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Spermophilus lateralisgolden-mantled ground squirrel

By Monet Belltawn

Geographic Range

Spermophilus lateralis is found in Canada and the United States. It ranges from southeast British Colombia and southwest Alberta, into the western United States as far east as western Colorado and down to northwestern New Mexico and southern California.

(Bartels and Thompson, 1993; National Wildlife Federation, 2000)

Habitat

Spermophilus lateralis is found from 1,220 m in the northern Sierra Nevada mountains of California, up to 3,965 m at Pike's Peak, Colorado. This species occurs in mixed coniferous forests of the Klamath, Cascade and Sierra Nevada ranges. Golden-mantled ground squirrels are found up to and above the timberline, provided that there is enough cover for them. Forest-edged meadows and rocky slopes can be occupied, as well as chaparral habitat in southern California. Spermophilus lateralis is abundant in campgrounds in where these squirrels enjoy human handouts.

(Bartels and Thompson, 1993)

  • Range elevation
    1,200 to 3,965 m
    to ft

Physical Description

Spermophilus lateralis is a strikingly colored ground squirrel. This species has a golden-red mantle that extends from the head down over their shoulders. One white stripe, bordered by two black stripes, extends horizontally down the body, similar to chipmunks. Although chipmunks have a white stripe through their eyes, Spermophilus lateralis has a whitish fur eye ring and no facial striping. The back is gray, brownish or buff, and their undersides are whitish or yellowish-gray. The tail is brownish-black above, and reddish brown on the underside. Winter pelage is grayer and the mantle is duller. The species is sexually dimorphic, with males having a brighter red mantle as well as a significantly larger brain size.

These squirrels range in weight from 120 to 394 grams, and in length from 235 to 295 mm.

(Bartels and Thompson, 1993; Iwaniuk, 2001; National Wildlife Federation, year unknown)

  • Range mass
    120 to 394 g
    4.23 to 13.89 oz
  • Range length
    235 to 295 mm
    9.25 to 11.61 in
  • Average basal metabolic rate
    0.967 W
    AnAge

Reproduction

As in many ground squirrels, males are polygynous. After emergence from hibernation, they compete with each other to establish territorial boundaries. Male territories encompass the territories of several females. When females emerge from hibernation, they typically mate with the male on whose territory they are found.

Copulation begins after adults emerge from hibernation, from March to May. Males emerge from hibernation in breeding condition. They compete with one another during this time, establishing territories. Females follow shortly, 2 to 3 weeks after male emergence.

The gestation period is 26 to 33 days, with young being born from May to the beginning of September, depending on altitude. Most litters arrive from May to late June. Females have one to two litters per year. Litter size ranges from two to eight pups, averaging five. Litter size is larger at lower elevations.

Like many rodents, S. lateralis pups are born hairless except for tiny whiskers and hairs on their head. Their toes are fused together and their ears are closed. They are able to squeak and squirm around, but have little control over their body position. After a week, their fur has grown enough that their markings are visible. Vibrissae are also longer by this time, and they are able to right themselves. After two weeks, teeth erupt, ears open, toes separate and they utter their first adult sounds. Between days 20 to 30, upper incisors erupt, eyes open and grooming begins. They begin to eat solid food at around a month old, at which time their growth rate is rapidly accelerated. Pups leave the natal burrow when they are at least 25% of the adult body size, and are weaned sometime after they are at least 29 days old.

(Bartels and Thompson, 1993; Bihr and Smith, 1998; National Wildlife Federation, year unknown)

  • Breeding season
    Breeding time varies with altitude, usually occurring immediately after hibernation.
  • Range number of offspring
    2 to 8
  • Average number of offspring
    5.12
    AnAge
  • Range gestation period
    26 to 33 days
  • Range weaning age
    29 (low) days
  • Range age at sexual or reproductive maturity (female)
    12 (high) months
  • Range age at sexual or reproductive maturity (male)
    12 (high) months

The mother cares for the offspring as they grow inside the natal burrow. Young are highly altricial, but develop rapidly. Nests are built of grasses, dried leaves and shredded bark in underground burrows that can extend up to 30m shallowly underground. Studies have shown that S. lateralis prefers to have burrow entrances under significantly larger than average rocks or stumps

Pups are altricial and require extensive maternal care, which declines when they are weaned between 24 to 32 days. Care for the pups is provided by the female only, and that declines 2 to 3 weeks after the pups leave the nest (when at about 25% of adult body size), after which the female becomes antagonistic towards her offspring. Females and males reach sexual maturity within the first year.

