Page:Natural History of the Ground Squirrels of California.djvu/16

602 fine pattern; the buif tone is deeper below than above; close inspection shows the hairing of the tail to be concentrically banded, three black bands and four light ones, the outermost black band being broadest, and the outermost light one constituting a peripheral whitish fringe.

Color variations.—As far as we can see, the two sexes are identical in coloration, save as caused by the greater rate of wear to which the pelage of the female is subject during the season when the young are being reared. Wear progresses in some cases until most of the colored ends of the hairs are gone, and a dingy light brown color is acquired, including also the tail. Molting begins anteriorly and progresses backward.

The material we have studied seems to show but one decided molt in adults each year, and this takes place during July and August. Young, however, seem to undergo two molts in the first six months of their lives. When one-third grown their pelage is characterized by a fluffy texture and a yellowish tone of color, but the general pattern is closely similar to that of adults; when nearly full grown the young are smooth-coated and show rather brighter tones of brown and clearer white shoulder patches that even fresh-pelaged adults.

There are not infrequent special, or "sport" variations, in the Beechey Ground Squirrel, such as albinos, either complete or partial, which have been reported from time to time. We have been told of "black" ground squirrels; and there is in the Museum of Vertebrate Zoology an adult male, from Stanislaus County, taken by W. C. Jacobsen, January 30, 1918, which is of a curious light pinkish-buff tone of coloration, save for the outermost concentric black band on the tail and for the whitish shoulder patches and a suggestion of dappling on the back.

The color description given above was taken from specimens from the vicinity of San Francisco Bay. Specimens from other parts of the general range of the Beechey Ground Squirrel depart from this slightly in different respects. Two specimens at hand from Marysville Buttes, Sutter County, are of paler, grayer tone of general color. A series of skins from the western slope of the central Sierra Nevada averages whiter underneath and darker brown on middle of back. Examples from the southern San Joaquin Valley are paler in tone of coloration and exhibit whiter shoulder patches, thus evidently constituting intergrades towards the Fisher Ground Squirrel. A series from the coast district of southern California, from Santa Barbara to San Diego, shows darker brown back, but whiter under surface of body, and the white shoulder patches are more conspicuously contrasted. Some San Diego County examples in rather worn pelage show a curious reddish tinge on the rump.

Measurements. —Average and extreme measurements, in millimeters, of twenty full-grown specimens from west-central California are as follows: Ten males: total length, 435 (405–475); tail vertebræ, 164 (150–175); hind foot, 57 (52–60); ear from crown, 20.5 (17–24); greatest length of skull, 59.1 (56.9–61.1); zygomatic breadth, 36.9 (35.0–39.2); interorbital width, 14.1 (13.3–15.0). Ten females: total length, 423 (400–460); tail vertebræ, 162 (150–175); hind foot, 57 (55–58); ear from crown, 18.4 (16–20); greatest length of skull, 56.2 (53.8–59.5); zygomatic breadth, 35.8 (34.3–37.6); interorbital width, 13.9 (13.0–14.7).

It will be seen from the above figures that females are decidedly smaller bodied than males though in tail length they are about the same. The skulls of the oldest individuals, particularly males, show greatest general size, greatest zygomatic breadth (as