they were abundant. For different kinds of birds 

 living in the same region, build their nests upon 

 very different plans, and very many of them build 

 of materials that are by no means abundant. It 

 is difficult to tell why the Great-crested Fly-catcher 

 uses the cast-off skins of snakes in building its 

 nests ; but, certainly, it is not because they are the 

 most abundant materials that it can find. 



If the exact material the birds wish for cannot 

 be found, they select that most like it as a substi- 



* "Natural Selection," p. 215. 



