Nebraska Ornithologists' Union 47 



western limit, where it meets the sand-hill region, is an irregular 

 but very definite line ; to the northward it merges into the plains 

 region in the Niobrara valley and south of the Platte it meets the 

 plains region again by a boundary which is ill-defined. 



3. The Sand-hill Region, a broad expanse of sand hills between 

 the Niobrara valley on the north and the Platte valley on the 

 south, together with several smaller outlying areas of sand hills 

 south of the Platte and north of the Niobrara. 



4. The Plains Region, high arid table-lands, westward from 

 the preceding to the boundary of the state, extending eastward 

 along the Niobrara and south of the Platte to meet the prairie 

 region. 



5. The Pine Ridge Region, a foot-hill area including the deep 

 canyons of the Pine ridge in Sioux and Dawes counties, the sides 

 of which are covered with an open growth of pines, while the 

 deep, cool recesses have a thicker growth of pine and deciduous 

 trees and harbor many plants of a northern distribution or of 

 higher altitudes. (Conditions here have been well described by 

 Gary in these Proceedings for the Third Annual Meeting, pp. 



63-750 



Of these regions the first two belong to the Carolinian faunal 



area, as defined by Merriam, which is the humid portion of the 

 Upper Austral life zone ; the third and fourth are in the Upper 

 Sonoran, which is the arid portion of the same life zone ; while the 

 fifth is to be referred to the Transition zone. The character of 

 the bird fauna in each region is determined by the conditions of 

 temperature and moisture which form the basis for the establish- 

 ment of these zones and areas, and also by other local conditions. 

 An enumeration of the more prominent environments in each 

 region will serve to indicate the character of each and its possi- 

 bilities as a place of residence for birds : 



I. The Missouri region. 



1. The river, with its shifting sand-bars. 



2. The thickets of willow, and young cottonwoods. 



3. The tall bottomland timber, largely cottonwood. 



4. The cleared areas, cultivated fields, and scattered shrub- 



bery of the bottom-lands. 



5. The cut-off ponds, and swamps or marshes.- 



