no. 3637 HERMIT THRUSH — ALDRICH 9 



of the birds and environmental conditions vary more markedly there 

 than anywhere else within the breeding range of this species. 



In the redwood section of the "Pacific Rain Forest" belt along 

 the coast of California and southwestern Oregon, as delineated by 

 Schantz and Zon (1924) and Ktichler (1964), occurs a very small, 

 pale hermit thrush with a large bill. This is sharply distinct from 

 larger, relatively small-billed and darker populations from the 

 adjoining mountain forests of the Cascades and the very much 

 larger, although similarly colored, birds of the adjoining mountain 

 forests of the Sierra Nevada. Thrushes from varying types of the 

 "Pacific Rain Forest" (Halliday, 1937; Rowe, 1959; Kiichler, 1964) 

 further north are slightly larger in wing and tarsus than those from 

 the California coast, have smaller bills, and break down into several 

 color variants, all quite distinct from the California coastal birds. 

 Thus, there is no uniform color type — conforming to Gloger's rule — 

 characterizing the very moist "Pacific Ram Forest" as a whole, as 

 delineated by Aldrich (1963). Rather, the hermit thrushes of this 

 zone, relatively uniform ecologically, exhibit the extremes in color 

 variation found in the species — from almost the most reddish to the 

 most grayish and from the darkest to the palest. 



Specimens from the Pacific coastal belt also exhibit the extremes 

 in bill size. The only characters they seem to possess in common are 

 small measurements of structures other than bill. These birds are 

 correlated with a milder coastal climate and, if indicative of body 

 mass as McCabe and McCabe (1932) found to be the case in wings of 

 hermit thrushes, they are in accordance with Bergmann's rule. 

 Pitelka (1951) found a similar situation in the variation of scrub 

 jays. An exception to Bergmann's rule would seem to be the small 

 size of hermit thrushes in the high interior mountains of southern 

 British Columbia and northern Idaho. 



The relatively large bill of the more southern Pacific coastal 

 population is in conformance with Allen's rule although the length 

 of legs does not follow this rule. The longest legs are found in eastern 

 populations but, contrary to Allen's rule, the northernmost ones 

 have longer legs than those from farther south. This is also the trend 

 on the Pacific Coast. 



Except for the coastal population from California north to 

 Washington, there appears to be a correlation in the dark color 

 tone of the plumage of hermit thrushes from the humid coastal area 

 as compared with the paler shade found in those from more interior 

 mountains. Thus, the grayish trend exhibited by birds of southern 

 British Columbia has its darkest expression in the rain forests of 

 Vancouver Island, while the more rufescent birds of northern British 

 Columbia and Alaska reach the peak of darkness on the extremely 



270-350—68 2 



