274 DISTRIBUTION OF AUDUBON's WARBLER 



cousin ; for Mr. Albert Salvin found both Eastern and Western 

 Yellow-rumps together, at San Geronimo, in November, 1859. 



As to the local and seasonal movements of Audubon's War- 

 bler within the extensive area thus sketched : The bird is migra- 

 tory, like all the rest of our Warblers, and the "tidal wave" 

 passes twice a year, bearing- the vast majority of individuals 

 north in spring and south in autumn. The extent of the spring 

 movement seems to be sufficient to bring all those that entered 

 Mexico the previous fall back into the United States : at any 

 rate, if some linger to breed in even the most elevated portions 

 of Mexico, the fact has not become known to us. The body of 

 birds thus thronging over our border takes upon itself two 

 movements: one of these, the ordinary to-and-fro migration, 

 spreads the species in latitude, until the limits of its geograph- 

 ical range are attained 5 the other is an up-and-down movement, 

 equally obvious and decided, though of course less extensive, 

 which carries the species into suitable breeding grounds, at the 

 higher elevations of the lower latitudes. Thus a breeding 

 range is secured which is almost coextensive, geographically 

 speaking, with the entire United States range of the species, 

 yet entirely dependent upon topographical features of the coun- 

 try 5 for while at the North the birds may breed anywhere, down 

 to sea-level, at the South their nesting-grounds are found only 

 along certain lines or in certain spots that attain sufficient ele- 

 vation. There is nothing peculiar in this 5 in fact, it is the rule 

 equally applicable to various other migratory birds. The case 

 of J). auduboni, however, is notable among the Warblers, as that 

 of D. coronata also is, in that the winter range of the species is 

 unusually extensive ; for only a part, perhaps only a small pro- 

 portion, of the individuals composing the species withdraw 

 from the United States in the fall. How far north the bird may 

 be enabled by the hardiness of its constitution to endure the 

 rigors of winter is not fully known, for ornithologists are neither 

 numerous nor active at this season in the Eocky Mountains. 

 But the bird has been seen in Washington Territory in March, 

 which is long before any general migration of birds occurs in 

 that latitude ; and the probability is that the lower levels and 

 sheltered situations generally may harbor numbers of the birds 

 in winter, even toward the northern extremes of their habitat, 

 just as the Eastern Yellow-rumps are sometimes seen in Massa- 

 chusetts at the same season. However this may be, it is certain 

 that the lower portions of the Colorado Basin, and of the coun- 



