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 Pl. xtv). 
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. 
ts Dele 
