10 
The following birds are representative of those that may be regarded 
as distinctive of each life-zone. All may not be entirely confined to these 
zones, but in them they reach the centre of their breeding abundance and, 
associated together, they give the dominant characteristics of the bird 
life. Nor may all these species occur throughout the faunal zone to 
which they belong; for instance, some Transition species of the prairies 
do not extend across the mountains into the Transition of British Colum- 
bia, and vice versa. The lists are merely suggestive and might be greatly 
extended. 
Upper Austral — ■ 
Sage Grouse 
Diekcissel 
Grasshopper Sparrow 
Chat 
Sage Thrasher 
Canyon Wren 
White-throated Swift 
Transition 1 — 
Bobolink 
Baltimore or Bullock's Orioles 
Eastern or Spotted Towhees 
Catbird 
Brown Thrasher 
Eastern and Western Bluebirds 
Ferruginous Rough-legged Hawk 
Sprague's Pipit 
Chestnut-collared Longspur 
Canadian — 
Hudsonian — 
Arctic — 
Brown-headed Chickadee 
Olive-backed Thrush 
Hermit Thrush 
Three-toed Woodpeckers 
Canada Jay 
White-throated Sparrow 
Slate-coloured Junco 
Fox Sparrow 
Northern Shrike 
White-crowned Sparrow 
Bohemian Waxwing 
Evening Grosbeak 
Pine Grosbeak 
Ptarmigan 
Snowy Owl 
Snow Bunting 
Gyrfalcon 
Lapland Longspur 
Leucosticte 
Eider Ducks 
MIGRATION 
The migration of birds, their periodical and seasonal appearance and 
disappearance, is one of the most obvious phenomena of nature. The fact 
that many birds disappear in winter is common knowledge and has attracted 
attention for ages. Though once regarded as a mystery, and still far 
from being thoroughly understood in many of its details, we are beginning 
to wonder less but admire more as accurate knowledge replaces vague 
speculation. Today, where most of our northern species spend the winter is 
known and many of the routes by which they come and go have been 
mapped. We know that on the whole they are governed by ordinary 
and well-known, though perhaps highly developed, senses and common 
every-day influences and not by the mysterious powers and instincts once 
ascribed to them. 
The fundamental cause of migration is obviously the waxing and the 
waning of the food supply. Birds leave the northern land of their birth 
because there is no other way by which to avoid starvation. Many species 
can withstand extreme cold but none can go long without food, and though 
some bird food still remains in Canada throughout the winter, its amount 
is small and sufficient for only a limited population and even that supply 
rapidly decreases, or, to the north, is buried under deep snow. The cause 
of the southward migration in the autumn then is obvious, but why should 
a bird leave the soft climate and plentiful food supply in the south to brave 
dangerous travel and finally find itself in a land where retiring winter still 
1 Most of the species of this zone also occur in the Upper Austral but reach their northern limit here. The 
occurrence of these, with the absence of the species mentioned as peculiar to the bordering zones, are the moat 
marked characteristics of the Transition zone. 
