292 University of California Publications in Zoology L VoL - 10 



tain, June 13, this being the northernmost station of observation. 

 Along the trail from Vandeventer Flat to Pirion Flat many were 

 noted as far east as Omstott Creek, 4500 feet to 3000 feet, this 

 being also about the limit in that direction of either species of 

 Aih nostoma. One bird was heard June 23 among the piiions 

 on Piiion Flat, half a mile east of Omstott Creek. Several 

 individuals were noted on a brushy ridge near Garnet Queen 

 Mine at about 6000 feet altitude, this being the most southeastern 

 point of observation. 



As already intimated, this vireo is pre-eminently an inhab- 

 itant of dry chaparral, thus conflicting in range with no other 

 species of the genus. Along the road below Strawberry Valley, 

 towards Keen's Camp, both this and the western warbling and 

 Cassin vireos were heard simultaneously. The notes of the latter 

 two. however, resounded respectively from the alder-lined ravine 

 bottoms, and from the golden or black oaks of the cool slopes, 

 while the gray vireo sang from the chamissal on the hot, steep 

 slopes near Chalk Hill. At Garnet Queen Mine, both the Ilutton 

 ami gray vireos were heard from the same stand, the former, 

 however, from the golden oaks, the latter, as usual, from the 

 brush belt adjacent. In upper Palm Canon, both the gray and 

 the least vireos were noted in one short stretch, the former in 

 some chamissal straggling down the west wall to the lowest limit 

 of its range, the latter species in some guatemote and chilopsis 

 along the stream bed. The presence of no less than five closely 

 related species of one family in so limited a region is obviously 

 closely dependent upon the separate, sharp, associational and 

 zonal preferments of each. The warbling, Cassin and Hutton 

 vireos are arboreal foragers; the least and gray vireos brush 

 foragers ; but the least is riparian, while the gray is distinctly 

 a dry-slope forager. We may surmise that the latter species has 

 only been able to find its way into the avifauna of southern 

 California from a Sonoran center of dispersal, through the exist- 

 ence of an associational niche not occupied by another vireo. 



It was in the vicinity of Ken worthy that most of our study 

 of the gray vireo was carried on. Here the bird was a con- 

 stant accompaniment of the belts of the two species of chaparral 

 bushes, Adcnostoma sparsifolium and A. fasciculatum. While 



