The Migration of Birds 181 
ocean to the headwaters of some river, where the 
eggs may be deposited in safety. The distance is 
remarkable in the case of the quinnat salmon. It 
ascends the Yukon to Caribou Crossing, two thou- 
sand two hundred and fifty miles from the ocean! It 
is well known that seals migrate regularly to certain 
islands, known as breeding grounds, where the young 
are born. These additional observations are helpful 
in the study of migration of birds, and I believe they 
strengthen the supposition that the existing conditions 
are the results of changes that have been slowly pro- 
gressing through past ages. 
Whatever may be the true theory, there is ever an 
increasing charm about the study of migration, as 
we note from year to year the comparative regularity 
with which the birds come and go. It is not, as some 
believe, a general helter-skelter movement among the 
birds, but quite the opposite; it seems to be a regular 
part of bird life, and they go about it in a business- 
like manner, as though they knew there was some- 
thing definite to be done. 
The extent of a bird’s migration must necessarily 
depend upon its food; a so-called resident bird, like 
the crow, generally changes its food with the season. 
Some birds depend upon fruit, others upon insects. 
The insect-eating birds must migrate the farther of 
