156 BRITISH SEA BIRDS. 
winter visitor. At that season, however, it may 
be met with pretty frequently off the British coasts, 
the young birds especially venturing into our bays 
and creeks and estuaries, older individuals, as a 
rule, keeping further out to sea. Adult birds are, 
however, often observed near the coasts of South 
Devonshire and Cornwall. I have known them 
linger in the waters near here until the summer has 
been well advanced. Young birds of this species, 
in the brown and white dress characteristic of im- 
maturity, may often be seen quietly fishing under 
the cliffs, notably in Tor Bay. One very remark- 
able thing about this Diver is its singular habit 
of immersing the body to such a depth that the 
back is quite under water. It often so sinks itself 
when menaced by danger, and then, almost out 
of sight, swims away with great speed. If pursuit 
is still continued all but the neck is sunk below the 
surface, and finally, if hotly pressed, the bird will 
disappear entirely, and swim along under water 
at a speed absolutely astonishing, Gatke records 
that this Diver, when chased by a boat under these 
circumstances, will dive and allow the boat to pass 
over it, rising again in the rear of it, a habit which 
my own observations of the bird completely 
confirm. How this act of immersion, without 
apparent effort, is accomplished remains a mystery, 
and offers a problem in animal mechanics by no 
means easy of solution. 
The Great Northern Diver is rarely seen on 
