LIST AND DESCRIPTION 135 
from them by the ordinary observer, though more rufous in color. 
In this three-fold migrating company the Olive-backed is by 
far the most numerous and dominates the group to such an ex- 
tent that the other two are apt to pass unobserved. The breed- 
ing range of the Wilson Thrush, as this bird is called, is north 
of South Dakota in our longitude. 
756a. WitLtow TuHRusH (Hylocichla fuscescens salicicola.) 
This Thrush is found among the lower willowy portions 
of the Rockies, and is named from this fact. It is quite common 
in migration in the eastern part of the State, and may be found 
nesting by the willow lined streams of the Black Hills. It is 
about the same size as the Gray-cheeked and Olive-backed 
Thrushes, but the upper parts are more russet. It is similar to 
the Wilson Thrush in coloration. 
757. GRAY-CHEEKED THRUSH (Hylocichla aliciae aliciae.) 
The ordinary observer will with difficulty distinguish this 
bird from the Olive-backed Thrush. It is about the same in 
size and coloration, except that its eye ring is whitish instead 
of buff, and its cheeks are gray instead of yellowish. It migrates 
through South Dakota to its northern nesting home about the 
same time as the Olive-backed, and few are aware that more 
than one species is passing. 
758a. OLIvE-BACKED THRUSH (Hylocichla ustulata swainsoni.) 
This Thrush is very abundant in the southeastern part of 
the State in spring migrations. At Vermillion it fairly takes 
possession of the town, being seen for a few days in every yard. 
A week or more is often required for the whole procession to 
pass. Sometimes it is mistaken for the Wood Thrush; but it 
arrives earlier, is a little smaller, and decidely more olivaceous. 
The white breast is not pure white and luminously spotted like 
that of the Wood Thrush, but has an olivaceous wash, with 
rather obscure and more blended spots. 
759b. Hermit THRusH (Hylocichla guttata pallasi.) 
Seen only as stragglers in migration in the eastern part of 
the State, arriving about ten days earlier than the other 
Thrushes. «It has been observed by the authors for several years 
