i62 THE STRUCTURE AND LIFE OF BIRDS char 



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 



Fig. 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. 



