Vol. VI] SWARTH— RACES OF BEWICK WREN 55 



For many reasons the genus Thryommics as occurring in 

 California is an attractive one to the student of geographical 

 distribution. The birds exist in numbers where conditions 

 are favorable. As the species is not sharply delimited associ- 

 ationally, conditions are more generally favorable than in many 

 other groups of birds, and Thryomanes is consequently abun- 

 dant and widely distributed throughout the state. The varia- 

 bility of the group is notable, birds from different regions ex- 

 hibiting to a marked degree the types of characteristics which 

 we have learned to look for in animals of the various areas. 

 Thus there are these several factors : — abundance, with conse- 

 quent accumulation of extensive series of specimens; dis- 

 regard of associational barriers effective in many other species, 

 with resulting general distribution, this condition permitting 

 careful scrutiny of conditions existing between many stations 

 but slightly separated geographically, though of different 

 faunal aspect; and variability, birds from different regions 

 exhibiting peculiarities of color, etc. — all combining to make 

 this genus a profitable subject for careful examination. 



MANNER OF OCCURRENCE 



Wrens of the genus Thryomanes occur in fair abundance 

 practically throughout the state of California. The genus in 

 this state belongs pre-eminently to the Upper Sonoran zone, 

 but it also occurs commonly in places in Transition, as in the 

 northern coast region, and sometimes in Lower Sonoran, as 

 in parts of the San Diegan region and the San Joaquin Valley. 

 It is not found, however, in the high Transition and Boreal of 

 the Sierra Nevada and the southern Sierras, and it is notably 

 absent from the arid Lower Sonoran of the Colorado and Mo- 

 have deserts. This last was unexpected, as the species occurs 

 commonly in regions of similar zonal character elsewhere. The 

 above statements all apply to the breeding range of the bird. In 

 seasons other than the nesting time there are exceptions, as 

 noted beyond. 



In certain other variable groups, such as the Song Spar- 

 rows {Melospiza melodia), Horned Larks (Otocoris al- 

 pestris) and Bush-tits ('P,ya//n/)ar«.?J^ associational requirements 



