STABILITY 33 



more so. But the area varies so much, according 

 as they are expanded or not, that I have found 

 it very difficult to give measurements. However, 

 we can bear in mind that the tail of the Sparrow- 

 Hawk, for example, is not only very long but very 

 broad, whereas the tail of the Duck is not only short, 

 but narrow and weak, its inefficiency being even 

 more marked than its small size. 



It is noteworthy that the bird which stands 

 at the head of the list as being remarkable for size 

 of tail is not a particularly short-legged bird. Two 

 cock Sparrow-Hawks, of which I took measurements, 

 had each legs 7 inches long (the toes being included). 

 However, the legs are very thin, as if not intended 

 for standing, but, armed as they are with long, 

 efficient claws, for seizing a victim. It is often 

 maintained that Hawks hang their legs down during 

 flight, but this is certainly not usually the case. 

 However, they could on occasion be lowered, to give 

 the tail freer play, without much affecting the bird's 

 equilibrium. 



The main function of the tail is to prevent loss 

 of equilibrium, and when large it plays its part 

 wonderfully well. In spite of its great expanse, 

 its weight is a negligible quantity and its working 

 is splendidly prompt. Evolution has done wonders 

 in thus metamorphosing the long, heavy tail of the 

 bird's reptilian ancestor. A number of vertebrae 

 have been compressed to form the pygostyle, the 

 small bony base of this wonderful piece of machinery. 

 What weight there is is almost all accounted for 

 by this little bone and the muscles that move the 

 large spread of feathers. The muscles have the 



