Physical Characteristics

"16 7/8-20 3/4" (43-52.5 cm) long. Largest ground squirrel in its range. Mottled above, grayish brown in front, brownish behind: buff-white or pinkish b uff below. Long bushy tail variegated buff and brown with white edges."(1)

"Diagnosis. Size large; tail long; ears long; color giving general appearance of grayish or brownish, pelage dappled; three regions of color usual ly recognizable: head grayish black or brown, shoulders and anterior part of back usually grayish, rump usually brownish, reddish brown, or blackish; top and bottom of tail about same color as back; braincase not inflated, relatively flat; interorbital region relatively wide, bullae not inflated; upper inci sors stout; length of maxillary toothrow greater than 11 mm....

Comparisons. No other Arizonan ground squirrel is as large as S. variegatus. The nearest in size to it is the prairie dog, Cynomys. In S. variegatus, the large bushy tail and mottled gray sides, as well as size, separates it from other Arizonan ground squirrels. S. variega tus differs from prairie dogs in having darker coloration, much longer tail, narrower skull, shorter rostrum, and upper toothrows that do not converge posteriorly."(2)

"These large gray bushy-tailed squirrels might be confused with the Arizona gray squirrel, Sciurus arizonensis; but in that species the gray of the back is solid, not flecked with whitish and blackish colors, and the gray squirrel is limited to a small area in western Grant and Catron counties. Tass le-eared squirrels, S. aberti, are also gray and bushy tailed, but they have white or black underparts, long tufts of hair on their ears, a lateral black line separating dorsal from ventral coloration, and often a rusty wash down the middle of the back."(3)

"In large size, gray color, and long bushy tail Spermophilus variegatus resembles only the tree squirrel Sciurus arizonensis among New Mexic an sciurids. From this tree squirrel, which has a very limited range in New Mexico, rock squirrels are distinguished by their mottled, rather than solid, dorsal coloration, and by their shorter, less bushy tails that do not have a definite white fringe." (4)

Habitat

"Open rocky areas; oak-juniper growth in canyons." (1)

"Life History. Rock squirrels, Spermophilus variegatus, are most commonly found in or among rocks, either on slopes, canyon wall, or rock p iles. However, these squirrels live in a wide variety of places: marshy gound in marsh grass at Fort Whipple (Arizona), under cottonwood roots, inside a hay shed, under log fences and cabins. They occur from as low as 1,600 feet elevation at Vicksburg, Yuma Co. (Arizona), to above timberline in the San Fr ancisco Mountains, Coconino Co. (Arizona), well over 11,000 feet. They are absent from the rock-covered mountains of southwestern Arizona but are found e lsewhere through the state.

Rock squirrels are ground dwellers, not to be confused with tree squirrels. They dig holes in the ground and have burrows and nests in and among the rock s which makes it most difficult to excavate their tunnel systems. They move up and over large rocks with ease and speed. When found in bushes and trees, they are usually in quest of food. In Arizona they climb to the tips of the slenderest branches of the junipers to reach new green buds; into fruit tree s when the fruits are ripe. There are reports that some frequent holes in trees as if the holes are established refuge sites: at Calabass, Santa Cruz Co. (Arizona), three squirrels ran 12 feet up a walnut tree and went into a hole; near Oracle, Pinal Co., Bailey found them "Occasionally living in hollow oa ks which they climb readily" (12). Once in the Graham Mountains (Arizona), when a squirrel escaped and we pursued it, the animal unhesitantly climbed an oak to a point 65 feet above the ground. We have records of them commonly climbing into cottonwoods, oaks, walnuts, juniper, mesquite, apricot, and peach trees. At Flagstaff (Arizona), I watched one climb 8 feet into a ponderosa pine to a bird feeder to eat suet."(2)

"Rock squirrels tend to be found in the lower life zones, from about the ponderosa forest down into the desert. They seem to require broken, usually rock y terrain, and are common in rocky hillsides and along arroyos. They are found almost throughout the state (New Mexico) and are absent only from the east ern plains."(3)

"This species seems to depend on broken terrain, especially rock areas, for its cover. Wherever such habitat exists, rock squirrels are likely to be foun d, except in the higher montane forests. Altitude itself is no barrier to the species, however. We have seen them on Sandia Crest, on the open, rocky, w est-facing cliffs. Open grasslands and deserts do not support these animals, unless steep-sided arroyos are present in which burrows can be excavated. I n the cottonwood bosques of the middle Rio Grande Valley these squirrels may occasionally be seen high in the trees but always seek shelter on or under th e ground."(4)

