POCKET MICE 145 



The three' species of pocket mice in the Yosemite region belong to 

 distinct groups, and were we as fully informed upon the details of their 

 life histories as we are for example upon those of the chipmunks, these 

 three pocket mice would doubtless merit separate consideration. But at 

 the present time we know little more than their structural characters, their 

 ranges, and the sort of immediate surroundings which each inhabits. The 

 San Joaquin and Great Basin pocket mice live in open situations, recalling 

 in this respect the Merced and Pale-faced kangaroo rats, while the Califor- 

 nia Pocket Mouse lives in places beneath the foothill chaparral {Adeno- 

 stoma) which are somewhat gravelly or rocky. The latter species parallels 

 in choice of habitat the Heermann Kangaroo Rat. In certain parts of the 

 country 2 or even 3 species of pocket mice are to be found in a single 

 locality, each occupying a separate type of habitat or niche; but in the 

 Yosemite region the ranges of the 3 species are distinct geographically as 

 well as ecologically. 



Pocket mice are exclusively nocturnal. They spend the day below 

 ground in their short simple burrows, coming out as soon as darkness falls 

 to forage on the surface of the ground. Their mode of progression is like 

 that of a kangaroo ; they bound along on the enlarged and proportionately 

 long hind feet, using the tail as a stabilizer and counterbalance. The 

 forefeet come into particular service when the animals feed. Then they 

 function as hands and are used with great dexterity to hold food materials 

 and to thrust these into the fur-lined pouches or pockets on either side of 

 the face. When the cheek pouches are filled with seeds or other food the 

 animals make for their burrows and store the food there for use at times 

 when it is too cold or rainy out-of-doors for them to venture forth. 



A specimen of the Great Basin Pocket Mouse was captured alive at the 

 Farrington ranch on June 21, 1916, and retained in captivity for a time. 

 It was kept in a can, well wrapped with cloth. One morning the mouse 

 was found cold and stiff, seemingly dead ; but when the sun had warmed 

 the air it revived completely. 



One afternoon this mouse was taken to a large clear sandy area and set 

 loose in order that its habits might be observed. It seemed quite averse 

 to facing the sun and would always turn its back to the strong light. In 

 attempting to dig a burrow the mouse used its front feet to shove out the 

 loosened sand. Its actions in this respect resembled somewhat those of a 

 pocket gopher. When not disturbed the mouse moved along the sand 

 slowly like a cat when stalking a bird, but when alarmed the animal 

 bounded over the sand in three-foot leaps using only its hind legs, at such 

 a rate that the observer could scarcely keep up. When offered some rolled 

 oats the mouse, using its forefeet, stuffed the material into its cheek pouches 

 but ate none. 



