WHITE-FOOTED MICE 



107 



The True and Gilbert white-footed mice (which are subspecies of the 

 one species, Peromyscus truei) have much larger ears, measuring 20 to 

 26 mm. ; and the hind feet average longer, measuring 22 to 25 mm. Also 

 the pelage is longer (hair on rump 11 mm., instead of 7 or 8 mm. as on 

 the Boyle Mouse). The Gambel and Sonora Mice are short-haired, while 

 the Parasitic is long-haired. 



The fourth species in the series, the Parasitic White-footed Mouse 

 (Peromyscus calif ornimis) , is decidedly larger than any of the other three; 

 its hind foot is longer, measuring 25 to 28 mm., but its ear is no larger 

 than that of the True and Gilbert, since it measures 21 to 23 mm. above 

 crown of head. (See accounts of each of the species for detailed measure- 

 ments.) The relative size of each of the four species of white-footed mice 

 may be judged from the following weights, which are averages obtained 

 from selected adult specimens: Peromyscus maniculatus, 21.0 grams; 

 P. hoylii, 26.5 ; P. truei, 29.5 ; P. calif ornicus, 45.0. 



Fig. 11. Cross-section of the Sierra Nevada through the Yosemite region showing 

 zonal and altitudinal ranges of White-footed Mice (genus Peromyscus). 



The Avhite-footed mice are practically all under cover through the 

 daylight hours. Occasionally a few are trapped during the day, especially 

 when traps are set in shaded places; but they are by no means as active 

 then as are the meadow mice. Their 'day' comes at night. As soon as 

 the dusk has claimed all but the nearest of objects, these mice begin to 

 venture abroad. Most of their running about is done during the earlier 

 hours of the night, but some are still abroad when the Wood Pewees utter 

 their first calls shortly before the break of day. 



The camper who goes early into his sleeping bag and there listens for 

 the night sounds is likely to hear little rustlings among the leaves, indicat- 

 ing that the white-foots are abroad. One evening in mid-May at Hazel 

 Green, one of us happened to put his sleeping bag close to the base of a 

 large tree beneath which there M^as an accumulation of leafy debris. Soon 

 after dark a Common White-footed Mouse began exploring the neighbor- 

 hood. For some time it stayed within a radius of 6 or 8 feet, rustling 

 among the leaves and occasionally making larger shifts of position. These 