(Bartels and Thompson, 1993; Bihr and Smith, 1998; National Wildlife Federation, year unknown)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Lifespan has been recorded by Bartles and Thompson (1993) as an average of 7 years in the wild, and 5 years in captivity. This seems odd, as captive animals, not facing dangers of predation and food shortage, typically live longer than their wild counterparts. The difference in wild and captive lifespans reported by Bartles and Thompson may relfect differences in populations of S. lateralis, which vary greatly in habitat, hibernation pattern, and sociality. Also, it seems likely that their reported average for wild gound squirrels does not take into account juvenile mortality, much of which must remain unknown to observers as the young are hidden away in burrows.

  • Average lifespan
    Status: wild
    7 years
  • Average lifespan
    Status: captivity
    5 years
  • Range lifespan
    Status: wild
    7 (high) years
    AnAge

Behavior

The home range of S. lateralis varies from 0.5 to 1 ha, depending on vegetation density. Females and males do not share territories, which include their burrow and up to 30m surrounding it, except during the mating season, when males overlap their territories with females. Studies have not shown conclusively if S. lateralis defends its territory exclusively, or if some overlap occurs. Offspring disperse, with males ranging somewhat farther than females. Young establish individual territories.

This species of ground squirrel is classified as asocial, which is the least social out of five social group types. Cohesiveness between individuals has only been seen in brief intervals between males and females (breeding), for a longer duration between females and young (until dispersal) and between littermates (until dispersal). Social interactions are mainly agonistic. Even play behavior consists of a high percentage of “rough and tumble” games, rather than social grooming, resting, etc. Agonistic behavior sometimes includes a threat, but a chase is usually launched without warning. Fighting occurs occasionally between adults. The main goal of the agonistic behavior seems to be to exclude all conspecifics from the area a given animal is in. Prior to dispersal, littermate interactions are rarely agonistic. Studies have not been done post-dispersal to see when agonistic behavior between littermates begins in S. lateralis, although studies in S. richardsonii show kin preferences dissolved by the first hibernation.

However, it should be noted that these squirrels are known to make alarm calls to warn conspecifics of danger from predators. This behavior imparts a potential cost to the caller, as it allows a predator to focus on it. It may succumb to predation because it has given the call. This type of behavior is typically seen only in species where kin are likely to be alterted and saved because of the alarm call. This behavior, then, may be considered a kind of kin preference, even if other behavior of the squirrels does not seem to indicate preferential treatment of kin.

Golden-mantled ground squirrels are mostly diurnal, but can be active at any time during the summer. They hibernate in areas where the ground freezes, or is covered in snow. Hibernation begins between late August and November, depending on elevation, and ends between late March and May. The squirrels curl up in a ball to minimize surface area. Hibernation is broken up into bouts of torpor, interspersed with wakeful periods. S. lateralis rarely eats between torpor bouts. Their diet is high in linoleic acid, which reduces the melting point of fat deposits, making them easier to metabolize at low temperatures. When aroused from torpor, S. lateralis spends most of its time moving about and rearranging nest materials, occasionally emerging to the surface. Females and males have the same annual period of torpor, but females have a significantly longer total hibernating period than males, who have longer bouts of continuous torpor, but longer arousals.

(Ferron, 1985; Bartels and Thompson, 1993; Frank and Storey ,1995; Holmes, 1995)

Communication and Perception

Food Habits

Spermophilus lateralis is omnivorous. Individuals of this species dig up and consume underground fungi, locating it by smell. The nuts of Pinus are a dietary staple. They also eat other nuts, acorns, seeds, forbs, flowers, bulbs, fruit, shrubs and leafy greens. Animal matter consumed consists of adult and larval insects, birds and eggs, including mountain bluebirds (Sialia currocoides) and Oregon juncos (Junco oreganus), young microtus, voles, entrapped yellow-pine chipmunks (Tamias amoenus), lizards (Sceloporous gracilis), and carrion, including road-killed conspecifics.

