288 BIOLOGY FOR BEGINNERS 



very large powerful heart and well-developed blood vessels. The 

 rate of the heart beat is also very rapid. 



Other Adaptations. Since the bird has devoted its forelegs 

 (arms or wings) to flight, it must needs balance the body on the 

 other pair, a thing which is done by no other group of animals 

 except man. As an adaptation for this, the legs are attached high 

 on the hips, so the body hangs suspended between them like an 

 ice pitcher. This prevents any tendency to lose balance when 

 walking, and permits the bird to bend easily and to pick up food, 

 which has to be done with the beak since the fore limbs cannot 

 be used for prehension. 



Man, although he can balance on two legs, falls easily and has 

 to learn to walk, but no one ever saw a bird fall down, or have 

 any difficulty in walking. The difference is due to the fact that 

 the bulk of man's body is above the point of support at the hips, 

 while that of the bird swings below. 



Perching. The bird usually perches on a support when at rest 

 or asleep and for this purpose has a very curious arrangement. 

 The tendon that doses the claws passes over the leg joints, hence 

 the more the leg is bent, the tighter the claws close up. Thus 

 when the bird settles down on a branch to sleep, the more it relaxes 

 and the more its legs bend, the closer the claws grasp the perch. 

 This and the balancing adaptations enable them to cling to a 

 swinging twig when awake, or to a perch when asleep, with no 

 possibility of falling. 



Neck. The very flexible neck is another adaptation, especially 

 for food-getting, since the wings cannot be used for that purpose. 

 Not only is the bird balanced so as to bend easily but the length 

 of the neck corresponds to that of the legs; because of this the 

 bird can always reach the ground to pick up food. 



Feet. The feet of birds differ widely in structure, depending 

 on the particular purpose required, and are a splendid example of 

 adaptation in themselves. 



The common perching birds have three toes in front and one 

 behind. Climbing birds, like the woodpecker and parrot, have 

 two on each side, while swimming birds may have each toe with a 



