1936] 



MAMMALS OF OREGON 



245 



base ; cheek pouches well developed and lined with short hairs ; upper incisors 

 deeply grooved as in all of the family ; skulls with mastoids and audital bullae 

 moderately inflated ; pelage long, appressed, and very silky. Upper parts buffy 

 gray with clear buff along sides; ears dusky inside with buff spot at lower 

 base; lower parts buffy with usually white on breast; feet buffy gray; tail 

 clear buff below, buffy brown above with dusky tip. Young grayish buff. 



Measurements. Average of adult specimens: Total length, 172 mm; tail, 

 92; foot, 22.4; ear (dry), 7. Adult male at Voltage, Oreg.: Total length, 170; 

 tail, 97; foot, 24; ear, 8. Weight 18 g. 



Distribution and habitat. These pocket mice occupy practically 

 the whole Upper Sonoran area of eastern Oregon and extend into 

 southern Washington as far as North Yakima and slightly into Idaho 

 along the Snake River Valley (fig. 55). In the sandy or mellow 

 soil of the arid valley bot- 

 toms they are often abun- 

 dant and so easily taken 

 as to be well represented 

 in collections by large 

 series of specimens. One 

 specimen was taken by 

 Jewett at about 7,600 feet 

 on the Steens Mountains , 

 in aspen country, where 

 the ground was barren 

 and much sheeped over. 



General habits. In the 

 dry sagebrush valley 

 south of Malheur Lake 

 these beautiful, silky little 

 pocket mice were as com- 

 mon as the writer ever 

 found them anywhere, 

 ranking next to the white-footed and meadow mice in abundance. 

 Some mornings as many as 5 or 6 were found alive in his line of a 

 dozen tin-can traps placed near their burrows where the slender 

 tracks and tail marks were noticed. 



Their burrows are generally placed under sagebrush in mellow soil 

 where the scattered vegetation furnishes food and some concealment, 

 but still leaves open spaces for free travel. Usually a little heap of 

 fresh sand marks the main entrance, which is securely closed during 

 the daytime. Half a dozen other doorways may be standing open 

 under the bushes, but these are unmarked by earth and are used only 

 as exits. Still others come close to the surface but are not opened 

 except in case of danger when the animals burst out and flee to other 

 burrows. Several escaped in this manner as the writer dug out their 

 dens and kept a careful watch for them. Usually the burrows run 

 2 or 3 feet deep, with many branches and winding shafts, one or more 

 storage chambers, and a nest cavity. 



The animals are strictly nocturnal and spend the daylight hours in 

 their closed underground retreats, but if a closed burrow is opened 

 up at any time of day they soon close it again with earth from within. 

 They are dazed by bright sunlight when driven out of their burrows, 

 but in the house or in the shade of bushes they see well. 



FIGURE 55. Range of the five species and subspecies 

 of pocket mice in Oregon : 1, Perognathus parvus 

 parvus; 2, P. p. mollipilosus; 3, P. lordi lordi: 

 4, P. I. columbianus; 5, P. nevadensis. Type 

 localities circled. 



