Vol. VI] SWARTH— RACES OF BEWICK WREN 63 



In fact, in the insular forms of Thryomanes bewkki (as 

 well as in other races of birds occurring upon the 'several isl- 

 ands of the Santa Barbara group) it is at present impossible 

 to detect generally uniform results of any factor or factors, 

 either as to the occurrence or non-occurrence of species upon 

 the different islands, or in the amount and nature of differen- 

 tiation that has taken place. 



Possible criticism may be invited by the fact that in the 

 present paper certain local races (subspecies) are pointed out 

 and their characteristics described, but no names affixed. This 

 applies particularly to the Vancouver Island form of calo- 

 phonus, and to the wren of the southern boundary of the Great 

 Basin region as distinguished from typical eremophihis of the 

 Gila Basin. It is the writer's opinion that the aggregations of 

 individuals occupying these several areas are geographically 

 separated from the typical forms. whose names they bear. They 

 are also probably to be distinguished, though with some dif- 

 ficulty, by the average differences indicated; possibly they arc 

 local races in early stages of differentiation. The objections 

 to formally affixing names in their cases are two in number: 

 first, in the slightly distinguished races in question it is impos- 

 sible to indicate miore than obscure average distinctions; and 

 second, the extreme variability shown in individuals of even the 

 most strongly marked of the several described forms militates 

 against the recognition of these apparent geographic variants 

 even though they appear to be isolated. The peculiar char- 

 acters of the Vancouver Island wren are perhaps to be ex- 

 plained as solely a result of isolation. The Desert Wren of 

 southeastern California, in its departure from typical ere- 

 mophilus, shows a distinct approach to charienturus, and it 

 may be that in its affinities, as it is geographically, it is inter- 

 mediate between the two. 



