214 NORTH AMERICAN FAUNA [No. 55 



MICROTUS PAUPERRIMUS (COOPER) 

 PYGMY MOUSE 



Arvicola pauperrima Cooper, Amer. Nat. 2 : 535, 1868. 



Microtus (Laffurus) curtatus artemisiae Anthony, Amer. Mus. Nat. Hist. Bull. 

 32: 14, 1913. Type from Ironside. 



Type. Collected on Plains of the Columbia, near Snake River, Wash., by 

 J. G. Cooper, in 1860. 



General characters. A small, short-tailed, light-gray mouse with lax fur; 

 soles of hind feet with only five tubercles ; side glands in males on flanks ; 

 skull short, wide, and rectangular. Upper parts uniform buffy gray; ears and 

 nose tinged with clear buff ; lower parts and feet pale buffy ; tail buffy, with 

 darker upper surface. Browner in summer and grayer in winter. 



Measurements. Average of three immature from Antelope, between Deschutes 

 and John Day Rivers: Total length, 115 mm; tail, 20; foot, 16; ear (dry), 8. 

 Of adult female from Waterville, Wash., on the Plains of the Columbia north- 

 west of the type locality, 128 ; 27 ; 17 ; 9. 



Distribution and habitat. There are specimens of these little gray 

 mice from Bakeoven, Antelope, Steens Mountains, Cedar Mountains, 

 Skull Spring, McDermitt, Disaster, Creston, Ironside, Fort Rock, 

 and Rock Creek ( north of Hart Mountain) (fig. 48). Undoubtedly 

 they occupy all of the sagebrush country of eastern Oregon that lies 

 within Transition Zone or upper edge of Sonoran but are very irreg- 

 ular in distribution and abundance. Also their habits are ^uch as to 

 shield them from observation and even render them difficult to locate. 

 They live usually on dry ground among the sagebrush where trails 

 and signs do not show and in burrows well hidden under the bushes. 



General habits. More than any other members of the genus 

 Microtus, these little mice are adapted to desert conditions, usually 

 living where no permanent water supply is within reach and where 

 infrequent rains, snows, and dew must leave them for months at a 

 time without available moisture, other than that obtained from 

 succulent food. They live mainly in burrows, coming out to gather 

 green plants for food and generally carrying them into the burrows 

 to be eaten. To what extent they burrow for roots and underground 

 vegetation is not fully known. They rarely make noticeable run- 

 ways but run over the barren surface of the ground from one burrow 

 to another, merely leaving lines of tiny footprints in sandy or dusty 

 spots. 



They seem to be largely diurnal as more are usually caught in the 

 daytime than at night, and they are often seen running through the 

 sagebrush even in bright sunlight. At three different localities in 

 Malheur County, Preble caught them in his hands in the daytime. 

 He and Anthony each found one in the stomach of a rattlesnake, 

 and as these snakes are mainly diurnal the mice were probably taken 

 during the warm part of the day. 



Breeding habits. The females have the common microtine ar- 

 rangement of 8 mammae in 2 pairs of inguinal and 2 pairs of pec- 

 toral. The young are probably 4 to 8, as in the closely related 

 cwtatus; 5 to 7 embryos have been recorded. 



Food habits. Apparently their food consists largely of green 

 vegetation, grass, lupines, and other small plants found growing 

 under or among the sage bushes. The little dry pellets scattered 

 along the trails or on the feeding grounds are usually green in color 

 but give no further clue to the nature of the food. Roots and bulbs 



