[a3 The Bird 
cular as that of the Hoatzin, yet there must be powerful 
movements of the walls, for the mice and birds are de- 
nuded of hair and feathers and even the bones are in 
some way removed from the body, and all are ejected 
in a neat oval ball. 
If we find some hollow tree where an owl has its 
Fic. 103.—Keel of Hoatzin, repressed by crop. 
regular sleeping-place, many of these pellets may be 
found on the ground below, showing the results of each 
night’s hunting. The skulls in them are often in such 
perfect condition that the species of rodents may be 
identified. Besides allowing the bird conveniently to get 
tid of the indigestible portions of its food, this habit 
seems to be necessary to the health of the bird. In 
