240 The Bird 



then pried open and eaten. The bill of this bird shows 

 the wear and tear of forcing apart the shells, and it is 

 sometimes slightly bent to one side. The short-billed 

 gulls are denied the power of opening these oj^'sters and 

 mussels, but they sometimes get an unlawful feast by fol- 

 lowing up and robbing the Oyster-catchers of the shells 

 which the latter have opened. 



The bill of the Shell Ibis of India may be likened to 

 an ordinary lemon-squeezer, having a cavity in which 



Fig. 184. — Bill of Oyster-catcher; used for prying open the shells of moUusks. 



the half -lemon rests before it is compressed. When 

 the mandibles of this bird are closely opposed the central 

 portion of the beak gapes slightly. In this cavity the 

 bird firmly holds the shells of the land-snails upon which 

 it feeds, until it can bring the pressure of both mandibles 

 to bear and so crush the shell of the mollusk. 



The asymmetry of the bill — as seen in the Oyster- 

 catcher — is not accidental, but constant, in the Crook- 

 billed Plover of New Zealand. In this bird the bill is 