Range

"S. Nevada, Utah, Colorado, panhandle of Oklahoma, W. Texas, Arizona, New Mexico." (1)

Diet

"In Arizona, these squirrels have been observed feeding on buds and seeds of mesquite, fruit of Opuntia, juniper berries, blooms of Agave, s eeds of Ephedra, ripe fruits of Ribes cereum, ripe berries of gray thorn, bulbs of mariposa lilies, seeds of serviceberry, squawbush, lupine , apricots and peaches from the trees, acorns, hackberry, grapes, walnuts, and cultivated corn and wheat. Bailey records in field notes made in the Grand Canyon, 1929, an interesting way a squirrel was feeding on the "top of a fresh, green, juicy Agave spike that stood six feet above the green basa l leaves. He had jumped above the spiked points, climbed to the top and eaten several inches of the tender asparagus-like stem." The inhabitants at Supa i are so harassed by these squirrels damaging apricots in the trees that they chained dogs to the trees for protection. Mearns (5) says rock squirrels ea t flesh and carrion, and he routed one from inside the desiccated remains of a cow in the Pajaritos Mountains (Arizona). Cahalane (6) found that when a s quirrel from the Chiricahua Mountains (Arizona) had access to the cage of a banner-tailed kangaroo rat, it proceeded to kill the rat and eat its head. Lo ye Miller (7) happened upon a rock squirrel in the Chiricahua Mountains that had just caught a robin. The squirrel, surprised by the intruder, dropped th e dead bird and ran off." (2)

"Stalheim (13) studied S. variegatus in Embudo Canyon on the west side of the Sandia Mountains. He found that the squirrels in the area preferred the reproductive rather than vegetative parts of plants as food. Rhus trilobata, Fallugia paradoxa, various grasses, Ambrosia sp., Ribes sp., and Quercus provided the bulk of the diet. V. Bailey (12) provided a more extensive review of food habits. According to Stalheim, as di fferent plants bloomed or came into fruit, the Spermophilus fed on them in turn." (4)

Reproductive Characteristics

"Relatively little is known about the breeding habits of rock squirrels. In Grand Canyon a nest contained six young, barely able to crawl, on May 20 (8). At Flagstaff, a female was nursing young on June 20 (5). A female was suckling young at Continental, Pima Co. (Arizona), on April 30 (10). Near Fort V erde, a young, more than half-grown, was shot on May 6 (5). I suspect that rock squirrels in the southern parts of Arizona and at lower elevations may ha ve young as early as March, whereas those living in areas of longer and more severe winters may not have young until mid-May. In Cochise County squirrels have two litters per season which may be true for all of southern Arizona. Rock squirrels may have more difficulty in raising two litters in some parts of northern Arizona where there is a shorter season. Nests in the Chiricahua Mountains were made of dry pine needles, fibrous material fom decaying agave s and Arizona grape, and some dry leaves, judging from the observations of Steiner (10)."(2)

Etc.

"Active in early morning and late afternoon. In the north it hibernates, but only for short periods, and is often abroad during winter warm spells; in th e southern parts of its range it is active all year." (1)

"Rock squirrels are the largest ground squirrels in Arizona. They are the size of tree squirrels and have long, bushy tails. However, they live on and a round rocks and do not commonly climb and nest in trees....

In Arizona rock squirrels become dormant for parts of the winter, but whether they truly hibernate is not known. All reports indicate that these squirrel s are less abundant in winter, but some are seen during this period, especially on warmer days. For example, Mearns (5), writing about the rock squirrel in the Verde Valley, says " it is muich less active during winter, but was seen at all seasons, coming out oftenest when the sun was shining, and during t he warmest part of the day in winter." He says that at Fort Whipple, "General Crook had dormant specimens brought to him in winter by Hualapai Indians." Price (11) thought they might hibernate in the Huachuca Mountains, but he saw one on February 7. Near Flagstaff I found that even when the temperatures go to near 0 degrees F at night and 50 degrees F during the day, some of these squirrels came out to sun themselves. One suspects that rock squirrels ent er a state of torpor during certain periods of the winter as required. Whether this is a condition of hibernation is not known.

Albinism in these squirrels must be rare since such a conspicuous white animal would be noted. However, Mearns (5) reports an albino young of the year at Wipple Barracks, Fort Whipple, on September 20, 1887.

The high-pitched, metallic whistle of these squirrels can be readily heard, but since it is not given often, this cannot be depended upon to indicate thei r presence.

