102 NATURAL SELECTION v 



form and structure of nests, that vary so much, and are so 

 wonderfully adapted to the wants and habits of each species ; 

 how are these to be accounted for except by instinct? I 

 reply : They may be in a great measure explained by the 

 general habits of the species, the nature of the tools they 

 have to work with, and the materials they can most easily 

 obtain, with the very simplest adaptations of means to an 

 end, quite within the mental capacities of birds. The delicacy 

 and perfection of the nest will bear a direct relation to the 

 size of the bird, its structure and habits. That of the wren 

 or the humming-bird is perhaps not finer or more beautiful in 

 proportion than that of the blackbird, the magpie, or the 

 crow. The wren, having a slender beak, long legs, and great 

 activity, is able with great ease to form a well- woven nest of 

 the finest materials, and places it in thickets and hedgerows 

 which it frequents in its search for food. The titmouse, 

 haunting fruit-trees and walls, and searching in cracks and 

 crannies for insects, is naturally led to build in holes where it 

 has shelter and security; while its great activity, and the 

 perfection of its tools (bill and feet) enable it readily to form 

 a beautiful receptacle for its eggs and young. Pigeons 

 having heavy bodies and weak feet and bills (imperfect tools 

 for forming a delicate structure) build rude, flat nests of 

 sticks, laid across strong branches, which will bear their 

 weight and that of their bulky young. They can do no 

 better. The Caprimulgidae have the most imperfect tools of 

 all, feet that will not support them except on a flat surface 

 (for they cannot truly perch) and a bill excessively broad, 

 short, and weak, and almost hidden by feathers and bristles. 

 They cannot build a nest of twigs or fibres, hair or moss, like 

 other birds, and they therefore generally dispense with one 

 altogether, laying their eggs on the bare ground, or on the 

 stump or flat limb of a tree. The clumsy hooked bills, short 

 necks and feet, and heavy bodies of parrots, render them 

 quite incapable of building a nest like most other birds. 

 They cannot climb up a branch without using both bill and 

 feet ; they cannot even turn round on a perch without holding 

 on with their bill. How, then, could they inlay, or weave, 

 or twist the materials of a nest ? Consequently they all lay 

 in holes of trees, the tops of rotten stumps, or in deserted 



