no. 3637 HERMIT THRUSH — ALDRICH 29 



extreme northeast, palest with more southern Pacific Coast and 

 interior mountains. 



Color variation seems to be correlated at least in part with environ- 

 mental moisture of the breeding areas (Gloger's law), but there are 

 a few exceptions. 



Body mass, as indicated by wing length, and length of appendages 

 are correlated with temperature in accordance with Bergmann's and 

 Allen's laws, respectively, in some breeding areas but not in others. 



Failure of certain populations to conform to these laws of geo- 

 graphical variation with respect to breeding distribution may be 

 explained in some cases by adaptation to environments in wintering 

 areas. 



Adaptation to environmental conditions appears to be more impor- 

 tant in producing morphological variation in populations than physio- 

 graphical or ecological barriers to gene flow. 



Regional trends toward dark pigmentation associated with moist 

 climate may be enhanced by physical isolation on offshore islands. 



The hermit thrush and others recently included in the genus 

 Hylocichla, excepting the woodthrush, are better classified on the 

 basis of morphology and behavior in the genus Catharus. 



Populations of hermit thrushes grouped by morphological, ecologi- 

 cal, and geographic characteristics break up into 10 recognizable 

 groups that may be considered as distinct races or subspecies; all of 

 these have previously supplied names. 



Each named subspecies is characterized as to color, size, breeding 

 distribution, and winter distribution; and the history of its char- 

 acterization and nomenclature are discussed. 



