64 



YOSEMITE NATURE NOTES 



RODENTS OR GNAWING MAMMALS — Rodentia 



The Sierra mountain beaver bears 

 no close resemblance to the true beaver. 

 It looks much like a tailless muskrat or 

 a gigantic meadow mouse, blackish brown 

 in color. It will seldom be seen by the 

 park visitor, for it utilizes extensive tun- 

 nels safely to reach food above ground 

 and is chiefly nocturnal. The burrowings, 

 six or seven inches in diameter, running 

 parallel to the surface, roofless in spots, 

 may be found on bottom land near 

 streams in widely scattered locations at 

 elevations ranging from less than 4,000 

 feet to more than 10,000 feet. 



The food consists of almost any 

 "greenery," but bark is also eaten. Moun- 

 tain beavers are known to stack and cure 

 vegetation near the mouths of their run- 

 ways. This is now believed to be done in 

 order to have a supply of dry bedding, 

 rather than in preparation for the season 

 when green food will not be available. 



The California gray squirrel should 

 be identified easilv by any visitor to Yo- 

 semite Valley. Some two feet long, with 

 a beautiful, bushy gray tail, it is ade- 

 quately described by its name. The Sierra 

 ground squirrel, which sometimes climbs 



California gray squirrel 



trees, might be confused with this spe- 

 cies, but the ground squirrel may be 

 distinguished by its two white or gray- 

 ish shoulder patches and the much nar- 

 rower tail. The upper limit of the range 

 here seems to correspond with that of 

 the oaks, although gray squirrels also 

 feed freely on pine seeds. It is thought 

 that in the higher forests, competition 

 from the Sierra chickaree prevents the 

 gray from flourishing. 



The California gray squirrel sometime 

 builds large nests of twigs, needles, grass 

 and similar materials, in trees, or, soft 

 linings may be made in cavities of trees. 

 The California black oaks in Yosemite 

 Valley are so old that plenty of holes 

 seem to be available, for outside nests 

 are not too common there. I have reason 

 to believe that some individuals make an 

 outside nest in summer, then move to 

 a cavity with the approach of autumn. 

 However, this cannot be positively stated 

 to be a universal practice. 



The preferred food here appears to be 

 acorns and pine seeds. Acorns are cached 

 individually in the ground in autumn, 

 some oi which are dug up later, especially 

 in winter. I have seen a gray squirrel 

 dig down through several inches of snow 

 and successfully locate an acorn buried 

 in the ground beneath. Perhaps this food 

 storing habit helps explain why gray 

 squirrels do not hibernate, but are active 

 all the year. 



dray squirrels were virtually w iped 

 out in Yosemite by an epidemic of sca- 

 bies in the early 1920's. They were ex- 

 tremely rare here tor a number of years; 

 an all-day census of the Valley in the 

 summer of 1 9 3 S revealed but two indi- 

 viduals. By the early 1940's the species 

 had made its way back to such .\n extent 

 that a considerable number were killed 

 by motor cars. They are now abundant 

 throughout their proper range in the 

 park. 



