28 
BIRD-LIFE. 
contrary, shaken loose, and the bird ascends without the 
rowing motion; while diving and swimming under water 
the bird elongates itself as much as possible; many use 
only their feet for the forward motion, though others use 
the wings also. The Cormorant, Eiderduck and Diver 
use the combined method to enable them to reach the 
surface more rapidly. Flying Divers live almost, without 
exception, on the sea, and are capable of diving to an 
immense depth below the surface ; they use their wings 
as fish do their fins. It is wonderful to see our Moorhen 
( Stagnicola ) swim and dive, although it appears scarcely 
fitted at all for the purpose. With some birds the tail is 
used as a rudder, and in that case it is always long, stiff 
and elastic; though we cannot determine the assistance 
it affords in diving, inasmuch as the true fishing-birds, 
the Penguin and Great Auk, possess scarcely any tail at 
all; on this account, indeed, we find their feet and wings 
singularly developed. 
The depth to which Divers can descend, and the length 
of time they can stay under water, varies very much. 
Among northern birds the Eiderduck dives the deepest, 
and remains longest under water. From a knowledge of 
its food, which consists of small, soft-bodied molluscs 
and crab-like animals living on the bottom of the sea, we 
have been able to determine both, and have found that 
the depth is 200 ells (about 400 feet). Usually the 
Eiderduck remains from four to five minutes submerged, 
as does also the northern Diver (■ G . glacialis ) on rare 
occasions; sometimes, however, it is said to stop under 
as long as nine minutes; after that, however, it seems 
very exhausted. All the birds keep under as long as 
they can hold their breath; in which case, should they 
become entangled during their return to the surface, 
