1936] 



MAMMALS OF OREGON 



189 



General habits. At both localities where specimens were taken 

 they were caught at the base of cliffs or canyon walls. This would 

 indicate habits more nearly like those of truei, which is largely a 

 cliff dweller, than like the timber and brush-loving gilberti. 



REITHRODONTOMYS MEGALOTIS MEGALOTIS (BAIRD) 

 DESERT HARVEST MOUSE 



Reithrodon megalotis Baird, Mammals North Amer., p. 451, 1857. 

 Reithrodontomys megalotis nigrescent Howell, North Amer. Fauna No. 36, p. 32, 

 1914. Type from Payette, Idaho. 



Type. Collected in northeast corner of Sonora near San Luis Spring, N. Mex., 

 by C. B. R. Kennerly, in 1855. 



General ohwraoters. Slight- 

 ly smaller and paler colored 

 than the common house 

 mouse, with longer and softer 

 fur and whiter lower parts, 

 with deeply grooved upper 

 incisors, terete, well-haired, 

 tail, and hairy ears. Color, 

 upper parts buffy gray, paler 

 on the sides ; lower parts, 

 feet, and lower half of tail 

 white or whitish. 



Measurements. Average of 

 several typical adults: Total 

 length, 140 mm ; tail, 71 ; foot, 

 17.6; ear (dry), 12 to 13. 



FIGURE 39. Range of the two subspecies of harvest 

 mice in Oregon : 1, Reithrodontomys megalotis 

 lonyicaudus ; 2, R. m. megalotis. 



Distribution and habi- 

 tat. These mice show 

 surprisingly little varia- 

 tion over a range extend- 

 ing from central Mexico up through the interior desert country to 

 eastern Oregon and southeastern Washington (fig. 39). They prac- 

 tically fill the dry Upper Sonoran Zone area of Oregon east of the 

 Cascades wherever there is enough moisture for a good growth of 

 vegetation. They are partial to marshes, meadows, ditch banks, or 

 the borders of irrigated fields. Often they, are locally abundant in 

 suitable situations, but over the dryer parts of the region they are 

 entirely absent. 



General habits. These little harvest mice are mainly ground 

 dwellers, making their little roadways over the surface of the ground 

 under cover of growing or fallen vegetation, and living in grass 

 nests, on or under the surface of the ground. They make tiny bur- 

 rows, but seem to spend much of their time in their runways or in the 

 nearby vegetation searching for choice bits of food. They are 

 active all winter, and seem to be almost as diurnal as nocturnal, often 

 getting into traps during the daytime and occasionally seen darting 

 through their runways. 



Breeding habits. The females have normally 3 pairs of mam- 

 mae 2 inguinal on 2 large mammary glands and 1 pectoral on a pair 

 of smaller glands. The young, as indicated by sets of embryos, are 

 usually 4 to 6. They seem to be found at all seasons except mid- 

 winter in the North, and evidently several litters are raised in a 

 season. 



