MEADOW MICE 



129 



SECTION AT "A-B" 



sump 



An area approximately nine feet square was gone over in detail and 

 the sod lifted off so as to expose the tunnel system. The ground was so 

 soft that for the most part the work could be done with the hands, only a 

 few of the deeper parts requiring the use of a shovel. Some of the tunnels 

 contained evidence of recent occupation by meadow mice in the form of 

 scattered short cuttings of grasses and composites; in a few places there 

 were footprints of the mice in the soft earth on the tunnel floor. A reddish 

 material covered the floor in some of the old galleries, and here the foot- 

 prints showed to good advantage. Scattered along the tunnels were the 

 droppings of the mice. Only about half the tunnels which were opened 

 up gave any evidence that they were in use during the current season. 



One recently built nest of 

 dry grass, and part of an old 

 one, were found in side pockets 

 off two main tunnels. The newer 

 nest cavity had two entrances, 

 serviceable also as avenues of 

 escape in time of danger, and 

 there was also a short accessory 

 loop leading around the nest. 

 In various places there were 

 'sump' holes (fig. 18) which 

 were dug to a lower level than 



the tunnels off from which they branched. These undoubtedly served 

 to keep the tunnels drained, as each sump had more or less mud in its 

 bottom. At other places there were slight side pockets or 'turn abouts' 

 just large enough to hold a mouse. Only one hole connecting the surface 

 runwaj^s and tunnel systems was found in the area studied. This is an 

 unusual condition as compared with other 3Iicrotus runways which we 

 have examined. Only one Microtus, quite a young individual, was obtained 

 at this system of runways, though trapping was continued there for several 

 nights. 



Sierra Cantankerous Meadow Mouse 

 Microtus mordax sierrae Kellogg 



Field characters. — Body size more than twice that of House Mouse; tail slightly more 

 than % head and body; pelage soft and dense. (See figs. 166, 20a.) Head and body 

 41/4 to 5 inches (108-128 mm.), tail 2 to 2% inches (50-66 mm.), hind foot about 

 % inch (20-23 mm.), ear from crown % to % inch (13-17 mm.); weight about 1 to 

 1% ounces (30.3-48.0 grams). Coloration above dark brown with a grayish cast; sides 

 of body conspicuously grayish; under surface grayish white; tail distinctly darker above 

 than below. 



Occurrence. — Common resident, chiefly in Canadian and Hudsonian zones, on both 

 slopes of Sierra Nevada. Eecorded commonly from Merced Grove Big Trees and Chin- 



Pig. 18. Enlarged section through part of 

 burrow system shown in figure 17 in region 

 indicated at "A-B." 



