Migrations of North American Birds. 191 
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 Jeteria longicauda of the Western and Middle provinces is 
only to be distinguished from L. viridis of the Eastern by the 
longer tail, while Mémus polyglottus, and Harporynchus 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 
of supposed species to this rank, and have aided in materially 
diminishing the accepted number of species of both mammals 
and birds. 
near the mouth of the Yellowstone River, and all along that 
portion of its course we find Colaptes of every possible grade of 
Species; scarcely any two exactly alike, and the same individ- 
ual not even agreeing in the markings of opposite sides.” A 
Similar combination of characters of Cyanura Stellert and macro- 
phaga celata and peregrina. Other instances can be adduced, but 
these will be sufficient to illustrate the facts. ol ares 
* This dis rtionate difference of size at Cape St. Lucas and south Florida is 
Probably eaatind a the limited range of the species in those regions which — 
lave thus an insular rather than continental relationship. a 
~~ See Baird. Birds of North America, 1858, 122. 
