J 40 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



occurrence in this tree alone. Clay reports that although the 

 Douglas fir seems to be preferred, he has found many nests 

 in the lowland (or grand) fir in the Mad River country 

 (Humboldt County, California), and has taken several from 

 the Sitka spruce. His record of nests in the Sitka spruce are 

 so far unique. 



It is quite probable that the larger numbers and general 

 availability of the Douglas fir in the area of occurrence of the 

 tree mouse have much to do with the observed occurrence 

 of most of the nests in trees of that species. 



3 COLONIAL TENDENCY 



Although Wilder says that he has never found the Phe- 

 nacomys in Humboldt County nesting in colonies, the ex- 

 perience of other investigators in other places shows that 

 there is a pronounced grouping tendency observable. At 

 Mendocino City, for example, our party made studies of two 

 groups or colonies of nests, and all nests observed later ex- 

 hibited a similar colonial arrangement. It should, however, 

 be stated that in no case were the nests closely grouped, 

 though they were located in the same general section of forest. 

 Clay asserts that they live in colonies as a rule, although they 

 spread to isolated positions in individual cases, and cover a 

 vast expanse of territory. 



One colony studied at Mendocino City was located on a 

 flat north of town, in a grove of tall Abies grandis intermixed 

 with scattering Bishop pines. The second was found on the 

 side of a ravine a little farther to the north. Here, although 

 the grand firs formed an almost pure stand, there were a few 

 Douglas firs and an occasional Bishop pine. Examples of 

 Phenacomys were taken in both these colonies. 



Another colony was later located in large Douglas firs in 

 an isolated position on the south-facing slope of a small 

 hill, near the Eden Valley road, four miles north of Hearst, 

 Mendocino County, California. A group of nests resembling 

 those of gray squirrels, and possibly now belonging to 

 Phenacomys longicaudus, was also encountered in a grove 

 of Douglas firs about 500 feet above the South Fork of 

 Eel River, and a mile distant therefrom, on the north side, 

 four miles east of Hearst. Shortness of time did not permit 

 of its examination. 



