Life and Instinct 207 



branch had been drawn down about a foot by means of a cord, 

 but was not otherwise disturbed. 



In sitting over the eggs or young, birds quickly acquire the 

 habit of facing the same way, in the direction of habitual ap- 

 proach, and in going to sleep, of twisting the head habitually to 

 the same side. 



In cleaning the nest the attitude is frequently the same in 

 successive visits, the birds often clasping the same twigs, so 

 that a number of photographs of the act taken without moving 

 the camera may be so nearly identical that only the most careful 

 inspection will reveal the least difference in pose or position. 



While engaged in studying some Redwing Blackbirds in 

 July the weather was hot, and the young had to be brooded 

 almost constantly. The female would sit on the nest, often 

 with back to the tent, with feathers erect and mouth open in 

 her efforts to keep cool. Suddenly the shriek of a steam whistle 

 sounded the hour of noon at a mill scarcely three rods away. 

 It startled me, but the bird did not budge a feather. It is not 

 difficult to imagine that her first experience with this instrument 

 of torture was quite different in its result, but the case illus- 

 trates the ease with which birds become quickly accustomed to 

 strange and uncouth sounds, when, as sometimes happens, they 

 place their nests in a saw-mill a few feet from the buzzing saw 

 or above the grinding trolley cars of a city street. 



Every animal must adapt itself in some measure to changes 

 in its surroundings, and with birds this necessity is well ex- 

 pressed in the nest, the position, materials, and construction of 

 which are subject to incessant change, and in the diet. The 

 change in nesting habit may be slight or of a very marked 

 character, as when the common type of architecture is aban- 

 doned, or a distinct nest-structure wanting. Only a single ex- 

 ample of change in nesting habits need now be considered since 

 the facts are matters of common observation. 



The Swift of this country is often quoted as one of the most 

 remarkable examples of birds whose nesting habits have changed 

 in recent times. Formerly breeding in hollow trees and still 

 doing so in places remote from mankind, it now attaches its little 



