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Mexican ground squirrel
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.
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.
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Mexican ground squirrel
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.
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.
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.
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.
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 occurring in early May with a litter size from 2 to 13. Unlike many other species of scuirids, S. mexicanus
only produces one litter per year. 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. At birth the young weigh from 3 to 5 grams,
and are toothless, naked, blind and are covered with and un-pigmented
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. The lifespan of S. mexicanus is from 2 to 5 years.
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 non-aggressive 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. In defense
these squirrels give a shrilled whistle call and lie on their side,
hiss and grind their teeth.
The evidence is inconclusive, but 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.
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. 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. 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.
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 road kill on highways, and does
seem to have cannibalistic tendencies.
In captivity they should be offered a complete diet of rodent lab blocks, and rat or mouse
mix, with bits of fruit or veggies regularly. Cheerios or wheat
bread are great treats, in small quantities. Do NOT feed chocolate,
fried foods, salted foods, candy or junk food! They may enjoy
crickets and mealworms if they are captive bred, never feed wild
insects as they may carry parasites. Vitamins, like Nutri-Cal are a good addition to their diet, and added calcium
during nursing and growth due to demands on their systems at those
times, but take care not to overdo it. Water bottles should be used
to proved constant, clean water. Ceramic or stoneware food dishes
work well for keeping seeds or fresh foods off the floor, and a wire
mesh hopper that allows them to eat the lab blocks through without
extra waste.
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