LOCAL AVIFAUN.E OP THE GREAT RASIX. 317 



alkaline salts in the soil, and other causes, we may easily correlate the bird- 

 tauna into corresponding sections. 



The boundaries between local floras of entirely different character are 

 usually so abrupt in the Great Basin that often a single step will lead from 

 one to the other; thus, the upper limit of ^he "pine belt" on the mountains 

 marks a given line where the trees disappear almost immediately, and these 

 begin almost as suddenly at the lower edge of the zone; narrow belts of 

 mountain mahogany, western cedar, or cedar and pinon together, may fol- 

 low in the order given, but there is usually no marked straggling of these 

 trees where they meet the sage-brush, as if disputing possession of the 

 gr<nind. The sage-brush reigns supreme from the base of the foot-hills to the 

 brink of the mesa, or over the elevated plain extending from the foot of the 

 mountains to. the narrow valleys of the streams, where only the steep, nearly 

 naked bluffs separate the. squalid growth of the higher level from the more 

 thrifty growth of the same plants, first with grease-wood intermingled, 

 which occupies the outer portion of the valley-floor; then follows the green- 

 sward of salt-grass in the moister portion of the valley, while nearer the river 

 are thickets of low Avillows, or in exceptionally rich valleys buffixlo-berry 

 and other shrubs, with cotton-wood trees interspersed. In a like manner 

 the luxuriant shrubbery of the mountains is usually restricted to the margin 

 of the brooks in the bottom of the cafions or ravines, where often the slopes 

 so nearly meet that scarcely room is left for a trail. Such are the main 

 features of the distribution of vegetation in this region, subject, of course, 

 to numerous and sometimes, but not often, complicated local modifications. 



The strict correlation between the birds and plants in this matter of 

 distribution was a fact immediately noticed, and the more firmly impressed 

 toward the close of our long period of observations in the field ; each local- 

 ity of particular vegetation being inhabited by its own peculiar set of birds 

 with almost unvarying certainty. In order to familiarize the reader with 

 the local causes which govern the distribution of the birds within the Great 

 Basin the accompanying arrangement of the more distinct types of locali- 

 ties is given, followed by lists of the species of birds characteristic of each. 

 It is of course to be understood that by characteristic we do not mean that 

 a bird is found in the sort of locality to which it is assigned, and nowhere 



