Animal Diversity Web

Ge­o­graphic Range

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).

• Biogeographic Regions
• nearctic
  • native
• neotropical
  • native

Habi­tat

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).

• Terrestrial Biomes
• savanna or grassland

Phys­i­cal De­scrip­tion

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).

• Other Physical Features
• endothermic
• bilateral symmetry

Re­pro­duc­tion

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).

• Key Reproductive Features
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual

Be­hav­ior

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).

• Key Behaviors
• motile

Com­mu­ni­ca­tion and Per­cep­tion

• Perception Channels
• tactile
• chemical

Food Habits

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).

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

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.

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

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.

Con­ser­va­tion Sta­tus

The species is not threat­ened and by all ac­counts thriv­ing in its south­west­ern habi­tat.

• IUCN Red List

  Least Concern
  More information

Other Com­ments

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)

Con­trib­u­tors

Corey Sides (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

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.