THE BOOK OF MIGRATORY BIRDS 75 



the rapidity of the descent, permit it to alight gently on 

 the earth. It is by the assistance of the tail that certain 

 birds are enabled to descend with precipitation from a 

 great height. By spreading the tail and closing the wings 

 they cause the action of the air to predominate on the hind 

 part of the body, which directs the fore part downwards 

 and leaves it entirely to the influence of gravitation. The 

 tail may strengthen the action of the wing by moving 

 towards the same side." 



Though it is obvious that birds could not fly without 

 wings, yet the peculiar mechanism of the process is not, 

 as it were, generally understood. It is no uncommon 

 thing to see a goose, while walking on a common, spread 

 out its wings to their full extent, and begin to flap them 

 about with great violence, and yet the bird is not thereby 

 moved an inch from the ground a circumstance that, 

 without inquiry into the cause, seems contrary to what 

 might have been anticipated. 



By observing the difference between this ground-flying 

 if I may call it so of the goose and the actual rising 

 of a pheasant, for example, into the air, one may arrive 

 at the reason w r hy the goose does not, while the pheasant 

 does, ascend. The goose, it may be remarked, keeps her 

 wings spread both in the upward and downward motion, 

 and, consequently, the resistance of the air in the first case 

 will press her body downwards rather than upwards; 

 while, as her evident intention is not to rise above the 

 ground, she forcibly expels the air from her air-cells, as 

 may be inferred from the screaming always uttered on 

 those occasions, and caused, one has reason to believe, by 

 the forcible expulsion of the air. Her body is thus rendered 

 specifically heavier, and, consequently, resists the upward 

 impulse given by the downward motion of the wings. 

 The pheasant, on the other hand, instead of expelling the 

 air, takes a deep inspiration, increasing the size of the 

 body as much as possible, inflating at the same time the 

 wing feathers and bulging them outwards without 

 separating their tips from the sides. While taking deep 