Findley et al. (4) refers to the work of W. Stalheim on rock squirrels near Albuquerque, New Mexico. Sixteen squirrels reportedly had overlapping home ra nges averaging about 4,900 square yards each. Even casual observation indicates that rock squirrels defend parts of their territory, but the size of such a territory must depend on many factors. Around picnic areas, campgrounds, or ranch buildings, rock squirrels are usually more abundant than in other ad jacent areas. These conditions must greatly affect their home ranges.

Molt. Animals begin to molt as early as May 20. One specimen taken on March 26 is molting, but this may not be an adult molt. They molt as late as August 18. According to Stalheim (4), the molt is completed in five to six weeks. Adult S. beecheyi have only one molt per year, and apparentl y the same is true for S. variegatus." (2)

"The animals may live alone or be arranged in loose colonies. Each individual has a home range, but these may overlap broadly, and territoriality has not been observed. There is some evidence that males may live in groups apart from females. The young may be brought forth from April through the summer. It may be that females can produce two litters a year, but that is not certain. The animals deposit fat in late summer, and many disappear with the adven t of cooler weather. However, they may be seen at any time during the winter in more southern areas. Probably the majority hibernate, but this aspect of their biology has received little attention. Rock squirrels are quite vocal, and make a loud, somewhat whistlelike cry, which is a distinctive sound in many New Mexican canyons."(3)

"The home ranges of sixteen marked animals averaged 4,893 square yards (but appeared to overlap broadly) and were elongate in shape, extending along the c anyon slope parallel to the arroyo bottom. The distribution of the activity centers of these sixteen animals suggested that males occupy an area somewhat distinct from that of the females. The squirrels molted from June 22 to August 12, the process seeming to require five to six weeks. Several burrows th at were excavated beneath boulders were shallow, and contained a nest chamber and two or three openings. Young first appeared on August 18, at which time they were estimated to be ten weeks old. Elsewhere, or in other years, young must also be born in spring, as we have taken young as early as June 26.

Though the squirrels are rarely seen in winter, we have taken them as late as December 12 in Albuquerque. Our earliest specimen is from March 31. V. Bai ley (12) reported that most disappeared in October and reappeared in April, but that in southern areas they occasionally failed to hibernate.

Geographic variation in New Mexico is not evident, except for the somewhat blackish population on the Carrizozo Malpais."(4)

Literature Cited

1. MacMahon, J. A. 1985. The Audubon Society Nature Guides: Deserts. Alfred A. Knopf, New York, p.565.
2. Hoffmeister, D.F. 1986. Mammals of Arizona. University of Arizona Press, Tucson, p 175-77.
3. Findley, J.S. 1987. The Natural History of New Mexican Mammals. University of New Mexico Press, Albuquerque
4. Findley, J. S., A. H. Harris, D. E. Wilson, and C. Jones. 1975. Mammals of New Mexico. University of New Mexico Press, Albuquerque, p 125-128.
5. Mearns, E.A. 1907. Mammals of the Mexican boundary of the United States: A descriptive catalogue of the species of mammals occurring in that region, with general summary of the natural history, and a list of trees. U.S. Natl. Mus. Bull. 56:530.
6. Cahalane, V. 1939. Mammals of the Chiricahua Mountains, Cochise County, Arizona. Journal of Mammalogy, 20:418-40.
7. Miller, L. 1935. A predatory squirrel. Journal of Mammalogy, 16:324-25.
8. Hoffmeister, D.F. 1971. Mammals of the Grand Canyon. Univ. Illnois Press, Urbana, Illinois, 183p.
9. Steiner, A.L. 1975. Bedding and nesting material gathering in rock squirrels, Spermophilus (Otospermophilus) variegatus grammurus (Say) (Sciuridae) in the Chiricahua Mountains of Arizona. Southw. Nat., 20:363-69.
10. Burt, W.H. 1938. Additional notes on the mammals of southern Arizona. Journal of Mammalogy, 14:114-22.
11. Allen, J.A. 1895. On a collection of mammals from Arizona and Mexcio, made by Mr. W.W. Price, with field notes by the collectors. Bull. Amer. Mus. Nat. Hist., 7:193-258.
12. Bailey, V. 1932. Mammals of New Mexico. N. American Fauna 53:1-412.
13. Stalheim, W. 1965. Some aspects of the natural history of the rock squirrel, Citellus variegatus. Master's thesis, University of New Mexico. 55pp.