FUNCTIONS. 
221 
again subdivided into those which dive solely by means 
of their feet, and those which also use their wings 
for that purpose. The former do not dive to any great 
depth while in search of food at the bottom; their 
prey mainly consists of aquatic insects and molluscs. 
The latter, among which we find the Eider Duck, are 
the best adapted for this purpose; they dive a depth 
of several hundred ells, and feed upon the different 
shell-fish they find on the bottom, besides young fish 
and spawn. In agility they are surpassed by the 
Mergansers, the most active of all the tooth-billed 
divers. These last dive, it is true, only by means of 
their feet, and do not go down to so great a depth 
as the Eider Duck; but they feed almost exclusively 
on fish, which kind of chase requires the most active 
swimming and diving powers. The saw-billed divers 
are, to a certain extent, pigs among Water-fowl, rooting 
and stirring up the ground, anywhere and everywhere, 
while seeking food. 
The long-winged aquatic birds are possessed of quite 
a different accomplishment ; with them swimming is a 
secondary business, and flying, on the contrary, their 
principal power. They obtain their food mainly by 
partial diving, and that at a distance from the water’s 
surface; and in this art different degrees of perfection 
may be observed. The Skuas are, as far as mere 
strength goes, well able to provide for themselves, but 
always prefer feeding at the expense of their neigh¬ 
bours in the most graceless manner possible. The true 
Gulls are, to a certain degree, bunglers in the art of 
catching, and the larger more so than the smaller. 
Their principal nourishment consists of the refuse of 
the sea, and offal thrown from ships, which they find 
