30 ] How to Understand the Birds 



have keen vision, but some of them are remarkably well adapted 

 for seeing objects both far away and at close range. Thus a hawk 

 flying so high that it would appear as a mere speck to us, may 

 look down and see a rabbit or even a mouse on the ground! The 

 hawk has two centers of vision, and as it swoops down from the 

 heights, its vision shifts from one center to the other so that its 

 eyes are adjusted for short-range work when it seizes its prey. 



Yet most birds, despite their sharp eyes, do not have bifocal 

 vision like the hawk. One consequence is that they do not detect 

 telephone and telegraph wires, and many birds are injured or 

 killed every year by collision with such obstacles. 



Among birds there is quite a bit of variety in the color of the 

 iris; it may be brown, gray, blue, yellow, white, pink, purple, 

 green, and even red. The red-eyed vireo takes the first part of 

 its name from this striking feature. The hen, which is ideal for 

 bird study, has a yellow iris. It is equipped with an eyelid that 

 shuts out vision, coming up from the bottom of the eye, however, 

 rather than down from the top. It also has another kind of eyelid 

 -a film that moves across the eye from the inside corner to the 

 outer side. 



You may escape questioning about a bird's hearing ability 

 because their ears are fairly well hidden. Then suddenly this 

 very fact may be the basis for a query from your young observer: 



"How can that bird hear? I don't see any ears!" 



Except for the owls, which have noticeable "ear tufts," the 

 ear of a bird is no more than a hole, rather well covered with 

 feathers, on the side of its head. Yet a bird's hearing is just as 

 remarkable as its sight perhaps even more remarkable. Walking 

 in a field or forest you may notice how the snapping of a small 

 twig will startle and put to flight a bird that is a considerable 

 distance away. And when you see a robin cocking its head and 

 realize it is listening for an earthworm under the surface of the 

 ground, you develop a well-deserved respect for birds' hearing. 



How Birds Fly 



"How do birds fly?" is a question that most children ask at 

 some time. The child may accompany his query with a leap into 



