104 ANIMAL LIFE IN THE YOSEMITE 



At Snelling, in January, 1915, a number of roof rats were taken in 

 piles of drift and thickets along the Merced River. There were old deserted 

 nests of the Streator Wood Rat in the same locality and the suggestion 

 presented was that jjossibly the alien, with similar associational predilec- 

 tions, had driven out the native species. Along the Tuolumne River below 

 Lagrange the roof rats had made numerous pathways which were at first 

 mistaken for large runs of meadow mice. At El Portal two of the rats were 

 captured November 23 and 25, 1914, in the upper stories of the large hotel 

 building then there. The species is unknown at Coulterville, according to 

 Mr. Donald D. McLean, though House Mice are present there. The mice 

 are transported readily in bales of hay hauled on wagons, but the rats 

 require larger vehicles such as river boats or railroad cars. 



Common White-footed Mice. Peromyscus maniculatus (AVagner)^ 



Field characters. — Size slightly greater thau that of House Mouse; ear larger and 

 tail shorter (pi. 256 and text fig. 10a) ; tail distinctly less than length of head and 

 body, not scaly in appearance. (For measurements, see footnote 8.) General color above 

 yellowish brown (blue-gray in young) ; below pure white, sharply set off from color of 

 upper surface; tail bicolor, that is, white, with a dark stripe above; feet pure white. 



Occurrence. — Abundant resident throughout the entire Yosemite section from the 

 San Joaquin plains at Snelling eastward without interruj)tion across the mountains to 

 Mono Mills; range upward to at least 10,800 feet.s Inhabit every sort of cover from 

 stream margins to the dryest slopes and most barren rock slides. Nocturnal. 



The Common White-footed Mice are without any doubt the most 

 abundant mammals in the Yosemite section. Indeed, it is not unlikely that 

 the total population of this one species nearly or quite equals that of all 

 the other mammals in the region together. Its numbers do vary somewhat 

 according to place and season, but it is always present, and in some places 

 it may be said to fairly swarm. In whatever locality we placed our traps 

 this kind of mouse was sure to be caught. In places these mice simply 

 have to be 'trapped out' before representatives of other species can be 



8 Two subspecies of these mice occur in the Yosemite section, one on the west slope, 

 the other on the east side of the mountains, the two intergrading over the crest of the 

 Sierras. 



Gambel White-footed Mouse, Peromyscus maniculatus gambeli (Baird). The form 

 which is distributed throughout most of California west of the Sierran crest. It is 

 found from Snelling and Lagrange eastward in more or less typical form to the vicinity 

 of Tuolumne Meadows, and intergrades insensibly over the Sierran crest with the Sonora 

 White-footed Mouse. 



Sonora White-footed Mouse, Peromyscus maniculatus sonoriensis (LeConte). A 

 paler, less dusky, and slightly larger subspecies which inhabits the Great Basin and, 

 desert country to the east of the Sierran crest. It was recorded from Walker Lake east- 

 ward to Mono Mills. 



Measurements. — Gambeli: head and body 3 to 3% inches (75-95 mm.), tail 2-2% 

 inches (52-72 mm.), hind foot about % inch (18-20 mm.), ear from crown % inch 

 (13-16 mm.), weight about % onnce (12.8-21.1 grams); sonoriensis: head and body 

 31/2 to 4l^ inches (83-106 mm.), tail 21/8-3 inches (55-75 mm.), hind foot about % inch 

 (19-21 mm.), ear from crown % inch (15-17 mm.), weight % ounce (19.9-28.5 grams). 



