Caban., and aliciæ, Baird. The first-named is totally unlike the rest, which are more closely related in appearance.
In studying carefully a very large series of specimens of all the species, the following facts become evident:—
1. In autumn and winter the “olive” color of the plumage assumes a browner cast than at other seasons; this variation, however, is the same in all the species (and varieties), so that in autumn and winter the several species differ from each other as much as they do in spring and summer.
Turdus ustulatus.
Of these five species, two only (pallasi and swainsoni) inhabit the whole breadth of the continent; and they, in the three Faunal Provinces over which they extend, are modified into “races” or “varieties” characteristic of each region. The first of these species, as the pallasi var. pallasi, extends westward to the Rocky Mountains, and migrates in winter into the South; specimens are very much browner in the winter than in spring; but in the Rocky Mountain region is a larger, grayer race, the var. auduboni. This, in its migrations, extends along the central mountain region through Mexico to Guatemala; specimens from the northern and southern extremes of this range are identical in all the specific characters; but the southern specimens, being in the fall and winter dress, are browner in color than northern ones (spring birds); an autumnal example from Cantonment Burgwyn, N. M., is as brown as any Central American specimen. Along the Pacific Province, from Kodiak to Western Mexico, and occasionally straggling eastward toward the Rocky Mountain system, there is the var. nanus, a race smaller than the var. pallasi, and with much the same colors as var. auduboni, though the rufous of the tail is deeper than in either of the other forms. In this race, as in the others, there is no difference in size between specimens from north and south extremes of its distribution, because the breeding-place is in the North, all Southern specimens being winter sojourners from their Northern birthplace.
The T. swainsoni is found in abundance westward to the western limit of the Rocky Mountain system; in the latter region specimens at all seasons have the olive of a clearer, more greenish shade than in any Eastern examples; this clearer tint is analogous with that of the Rocky Mountain form of pallasi (auduboni). In precisely the same region inhabited by the pallasi var. nanus the swainsoni also has a representative form,—the var. ustulatus. This resembles in pattern the var. swainsoni, but the olive above is decidedly more rufescent,—much as in Rocky Mountain specimens of
T. fuscescens; the spots on jugulum and breast are also narrower, as well as hardly darker in color than the back; and the tail is longer than in Rocky Mountain swainsoni, in which latter it is longer than in Eastern examples. The remaining species—mustelinus, fuscescens, and aliciæ—extend no farther west than the Rocky Mountains; the first and last only toward their eastern base, while the second breeds abundantly as far as the eastern limit of the Great Basin.
The T. fuscescens, from the Rocky Mountains, is considerably darker in color above, while the specks on the throat and jugular are sparser or more obsolete than in Eastern birds.
In T. mustelinus, the only two Western specimens in the collection (Mount Carroll, Ills., and Fort Pierre) have the rump of a clearer grayish than specimens from the Atlantic Coast; in all other respects, however, they appear to be identical. Some Mexican specimens, being in winter plumage, have the breast more buffy than Northern (spring or summer) examples, and the rufous of the head, etc. is somewhat brighter.