GRAY VIREO 269 



heard simultaneously. "The notes of the latter two, however, re- 

 sounded 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." Likewise, they heard 

 both the Button's and the gray vireos from the same stand, "the 

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

 brush belt adjacent." To make representation in the genus complete as 

 far as normal distribution is concerned, they also found both the gray 

 and the least vireos 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 chilopsos along the stream bed." 

 They summarize the relationships of the various members of the 

 genus as follows: "The presence of no less than five closely related 

 species of one family in so limited a region is obviously closely depend- 

 ent 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." They conclude that 

 the gray vireo "has only been able to find its way into the avifauna 

 of southern California from a Sonoran center of dispersal, through 

 the existence of an associational niche not occupied by another vireo." 



Grinnell (1922) found an adult pair on the west slope of Walker 

 Pass in northeastern Kern County, Calif., on July 25, 1922. The 

 location was at an altitude close to 4,500 feet on a steep, north-facing 

 hillside. Upper Sonoran Life Zone, but in a semiarid phase of it. "The 

 birds were in sparse brush {Garrya^ Kvmzia, Artemisia tridentata^ 

 and Cercocarpus hetulaefoUus) ; and a digger pine and a piny on both 

 grew within one hundred feet of where they were discovered." 



W. E. D. Scott (1885) took a specimen in Arizona on April 1 "in a 

 pretty rolling grass country, where the trees are rather scattered, 

 and at an altitude of 3500 feet." He says further : 



On the San Pedro River foothills of Las Sierras de Santa Catalina, at an 

 altitude ranging from 2S00 feet to 4000 feet (which is here the point of meeting 

 of the mesquite timber and the evergreen oaks), [the species] is, excepting the 

 Least Vireo (,Virco pusillus), the commonest form of Vireo, being fairly abun- 

 dant. * * * The two altitudes mentioned seem to be about the limits of the 

 species while breeding, and most of the birds secured were obtained between 

 3000 and 3500 feet altitude. * * * The locality where the species is most 

 abundant is where the mesquites terminate and the oaks begin; there being 

 of course a sort of gradual transition and no well or clearly defined line, the two 

 forms of trees being mingled about equally, I have found that the smooth flat 

 mesas, and the broad open bottoms of the wider canon are quite as much 

 frequented by them as the rough and broken hillsides, and it is difficult to ride 

 about anywhere between the altitudes above mentioned, without hearing the 

 very characteristic song of the species. 



It is interesting to note that on June 26 he did find one bird well 

 up within the oak belt. 



