Page:Natural History of the Ground Squirrels of California.djvu/50

636 of squirrels, with results already given. These, summarized, show that one ounce of dry grain or seeds, or four ounces of green vegetation, is consumed each day by an average California Ground Squirrel. If we take fifty pounds of green stuff as representing the amount of forage consumed daily by one steer on open range, then 200 squirrels would appropriate the forage which would keep one steer. Twenty squirrels would eat as much as one sheep, and this last estimate would be most significant, because sheep graze closer and hence the competition here would be sharpest.

Expressing this relationship in another way, taking the average population of ground squirrels on open range as one per acre or 640 per square mile, the squirrels on each square mile appropriate the forage of three steers or 32 sheep. If the entire range of the California Ground Squirrel be taken into account and be supposed to consist purely of grazing lands (and so of minimum land value) grazed to their fullest capacity, then the squirrels of this species take the place of 160,000 cattle or 1,600,000 sheep. Of course, it is not likely that the squirrels come into actual close competition with livestock in ordinary years; but in extra dry years, such as that of 1917–18, when all the living things which depend on vegetation for support are hard pressed to maintain existence, then the squirrels cannot help but crowd the cattle interests of the country, which are of such vital human importance.

Other names.—Fisher Spermophile; Digger Squirrel, part; Spermophilus beecheyi, part; Spermophilus beecheyi fisheri; Spermophilus grammurus fisheri; Citellus variegatus fisheri; Citellus grammurus fisheri; Otospermophilus beecheyi fisheri; Spermophilus grammurus beecheyi, part.

Field characters.—As for the Beechey Ground Squirrel, differing in paler tone of general coloration, and in more extensive and purer white shoulder patches. Length of body alone about 9¾ inches, with tail about 6 inches more.

Description.—In all pelages: Closely like beecheyi, except for pallid tones of color predominantly light cinnamon-drab, and extension of light areas. The shoulder patches in typical fisheri are much clearer white and tend to meet on the fore back between the shoulders; in some specimens the mid-dorsal grayish brown stripe is almost obliterated by these white invasions. The back of the ear is usually grizzled buffy in fisheri instead of chiefly black, and its hinder margin and base are silvery white. The lower surface of the body and the upper surfaces of the feet are usually much whiter, less buffy, than in beecheyi.

Color variations.—The range of individual and seasonal variation in fisheri seems to be about the same as in beecheyi.

The extreme of the characters of fisheri are developed in the Inyo region, and gradual intergradation or blending takes place towards beecheyi chiefly through southern Tulare aud Kern Counties. The dotted line on the map (fig. 17) separating the ranges of fisheri and beecheyi represents no place of abrupt demarcation but only somewhere near the middle of the belt of intergradation. Many individuals from the vicinity of this hypothetical line are so nearly betwixt typical beecheyi and typical fisheri that they can only arbitrarily be placed under one name or the other. This has been done with such intermediate examples in the lists of specimens examined.