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. WILLOW THRUSH (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 



