234 DURHAM 



populations of the North Rim, as well as differences between these rodents 

 and those of areas not far distant, show certain responses of the animals 

 of the North Rim to the environment and illustrate basic rules of 

 ecological variation. 



It was through the generosity of Captain Allan Hancock that I was 

 able to spend two months collecting on the North Rim. Dr. Harold C. 

 Bryant, then superintendant of Grand Canyon National Park, negotiated 

 the special permits, arranged for cabins at several collecting stations and 

 acted as guide through much of the wilderness country over which Cap- 

 tain Hancock had previously flown the reconnaissance party. Grand Can- 

 yon rangers and naturalists generously contributed information on roads, 

 collecting stations, water holes and weather. I am indebted also to Dr. 

 John S. Garth, of the Hancock Foundation, who arranged and led the 

 trip in 1947 and thereafter encouraged me in this project. Dr. William 

 V. Mayer of the Biology Department, University of Southern California, 

 kindly read the manuscript and offered helpful suggestions. 



ACCOUNTS OF SPECIES 

 Spermophilus variegatus grammurus (Say) 



Habitat: Rock squirrels were found among rocks, on cliffs and in 

 sparse vegetation at the edge of the Canyon where insolation is high. 

 They are not widely distributed on the North Rim. Wary animals were 

 seen at Dutton Point (Map 2) and four adults were trapped at Muav 

 Saddle. In contrast to the exposed Sonoran environment of these two 

 places is a cool, shady, leafy canyon just north of Swamp Point where 

 one juvenile squirrel, possibly in migration, was shot. 



Color: Available for comparison with the rock squirrels from the North 

 Rim are one adult from southeast Arizona, typical of the pale subspecies 

 grammurus, and two adults from Zion National Park, Utah. The latter 

 animals appear to be dark enough on head and posterior back to belong 

 to the subspecies Utah. The specimens from the North Rim are nearly as 

 dark as those from Zion National Park and much darker than the above 

 mentioned one from southeast Arizona. I agree with Howell (1938, p. 

 146) that those from the Kaibab Plateau are nearer S. v. utah, but be- 

 cause Kelson (1951, p. 31) and Durrant (1952, p. 121) considered speci- 

 mens even as dark as those from Zion National Park to be grammurus, 

 and Hall and Kelson (1952, p. 346) so considered the single specimen 



