128 Allen, Origin and Distribution of N. A. Birds. [April 



present writer, 1 on practically the same lines. The last two 

 were first defined by Mr. E. W. Nelson 2 as respectively the 

 'Sitkan District' and the 'Aleutian District,' and re-defined and 

 mapped in my recent paper on the 'Geographical Distribution 

 of North American Mammals.' 8 As noted later in the present 

 paper (p. 139), there remain to be defined, when our knowledge 

 of the subject becomes sufficiently detailed, a series of local 

 mountain faunae in the Rocky Mountains and other principal 

 mountain chains in the West. 



The Warm Temperate Subregio?i occupies middle North 

 America, extending from the southern boundary of the Cold 

 Temperate Subregion, as defined above, to the northern edge of 

 the American Tropical Realm (see PI. III). It is thus 

 geographically the same as Dr. Merriam's 'Sonoran Province.' It 

 includes the greater part of the United States, Lower California, 

 and the Mexican tableland. It is cut into along the principal 

 mountain systems by the southern prolongations of the Cold 

 Temperate Subregion, and also extends northward over the 

 Saskatchewan Plains. The extreme southern parts of the 

 peninsulas of Florida and Lower California, however, are excluded, 

 as also the lower coast region of Texas, these excluded districts, 

 though of comparatively small extent, belonging to the Tropical 

 Realm. 



The Warm Temperate Subregion contrasts strongly with the 

 Cold Temperate in respect to its topographic and climatic 

 features, as well as in its faunal aspects. Aside from the very 

 marked difference of temperature between the two, the Cold 

 Temperate is a homogeneous region, covered almost continuously 

 with principally coniferous forests ; and aside from its southern 

 extension along the mountain ranges, presents little diversity in 

 topography. The Warm Temperate, on the other hand, is 

 highly diversified topographically, and consequently in climate, 

 especially in respect to rainfall, which of course greatly modifies 

 the distribution of forests, and of plants in general, which in turn 

 exerts a marked influence upon the distribution of animal life. 

 We have hence conditions favorable for the development of 



1 Bull. Am. Mus. Nat. Hist., IV, 1892, pi. viii. 



2 Rep. Nat. Hist. Coll. made in Alaska, 1887, pp. 24-27. 



3 Bull. Am. Mus. Nat. Hist., IV, 1892, pp. 223, 224, pi. viii. 



