Migrations of North American Birds. 263 



along the Platte, sometimes eastward. It crosses the Platte 

 between Forts Kearney and Laramie, and intersects the Missouri 

 between Fort Randall and Fort Pierre, perhaps near Fort Look- 

 out, as it is between the first-mentioned two points that in as- 

 cending the river we find the change to take place in the orni- 

 thology of the country. Soon after crossing the northern 

 boundary of the United States and to the western side of Lake 

 Winnipeg, the line rapidly inclines westward, especially beyond 

 the Saskatchew^an, and extends to the Eocky Mountains, inclu- 

 ding the valleys of Athabasca and Great Slave Lakes, and both 

 sides of the Mackenzie River, north to the Arctic Ocean, even 

 crossing the Rocky Mountains to the Porcupine River, and into 

 Russian America at least to 145°, or beyond the forks of the 

 Yukon, where Mr. Kennicott found many of the most charac- 

 teristic summer land birds to be almost identical with those of 

 Slave Lake, Lake Winnipeg, and Northern Canada. 



The western province occupies the western slope of the Cas- 

 cade and Sierra Nevada ranges of mountains in the United 

 States, although its extent southward along the peninsula of 

 Lower California is not well determined. To the north-west it 

 extends at least to the 1 10th meridian, beyond that probably 

 replaced by a more Arctic fauna. We are not sufficiently 

 familiar with the birds occurring between the northern Rocky 

 Mountains and the coast to tell how far inland in Stickin 

 Territory or even in northern British Columbia the coast fauna 

 extends, perhaps not further than in California or Oregon, 

 although it is possible that, owing to the absence of a continuous 

 longitudinal range of great height, the western and middle 

 regions may there be more thoroughly blended into one. 



The middle province, or that of the great plateau, occupies 

 the space between the two just mentioned, probably not passing, 

 in its integrity or as a peculiar province, north of the valley of 

 the Saskatchewan, and is thus wedged in between the two. As 

 already stated, it extends along the eastern slope of the Cascade 

 and Sierra Nevada Mountains, and apparently along the east 

 side of Lower California to Cape St. Lucas ; at least the birds of 

 the Cape, as will hereafter be explained, belong much more 

 emphatically to it than to the western province. A break in 



