The Mexican Ground Squirrel ranges from Northern Mexico to along the Gulf coast of Texas, extending to western and central Texas and into southeastern New Mexico (Young and Jones 1982).
The species inhabits level grasslands and typically avoids rocky areas. It is typically found in sandy and mesquite regions of savannas. The species is well adapted for digging and burrowing and makes its home in underground burrows. The burrows are not marked externally. An individual occupies more than one burrow, with many escape burrows in addition to the home. The home burrows are 60 to 80 mm in diameter and reach a depth of 125 mm, while the refuge and escape burrows are not as deep. The burrows can also be found on golf courses, cemeteries, and along highways (Young and Jones 1982).
The pelage of S. mexicanus is dense and of moderate length; the dorsal coloring is variable and ranges from olive gray to brown with rows of squarish pale and whitish spots. The head has the same coloring as the the dorsum except the tip of the nose is either yellow or cinnamon and there is a white orbital eye ring. The feet and undersides are white to pinkish (Davis 1974)
The tail is flattened and somewhat bushy with a cylindrical base; the color is grayish white mixed with black and its length ranges from 110 to 134 mm and is less than half the total body length, which ranges from 300 to 350 mm (Mearns 1907; Young and Jones 1982). The skull length is 43 to 44 mm and lightly built with prominent pareital ridges. The dental formula is the same as other scuirids. These squirrels have narrowly triangular cheek teeth with high crowns and lophs (Young and Jones 1982).
The species S. spermophilus is distinguished from other species in the subgenus Ictidomys by its 9 rows of pale and whitish spots on the dorsum, and from other ground squirrels by the absence of a continous metaloph on the fourth premolar (Young and Jones 1982).
The breeding season occurs in late March and early April, lasting one to two weeks. The period of gestation is 23 to 28 days, with parturition occuring in early May with a litter size from 2 to 13 (Walker 1975). Unlike many other species of scuirids, S. mexicanus only produces one litter per year (Lawlor 1979; Walker 1975). The mother builds a brooding chamber off of the deepest portion of a burrow that is 180 to 200 mm in diameter. The chamber contains a nest of mesquite and grasses. After the young have left, the nest is removed to the sleeping area and the brooding chamber is filled in (Young and Jones 1982). At birth the young weigh from 3 to 5 grams, and are toothless, naked, blind and are covered with and unpigmented fuzz. Although rather helpless and altricial at birth, the young develop rapidly and are completely independent 3 months after birth. The young occupy old or refuge burrows and do not breed until the following spring. (Young and Jones 1982). The lifespan of S. mexicanus is from 2 to 5 years (Walker 1975).
Although the species is colonial, it tends to be rather unsocial and solitary except during the brief breeding season. They tend to tolerate overlap in territory and are rather unaggressive except when others attempt to occupy their home burrows. The home range is typically less than 90 m from the home burrow, and squirrels have a specific defecation area outside the nest (Edwards 1946). In defense these squirrels give a shrilled whistle call and lie on their side, hiss and grind their teeth (Young and Jones 1982).
The evidence is inconclusive, bu there is considerable debate whether the species hibernates like many species of northern ground squirrels. Several studies in Texas claim that S. mexicanus does hibernate (Davis 1974; Edwards 1946), while others report the species remaining active during the winter (MacClintock 1974).
The Mexican Ground Squirrel,is omnivorous and like other ground squirrels is adapted for life on the ground foraging for seeds, nuts, roots, bulbs, plant stems, leaves, mice, insects and eggs (Walker 1975). Like other ground squirrels, S. mexicanus typically is active and feeds during the day. Once it finds seeds, nuts or grains, it is able to store them in cheek pouches and carry them to storage chambers within the burrow (Walker 1975). The food habits vary seasonally. In the spring the diet is distinctively herbivorous, consisting of mesquite beans and leaves, nuts and fruits. Studies in New Mexico suggest that S. mexicanus occasionally climb low bushes and forage for seeds and fruits (Bailey 1932). However, in the early summer, half the diet is composed of insects commonly encountered in the squirrels burrows. The species also consumes meat and can be seen eating roadkill on highways, and does seem to have cannabalistic tendencies (Davis 1974).
As an insectivore during the summer months, S. mexicanus greatly benefits man by controlling the insect population and reducing the need for harmful and costly pesticides.
Due to its burrowing and digging, the Mexican Ground Squirrel can cause a bit of damage to farmland and golf courses. They can also damage crops in the spring when they typically consume grain, nuts, seeds and fruits.
The species is not threatened and by all accounts thriving in its southwestern habitat.
Studies in Texas revealed a number of parasites associated with S. mexicanus, including nematodes, spirachaete, two species of mites and one species of flea. (Doran 1955; Eads and Hightower 1952; Whitaker and Wilson 1974; Edwards 1946)
Corey Sides (author), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
living in the southern part of the New World. In other words, Central and South America.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
reproduction that includes combining the genetic contribution of two individuals, a male and a female
uses touch to communicate
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
Bailey, V. 1932. Mammals of New Mexico. North American Fauna 53:1-412.
Davis, W. B. 1974. The Mammals of Texas. Bull. Texas Parks and Wildlife Dept. 41:1-294.
Doran, D. J. 1955. A catalogue of the Protozoa and helminthes of North American rodents. III. Nematoda. American Midland Nat. 53:162-175.
Edwards, R. L. 1946. Some notes on the life history of the Mexican ground squirrel in Texas. Journal of Mamm. 27:105-121.
Eads, R. G. and B. G. Hightower. 1952. Blood parasites of southwest Texas rodents. Journal of Parasitology 38:89-90.
Lawlor, T. E. 1979. Handbook to the Orders and Families of Living Mammals. Mad River Press, California.
Walker, E. P. 1975. Mammals of the World. Third Edition. Johns Hopkins University Press, Baltimore.
Whitaker, J. O., Jr. and N. Wilson. 1974. Host and distribution lists of mites (Acari), parasitic and phoretic, in the hair of wild mammals of North America, north of Mexico. American Midland Nat. 91:1-67.
Young, C. J. and J.K. Jones Jr. 1982. Spermophilus mexicanus. Mammalian Species 164:1-4.