72 



FOOD 



of insects and small land molluscs. They thus reverse the 

 policy of the frog. The thrush is fond of snails and it will 

 break their shells by pounding them on "sacrificial" stones 

 until they are all in pieces. The shell-fragments are carefully 

 picked off, and the soft body of the snail disappears in one 

 gulp. Certain sea-birds, such as petrels, have in their beaks 

 a mechanism for straining off the smaller marine organisms 



Fig. 22. The Duckbill, Ornithorhynchus anatinus. 



from the sea- water which escapes at the sides of the mouth, 

 just as in certain fishes. 



Fledglings are notoriously voracious and their parents are 

 kept pretty well occupied in catching caterpillars and other 

 insect food for their young. In some cases this food is half 

 digested by the parent and then regurgitated into the gaping 

 mouths of their young. 



Mammals are as varied in their food as birds, but they have 

 one point in common. Their young invariably feed on milk, 



