MOUNTAIN BEAVEB 155 



Sierra Mountain Beaver. Aplodontia rufa calif ornica (Peters) 



Field characters. — Size of small Marmot, with general appearance of Meadow Mouse; 

 tail so short as to appear to be wanting, shorter than hind foot ; head blunt, eyes and 

 ears small (pi. 31a). Head and body 11 to 14 inches (280-354 mm.), tail % to-1% 

 inches (19-40 mm.), hind foot 2% to 2^4 inches (55-63 mm.), ear from crown i^ to % 

 inch (13-21 mm.); weight 30 to 48 ounces (852-1375 grams). General coloration every- 

 where plain blackish brown. Workings: Underground burrows or tunnels about 6 to 7 

 inches in diameter with numerous openings to surface; located usually along brush- 

 covered banks of swift -flowing streams. 



Occurrence. — Eesident locally in small numbers in Canadian and Hudsonian zones on 

 west slope of Sierra Nevada. Eecorded at Aspen Valley, Gentrys, Chinquapin, near 

 Ostrander Eoeks, in both forks of Indian Canon (above Yosemite Valley), near Porcupine 

 Flat, and in head of Lyell Canon. Altitudinal range, 5800 to 10,000 feet. Lives along 

 swift-flowing streams bordered by willow and creek dogwood. Colonial; nocturnal. 



One of the most interesting and at the same time reclusive members of 

 the Yosemite fauna is the Mountain Beaver or Aplodontia. This animal, 

 like the redwood tree and the wren-tit, is peculiar to the west coast of 

 North America, where it occurs scatteringly in the Sierras and northern 

 coast ranges. Although called Mountain Beaver it is in nowise related by 

 structure or mode of life to the true beaver save that both are rodents. 

 The present species has, indeed, no close living relatives anywhere so far 

 as known. Locally we found that some of the workmen on road gangs 

 who knew of the animals called them 'mush-rats' because of their general 

 resemblance to the muskrat. The latter animal does not, to the best of 

 our knowledge, occur anywhere in the Yosemite region. 



The Sierra Mountain Beaver is of the size of a small marmot. If one 

 can imagine a meadow mouse grown to fifteen or twenty times its ordinary 

 size, and practically without any tail, one will have a good idea of the 

 mountain beaver. (See pi. 31a.) The animal is of stout build, has a short 

 blunt head, small eyes, small nearly naked ears, no obvious neck, a thick 

 body, normal legs and feet, and a mere stub of a tail. The tail is less than 

 the hind foot in length, and in this character the animal is unlike all local 

 small mammals except the rabbits and the cony. The body is covered 

 evenly with a uniform blackish brown pelage of considerable length and 

 of soft texture. 



Aplodontia is a timid, retiring animal, practically never seen except 

 when trapped. Its activity is confined to the night-time, and it spends the 

 day in underground retreats. When in captivity the least injury seems 

 sufficient to cause its death; its general resistance seems extremely low. 

 When kept as a captive it may be tamed rapidly, and even at the first its 

 only indication of displeasure is a rapid chattering or grinding with its 

 teeth. 



