380 BRITISH BIRDS. 



down, and at once the wool was left and the cotton seized ; 

 finally, down was supplied, and with this the nest was 

 completed, but withal typical, in shape and neatness of 

 workmanship, of the Goldfinch. 



By way of contrast we may quote the case of the Yellow- 

 hammer which laid its eggs on the bare gromid and 

 successfully hatched them ! 



But apart from the question of the choice of materials — 

 the individual taste between more or less attractive and 

 suitable objects to be employed — we have to consider the 

 evolution of the nursery itself, as distinct from the com- 

 ponent elements in its fabrication. And here natural 

 selection must be regarded as the prime factor at work. 

 We do not suppose, of course, that the origin of nest- 

 building- is to be traced thereto. The nest-building instinct 

 was due rather to a "fortuitous variation" — a happy 

 .inspiration, due, as we have already remarked, to the 

 desire to secure increased comfort when brooding on cold, 

 damp ground. Over elaboration in the size and character 

 of the nest has ahvays been controlled by selection, and 

 this factor has been most active in the case of ground- 

 breeding birds where cover is practically wanting, as in 

 the case of the Ringed Plover. 



Assuming that the habit of nest-building began as we 

 have suggested, it is easy to see how arboreal nests 

 gradually came into being, for a bird which had learned 

 the art of constructing a jjlatform of sticks, or other 

 materials, on the ground w^ould — if driven, from one cause 

 or another to . seek safety during incubation in trees or 

 bushes — adopt the same device in the new situation. And 

 from this the passage to the more elaborate nest is easy. 



Such are the broad outlines of the possible evolution of 

 nests. Later we propose to return to this subject, filling 

 up obvious gaps. Meanwhile, we would suggest that bird- 

 photographers should turn their attention to the different 

 types of nests, and the difi:'erent choice of nest-building 

 materials, exhibited by difi^erent individuals of the same 

 species among our native birds. 



