231 



VII. 



A THEORY OF BIRDS' NESTS ; 

 SHOWING THE RELATION OF CERTAIN DIFFERENCES OF 

 COLOUR IN FEMALE BIRDS, TO THEIR MODE OF 



NlDIFICATION. 



THE habit of forming a more or less elaborate struc- 

 ture for the reception of their eggs and young, must 

 undoubtedly be looked upon as one of the most re- 

 markable and interesting characteristics of the class of 

 birds. In other classes of vertebrate 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 existence 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 impulse, has 

 had the bad effect of withdrawing attention from the 

 very evident relation that exists between the struc- 

 ture, 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 



