6 



PROCEEDINGS OF THE NATIONAL MUSEUM 



between extremes are quite sharp. Trends in geographical variation 

 of the hermit thrush indicated by Ridgway's (1907) detailed descrip- 

 tions of subspecies recognized at that time agree in general with 

 findings of the present study. 



If we assume that wing length is an indicator of overall size of 

 hermit thrushes — and studies by McCabe and McCabe (1932) indi- 

 cate that it is — the smallest birds breed in the immediate vicinity 

 of the Pacific Coast. On the other hand, the bill lengths of birds in 

 this area, correlated with distribution from north to south, range 

 from the smallest to the largest found in the species (averages of 

 males 12.2-15.6 mm). There is a trend of decreasing tarsal length 

 from north to south. Based on wing measurements, there is a rather 

 abrupt increase in size of hermit thrushes in passing from Pacific 

 coastal populations to those of interior mountain ranges. Examples 

 from the Cascade range are slightly but significantly larger than 

 California coastal birds and those from the Sierra Nevada consider- 

 ably larger. Those from the Great Basin mountains and middle and 

 southern Rockies are still larger, reaching the largest extreme for 

 the species in the latter area. Eastern hermit thrushes are uniform 

 sized with wings of medium length and relatively long legs (fig. 3). 



Table 1. — Comparison of ratios of bill to wing length (culmen: wing) in males and 

 females among subspecies of Catharus guttatus 



Subspecies 



Male 



Female 



auduboni 



guttatus 



euborius 



vaccinius 



nanus 



oromelus 



faxoni 



sequoicnsis 



crymophilus 



slevini 



14. 



14. 4 

 97. 2 

 12.2 

 84.2" 

 12.2 

 91.2" 

 13. 1 

 89. 4" 



12. 9 

 85. l" 



13. 1 



88. 9" 

 13.8 



89. 2" 

 13. 8 

 92. 5" 



13. 8 

 88. 3" 



14. 9 



81. 7" 



--. 1481 

 :. 1448 

 = . 1337 

 --. 1465 

 --. 1515 

 --. 1473 

 ■-. 1547 

 ■-. 1491 

 ■-. 1562 

 ■■. 1823 



