Nest-building, Incubation, and Migration. 235 



frequently birds, as Mr. Headley says, in his interesting 

 book on " The Structure and Life of Birds," * " adapt 

 themselves to new situations. The swallow and the 

 house-martin have availed themselves of barns and houses. 

 The palm-swift in Jamaica, till 1854, always built in 

 palms. But in Spanish Town, when two cocoanut-palms 

 were blown down, they drove out the swallows from 

 the piazza of the House of Assembly and built between 

 the angles formed by the beams and joists. In America 

 the tailor-bird now uses thread and worsted for its nest, 

 instead of wool and horsehair, and wool and horsehair 

 may originally have been substitutes for vegetable fibres 

 and grasses. In Calcutta an unconventional crow once 

 made its nest of soda-water bottle wires, which it picked 

 up in a back yard. In districts liable to floods, moorhens 

 often build in trees. In New Zealand the paradise 

 ducks, which usually build on the ground near rivers, 

 have been known, where disturbed, to build on the tops 

 of high trees, and to bring down their young on their 

 backs to the water." But all this, as Mr. Headley points 

 out, does not show that birds have not a nest-building 

 instinct of congenital definiteness. It only shows that, as 

 we have had occasion to note in many other cases, their 

 instinct is modifiable by intelligence and experience. 

 The habit may well be built upon an instinctive basis, and 

 receive its final touches through individual experience. 



Mr. Jenner Weir, writing to Darwin in 1868, says t •" 

 " The more I reflect on Mr. Wallace's theory, that birds 

 learn to make their nests because they have themselves 

 been reared in one,| the less inclined do I feel to agree 



* Pages 334, 335. 



t Quoted in Romanes' ■ Mental Evolution in Animals," p. 226. 

 X This was Mr. Wallace's earlier view ; his later view introduces 

 tradition in a broader sense. 



