398 
BIRD-LIFE. 
same thing probably occurs ; and in the Himalayas we are 
well aware that a similar movement takes place. 
The difference between migration proper and the 
second class of migratory action among birds is, as we 
have before remarked, shown by the irregularity of the 
latter. When in high latitudes the unusual severity of 
the winter hides from view the thousands of plants and 
millions of seeds wdiich could furnish food to numbers of 
birds, these last are forced to move southwards, where 
they remain and breed, sometimes never again returning 
to their old haunts. While on the road they halt wherever 
they find food, often remaining weeks in one locality, 
until all means of subsistence have vanished. In this 
manner we find the Eedpole and Siskin wandering from 
one birch-wood to another, from one alder-tree to 
another. If they find sufficient nourishment in the north 
they do not come to us. This is the reason why we do 
not see them every winter, or, at all events, not in the 
immense flocks which occasionally visit us. Exceptional 
circumstances, also, oblige other birds, whose true 
home lies still further north, to come to us; because, 
however, this is not a usual occurrence, and because 
the feathered strangers are accustomed to regard man 
with distrust, they inadvertently attract observation, and 
their presence is regarded by the common people as 
next door to a miracle, which they in some way connect 
with the old mystic number seven. Thus, with us, it is 
a saying that the lovely Waxwing and the curious Nut¬ 
cracker appear every seven years. Close observation has, 
however, taught us that this is in no way the case. 
The number of species which may be reckoned as 
partial migrants is incomparably less than that of the true 
birds of passage. Among our native birds we may count 
