Mip-ations of Nurih American Birds. 279 



specimens from localities widely remote in latitude, I have found 

 the difference referred to. A similar law prevails in regard to 

 mammals, as shown very clearly in the American Deer, Cervus 

 virginianus, and in the Grey Squirrel, Sciurus carolinensis, which 

 are much larger in the north than in the south, and larger in the 

 mountains than in the lowlands. In mammals, if not in birds, 

 a second law comes into play — that in the same latitudes in 

 North America the specimens from the greater altitudes are the 

 larger, — this law appearing to extend even to man, as shown by 

 the greater size of the inhabitants of the Appalachian region, 

 than of those of the lowlands. 



If we assume the parallel of 40° as an average line, while the 

 specimens born further north are larger, those born in the most 

 southern localities are even disproportionately smaller. This is 

 very evident in species from Cape St. Lucas, the extreme southern 

 limit of the Middle province, where, almost without exception, 

 the indigenous birds are so much smaller than specimens of 

 the same species inhabiting the United States as readily to 

 convey the impression of being distinct new species. The same 

 is the case, although to a less degi'ee, in Florida, where there 

 appears to be a tendency (found to some extent also at Cape St. 

 Lucas) to absolute increase of the size of the bill, even with 

 diminution in general bulk, seen especially in Corvus americanus, 

 and Ortyx virginianus^ . 



While some Florida birds are thus characterized by larger 

 bills than their more northern brethren, several of the birds of 

 the Middle and Western provinces have an increase in the length 

 of the tail as compared with the same or allied species in the east. 

 Thus Icteria longicauda of the Western and Middle provinces is 

 only to be distinguished from /. viridis of the Eastern, by the 

 longer tail, while Mimus polyglottus, and Harpoi'hynchus rufus 

 have each a long-tailed Western variety. 



Both these generalizations in regard to varieties of size and 

 proportion have been used with advantage in testing the claim 



* This disproportionate difference of size at Cape St. Lucas and South 

 Florida is probably connected with the limited range of the species in 

 those regions, which have thus an insular rather than continental 

 relationship. 



