ARGENTINE COURLAN £73 
of the beak; at the end it is of a horny toughness, 
and frayed or split into filaments. This beak is a most 
effective instrument in opening shells; for where 
molluscs abound the Courlan subsists exclusively 
on them, so that the margins of the streams which 
this bird frequents are strewn with innumerable 
shells lying open and emptied of their contents. 
Every shell has an angular piece, half an inch long, 
broken from the edge of one valve. Mussels and 
clams close their shells so tightly that it would perhaps 
be impossible for a bird to insert his beak, however 
knife-like in shape and hardness, between the valves 
in order to force them open; therefore I believe 
the Courlan first feels the shell with his foot whilst 
wading, then with quick dexterity strikes his beak 
into it before it closes, and so conveys it to the shore. 
Otherwise it would be most difficult for the bird to 
lift the closed shell from the water and to carry it to 
land ; but supposing it could do this, and afterwards 
succeed in drilling a hole through it with its beak, 
the hole thus made would have jagged edges and be 
irregular in shape. But the hole is, as I have said, 
angular and with a clean edge, showing that the bird 
had just thrust his beak half an inch or an inch 
between the valves, then forced them open, breaking 
the piece out during the process, and probably 
keeping the shell steady by pressing on it with its 
feet. 
By day the Courlan is a dull bird, concealing 
itself in dense reed-beds in streams and marshes. 
When driven up he rises laboriously, the legs dangling 
