CRICK ABEE 211 



that one-half or more of the terminal foliage of this particular tree had 

 been removed. 



Other cuttings of similar sort were seen in the head of Lyell Caiion in 

 mid- July. On July 24, 1915, in the same locality, a chickaree was shot 

 while running over a rock slide. The animal was found to have a bundle 

 of bark in its mouth. This was probably intended for nest lining. 



Most of the young chickarees in the Yosemite region are born in June 

 and July, though our data leading to this statement are rather meager. An 

 adult female taken July 19, 1915, in Lyell Canon contained 5 embryos. 

 This is probably an average litter. A female taken as late as October 3 

 (1915) was found to have the mammary glands functional; hence, to be 

 the mother of a late litter. The young are cared for by the parent until 

 late September or early October, when they are half- or two-thirds grown; 

 at this time the visible chickaree population is considerably augmented by 

 the appearance of the young, whose softer voices are then to be heard on 

 every hand. 



Sierra Flying Squirrel. Glaucomys sabrinus lascivus (Bangs) 



Field characters. — Body size about % that of House Eat; body flattened, with a 

 broad fur-covered extension of the skin along each side between fore and hind feet 

 (fig. 32); tail heavily furred, flat; eyes large; pelage dense and soft, silky in texture. 

 Head and body 51/2 to 61/2 inches (142-166 mm.), tail 41/0 to 5% inches (116-145 mm.), 

 hind foot about l^o inches (36-39 mm.), ear from crown % to 1 inch (18 to 26 mm.) ; 

 weight 31^ to 5% ounces (103.5-164.5 grams). General color above dark leaden gray; 

 under surface of body dull white; both surfaces of tail dark gray. Voice: A low whurr. 



Occurrence. — Moderately common resident in Transition and Canadian zones on west 

 slope of Sierra Nevada. Eecorded from Smith Creek, 6 miles east of Coulterville, and 

 from Sweetwater Creek, eastward to Merced Lake and Porcupine Flat. Inhabits trees, 

 chiefly black oaks and red firs, dwelling in holes in daytime, coming forth at night. 



The Sierra Flying Squirrel is relatively common in the main coniferous 

 belt of the Sierra Nevada, and a considerable population of the species 

 lives right in Yosemite Valley. Yet, because it comes forth only under 

 cover of darkness and then goes about in a very quiet manner, its activities 

 and even its presence are known to very few persons. 



The use of the word 'flying' in connection with this squirrel is not 

 strictly accurate. The animal is unable to course about freely in the air, 

 in the way of a bat or a bird. It can only volplane from a high perch to 

 a lower one and is therefore a ' glider, ' rather than a ' flyer. ' The structure 

 of the Flying Squirrel is modified importantly in several respects to ensure 

 success in this mode of progression. Yet it has not, of course, reached an 

 extreme specialization of structure anywhere near that of a bat. Its feet 

 are nearly normal in form, and its toes are provided with claws like those 

 of other squirrels, so that it is able to run about on all fours. It has a 

 broad brush-like tail, roughly similar to that of other arboreal squirrels. 



