CHIMNEY SWIFT 



25 



are so little used that they are small and weak 

 (Fig. 7). They serve mainly as pic- 

 ture-hooks, for the birds hook them 

 over the edge of the nest or into a 

 crack in the chimney, and proceed to 

 go to sleep hanging like pictures on 

 a wall. Even when thus employed, 

 the feet do not have to do the ' whole 

 duty of man ' ; for the tail comes in to 

 act as a prop, being bent under the bird to brace 

 against the wall. Doubtless, by this habit, the 

 end of the tail has gradually 

 lost its feathery character, the 

 webbing being worn off, till now 

 only the stiff, bone-like quills of 

 the feathers remain. These he 

 uses like little awls, to stick into 

 the bricks (Fig. 8). 



As the Swifts get their meals 

 on the wing — they are exclusively insectivorous, 

 and are good enough to eat mainly what are to us 

 either disagreeable or positively injurious insects 

 — they have wide gaping mouths and tiny bills, 

 in marked contrast to the Hummingbirds, which, 

 though in the same order, have with different food 

 habits developed in the opposite direction, and 

 have long probe-like bills to suit their needs 

 (Figs. 9 and 10). 



Another phase of this wonderful adaptation of 

 form to habit is shown when the Swift comes to 



Fig. 8. 



Tail feather of 



Chimney Swift, used 



to brace against 



wall. 



