46 3 The Bird 
summer, or may drop out as soon as begins the hard 
work of building the nest or feeding the young, with which 
labor they might interfere. 
To return for a moment to the fall moult. If a spar- 
row or lark should shed all of its large wing-feathers 
simultaneously, it would have slight hope of ever living 
long enough for new ones to grow out again. If such 
defenceless birds were compelled to hop helplessly along 
Fic. 28.—Wings of English Sparrow, showing two feathers of each wing being 
moulted simultaneously. 
the ground, weasels and cats would be able to catch 
hundreds of them without effort. This is avoided in all 
land birds by the moulting of only a pair of primaries, 
as the large flight-feathers are called, at a time, one from 
each wing. This process usually starts with the pair 
farthest from the front of the wing, and the second pair 
does not fall out until the first pair of new feathers is 
nearly of full size. Thus all danger of a crippled flight 
is avoided. 
One of the most interesting phases of Nature is the 
way she provides for exceptions to what we are pleased 
to call her laws. Some birds, unlike those mentioned 
