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. 
