144 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



air, and moderately heavy rainfall. It is quite probable that 

 the animal's need of moisture is supplied by the water which 

 gathers on the foliage of the trees in which it lives, if, indeed, 

 it needs more moisture than is contained in its food. 



7 HOME RANGE OF THE INDIVIDUAL 



The fir trees in which our party found colonies of Phena- 

 comys longicaudus were close together, and transit from tree 

 to tree by way of the foliage route would be comparatively 

 easy. In one nest a branchlet of Bishop Pine (Piniis miiri- 

 cata) was found, as has already been noted. This could only 

 have been brought in by the tree mouse or some other animal. 

 It will be remembered that Shelton (see page 141 above) noted 

 a mouse traveling from tip to tip of the fir boughs, quickly 

 escaping in a Thuja plicata which was the fourth tree from 

 the nesting site. It is not improbable that the tree mouse 

 ranges freely through the foliage of several trees in the vicin- 

 ity of his home nest tree. 



8 HIBERNATION 



Wilder suggests the possibility that the tree mice may 

 hibernate in the cold region back from the coast, and records 

 finding one in February, presumably at Carlotta, Humboldt 

 County, California, curled up and dormant. The same day, 

 however, he found two females with half grown young; so 

 he concluded that the first must have been chilled into tem- 

 porary inactivity by the storm just ended. Todd (1891, 

 p. 242) suggests that the tree mice probably do not hibernate, 

 on the basis of the tracks seen about the nest trees in the 

 snow. But allusion has already been made to his uncertainty 

 as to whether or not the tracks were those of Phenacomys 

 longicaudus. 



It is doubtful whether the cold weather is severe enough 

 in the area of occurrence of Phenacomys longicaudus to make 

 true hibernation necessary, although there may be inactivity 

 during the colder periods. The writer has been unable to 

 find any definite records of hibernation among the Microti, 

 although Barrett-Hamilton and Hinton (1914, p. 466) refer 

 to the inactivity during cold weather of Micro tus oread ensis 

 sandayensis. Bailey definitely asserts (1900, p. 6) that no 

 American species of Microtus is known to hibernate. 



