Jotirnal of Travel mid Natural History 73 



A THEORY OF BIRDS' NESTS: 



SHEWING THE RELATION OF CERTAIN SEXUAL DIFFERENCES OF 

 COLOUR IN BIRDS TO THEIR MODE OF NIDIFICATION. 



By Alfred R. Wallace, F.Z.S., &c. 



ONE of the most remarkable and interesting characteristics of 

 birds, is the habit which the great majority of them possess 

 of forming a more or less elaborate structure for the reception of 

 their eggs and young. 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 

 structure, habits, and intelligence of birds, and the kind of nest 

 they construct. It will be necessary to point out a few of these 

 primary relations, since they have an important bearing on the 

 subject we are about to discuss. 



A considerable number of birds form no nest whatever, but lay 

 their eggs and hatch their young upon the bare ground. Such are 

 a large portion of the wading and swimming birds, many of the 

 Gallinaceae, and, among perching birds, almost all the Capri- 

 mulgidae. These may be considered to form one extremity of the 

 scale, while such birds as the Icteridse, the weaver birds, and the 

 wren, which build elaborately woven, domed, or pensile nests, are 

 at the other. Now, the general structure and mode of life of the 

 birds in question, almost of itself explains this difference. The 

 large head and excessively small broad bill of the Caprimulgidre, 

 and their small weak feet, with scarcely any power of grasping, 

 render them physically unable to weave together grass, or moss, or 

 fibres, or wool, into a strong and well-constructed nest. The feet 

 of terns or of sandpipers are equally ill adapted to this purpose ; 

 and while engaged in seeking their food, they chiefly frequent 

 places where no materials for making a nest are to be found. 

 Those birds, on the other hand, which form the most elaborate 



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