WHITE-FOOTED MICE 113 



often found about nests of the wood rat and for a time was believed to 

 live habitually with that species. Now it is known that the Parasitic 

 White-footed Mouse, while using deserted wood rat nests to some extent, 

 is also to be found in other sorts of shelter. Its particular niche in the 

 fauna of the foothill oak-chaparral belt is not surely known, though this 

 species does not seem to be greatly different in habits from the Boyle and 

 Oilbert mice. 



The present species is the least common of our white-footed mice. Only 

 6 specimens were obtained in all the trapping which we did within its 

 range, while at the same time the other white-footed mice were obtained 

 literally by the score. 



In one instance a trapped Parasitic Mouse was found to have its stomach 

 enormously distended with some finely chewed material that smelled like 

 oak mast. The stomach with contents weighed 9.7 grams, which was one- 

 fifth the total weight of the mouse. 



Short-tailed Grasshopper Mouse 

 Onychomys leucogaster brevicaudus Merriam 



Field characters. — Size nearly twice that of House Mouse; tail very short, about 

 one-third length of head and body, and clothed evenly and densely with very short hairs ; 

 claws on front feet long and sharp. Head and body about 4 inches (85-105 mm.), tail 

 about 11/2 inches (32-40 mm.), hind foot % inch (18-22 mm.), ear % inch (13-16 mm.) ; 

 Aveight nearly 1 ounce (23-30 grams) [measurements and weights from eastern Mono 

 County specimens]. Coloration sharply bicolor; upper surface pale sandy brown (light 

 gray in young); under surface of body, and legs and feet, pure white; a large white 

 spot at forward base of each ear. 



Occurrence. — Eesident in Great Basin region east of Sierra Nevada. Eecorded in 

 our Yosemite section only on the Farringtou Eanch near Williams Butte. Lives on 

 ground beneath sagebrush. 



Very little is known of the habits of the Short-tailed Grasshopper Mouse. 

 Our own experience with it in the Yosemite section was limited to the 

 capture of a single individual, September 23, 1915, in an oat-baited trap 

 set beneath a small sagebush on the flat south of Williams Butte. This 

 mouse was caught on exactly the same sort of ground as the plentiful 

 Sonora White-footed Mouse, which species the Short-tailed Grasshopper 

 Mouse resembles in a general way. There are pronounced differences, 

 however, in that the latter species has a conspicuously shorter tail, rather 

 smaller ears with a white spot at forward base, and front feet which are 

 armed with longer and sharper claws. 



The grasshopper mice, as the name suggests, have a well-known predi- 

 lection for feeding extensively upon insects. Furthermore, examples cap- 

 tured alive elsewhere and introduced into a cage with Harvest Mice and 

 White-footed Mice promptly killed and proceeded to eat those mammals. 



