11 
lingers and the danger of starvation is imminent? Many ingenious explana- 
tions have been advanced to account for this: homesickness, hereditary 
memories of an ancient home that had endured through geological 
ages; the seeking of special food for nestlings, and insufficiency of 
nesting sites in the southern areas, have all been given as possible reasons. 
However, it is unnecessary to advance an extraordinary explanation when 
a simple one exists. If we remember that in the nesting season the bird 
population is increased many times by the birth of young; that though in 
winter there may be room for a considerable number of birds in the southern 
stations, the natural spring increase in population outgrows the supporting 
power of even that fruitful land; and that just at this critical time the 
whole northern temperate region is by the coming of summer thrown 
open to occupation with an abundance of food, the subject is mysterious 
no longer. In fact, it is only by migration that it is possible to use the support- 
ing power of the temperate regions unless the birds fast or hibernate through 
the winters, to neither of which customs the avian nature takes kindly. 
Though food supply is the fundamental or originating reason for 
migration we must look for other and more immediate impulses for an 
explanation of its methods today. Originally forced to and fro by hunger, 
the annual movements now have become instinctive and take place before 
the actual hunger pinch is felt, or the physical system weakened by 
want. 
The extent of the migrations of the different species varies. A very 
few species do not, in the true sense of the word, migrate at all. In other 
species only the more northern individuals recede from their stations, the 
southern remaining almost stationary, though in the majority of 
Canadian species the whole body moves south. Though the general rule 
is that migrant birds move south in winter, some do it by rather indirect 
routes; others, although they make considerable geographic or climatic 
change in their situations, lose little or none of their northing in the process 
and winter at nearly as high a latitude as they summer. A few achieve 
milder climate simply by descending a mountain-side to the valleys. A 
number of the birds of the interior cross the mountain ranges at various 
points to the adjacent Pacific seacoast; others nesting nearby traverse in 
migration all the central provinces in a nearly easterly line, and winter on 
the Atlantic coast. The whole country is thus crisscrossed with aerial 
lines and each species is more or less a law unto itself as to the route and 
objective of its journey. The bird performing the greatest migratory 
journey is doubtless the Arctic Tern, a bird that nests from the gulf of 
St. Lawrence to the polar regions and winters as far south as the Antarctic 
continent. 
The methods of migration are nearly as varied as their direction or 
extent. Some species drift along throughout the day from treetop to 
tree top, from wood patch to wood patch, gradually working their way in 
the desired direction. Others take long flights, some high in the air, some 
lower. Some travel altogether by day; others travel at night and we are 
aware of their passage only through accidental opportunities, their faint 
voices coming down to us from overhead in the darkness, or by their sudden 
appearance about us in the morning. They travel in flocks of single or 
mixed species, scattered groups, or as individuals. 
Many species, if not all, follow more or less definite routes to and from 
their breeding grounds, and some go and return by altogether different 
