MEADOW MICE 127 



Occurrence. — Common resident in Lower and Upper Sonoran zones on west slope of 

 Sierra Nevada, Eeeorded from Snelling (subspecies aestuarinus) eastward to El Portal 

 and Cascades (subspecies mariposae) Ao Inhabits grassland. 



The California Meadow Mouse is an inhabitant of grassy fields and 

 marsh lands near the rivers and streams of the western part of the Yosemite 

 region. Its range here is restricted to those rather scattered portions of 

 the region which are open and fairly level. The species is common in the 

 flat areas along the eastern margin of the San Joaquin Valley, but in the 

 foothill districts it is for the most part found only in the scattered stream- 

 side tracts which man has found to be most suitable for his own purposes. 



In general appearance and habits the California Meadow Mouse is much 

 like the Yosemite Meadow Mouse which lives in the territory from Yosemite 

 Valley to the crest of the Sierras, It is, however, of somewhat larger size 

 and makes slightly wider runways. 



As with other meadow mice, the breeding season of this species is long. 

 At Pleasant Valley and near Coulterville, in late May and June of 1915, 

 young were already about in some numbers; and near El Portal in late 

 November and even as late as December 5 (1914), half -grown individuals 

 were trapped. On November 29, an adult female captured at El Portal 

 was found to contain 5 large embryos. This number is probably an 

 average. 



The food of this mouse consists chiefly of grass, which is freshly cut 

 in lengths of about 1 inch, presumably so that it can be more readily 

 carried along the runways and burrows. 



This meadow mouse, like others of its tribe, is subject to decided fluctua- 

 tions in population from year to year. If one examines for a number of 

 successive years the ground where the animals occur, one will note decided 

 changes in the extent of their operations. In 1915, the population in the 

 meadows adjacent to Bean Creek east of Coulterville seemed to be at a 

 low ebb, for only by vigorous efforts in trapping could we obtain even a 

 few individuals ; whereas, as a rule, the capture of meadow mice in numbers 

 is a relatively easy matter. Many of the burrows and runways which we 

 examined in this place were in a state indicating disuse. The holes were 

 frequently covered with cobwebs, and small plant growths had sprung up 

 in the runways. Neither of these conditions is to be noted in runs which 

 are in current use by the mice. In 1920, trapping a short distance to the 

 east of this locality, on Smith Creek, produced a number of the animals. 



At El Portal, on December 4, 1914, an adult meadow mouse was found 

 with its hair firmly entangled on a twig in a brush pile. It had evidently 

 made frantic efforts to escape, going round and round the twig, but this 

 had only served to bind its hair all the tighter and being thus held the 

 mouse perished, either from exposure or starvation. 



