GENERAL HABITS 191 



swimming only. This aquatic progress is 

 usually associated with webbed or lobbed feet, 

 but some species are equally expert at swim- 

 ming and diving with no such appliances. The 

 Water-Hens furnish us with a capital instance 

 of this. Another very curious habit of certain 

 aquatic birds (notably Divers and Grebes) is 

 that of gradually sinking the body into the 

 water until all but the beak or the head is sub- 

 merged. Lastly, we may mention the peculiar 

 motions of certain Petrels, these birds frequently 

 running, as it were, over the smooth surface of 

 the ocean waves, pattering the water with their 

 webbed feet. 



Now a few words concerning the Food of 

 Birds and the various methods of obtaining it. 

 Our study of the structure of birds has already 

 suggested the great variation in the food which 

 must prevail among the many thousands of 

 species. The diverse way of obtaining it, the 

 immense amount of modification in the struc- 

 ture of the bill and feet, to say nothing of 

 the internal organs of digestion, are none the 

 less interesting. Generally speaking, the bill of 

 a bird is a sure indication of the general food 

 of a species, whilst the feet and wings suggest 

 to some extent the method of securing it. The 



