THE HUMMING BIRDS. 267 



On the other hand, the decrease to the southeastward from the (t focal 

 center" in the true Brazilian Province is very great; it is impossible, 

 at present, to properly estimate the total number of species found tbere, 

 but it is probably considerably less than 50, with, however, perhaps more 

 than half of them peculiar. 



MIGRATIONS. 



While in tropical regions the Humming Birds are, like other kinds, 

 permanent residents, or at most make comparatively slight migrations 

 when the food supply of a given locality fails them, or when, on high 

 mountains, the increasing cold forces them to descend to the warmer 

 slopes and valleys, those of temperate regions make extensive and 

 regular migrations like other birds of the same regions, coming from 

 the south in spring and returning in autumn. Thus, the common Ruby- 

 throated Humming Bird (Trochilus colubris) has its summer home in 

 eastern North America, where it occupies the extensive region stretch- 

 ing from the Gulf of Mexico to half way across the British Provinces 

 (at least to latitude 57 degrees north), and from the Atlantic coast to 

 beyond the Mississippi. It breeds throughout this area, but is not 

 known to do so south of the United States. In winter, however, its 

 range is shifted far to the southward, the northern recorded limit at 

 that season being southern Florida (Pnnta Rassa, latitude about 29 

 degrees), and the southern limit in Veragua, the western portion of the 

 Isthmus of Panama, only about 8 degrees north of the equator. It is 

 thus evident that, notwithstanding their diminutive size, some individ- 

 uals of this species perform an annual migration of at least 28 degrees 

 of latitude, equivalent to nearly 2,000 statute miles ! On the opposite 

 side of the continent the highest latitude attained is about that of Gl 

 degrees, on the coast of Alaska, where the Rufous-backed Humming Bird 

 was found by Kotzebue. The same species winters in Mexico, so that in 

 their migrations those individuals which pass the summer farthest north 

 traverse considerably more than 2,000 miles of territory ! It is only 

 in the warm valleys of California and in southern Florida that any 

 species of Humming Bird regularly passes the winter within the borders 

 of the United States ; in the former the Anna Humming Bird (Calypte 

 anna) , and in the latter the Ruby-throat (Trochilus colubris). All the 

 species of western North America (including many individuals of G. 

 anna) winter in Mexico, only one of the truly northern species (Selas* 

 phorus platycercus) extending its winter range as far as Guatemala. 



The vertical range of some species in mountain districts is quite 

 remarkable. In July, 1868, the writer observed examples of Selaspliorus 

 platycercus in the dooryard of a ranch in Ruby Valley, Nevada, the 

 altitude being between 6,000 and 7,000 feet, and later during the same 

 day saw a single individual of the same species at the extreme sum- 

 mit of the immediately adjacent East Humboldt Mountains, nearly 6,000 

 feet higher. 



