Vol. VI] SWARTH— RACES OF BEWICK WREN 57 



of the mountains separating the desert and coastal regions, 

 there is no known instance of an individual of this subspecies 

 having crossed the divide and invaded the Pacific slope. 



While I am convinced of the truth of the statements made 

 above regarding the generally non-migratory habits of the Cal- 

 ifornia wrens of the genus Thryomanes, excepting ere- 

 mophilus, there do take place certain limited and irregular 

 movements which are not to be considered as migrations. The 

 late summer dispersal of birds in general, the "scatter move- 

 ment," as it has been called, is common to many parts of the 

 country, and may take individuals, mostly immatures, in any 

 direction. The northward wandering of herons at the close of 

 the breeding season is a well-known instance in point. In parts 

 of California this movement takes the form of an invasion of 

 high mountain regions by many low zone species from the ad- 

 jacent valleys and foothills (see Grinnell, 1908, p. 22), and 

 Thryomanes participates in this to a notable extent. In south- 

 ern California during July and August, T. b. charienturus 

 is one of the most abundant birds in the higher mountains, 

 at altitudes where it never breeds, occurring in numbers to the 

 summits of the highest peaks. As early as the middle of Sep- 

 tember this invading army has again withdrawn. Several 

 specimens at hand from parts of the Sierra Nevada seem also, 

 from dates and altitudes, to have been wanderers from lower 

 elevations. 



This general movement is apt to carry occasional indi- 

 viduals of any of the forms slightly beyond the usual faunal 

 confines of their respective races, and there are several in- 

 stances in the assemblage of skins examined where circum- 

 stances seem to indicate a happening of this nature. 



The occurrence of T. b. charieniiims in winter at stations 

 in the western parts of the Mohave and Colorado deserts 

 (as at Barstow, Victorville and Palm Springs), is easily ex- 

 plained as due to continuous favorable avenues of approach 

 from the normal breeding grounds in the foothills of the near- 

 by mountains. Other species properly belonging to the San 

 Diegan faunal region have been similarly found at the same 

 places. 



