MOLES 45 



ridge, leaving numerous small lengthwise cracks showing on the outside 

 (pi. 28a). These runs go here and there along the ground, between rocks 

 and beside logs; they are made when the mole is searching for the worms 

 and ground-dwelling insects which it uses as food. The second type of 

 shelter, formed by actual excavation as in a gopher's burrow, is a regular 

 underground tunnel, circular in section, and situated at a greater depth 

 in the ground. The mole's tunnels are not so extensive and are of less 

 diameter than those of any of the gophers of the region. To make these 

 deep burrows the mole must force the loosened earth out onto the surface 

 of the ground. This it does through laterals constructed at short intervals. 

 Earth is loosened below ground (by the use of the forefeet ?), then is forced 

 along the existing tunnel way presumably by the joint use of forefeet 

 and chin (though the actual method of operation has yet to be seen), 

 and it is then forced up a lateral. As we stated before, there is never 

 any direct opening to the exterior. Each fresh lot of earth is forced into 

 the vertical or nearly vertical lateral, pushing the earth already there out 

 on top of the ground to topple over in one direction or another (see pi. 28& 

 and fig. 22). Because of this method of digging, there are usually six 

 inches or so of earth between the mole and the outside world. The freshest 

 earth forms a central 'core' in the molehill. This core, of whose position 

 there is seldom any external indication, can often be distinguished if the 

 mound be sectioned in a vertical plane. 



Practically all of our specimens of moles were taken in special mole 

 traps designed to be set over a surface runway, and the use of such traps 

 gave some information concerning the use of these runways. Sometimes 

 a trap set over a newly made runway would catch a mole within a few 

 hours; in other instances the trap remained several days before being 

 disturbed. These facts indicate that there is considerable variation in the 

 frequency with which the surface runways, once made, are traversed. On 

 still other occasions no reoccupation of the run was noted. After one 

 mole was caught in a runway, another individual sometimes appropriated 

 the vacated system to its own use. On November 18, for example, a mole 

 was taken in a run on the forest floor of Yosemite Valley. On the nine- 

 teenth the trap was sprung again, and being reset, caught a second mole on 

 the twenty-first. It is believed that ordinarily but one individual inhabits 

 a particular system of runways and tunnels at any one time. 



Evidence of the activity of moles was found below the 5000-foot contour 

 during every month of the year. In the summer and the fall months both 

 surface runs and molehills indicative of deeper excavations were observed, 

 in Yosemite Valley ; and at the end of December new runways were noted 

 in places in the Valley where the ground was not frozen. During the 

 height of winter in the high mountains when the ground is frozen to a 



