MAMMALS OF YOSEMITE NATIONAL PARK 



77 



Photo by R. G. BtiJIeman 

 Young white-footed mouse. Probably Gambel. 



The winter nest must be especially warm, 

 for they do not hibernate. 



Certain studies in the Sierra indicate 

 that there may be from five to ten white- 

 foots per acre. They are undeniably pro- 

 lific, breeding when from five to eight 

 weeks old, and having up to four litters 

 a year. In such numbers, being mainly 

 seed eaters, vhey must have an important 

 impact on the plant life of the area. Nat- 

 ural checks, such as disease and seasons 

 of poor food supply, have prevented them 

 from becoming a plague here. As food 

 for other interesting animals, from 

 shrews to mountain lion, they make a 

 significant contribution to the wildlife 

 picture in the park. 



The patient observer of white-footed 

 mice in his camp or home may encounter 

 two interesting types of behavior — 

 "drumming" and "singing." The drum- 

 ming is done by the rapid vibration of 

 the forefoot or forefeet. It can easily be 

 heard if the mouse is among dry leaves, 

 or on a piece of paper, so that the sound 

 is amplified. The singing is so high- 

 pitched that not all ears may catch the 

 sound. I have never heard it, but it has 

 been described as being something like 

 the trill of a bird, though much weaker; 

 or, again, as a shrill buzzing. Certain!}' 

 the white-footed mice will bear acquaint- 

 ance, beautiful, attractive little animals 

 that they are. 



Two kinds of wood rcrts are in our 

 area, both of which are found at one 

 time or another in Yosemite Valley. 



Westerners may be accustomed to refer- 

 ring to these animals as pack rats, 

 trade rats or miner's rats, varying with 

 the locality. It is true that wood rats 

 seem interested in collecting strange ob- 

 jects, and adding them to their nests. 

 Sometimes other things may be brought 

 back in place of those taken, but there 

 is no evidence that this was done to 

 replace them on an exchange basis. Nev- 

 ertheless, many an interesting experience 

 has arisen through the collecting habits 

 of wood rats, especially the bushy-tail 

 of the higher elevations. 



Superficially, wood rats resemble the 

 species of Cld World rats which infest 

 the haunts of man in "civilized" areas. 

 Our native rats, however, keep them- 

 selves cleaner and present a more attrac- 

 tive appearance — soft fur, white feet and 

 underparts, large, lucent eyes, and tail 

 fully clothed with hair. 



The Streator wood rat is grizzled 

 brown above, with the short, brown hairs 

 on the top of the tail contrasting with 

 its white under surface. It ranges from 

 the lowest elevations on the western 

 boundary up to the level of Yosemite 

 Valley, where it meets the range of the 

 bushy-tailed wood rat. In the lower 

 country this form makes conspicuous 

 nests, on the ground or in trees. It may 

 assemble nesting material in the crevices 

 between the boulders of the talus slopes. 

 These nests are constructed of almost 

 anything that is available, but sticks play 

 a large part in their makeup. 



The bushy-tailed wood rat ranges 



Bushy-tailed wood rat. 



