10 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 124 



wet offshore islands of northern British Columbia and southeastern 

 Alaska. In the opposite direction, the grayish populations of the 

 relatively moist cedar-hemlock-pine "Columbian Forest," a disjunct 

 of the "Pacific Rain Forest," on the west side of the Rockies in 

 southern British Columbia and northern Idaho, become paler in the 

 relatively dry mountain coniferous forests to the north, east, and 

 south 



Progressing eastward from the relatively dry Rocky Mountain 

 forests through the moister and fairly uniform boreal forests of 

 eastern Canada, the color of hermit thrushes becomes more rufescent 

 and slightly darker immediately upon departure from the Rocky 

 Mountains. Further darkening occurs when we reach the eastern part 

 of the "Closed Boreal" forest east of James Bay in Quebec and New- 

 foundland. The darker pigmentation in this northeastern part of the 

 species' range is correlated to some extent with the "Closed Boreal" 

 forest as distinguished from the "Northern-Hardwood-Conifer" area 

 that comprises the southeastern part of its range. This correlation, 

 however, is far from complete because west of James Bay and Lake 

 Mistassini, Quebec, the morphological differences correlated with 

 these two ecological zones disappear. It is possible that habitat 

 background values vary from one association to another within the 

 boreal forest belt to supply the basis for selection. The darker colora- 

 tion is correlated roughly with sections of the "Closed Boreal" area 

 that Halliday (1937) called the "Northeastern Coniferous Section," 

 the "Gaspe" Section," the "East James Bay Section," and the 

 "Hamilton-Ungava Valleys Section." These sections agree in having 

 relatively deep, well-drained soils and are characterized by upland 

 forests of a relatively luxuriant growth of large trees, chiefly black 

 spruce and balsam fir. Forest sections to the west, starting with the 

 "Central Laurentian Section" and the "Northern Clay Section" of 

 Halliday (1937), have either sandy or poorly drained soils that 

 support forests of more stunted or open type, chiefly of black spruce, 

 jack pine, aspen, balsam-poplar, and white birch. These differences 

 in forest growth type conceivably could produce color and light 

 differences of the substratum that would be the basis for differential 

 selection in darker and lighter colored hermit thrushes. However 

 this may be, the reason why the birds of the "Northern Hardwood- 

 Conifer" area are closer to the western "Closed Boreal" forest sections 

 than to the eastern is not evident. As far as is known, the winter 

 environments of the two differing eastern populations are similar. 



Although there are a few apparent discrepancies, there appear to 

 be certain correlations between climax forest type of breeding areas 

 and colors of plumages in the western part of the continent. There, 

 all the darkest types are in the moist areas of the Pacific Northwest. 



