380 OENlTUOLOCxY. 



of the Western Kegion at this season, thongh in summer their habitat may 

 be confined strictly to the area of Pacific-coast drainage. This circum- 

 stance we have previously alluded to, in these words: — ^ 



"Another very remarkable peculiarity of the Wahsatch region, which I wish par- 

 ticularly to mention in this connection, is the fact that in the case of representative 

 species or races, the Eastern or Rocky Mountain forms breed there, while the more 

 Western forms replace them in winter. Thus, ZonotricMa leucophrys and Junco hyemalis, 

 var. caiiiceps, are the only species of these two genera which breed on the Wahsatch, 

 and they nest there very numerouslj'; but in the fall their place is taken by the western 

 Z. leucophrys, var. gambeli [ — intermedia] and J. hyemalis, var. oregonus, which are un- 

 known in summer. Lanivireo solitaria, var. plumbea, breeds there, while var. solitaria, 

 coming from the northwestward, replaces it in autumn. The same is the case with 

 Titrdus 2)allasi, var. auduboni (summer resident), and vat. namis (autumnal migrant); 

 and apparently the case also with Helminthophaga virgi'niw (summer), and H. ruficapilla 

 (autumn)."^ 



The eastern species occiu'ring within the Basin were found to have 

 reached their maximum in the Salt Lake Valley and adjacent country to the 

 eastward, but, as was the case with the western series, some of them had 

 intruded so far within the western domain as to reach the opposite side. 

 Thus, Tyrannus carolinensis was not rare during the breeding-season in the 

 lower Truckee Valley, almost at the foot of the Sierra Nevada. Ectopistes 

 migratoria was obtained in the West Humboldt Mountains, although the 

 only individual seen was a young one, and evidently a straggler. In the 

 East Humboldt Mountains, Tardus swainsoni, Helminthophaga ruficapilla, and 



iProc. Essex Inst., Vol. V, Nov., 1873, pp. 170, 171. [" Notes on the Bird Fauna 

 of the Salt Lake Valley and the adjacent portions of the Wahsatch Mountains."] 



^ Other examples of species which have an extreme western or northwestern 

 distribution during the breeding-season, but which migrate in fall both eastward and 

 southward, are, Helminthophaga lutescens, Dendroeca occidentaUs, D. townsendi, and Selas- 

 phorus rujus, found as far east as the Clover Mountains, with the addition of Lanivireo 

 cassini, Melospiza guttata, Pipilo oregonus, Zonotrichia coronata, and Agelwus gubernator, 

 which in September and October were obtained in the West Humboldt range. The 

 most plausible explanation of this eastward migration would appear to bo found in 

 the supposition that nearly, if not all, these migrants were from the Valley of the 

 Columbia River, whose main tributary, the Snake River, heads almost directly north 

 of the Great Salt Lake; the birds of the Columbia basin would naturally follow the 

 valleys of these upper tributaries as the route offering the least obstacle to tlieir south- 

 ward passage, many species which do not breed eastward of the lower Columbia thus 

 regularly reaching the eastern border, if not the whole extent, of the Great Basin. 

 Whether their return northward is by the same route, remains to be determined. 



