Download Thirteen-Lined Ground Squirrel

Spermophilus tridecemlineatus
Thirteen-Lined Ground Squirrel
Reba Riedner
Description
Spermophilus tridecemlineatus is a rat-sized rodent reaching lengths from 225 –
300 mm (8.9 – 11.8 in) with a tail length of 75 – 109 mm (3.0 – 4.3 in). Weight ranges
from 100 – 220 g, depending on the season. The back is the most distinctive part of the
animal with seven dark brown stripes alternating with six thinner tan stripes beginning at
the top of the head and extending to the rump. Squarish light spots break up five of the
darker stripes. The stripes locating the sides of the body are less distinctive than those on
the back. The chest and belly are of a light color. The ears are very small and the tail
slender with a black stripe on the top. Their call is a high-pitched trilling ch-r-r-r (Kurta
1998).
The skull is small with a slightly shorter toothrow than other ground squirrels.
The bullae are not inflated and a postorbital process is present. The lower jaw is vshaped and the infraorbital foramen is small and shifted forward. The dental formula is
1/1, 0/0, 2/1, 3/3= 22. Like most rodents, incisors are very large and canines are lacking
(Struebel and Fitzgerald 1978).
Distribution in Wisconsin
S. tridecemlineatus is found north from central Alberta, Manitoba, and
Saskatchewan south to Texas and New Mexico, and east from central Ohio west to
Colorado. Originally, the animal was limited to the prairies of the North American Great
Plains but clear cutting and agriculture has increased its range (Kurta 1998). S.
tridecemlineatus is found throughout Wisconsin and inhabits grassland ecosystems as
well as parks, yards, fields, golf courses, and cemeteries. In Wisconsin, the species
greatly extended its range after forest areas were cleared for farming.
The fossil record includes lower jaws and maxillaries found in a Pleistocene
deposit in Kansas that appear to be identical to modern populations. Twenty cheekteeth
were collected from a mid-Pleistocene deposit in Texas (Struebel and Fitzgerald).
Ontogeny and Reproduction
Five days after emerging from hibernation female squirrels are in full heat. They
stay sexually active for 2 weeks. Ovulation occurs within 48 hours of copulation.
Gestation lasts for 28 days and litter size varies from 3 to 14, with an average of 9 young.
In Wisconsin, copulation dates can range from mid April to early May and litters emerge
in late June (Struebel and Fitzgerald 1978). Females produce one litter per year.
At birth, S. tridecemlineatus is naked, blind and toothless, and weighs about 3 – 4
g. Newborns grow at a rate of 1.3g/day and up to 90% of the litter may die from
predation. Newborns acquire a light coat of hair at day 4; stripes appear at day 12, lower
incisors show at day 17, upper incisors at 19, and molars at day 24, and eyes open at 21 31 days. Adult body length is reached at 11 weeks. After 6 to 12 weeks the young are
weaned and on their own. Shortly after being weaned they will construct their own
burrow, usually in close proximity (100m) from their birth site. Young squirrels are
sexually mature by 9 or 10 months (Kurta 1998).
Ecology and Behavior
S. tridecemlineatus typically inhabits grasslands, commonly avoiding wet regions.
Black or clay soil is preferred to sand and areas inhabiting short vegetation chosen over
those with vegetation receiving irrigation or fertilizer.
This species is strictly diurnal and rarely ventures out of the burrow on dark or
damp days. They survey the area around their burrow by standing in an upright position
with arms held closely to the chest (Cleary and Craven 1994). If the threat of danger is
suspected, they quickly retreat to the nearest burrow. Burrows are 2 inches in diameter,
often covered with vegetation, and may have 2 or 3 openings. The entrance descends for
6 inches until it angles and sharply turns an “L” shape to confuse predators. The nesting
chamber is 9 inches in diameter and lined with dry grass. S. tridecemlineatus also may
use burrows of other animals such as pocket gophers or prairie dogs.
Hibernation begins in late September or early October and emergence occurs
between late March and early May. Males tend to begin hibernation and emerge earlier
than females. Body temperatures decrease to within 3ºC of ambient air temperature.
Their heartbeat decreases from 350 to 5 beats per minute. Prior to hibernation,
individuals become more aggressive and intolerant of others, their home range is reduced,
and they become relatively inactive (Streubel and Fitzgerald 1978).
S. tridecemlineatus is omnivorous with 50% of their diet consisting of animal
matter. Prey items consist of grasshoppers, caterpillars, Lepidoptera larvae, beetles, ants,
insect eggs, mice, small passerines, small chickens, and even each other. Vegetation
consumed is seeds, green shoots, roots, vegetables, fruits and cereal grains (Kurta 1998).
Water is rarely consumed and hydration is achieved from their diet. Large quantities of
seeds are cached to be eaten during food shortages. Predators include hawks (especially
Circus cyaneus), badgers, weasels, foxes, coyotes, domestic cats, bull snakes, and black
snakes. Many parasites live internally and externally on this squirrel including fleas, lice,
mites, and ticks.
Males tend to have a higher mortality rate than females because of their longer
distances traveled away from the burrow after weaning, leaving them more vulnerable to
predation (Streubel and Fitzgerald 1978). The home range of males is about 5 hectares
and for females 1.5 hectares. Males extend to the greatest lengths of their home range
during the breeding season while females extend farthest during pregnancy and lactation.
Females tend to use the same home range area year after year. Both sexes are generally
non-territorial.
S. tridecemlineatus emits a distress call when threatened. Females give an alarm
call to young after their emergence from the burrow until three or four days later. Young
respond by diving into a burrow entrance, rather than returning to their mother (Arenz
and Leger 1999).
Remarks
S. tridecemlineatus exhibits cannibalism and infanticide, specifically in males
(Vestal 1991).
Thirteen-lined ground squirrels may also be referred to as Federation Squirrels,
striped gophers, or thirteen-liners.
Spermophilus means seed lover.
Literature Cited
Arenz, C.L. and D.W. Leger. 1999. Thirteen-lined ground squirrels (Sciuridae:
Spermophilus tridecemlineatus) antipredator vigilance decreases as vigilance cost
increases. Animal Behaviour 57:97-103.
Cleary, E.C. and S.R. Craven. 1994. Prevention and Control of Wildlife Damage:
Thirteen-Lined Ground Squirrels. Wildlife Damage Handbook B: 165-169
Kurta, Allen. 1998. Mammals of the Great Lakes. The University of Michigan Press,
Ann Arbor, Michigan, USA.
Streubel, D.P. and J.P. Fitzgerald. 1978. Mammalian Species: Spermophilus
tridecemlineatus. American Society of Mammalogists. 103:1-5.
Vestal, B.M. 1991. Infanticide and cannibalism by male thirteen-lined ground squirrels.
Animal Behaviour 41:1103-1104.
Reference written by Reba Riedner, Biol 378: Edited by Chris Yahnke. Page last updated.