76 THE BOOK OF MIGRATORY BIRDS 



inspirations he may be observed also several times rising 

 on tiptoe an'd puffing out and balancing his body, to feel 

 whether he has thrown enough air into the bones and 

 feathers to float him along. He then crouches back in 

 order to give additional force to his spring, and forthwith 

 leaps up into the air, at the same time rapidly raising his 

 wings from the sides, but keeping the individual feathers 

 close together, like a folded fan, which he takes care not 

 to open till he begins to bring them down. For this 

 purpose he spreads them out to their utmost extent, and 

 then, striking the air with all his force, its resistance 

 pushes him upwards, and he bounds aloft towards his tree- 

 perch, or wherever else he wishes to go. 



The same series of motions first raising the folded 

 wings and then forcibly bringing down the spread wings 

 must be incessantly repeated during the flight of every 

 bird, in the same manner as a swimmer, by pressing the 

 water downwards with his spread hands, keeps himself 

 afloat, and by directing the motion obliquely backwards is 

 thereby pushed forward. It may also be remarked that 

 the swimmer raises his hands before renewing the stroke 

 with the fingers closed, slanting, in a similar way to the 

 bird raising its folded wings, so as to diminish the surface 

 opposed to the resisting medium. 



When birds fly horizontally, their motion is not in a 

 straight line, but obliquely upwards, and they allow the 

 body to come clown to a lower level before a second stroke 

 is made by the wings, so that they move in a succession 

 of curves. To ascend obliquely, the wings must repeat 

 their strokes upon the air in quick succession, and in des- 

 cending obliquely these actions are proportionally slower. 



In birds of prey the form of the wings is very oblique, 

 so that they cannot rise in the air perpendicularly unless 

 they fly against the wind. They have, however, a greater 

 power of horizontal motion than other birds, because the 

 extreme parts of the wings are long, and the ends of the 

 feathers lap over each other, which opposes a uniform 

 resistance to the air, while in other birds the air passes 



