Life and Instinct 



209 



The Swift is yet capable of adapting its needs to conditions 

 far more unlike those of the ancestral tree, and cases are occa- 

 sionally reported in which it has nested in barns and other dimly 

 lighted buildings. 1 



In at least one respect birds resemble men in their ordinary 



Fig. 127. Male Redwing Blackbird cleaning the nest; photo- 

 graphed under the same conditions as Fig. 126, and illustrating the 

 formation of habit in the daily routine. 



building operations. They make use of the materials at hand, 

 but in the selection of the site for the nest many seem to obey no 

 rule, being ever on the alert to adapt themselves to their lot, 

 and a habit once formed often leads to a steady line of conduct. 

 The diet of an insectivorous bird is extremely varied at all 



* See p. 114 of the first edition of this work. 



