BIRDS 



263 



posterior toe, which is curved also. The tendons of the leg and 

 foot are self-locking. In the flamingoes and other birds, which 

 do not perch, balancing appears to be automatic, for these 

 birds are able to maintain an upright position even when asleep. 

 In swallows, rapid and untiring flyers, the feet are small. In 

 the case of the parrots, where the foot is used for holding food, 

 climbing, and clinging, we find the four-clawed toes arranged 

 two in front and two behind. 



The form of the bill shows adaptation to a wonderful degree, 

 varying greatly according to the habits of the bird. A duck has a 

 flat bill for pushing through the mud and straining out the food ; 

 a bird of prey has a curved or hooked beak for tearing ; the wood- 

 pecker has a sharp, straight bill for piercing the bark of trees in 

 search of the insect larvae underneath. Birds do not have teeth. 

 The edge of the bill may 

 appear to be toothed, as in 

 some fish-eating birds ; how- 

 ever, the projections are not 

 true teeth. Frequently the 

 tongue has sharp, toothlike 

 edges which serve the same 

 purpose as the curved teeth 

 of the frog or snake. 



Respiration. The rate of 

 respiration, of heartbeat, and 

 the body temperature are all 

 higher in the bird than in 

 man. Man breathes sixteen 

 or eighteen times a minute. 

 Birds breathe from twenty to 

 sixty times a minute. The 

 lungs of birds are connected 

 to large air sacs, found in the 

 abdominal cavity of the body, 

 which ,hold reserve air and 

 help make the bird lighter. A bird may be compared to a high- 

 pressure steam engine. In order to release the energy which it 







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Wright Pierce 

 What are the adaptations of the Golden eagle ? 



