Natural History of the Ground Squirrels of California/Palm Springs Round-tailed Ground Squirrel
PALM SPRINGS ROUND-TAILED GROUND SQUIRREL.
Citellus tereticaudus chlorus Elliot.
Other names.—Pale Spermophile; Citellus chlorus.
Field characters.—Exactly as for the Yuma Round-tailed Ground Squirrel.
Description.—As for the Yuma Round-tailed Ground Squirrel, but tone of coloration more grayish, avellaneous rather than light pinkish cinnamon. This difference holds through all pelages and gives the impression of an olive-colored animal, when close comparisons are made with series of the other related ground squirrels.
Color variations.—Specimens showing the spring molt to be in process bear dates from March 29 to as late as June 3. As with the other races of tereticaudus the pelage on the tail is not replaced during the spring molt and it becomes greatly faded and worn. In extreme cases the tail with its shortened, singed-looking hairs is a dirty pale brown color throughout, and as slender as a wood-rat's tail. The summer coat is so short and thin that any scars there may be in the skin show through as dark spots. These appear irregularly on certain specimens, usually those which examination of the teeth shows to be the older individuals.
Measurements.—Average and extreme measurements, in millimeters, of twenty adult specimens from Whitewater, Palm Springs and Mecca, in Riverside County, are as follows: Ten males: total length, 241 (220–251); tail vertebræ, 90 (79–97); hind foot, 36 (35–40); greatest length of skull, 36.6 (35.2–38.9); zygomatic breadth, 23.0 (21.6–24.6); interorbital width, 8.9 (8.0–9.7). Ten females: total length, 240 (229–264); tail vertebræ, 89 (80–102); hind foot, 35.7 (34–39); greatest length of skull, 36.1 (35.6–37.5); zygomatic breadth, 22.8 (22.0–23.4); interorbital width, 8.8 (8.6–9.4).
Type locality.—Palm Springs, Riverside Coimty, California (Elliot, 1903, p. 242).
Distribution area.—The northwestern arm of the Colorado Desert between Salton Sea and San Gorgonio Pass (see fig. 18). Life-zone, Lower Sonoran. More specifically, the Coachella Valley, entirely within Riverside County, from Mecca northwest to Whitewater Station; altitude from -200 to 1,130 feet.
Specimens examined.—A total of 41 from the following localities, all in Riverside County: Palm Springs, 6; Whitewater Station, 18; Mecca, 17.
This race of Round-tailed Ground Squirrel was first made known from specimens collected in the vicinity of Palm Springs, out on the Colorado Desert near the northeast base of San Jacinto Peak. Subsequent exploration has shown it to be limited to the relatively small area of flat desert lying between Salton Sea and the upper part of San Gorgonio Pass, and shut in narrowly by the mountain walls on either side.
The slight features by which this subspecies is distinguishable from the Yuma Round-tailed Ground Squirrel of the Imperial Valley southeast of Salton Sea may be inferred to have arisen as a result of the action of the body of water which formerly filled the Salton Sink to sea level in cutting off or isolating the animals in the northwestern arm of the Colorado Desert and thus giving them a chance to develop peculiarities all their own. The ancient predecessor of the present Salton Sea is known to geologists as Blake Sea, and this inland sea extended from the base of the Chocolate Range of mountains on the northeast to the very foot of the Santa Rosa Mountains on the southwest, thus constituting an impassable barrier to any animal closely restricted, as is the Round-tailed Ground Squirrel, to dry, level, sandy ground. However this may have been, the Palm Springs subspecies now ranges down the Coachella Valley from the northwest nearly to the upper end of the present Salton Sea, in the vicinity of Mecca. One can imagine the animal life of the desert floor now retreating, now advancing, with the fluctuations of the old Blake Sea since the time it was first cut off from the Gulf of California by the slowly growing delta of the Colorado.
The general habits of the Palm Springs Round-tailed Ground Squirrel are probably closely similar to those of the Yuma and Death Valley animals. The first-named is fairly common locally, though it rarely forces itself on the attention; it has to be specially looked for. At Mecca in March and April (1908) one or two were caught nearly every day in oat-baited rat-traps set on sandy mounds beneath mesquites. Yet the animals themselves were rarely seen. On April 26 one was surprised up in a mesquite; upon being shot it was found to have parts of a mesquite flower in its mouth. The senior author was told that at the experimental date farm near Mecca these squirrels had been seen eating the dates.
At the railroad station of Whitewater this animal was found by museum collectors to be common, June 3 to 5 (1908), in a tract of sand dunes nearby. The shrill calls or whistles were heard frequently, and many of the squirrels were trapped. Some of these were young, one-third to one-half grown. The old males and part of the old females taken then were very fat; all the rest lean. A female taken at Mecca, March 27, was found to contain five large embryos. The extent of the breeding season is thus indicated. Doubtless but one litter is raised each year.
Search in the vicinity of Palm Springs in December and January of different years has failed to show the presence of these squirrels actively abroad; so that it is likely that they hibernate during midwinter. In 1916, Swarth (MS) found them out on February 4 in a tract of sandy soil about a mile east of the village. They occurred in small scattered colonies, each "colony" marked by twelve to fifteen open holes on level ground among creasote bushes. "Parts of the burrows were shallow, so that a person would sink through into them ankle deep." The animals when alarmed would scurry to their holes and disappear into them, but would presently poke up their heads and utter "faint little barks."
No information has come to us that would indicate any decided economic bearing on the part of the Palm Springs Round-tailed Ground Squirrel. Because of its dry-land preferences it is likely that reclamation and irrigation of the land would drive it away rather than attract it. Thus the reaction would be just the opposite to that in the case of the Oregon Ground Squirrel and similar species.