Chap. 36 BIRDS — CONQUEST OF THE AIR 737 



of birds are covered with strikingly reptilian scales. The heel is the first back- 

 ward bending joint above the part of the foot that rests upon the ground. The 

 forward-bending knee is covered with feathers (Fig. 36.10). 



Perching birds are the crows, thrushes, warblers, swallows, larks, and others, 

 numbering more than half of the group. All of them have muscles so arranged 

 that sitting on a perch is automatic with holding to it with the feet. This 

 efficiency is due to the remarkable strength in the tendons which run through 

 each toe and enable it to clasp and to hold and balance the bird on its 

 branch. In all this, the hind toe is essential (Fig. 36.14). There are specialists 

 among the perchers. With the same arrangement of toes, American wood- 

 peckers clutch the surface of a tree trunk, lean back on their tails and hammer 

 with their bills. 



A nuthatch climbs down and around tree trunks as easily as up, with 

 stops to pick up insects, and no help from its tail. Swallows have little feet and 

 telephone wires are their favorite perches. The feet of chimney swifts are still 

 smaller, yet weak as its feet may be, a young swift can cling fast to the vertical 

 face of a brick chimney. Owls are as flexible as many human "liberals," being 

 able to move their outer toes backward or forward and perch like a robin or 

 to put two toes before and two behind Hke a parrot. 



A bird's feet tell where it lives (Figs. 36.8, 36.9). Herons that wade about 

 the shallow margins of ponds and streams have long legs that Hft their bodies 



Perching 

 Robin 



Grasping, Tearing 

 Howk 



Scratching Earth 

 Pheasant 



Climbing 

 Woodpecker 



Swimming 

 Duck 



L^- 



•iP 



•?" 



^'%^^^^ 



Stockinged by Feathers: 

 Snow Arctic Ptarmigan 



Fig. 36.8. The shapes of birds' feet are correlated with their habits and sur- 

 roundings. Their feet and beaks are often used like hands in finding food and 

 building nests. 



