The Force of Habit. 



Every animal must adapt itself 

 in some measure to changes in its 

 surroundings, and with birds this 

 power is well expressed in the nest, 

 the position, materials, and construc- 

 tion of which are subject to incessant 

 change. The change may be slight 

 or of a very marked character, as 

 when the common type of archi- 

 tecture is abandoned, or a distinct 

 nest-structure wanting. Only a few 

 examples of change in nesting habits 

 need 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 wicker crates to the inside of 

 chimneys. From the standpoint of 

 the Swift the change has really been 

 very slight, and had it not become so 

 widespread it would have attracted 

 little attention. This bird was proba- 

 bly drawn to the town and open coun- 

 try by the greater abundance of its 

 insect prey, and to the mind of the 

 Swift a chimney cannot be very differ- 

 ent from a hollow tree. Its instinct 

 probably does not lead it to select a 

 dead tree for its roosts or nests be- 

 cause it is a tree, any more than it 

 leads it to prefer a sycamore to an 

 oak. What is probably inherited is 

 the tendency to seek a dark or cav- 

 ernous place with easy entrance and 

 exit. The chimney which emits no 

 smoke in summer and usually stands 

 in the open, fulfils every requirement 

 in places where hollow trees arc- 

 scarce. 



The Swift is yet capable <>f 



K- 108. Cock Robin with large grasshopper ready. 

 Fig. 109. The same bird taking aim. 



