ADAPTATION TO HAUNTS 145 



parrots, and the way in which parrots may hang themselves 

 up by their strong curved bills is familiar. Hilzheimer 

 points out that the Grey-headed Parrot and the Woodpecker 

 press their stiff tail against the branch even when they are 

 climbing along underneath it with their back to the ground, 

 and suggests that it has a directive rudder function, perhaps 

 connected with the marked shortening of the legs in climbing 

 birds. We see, then, that adaptation to climbing may affect 

 the claws, the toes, the beak, and the tail. 



§ 2. Aquatic Life 



Many birds that are not aquatic can swim, as has been 

 observed in pigeons and quails, the buoyancy of the body 

 doubtless helping ; and the dipper or water-ouzel, which 

 swims with its wings against the stream or walks along the 

 bed of the river gripping the stones with its toes, is a notable 

 instance of what a creature can do in the way of mastering 

 a new medium without having any special adaptation thereto. 

 For the dipper might almost be called an aquatic wren. 



Yet there are many consummate adaptations facilitating 

 aquatic Hfe. (a) The legs are often very far back, as in 

 diver, grebe, and puffin, sometimes so far back that terrestrial 

 progression is difficult. Thus the penguins tumble down 

 on all fours on the snow, and toboggan along using both 

 " wings " and feet. The far back position of the legs 

 enables the aquatic bird to strike backwards behind the 

 body with little waste of power. The position recalls the 

 propeller of a steamship or sculling from the stern of a 

 boat. 



(b) Very familiar is the utility of the webbed foot, a 

 simple adaptation appearing first in frogs. But it is inte- 

 resting to notice how it occurs in birds which are but distantly 

 related to one another. Thus the Storm Petrel is not 

 related to the Gull Tribe, nor the Puffin to the Penguin, 

 nor the Duck to the Diver, though all are web-footed. The 

 adaptation of the web-foot is not restricted to affording a 

 continuous and resistant surface for striking the water ; 



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