Io8 ANIMALS OF LAND AND SEA 



If the wings cease their action the body drops almost instantly. 

 A small bird can approach a perch at full speed and alight upon 

 it with very little voluntary checking of its momentum, but 

 a heavy bird must expend much energy in checking its for- 

 ward impetus before it can alight with safety. The wings 

 of large and heavy birds serve chiefly to maintain speed, the 

 height being maintained by the momentum and the kiting 

 effect of the body upon the air. The wings of small and light 

 birds must constantly lift as well as maintain momentum — 

 or rather they must constantly lift the bird and pull it forward. 

 This is the reason why the larger the bird the smaller the wings; 

 but the large birds, while they fly with much less effort than 

 the small birds in spite of their smaller wings, have great 

 difficulty in getting started and in stopping. From this it 

 naturally follows that while small birds are found everywhere 

 in all situations, large strong ffying birds are mostly confined 

 to the sea and to very open regions where they can arise and 

 alight with safety. 



The speed at which birds fly varies very much, but it is not 

 so great as is commonly supposed. You can easily prove this 

 for yourself by pacing them in an automobile along a country 

 road. Only a few birds can fly as fast as the fastest express 

 trains, and none can go so fast as the speedier aeroplanes. 

 Wild ducks and geese have been found to travel on their 

 migrations at a rate of between 44 and 48 miles an hour. 

 Homing pigeons usually travel at between 50 and 55 miles an 

 hour. While some swifts may attain a speed as great as 100 

 miles an hour, most of our smaller birds fly at a rate of be- 

 tween 25 and 28 miles an hour, or at about the average speed 

 maintained by an automobile. 



The power of flight and the possibility of moving rapidly 

 from place to place high above such obstacles as water, trees, 

 fences, hills, etc., permits the birds to wander about from season 

 to season, visiting now one region now another in search of 

 food. In the autumn many of our common birds, like the 

 swifts, the swallows, the flycatchers and the warblers disappear 



