9 
strip of sea coast in southern British Columbia and marks the limit of 
extensive cultivation. 
The Boreal region is divided into the Canadian, Hudsonian, and the 
Aretic zones. The Canadian includes the remainder of the forested land 
north of the Transition and is mostly coniferous, continuing across the 
continent to the northern limit of general cultivation. The Hudsonian 
zone is in the more northern country of small shrubs or stunted tree growth 
unsuited to agriculture, and the Arctic zone extends across the barren 
grounds north to the pole. 
These life zones based upon temperature and roughly following the 
lines of latitude, are, however, deflected from their natural east and west 
sweep by varying local conditions, the vicinity of cold or warm ocean 
currents, the presence of large bodies of water, elevation above the sea, 
the prevalence of cold or warm winds or mountain barriers to the same, 
and other causes. Thus instead of being even belts they are irregular 
and only roughly follow parallels of latitude. 
Elevation is an important factor in the distribution of life depending 
upon temperature. In the tropics in ascending a high mountain, repre- 
sentatives of each zone between that of the surrounding lowland and the 
Arctic of the snow-covered peak, may be met with and appropriate assem- 
blages of species will be found inhabiting each. The juncture of Arctic 
and Hudsonian zones at the straits of Belle Isle, in the same latitude as 
Lands End in England, illustrates the enormous effect of the cold Arctic 
current, coming down from Davis strait, in contrast to the influence of 
the warm Gulf stream that dies against the English shores. 
We can also observe minor groupings east and west based upon con- 
ditions other than temperature, these determining factors being mostly 
variations of humidity. Thus the life of the eastern woodlands is plainly 
different from that of the more arid plains of the prairie provinces and both 
are strikingly different from that of the moist Pacific slope. 
Taking the eastern forms as typical in the ordinary acceptance of the 
word, comparable birds of the prairie will be found to be slightly smaller 
and considerably paler in coloration, whereas on the humid Pacific coast 
they will be larger and much darker in colour. Through these influences 
we, therefore, find in the west many subspecies of eastern forms. A com- 
paratively few species range unmodified across the continent, many are 
represented east and west by two or more subspecies showing greater or 
less differentiation, and in other cases they are replaced by closely allied 
species or not represented at all. ~ 
In noting these faunal divisions, however, it must be remembered 
that as far as birds are concerned, these associations have to be based 
entirely upon breeding individuals. Birds travel so widely and along so 
many devious routes in their migration, that they may pass through several 
faunal areas spring and autumn though breeding in only one. Therefore, 
in determining the faunal zone to which any given area should be referred, 
such transients must be disregarded. 
_ Though the distributions given under the specific headings following 
are rather vague and indefinite, many tend to foilow similar general lines. 
Thus some are given as ‘‘the lower Great Lakes region’’; these are prob- 
ably Upper Austral forms. ‘‘Southern Ontario and Quebec” refers to 
Transition species, whereas ‘‘beyond dense settlement or to the limit of 
cultivation”? would naturally be species of the Canadian zone. 
