106 ANIMAL LIFE IN THE TO SEMITE 



with most other rodents. It seems to be the most adaptable of all the small 

 mammals, fitting into types of habitat unused by any of the more specialized 

 mammals and venturing into the special territory of these which may not 

 be fully occupied. With this flexible nature it might be expected that 

 the White-footed Mouse could and would become a pest about human 

 habitations, but there has been no development in this direction. The 

 species does hold the last line of defense for the wild species, living, as it 

 does, about cabins and barns in newly settled territory ; but it quickly 

 retreats upon the arrival of that more aggressive alien, the House Mouse. 



The Common White-footed Mouse is somewhat larger, differently pro- 

 portioned, and differently colored than the well-known House Mouse. 

 (Compare pi. 25& and c.) The average weight of the Gambel Mouse is 

 0.62 ounce (17.5 grams), and of the Sonora Mouse, 0.86 ounce (24.5 grams), 

 while that of the House Mouse is 0.58 ounce (16.4 grams). The tail of the 

 Common White-footed Mouse is less in length than its head and body; 

 in the House Mouse it is about equal. The ear of the Common White-footed 

 Mouse averages larger, % inch (16 mm.), compared with about % inch 

 (13.5 mm.) in the House Mouse. The White-footed Mouse is conspicuously 

 white on its under surface, this white extending to the under side of the 

 tail and including the entire feet. The House Mouse, on the other hand, 

 is dingy gray underneath, with no sharp line of demarcation along the 

 sides ; the tail is monochrome, not bicolor ; and the feet are dusky. The 

 tail of the White-footed is well haired (though the hairs are very short), 

 not nearly bare and scaly, as is that of the House Mouse. 



It should be stated here that there are no less than four species of 

 white-footed mice in the Yosemite section, and in certain places on the 

 west slope of the mountains all four are to be found in close proximity 

 to one another. (See fig. 11.) All four of the species bear a general 

 resemblance to each other and two of them (the Boyle and True) are 

 enough alike to make it difficult to identify individuals. The Common 

 White-footed Mouse (Peromyscus maniculatus with subspecies), the sub- 

 ject of the present chapter, is the smallest of the four (see fig. 10 and 

 pi. 25). Its tail is shorter than the head and body, 3 inches or less (75 

 mm.), and is distinctly bicolor, that is, pure white with a dark stripe along 

 the top. The hind foot is shortest, measuring % to •% of an inch (18-21 

 mm.) ; its ear is smallest, measuring I/2 to % of an inch (13-17 mm.). 



The Boyle White-footed Mouse (Peromyscus ho.ylii) is the next in point 

 of size, and can be recognized further by the combination of medium sized 

 hind foot (21 to 23 mm.) and medium sized ear (from crown, 17 to 20 mm.). 

 In this and the following two species the tail is distinctly longer than that 

 of the Common White- footed Mouse, equaling or exceeding the combined 

 length of the animal's head and body. 



