376 THE THRUSH FAMILY 



quantities about the ground. To get the grass, however, it was 

 necessary to quit the thicket and fly to the open. In a plantation 

 of young spruce firs I found six thrushes' nests, two composed chiefly 

 of bracken, three of grass, and one of moss and twigs. Bracken, but 

 not grass, was available inside the plantation. From these examples 

 it is clear that the bird does not necessarily choose the most accessible 

 material, and that, when two or more kinds are equally accessible, 

 different birds will make different choices. The explanation may lie in 

 the fact that birds, like human beings, are creatures of habit ; they are 

 moved by the Wings of Custom, if not by its Wheels. It may be that 

 the young bird, when constructing its first nest, takes the first suitable 

 material that it finds. Its tendency will be to return to the same place 

 next season, and also to seek the same material just where it sought it 

 before. That birds do return to the same nesting-place year after year 

 has been proved in the case of more than one species. And a hen 

 blackbird, which built three years in succession in the same corner of 

 a garden, made the outside of the first nest (1906) of dry grass, short 

 straws, roots, paper; the second (1907) of dry grass, short straws, 

 roots and other material not mentioned ; the third (1908) of dry grass, 

 roots, leaves, paper. 1 If now, a nest built, let us suppose, of dry grass 

 in some tree in the open is destroyed, and the bird then constructs 

 another in an adjacent thicket, the force of custom may well lead it 

 to fly out and away to the old spot for its dry grass in spite of the 

 fact that doing so demands more time and labour than taking the 

 moss that lies in abundance right under its new site. Having been 

 accustomed to build its nest of grass, the bird continues to use 

 the same material whether it be the most accessible or not. This 

 theory, which would apply equally to cases in which both sexes took 

 part in building is plausible enough. But it requires to be verified ; 

 and this could be done without much difficulty by marking pairs of 

 birds, using leg-rings of different colours, and watching their pro- 

 ceedings from year to year. 



1 The pair were recognised by a peculiarity in the song of the cock. See note 3, p. 372. 



