VI 



A THEORY OF BIRDS' NESTS, SHOWING THE RELATION OF 



CERTAIN DIFFERENCES OF COLOUR IN FEMALE BIRDS 



TO THEIR MODE OF NIDIFICATION 1 



THE habit of forming a more or less elaborate structure for 

 the reception of their eggs and young must undoubtedly be 

 looked upon as one of the most remarkable and interesting 

 characteristics of the class of birds. In other classes of verte- 

 brate animals, such structures are few and exceptional, and 

 never attain to the same degree of completeness and beauty. 

 Birds' nests have, accordingly, attracted much attention, and 

 have furnished one of the stock arguments to prove the exist- 

 ence of a blind but unerring instinct in the lower animals. 

 The very general belief that every bird is enabled to build its 

 nest, not by the ordinary faculties of observation, memory, 

 and imitation, but by means of some innate and mysterious im- 

 pulse, has had the bad effect of withdrawing attention from the 

 very evident relation that exists between the structure, habits, 

 and intelligence of birds, and the kind of nests they construct. 



In the preceding essay I have detailed several of these 

 relations, and they teach us that a consideration of the 

 structure, the food, and other specialities of a bird's existence 

 will give a clue, and sometimes a very complete one, to the 

 reason why it builds its nest of certain materials, in a definite 

 situation, and in a more or less elaborate manner. 



I now propose to consider the question from a more general 

 point of view, and to discuss its application to some important 

 problems in the natural history of birds. 



1 Published in the Journal of Travel and Natural History, No. 2 ; 

 reprinted in Contributions, etc., with considerable additions and corrections. 



