164 ANIMAL LIFE IN THE YOSEMITE 



Ground Squirrel is present, but in very small numbers ; a single individual 

 was seen September 23, 1915, at 8000 feet altitude in Leevining Creek 

 canon, and a few were found in the vicinity of Mono Lake Post OflSce in 

 May and July, 1916. On parts of the Great Basin plains beyond, its place 

 is wholly taken by a small round-tailed species, the Stephens Ground 

 Squirrel. 



Over its entire range the California Ground Squirrel is resident through- 

 out the year. Those individuals which live above the snow line in the 

 mountains hibernate for considerable periods during the winter months. 

 In Yosemite Valley, ground squirrels in 1920 were first seen out of their 

 burrows about the middle of March, according to Mr. Forest S. Townsley. 

 One exceptional individual was seen out by one of us, on the Big Oak Flat 

 Road below Gentrys, on December 28, 1914. Those squirrels living at 

 still lower levels, even though they may not go into regular hibernation, 

 are still much less active in the winter season, when they are wont to appear 

 above ground only during the mid-day hours of warm, sunny days. 



As its common name indicates, this squirrel secures shelter for itself 

 and young, and safety from its enemies, by burrowing in the ground. It 

 seems to prefer to excavate its retreats in hillsides or in low earth banks, 

 where most of the necessary digging can be done in a horizontal direction. 

 But of course those members of the species which live on the plains or 

 on flats or meadows in the foothills or mountains must perforce dig 

 do^vn vertically for considerable distances to gain the requisite protection. 

 Most of the work of tunnel excavation is carried on during the spring 

 months, as is shown by the mounds of fresh, soft earth accumulated at the 

 mouths of the burrows in that season. In the lowlands, where there is a 

 large crop of wild oats in the springtime, this newly excavated earth 

 supports a ranker growth than do the surrounding parts of the field, so 

 that, as one of our party wrote in his field notes, "the plain looks like a 

 cemetery overgrown with grass," with these taller stands of oats about the 

 squirrel holes suggesting grave mounds. To some extent the ground 

 squirrels, like the pocket gophers, thus serve as natural cultivators of the 

 soil. Many of the squirrels which live in the granite country make their 

 homes under large boulders or in rock taluses, where a minimum of bur- 

 rowing is necessary to ensure safe retreats. This is notably the ciise in 

 Yosemite Valley. 



It is likely that the s(|uirrels construct new burrows from time to time, 

 or, what is even more probable, that each young individual as it comes to 

 maturity and is weaned from its mother leaves the parent burrow and 

 digs a home for itself. In any event, in places, there are many more 

 burrows than individual squirrels present at one time. These tunnels, 

 especially in the plains and foothill country, are joined together below- 



