Feathers 47 
above, shed every primary in their wings at once, so that 
their angular stump-feathered wings are perfectly useless 
for flight. In this class are many water birds—ducks, 
geese, flamingoes, snake-birds and others. Just before this 
wholesale moulting occurs, a flock of wild ducks will 
Fic. 29.—Wing of adult Mallard Duck, with the new set of flight-feathers 
just appearing. 
make their way, by an unfailing instinct, to some large 
body of water where they can swim and dive in safety 
and, if need be, never come within reach of enemies on the 
shore until the new feathers are strong enough to bear 
them up. 
Associated with this temporary disablement is another 
provision for the safety of certain birds of this class. Our 
common Mallard Duck, for example, is sometimes com- 
