180 The Migration of Birds 
were, it seems more than likely that the long arctic 
night, when for three months the sun does not rise 
above the horizon, alone would have taught the birds 
to migrate at least a few hundred miles north and 
south. These theories have an interest, and as we 
ponder over them we may get some light upon the 
subject; but let us remember to state them as theories, 
much as we should like to prove or disprove them. 
Some theorists, without attempting to see so far 
back into the early conditions causing the great an- 
nual pilgrimage of our birds, argue that the desire for 
a genial climate, where food is plentiful, can alone 
account for this great phenomenon. Another theory, 
urged by many, is that the annual nesting season is 
sufficient to cause migration. The believers of this 
argue largely from the conditions existing to-day. 
Birds, and in fact most animals, have an innate desire 
for seclusion during the period of reproduction, and 
will seek some retired locality in which to bring forth 
their young. This pertains not only to those birds 
which winter in South America and nest in Canada, 
for tropical birds also will seek secluded places 
within their own zone; and the seclusion habit con- 
cerning the eggs and young is very noticeable in our 
turkeys and Guinea fowl as well. Among the fish, the 
salmon is most noted for its long journey from the 
