The Force of Habit. 



1 1 



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 sliglit 

 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 ^\'hose 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 tlie 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 b)' the greater abundance of its 

 insect pre\', and to the mind of the 

 Swift a chimney cannot bever)' differ- 

 ent from a hollow tree. Its instinct 

 probably docs not lead it to select a 

 dead tree for its roosts or nests be- 

 cause it is a tree, an)- more than it 

 leads it to prefer a sycamore to an 

 oak. What is probabh' inherited is 

 the tendency to seek a dark oi- 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 are 

 scarce. 



The Swift is yet capable of 



Fig. 108. Cock Robin 'A'ith large grasshopper 

 Fig. log. The same bird taking aim. 



ready. 



