STABILITY 31 



great difficulty in detecting, and but for the camera 

 we should have had to own that, though the bird 

 could hardly dispense with this method of balancing 

 and steering, we could get no absolutely conclu- 

 sive optical evidence. For fore-and-aft balance the 

 means employed vary very much according to the 

 build of the particular bird. Long-necked birds can 

 move their centre of gravity forward and backward 

 by extending or bending their necks. Ducks and 

 Geese usually carry theirs stretched out, Herons 

 habitually make a crook in theirs. Long necks 

 are usually correlated with long legs, and long legs 

 are no less serviceable in the matter of balance. 

 This is shown by the fact that the long-legged have 

 usually small, short tails, the long legs to some extent 

 taking the place of the tail as balancers. A Flamingo, 

 to take a conspicuous example, having legs of 

 enormous length and a neck to match, has no need 

 of much tail to regulate his fore-and-aft balance. A 

 very little extension or retraction of legs or neck 

 will set matters right if they are going wrong. But 

 not only do long legs make a great expanse of tail 

 unnecessary for balancing purposes, they must in- 

 evitably hamper its movements if it is to be pulled 

 downward with a view to checking speed or steering 

 to right or left. It may well be that this necessary 

 inefficiency of tail is in part the cause of the compara- 

 tively clumsy steering of these big, heavy-legged 

 birds. 



It can be shown, too, that for purposes of balance 

 webbed feet very probably play a part of some 

 importance. Not only are they fairly heavy, but 

 they can be used as the tail is used, though not so 



