Page:Natural History of the Ground Squirrels of California.djvu/58

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Other names.—Douglas Spermophile; Digger Squirrel, part; Arctomys douglasii; Citellus douglasii; Citellus variegatus douglasii; Spermophilus grammurus douglasii; Spermophilus douglasii; Citellus beecheyi douglasii; Spermophilus grammurus beecheyi, part; Citellus grammurus douglasii.

Field characters.—As for the Beechey Ground Squirrel, from which differs noticeably in the possession of a blackish brown wedge-shaped patch on the fore part of the back; also shoulders more extensively silvery white, and tail longer. Length of body alone, in males about 11 inches, with tail about 8 inches more.

Description.—Adults in early summer pelage: Crown of head to nose buckthorn brown, becoming mixed with blackish toward eyes and ears; backs of ears deep bister brown margined behind broadly with clay color; insides of ears dull cinnamon-buff; eyelids white; whiskers black; side of head and of body behind shoulder deep bister brown, with much buffy white tippings to hairs; a conspicuous wedge-shaped patch on middle of fore part of back, with apex at nape of neck, solid deep bister brown in color, almost black in some specimens; shoulder patch extensively silvery white, this extending backwards to hinder end of median dark wedge. Hinder portion of body colored as in the Beechey Ground Squirrel, but dappling more conspicuous, due to the whiter tone of the light spots. Under surface of body of darker tone than in beecheyi, seemingly due to the darker, sepia brown, bases of the hairs showing through the dull white or buffy overwash. Feet as in beecheyi but clouded above with dusky. Tail colored as in beecheyi but light tippings to hairs greater in extent and whiter in tone, thus accentuating the white fringe, and producing a grayer effect throughout.

Color variations.—Young but a third grown usually show the characters of the species, both as to color and relative tail length, quite as well as do adults. In one example, however, the black dorsal wedge is considerably obscured by buffy mottlings, and it thus resembles beecheyi of the same age.

The effects of wear and fading rarely bring such extreme modification of color tones in douglasii as in beecheyi and fisheri, possibly due to the lesser intensity of the sunlight and dryness to which their habitat is usually subject. The black wedge on the fore back is most vivid in fresh pelage; in cases where wear and fading have progressed to an extreme degree, the black wedge is much dulled toward brown, and may be effaced almost entirely. The identity of the ground squirrels in any given locality can be determined with certainty by securing several individuals, when the normal, distinctive coloration is sure to be shown by some of them.

Measurements.—Average and extreme measurements, in millimeters, of seventeen full-grown specimens from the northwestern counties of California (Sonoma to Humboldt) are as follows: Twelve males: total length, 478 (438–504); tail vertebræ, 200 (175–221); hind foot, 60 (57–63); ear from crown, 23 (19–29); greatest length of skull, 60.5 (57.8–63.1); zygomatic breadth, 37.0 (34.9–38.2); interorbital width, 14.3 (13.5–15.7). Five females: total length, 439 (427–453); tail vertebræ, 192 (161–210); hind foot, 57 (56–60); ear from crown, 23 (18–26); greatest length of skull, 58.5 (56.8–60.4); zygomatic breadth, 35.9 (35.0–36.8); interorbital width, 14.0 (13.1–15.0).

Always taking age into account, there appear to be fairly diagnostic average skull characters for douglasii as compared with beecheyi, fisheri and nesioticus. Douglasii averages smaller in regard to auditory bullæ, and narrower as regards rostrum and braincase. Yet, as the above measurements show, the gross size of the skull is not especially different.

Type locality.—Probably somewhere in southern Oregon or northern California. The type was a hunter's skin "received from the banks of the Columbia" (Richardson, 1829, p. 172).

Distribution area in California.—Roughly, the northwestern section of the state, north of San Francisco Bay, west of the lower Sacramento River, and north of a diagonal line from near Chico northeast to the Nevada line near the southern