MIGRATION 
II 
stated times before the pinch of hunger is acutely felt. Superficially we 
eat by the clock; fundamentally to keep alive. The great question in 
bird migration is, what is the clock that strikes this migrational hour? 
Professor Rowan of the University of Alberta has conducted some ingenious 
experiments with captive birds and has advanced the theory that the seasonal 
lengthening and shortening of the days induces physiological changes in the 
birds that awaken or actuate this migrational impulse, and urge them to 
be gone. This hypothesis is being well considered by ornithologists. 
The extent of the migrations of 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 changes 
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 migra- 
tion all the central provinces in a nearly easterly line and winter on the 
Atlantic coast. The whole country is thus criss-crossed 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, which 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 nearl}'' as varied as their direction or 
extent. Some species drift along throughout the day from treetop to 
treetop, 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 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 paths. 
Comparatively small bodies of water deflect some species from their course; 
other species unhesitatingly cross vast reaches of sea, indifferent to nearby 
and convenient land passages that are used by closely allied species. In 
some species the older birds precede ; in some the males precede the females. 
How birds find their way is still only vaguely understood. Individuals 
far out of their natural range and course show clear evidence of being as 
hopelessly lost as any other animal would be on unfamiliar ground. Cer- 
tainly experience has much to do with it and undoubtedly young birds 
are largely guided by the movements of their elders, who, presumably 
through previous experience, already know and can lead the way. We can 
understand how birds can follow great landmarks — large river systems, 
mountain ranges, or seacoasts — in their journey, but no sense with which 
we are familiar explains how some species return unerringly to lonely 
oceanic islands over wastes of monotonous sea. It may be that they have 
a special sense which aids them in orienting themselves. 
