810 BRITAIN^S BIRDS AND THEIR NESTS. 



The situation of the nest is almost always in the fork of a 

 tree, rarely in bushes, and only exceptionally on the ground 

 or in a hole in a wall or among rocks. As often as not 

 there is no attempt at concealment. The nest itself is 

 made of grasses and lichens on a foundation of mud, and 

 is lined with dry grass. There is nothing in the way 

 of mud-lining like that in the nest of the Song-Thrush. 

 It is a very interesting question why three closely allied 

 birds like the Song-Thrush, the Mistle-Thrush, and the 

 Blackbird should build different tjipes of nests, when 

 they inhabit the same area, are under the same con- 

 ditions, and have similar habits and wants. It may be 

 noticed, or, better, experimentally proved, that an indi- 

 vidual bird is partly influenced by the materials which 

 happen to be most easily prociired. Nevertheless, how- 

 ever much it may adapt its nest to suit the supply of 

 materials and the circumstances of the site, the nest 

 almost invariably shows certain well-marked characteristics 

 typical of the species. Why does a bird adhere to the 

 species-type of nest ? It is, of course, a case of inborn 

 instinct ; but we do not really know what that is. And 

 why should there be a species-type at all ? And why 

 should one species-type differ from another, as in the 

 case in point ? It may to some extent be a case of 

 allied forms avoiding competition by developing in 

 different directions, as in the case of the Tits' feeding 

 habits already discussed ; but it is more difficult to 

 understand the application of the principle here. The 

 points, in fact, are very far from settled, and the 

 psychology of nest-bmlding is a subject of the future. 

 Before theories can profitably be matured, further 

 systematic study of the subject is needed. Therefore 

 we recommend the bird - nester to study, note, and 

 photograph nests both normal and abnormal. Hitherto 



