162 THE STRUCTURE AND LIFE OF BIRDS cuHap. 
In all birds the upper beak moves slightly, in parrots 
freely. It is always growing, but constant friction 
against hard substances and of the upper against the 
lower beak prevents this from being apparent. The 
duck’s beak acts as a strainer: the whale, in the so- 
called whalebone, has a similar instrument which lets 
the water pass away while retaining the food. The 
hs 
Fic. 42. 
(1), Beak of Falcon showing toothed edge ; (2), of Duck showing strainer. 
beaks of Humming-birds are bent or otherwise shaped 
so as to suit the forms of particular flowers down the 
corollas of which they dive for the honey. Falcons and 
other birds of prey have their upper beaks cut into 
teeth, an assistance in tearing their food. And in con- 
nection with this, it must be remembered that flesh- 
eating birds have nothing worthy of the name of a 
gizzard. Hence some tearing of the food is desirable. 
