May, 1914 
BIRDS OF NORTHERN MONTANA 
125 
ern part of the state, due to the fact that along the northern border the eastern 
prairie region extends farther westward than elsewhere, and in fact reaches 
the eastern base of the mountains forming the continental divide. I have in- 
cluded with Teton County that portion of Lewis and Clark County that lies 
in the drainage of the Sun River (see fig. 39). The southern boundary of 
Teton County is formed by the North Fork of the Sun River, but since my ob- 
servations covered both sides of the river, and the character of the country is 
essentially the same on both sides, I have made the divide between the drain- 
ages of the Sun and Dearborn rivers the southern boundary of the region stu- 
died. This divide forms a natural division between different regions of the 
state, the character of the country being markedly different on the two sides 
of it. 
In studying the distribution and occurrence of the birds of this region, it 
may l)e considered in two main parts, the prairies and the mountains. The 
Fig. 39. View ix the Canadian Zone on the Sun Riveu, Lewis and 
Ceakk County, Montana. 
prairies occupy the eastern portion, and cover considerably more than half of 
the total area. They lie entirely within the Transition zone, and their altitude 
varies from 3500 to 4500 feet. They consist of open grass land, rolling hills 
and flat-topped benches, steep-sided buttes, and broad valleys, watered by 
streams that are bordered by cottonwood groves and willow thickets. Alka- 
line ponds and lakes are quite frequent, in fact very numerous toward the 
westward, along the edge of the lower mountain slopes. 
The mountains occupy a comparatively narrow strip through the western 
part of the counties. They embrace the headwaters of the Sun, Teton and Two 
Medicine rivers, and Birch Creek (see fig. 40). They lie in the Transition, 
Canadian, Hudsonian and Alpine zones, and range from 4,000 to 9,500 feet in 
altitude. These mountains are extremely rough, consisting of numerous lime- 
stone ridges with precipitous sides. In many places most of the timber has 
