VARIATIONS OF RODENTS 239 



Tarniasciurus hudsonicus dixiensis Hardy 



Habitat: That chickarees were rather common in the Canadian forest 

 of the North Rim was indicated by the mounds of shucked cones, the 

 tree nests and the noisy chatter. How^ever, only two were shot (at 

 Tipover Spring) and a third was picked up on the road (near Robber's 

 Roost where they were common, as they also were at Bright Angel 

 Ranger Station). These three specimens, taken in late June and early 

 July, are in various stages of molt, one specimen still retaining from its 

 winter pelage the conspicuous ear tufts, gray sides, and heavy hair on 

 the hind feet. 



Color and size: This group of chickarees, isolated on the Kaibab 

 Plateau, was formerly assigned to the small, gray subspecies frefnonti 

 of Colorado. Available data indicate that the specimens of the North 

 Rim are too large, have nasals too long and pelage too dark for fremonti. 

 In size they compare favorably with those of the large chickarees of the 

 subspecies mogollonensis of the highlands of central Arizona, including 

 the San Francisco Mountains, from which they are separated not only 

 by the Grand Canyon but also by stretches of desert; but the lack of a 

 bright yellow-rufous dorsum indicates only distant relationship. In size 

 (length of head-body, length of hind foot, length and breadth of skull 

 and length of nasals) and in dorsal coloration (Hardy, 1942, p. 87) 

 they agree with dixiensis of the High Central Plateau of southern Utah. 



The form from the North Rim may prove to be a new subspecies 

 but until more specimens are available it seems best to assign it to 

 dixiensis, with which it shows close geographic, morphologic and chro- 

 matic affinities. The relationship of the populations of large chickarees 

 on the High Central Plateau, the Kaibab Plateau, and the San Francisco 

 Mountains is yet to be worked out. 



Thomomys bottae boreorarius Durham 



Habitat: The Botta pocket gopher was found for the first time on 

 the North Rim in 1947 (Durham, 1952, p. 498). This is the only 

 pocket gopher found at Swamp Point, ]Muav Saddle and Powell Plateau, 

 whereas the northern pocket gopher is common and widespread in boreal 

 areas of the Kaibab Plateau. The Botta pocket gopher occurs sparingly 

 and sporadically in the shallow, stony soil at or near the margin of the 

 coniferous forest. By July those individuals occupying the hardest, shal- 

 lowest soils became relatively inactive, and two days often elapsed before 



