VARIETIES OF WING AND OF FLIGHT 99 



great breadth of his wings at their outer extremities 

 may, as I have said, account for his well-known 

 tactics and the skill with which he carries them out 

 (see PI. xiv). 



The pace of the stroke varies very much in different 

 species, a subject on which I have already said 

 something.* A Stork goes along in very leisurely 

 style, taking no more strokes per minute than a 

 Heron, i.e. some 130, or even less. But one must 

 not imagine that little force is being used. The 

 Stork's wings are very long, and the upward bending 

 of the primary feathers shows the great rapidity 

 with which they are being driven through the air. 

 It is the birds with big, long wings that have the 

 slowest stroke. The great length of wing makes 

 each stroke very effective, and the slow beats that we 

 see so easily are not at all slow towards the wings' 

 farther end. Heavy birds that have short wings 

 have to take very rapid and very long strokes ; the 

 wing is lifted fairly high in horizontal flight, very 

 high when they are rising, and descends till the tip 

 has described a large segment of a circle. The Duck 

 is a familiar instance of this style of flight. His long, 

 strong strokes send him hurtling through the air 

 with ponderous momentum. The same style of 

 flight is carried to its extreme by the Guillemots, 

 Razorbills, Puffins, and other diving birds which use 

 their wings in swimming. It would be no good trying 

 to fly under water with big, long wings ; after the 

 completion of a stroke, to get the wing back into 

 position for the next would be a difficult operation. 

 These birds, then, have the largest wings with which 



* See p. 50. 



H 2 



