Migrations of North American Birds. 



271 



To sum up in brief the conclusions reached in the preceding 

 remarks, it may be stated that the ornithological provinces of 

 North America consist of two great divisions of nearly equal 

 size in the United States, meeting in the vicinity of the 1 00th 

 meridian, the western half divisible again into two, more closely 

 related to each other than to the eastern, though each has 

 special characters. These three sections form three great 

 provinces, to be known as the western, middle, and eastern : — or 

 those of the Pacific slope ; of the great basin, the Rocky 

 Mountains, and the adjacent plains ; and of the fertile plains 

 and region generally east of the Missouri. A northern or sub- 

 arctic fauna mixes with and melts into the three, extending far 

 to the south (even into Mexico) along the Rocky Mountains. 

 The middle and eastern provinces have each a southern sub- 

 division, the one bordering on Mexico, the other on the Gulf 

 and the Atlantic ; and each of these also exhibits a differentiation, 

 the former having a special subdivision again into Cape St. 

 Lucas, and the latter into Florida. Northward the eastern 

 province extends more and more westward, reaching the Rocky 

 Mountains and even westward of them towards the Yukon. 



The southern boundary of the middle province of North 

 America may be arbitrarily established as a straight line, drawn 

 from the mouth of the Rio Grande to that of the Yaqui near 

 Guaymas on the Gulf of California, thus throwing into North 

 America the whole of Florida and Lower California. 



Attention has already been called to the fact that certain 

 species characterizing the eastern province make their appear- 

 * Found all tlie way across to the Pacific. 



