150 ANIMAL LIFE IN THE YOSEMITE 



mode of progression this animal recalls the kangaroo rats and pocket mice 

 found at lower levels on either side of the Sierra Nevada, but its habitat 

 predilections are quite different, for it lives in damp meadows and along 

 the banks of streams. 



The body of the Allen Jumping Mouse is perhaps a fourth larger than 

 that of a House Mouse ; it is similar in size to a Gambel White-footed Mouse. 

 It is of slender form, the ears are comparatively small, and the pelage is 

 long haired and rather harsh. The forelegs and feet are relatively short 

 and small ; the hind legs and particularly the hind feet are proportionately 

 very much longer in the jumping mouse than in the white-footed mice. 

 The tail is the most striking feature; it is fully one-third again the length 

 of head and body (pi. 26a). These departures from the normal mouse 

 form are all adaptations to the particular and unusual mode of progression 

 used by this mouse. Instead of running on the surface with all four feet, 

 it bounds along, using the hind pair of feet alone for propulsion and the 

 tail as a counterbalance and support. 



At Chinquapin an Allen Jumping Mouse was captured alive, the tail 

 only having been slightly injured by the trap. The animal was released on 

 a sunlit slope and an attempt was made to photograph it, but to no avail. 

 It was off on the instant, bounding downhill two to three feet at a jump. 

 These leaps were the results of catapultic extension of the two hind legs 

 simultaneously. The front feet apparently took no part in the leaping. 

 All the movements were so rapid that it was impossible to observe in detail 

 the methods of its locomotion. Upon reaching a small pool the mouse took 

 to the water readily, and swam steadily and rapidly. 



Near Porcupine Flat a jumping mouse was startled from its nest at 

 7 :30 A.M. on June 25, 1915. One of us, in walking through a small grassy 

 place beside a stream, chanced to touch the nest where the animal had been 

 resting and it thereupon darted out into the open. In three leaps it covered 

 about 8 feet and then stopped, humped up in the shadow at the butt of 

 a willow stalk but not under cover. There it remained motionless for some 

 minutes, with its eyes closed and its long tail curled around to one side 

 of its body. When in motion the reddish yellow color of the animal quickly 

 attracted the naturalist's eye; and when the mouse came to rest, partly 

 in sunlight and partly in shadow, its coloration was anything but protective 

 against the gray stem of the willow and the brown leaf -littered ground. 

 Later an unsuccessful effort was made to drive the mouse out into the open, 

 but it alertly avoided this, and darted off in a zigzag course among the 

 willow roots, always by quick hops, barely touching the ground at each 

 bound. Finally it disappeared in a hole beneath a clump of willows. 



The nest out of which the mouse at Porcupine Flat was flushed was a 

 spherical affair about 5 inches (130 mm.) in diameter, snugly ensconced 



