THE MONTHLY BULLETIN. 



DOUGLAS GROUND SQUIRREL. 

 Citellus douglasii (Richardson). 



PLATE If. 



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 notice- 

 ably 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 vertebrae, 

 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 vertebrae, 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 bullae, 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 



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