GENERAL REMARKS ON THE BASIN AVIFAUNA. 379 



be observed the same day among the cotton-woods of the lowest valleys, 

 less than a hundred feet above sea-level (as in California), and in the alpine 

 woods, 10,000-12,000 feet above the sea. 



Independent of these local modifications of the fauna, as controlled by 

 conditions of environment, important changes were noticed in proceeding 

 eastward, which are of a truly geographical nature. Thus, although the 

 character of the country changed completely with the tei-mination of the 

 coniferous forests of the eastern slope of the Sierra Nevada, the change in 

 the fauna was by no means so abrupt. New forms of course immediately 

 made their appearance, or even predominated in number of species and 

 individuals, over those we had met with before, but still many of the latter 

 were not lost sight of completely until we had penetrated many miles into 

 the desert country, but reappeared on the higher ranges of the western depres- 

 sion. This was particularly the case with the West Humboldt Mountains, 

 where Lanivireo cassini, Pipilo oregonus, Melospiza guttata, Zonotrichia corotiata, 

 and Agclccus guhernator were found in the fall, all being birds of the Pacific 

 Province; while on the desert ranges, within sight of the Sien-a, Oreortyv 

 picttis was more or less plentiful. Along the eastern base of the Sierra 

 Nevada, near Carson City, Cyanocitta caHfornica—the "Valley Jay" of 

 California— was found in place of G. ivoodhoiisii, which was the only species 

 from the West Humboldt Mountains eastward, and the foi-m characteristic 

 of the Middle Province. 



As we approached the eastern border of the Basin we met with spe- 

 cies characteiistic of the Eastern Region or the Rocky Mountain District 

 of the Middle Province, as gradually as on the western side we had left the 

 Californian foi-ms behind; each successive high range introducing a larger 

 number to the list. But even in this district, where so many eastern forms 

 were met with, there was still a sprinkling of the extreme western element, 

 which, however, seemed to have reached nearly to its eastei-n limit in the 

 upper Humboldt valley or the neighboring mountains, where such birds as 

 Tmdus guttatus, Hdminthopliaga lutescens, Dendroeca occidentalis, D. townsendi, 

 and Selas2)hon(S rufus were noticed ^9 autumnal migrants. 



It seems to be a general rule, that western- birds have a tendency to 

 extend eastward during their tall migrations, thus spreading over the whole 



