78 BIRDS RISING FROM THE GROUND 

 feathers, subjected to the air-pressure, flatten 

 up against one another, but are supported by 

 graduated tiers of feathers at the back, thus 

 effectually stopping the air ; at the same time 

 the wing yields to the flattening process, which 

 naturally tends to increase the surface area. 

 Therefore it is obvious that when the wings 

 are actuated in the manner described, uplifting 

 force is enormously developed. 



Presuming the above description virtually 

 correct, we understand how a bird rises from 

 the ground ; the angle at which it rises, how- 

 ever, depends on the species, and also on the 

 nature of the place it happens to be in at the 

 time. For instance, a woodcock, surrounded by 

 dense covert, rises perpendicularly until clearing 

 the tree-tops, and does so with great rapidity. 

 Duck, especially teal, fly straight up from a 

 reed-bed, or from water overhung by trees. 



On the other hand, a swan, like an aero- 

 plane, must " taxi " along the surface before 

 it can rise. The reason for this is that the 

 weight of the bird counteracts any attempt at 

 a spring from the water in the first instance, 

 consequently the wings lose half their lifting 

 power by coming in contact with the water ; 

 but once clear it takes an upward inclination, 

 though this bird can never rise directly above 

 a certain angle on account of its weight. 



