MAMMALS OF YOSEMITE NATIONAL PARK 



79 



live where the runways are more than 

 half submerged. They are found from 

 the lowest level of the park nearly up 

 to timberline. 



These are the path-cutters. Part the 

 lush grass in the drier portions of the 

 meadows, and a maze of runways will 

 usually be revealed. The covered passage- 

 ways reduce detection of the mice from 

 above by predators. A system of under- 

 ground tunnels may also be employed 

 and, if the site is dry, the nesting cham- 

 ber placed below ground. Often, the nest 

 is made in a clump of grass or sedge, 

 above the water level. Many other crea- 

 tures, such as shrews and weasels, find the 

 runs convenient highways and use them 

 frequently. 



Activity is carried on through all sea- 

 sons. In winter, tunnels are made in the 

 snow and nests are often built beneath 

 the surface, which insulates them from 

 the colder giound below. In 1942, an in- 

 dividual was seen traveling on the sur- 

 face of the snow, then 3 2 x /z inches deep, 

 near the Rangers' Club. 



Meadow mice are among the most fe- 

 cund of mammals. They start breeding 

 when less than two months old and pro- 

 duce several broods, of half a dozen each, 

 a year. 



Green food, grass in the main, is pre- 

 ferred. Vegetable matter may provide 

 99 per cent of the diet. These prolific 

 little creatures are part of the common 

 currency which provides the carnivores 

 with energy — energy which the grass 

 gets from the sun, which the mouse gets 

 from the grass, and which flesh-eaters 

 cannot get in sufficient quantities directly 

 from the plants because they are flesh 

 eaters. 



Three kinds have been recorded in the 

 park, but they will be undistinguishable 

 to the layman. Two are found in mead- 

 ows and grasslands, not far from water. 

 The Sierra meadow mouse is freer run- 

 ning, often using the ground under 



Pboto by Author 



Mouse runs in parted grass, Yosemite Valley. 



bushes and in thickets. Generally, it 

 makes no runways, though poorly de- 

 fined paths may be found. Unlike the 

 others, which are active any time, this 

 form is not abroad so much in the day- 

 time. 



At the time of the Grinnell and Storer 

 survey (1914-20), the house mouse 

 was found about barns and dwellings in 

 Yosemite Valley. The Yosemite Museum 

 has a specimen of the Alexandrine or 

 roof rat, taken in the valley in 1936. At 

 this writing, I am unable to determine 

 that Old World rats and mice, such as 

 infest more "civilized" areas, are present 

 in the park to a conspicuous degree. Men- 

 tion has already been made of the dif- 

 ferences between certain native forms 

 and these species that were introduced 

 from the Old World (see pp. 75-77). 



An Allen jumping mouse is a pretty 



From Kodachrome by M. V. Hood 

 Allen jumping mouse. 