(Bartels and Thompson, 1993)

  • Animal Foods
  • birds
  • mammals
  • reptiles
  • eggs
  • carrion
  • insects
  • Plant Foods
  • leaves
  • roots and tubers
  • seeds, grains, and nuts
  • flowers
  • Other Foods
  • fungus

Predation

Golden-mantled ground squirrels are primary consumers, and are eaten by many different secondary consumers. Predators include various diurnal and nocturnal raptors, including red-tailed hawks and northern goshawks; mammals like coyotes, bobcats, skunks and various weasles; and snakes.

Predator avoidance behaviors include alarm calls accompanied by tail jerks. Spermophilus lateralis and yellow-bellied marmots respond to each others' alarm calls for predator warnings. Golden-mantled ground squirrels will ascend rocks and logs as lookout stations, occasionally sitting upright for a better view. They will also dive into the nearest cover or hole when a predator is spotted or an alarm call heard. Spermophilus lateralis keeps a series of burrow openings around their feeding areas to escape predation.

(Bartels and Thompson, 1993; Shriner, 1998)

Ecosystem Roles

Spermophilus lateralis is a primary consumer, and is therefore responsible for converting plant energy into a form useable by predators in the animal kingdom. There are many different types of predators that prey upon S. lateralis (listed under Predation). Golden-mantled ground squirrels probably affect predator populations and reproduction, depending upon how heavily any predator species relies on S. lateralis as a food source.

Spermophilus lateralis may also regulate populations of birds, lizards, and other small mammals upon which it preys.

Tunneling behavior can aerate the earth.

Competition between S. lateralis and other rodents can occur over food sources, which can therefore cause a negative effect on other rodent populations.

(Bartels and Thompson, 1993)

Economic Importance for Humans: Positive

Golden-mantled ground squirrels have little positive economic importance to humans. They do however, provide amusement and enjoyment for many campers as they can become quite tame, living at campgrounds and taking food from eager campers hands. (Bartels and Thompson, 1993)

Economic Importance for Humans: Negative

Spermophilus lateralis can have a negative impact on the timber industry. In the fall, coniferous seeds make up a large portion of their diet, and S. lateralis can harm reforestation efforts by eating newly sprouted conifer seeds. They have little impact on agriculture because of habitat selection.

Spermophilus lateralis is a vector for zoonotic diseases, and they are the main mammalian reservoir for Colorado tick fever, a non-lethal, tick-born viral disease. They are also vectors for the plague. Although campers enjoy feeding the squirrels, care should be taken not to get bitten or inhale dried fecal matter.

(Bartels and Thompson, 1993; Encyclopedia Britanica, online, 2001)

  • Negative Impacts
  • crop pest

Conservation Status

These squirrels are common in the areas where they occur.

Other Comments

Spermophilus lateralis fossils have been found in late Pleistocene deposits. Possibly due to more moisture in the past, the range in which the fossils of this species have been found is larger than their current range. They have been found in many caves throughout Wyoming, Colorado, Idaho, Montana, California, Nevada, and Arizona. Their presence in Ventana Cave, Pima Co., Arizona, is interesting because this site is over 260 km south and at an elevation 1,400 m lower than the nearest extant population.

(Bartels and Thompson, 1993)

Contributors

Monet Belltawn (author), Humboldt State University, Brian Arbogast (editor), Humboldt State University.

Glossary

Nearctic

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.

World Map

altricial

young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

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.

carrion

flesh of dead animals.

chaparral

Found in coastal areas between 30 and 40 degrees latitude, in areas with a Mediterranean climate. Vegetation is dominated by stands of dense, spiny shrubs with tough (hard or waxy) evergreen leaves. May be maintained by periodic fire. In South America it includes the scrub ecotone between forest and paramo.

chemical

uses smells or other chemicals to communicate

endothermic

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.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

omnivore

an animal that mainly eats all kinds of things, including plants and animals

polygynous

having more than one female as a mate at one time

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

soil aeration

digs and breaks up soil so air and water can get in

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

References

Bartels, M., D. Thompson. April 23, 1993. Spermophilus lateralis. Pp. 1-8 in Mammalian Species No. 440. American Society of Mammalogists.

Bihr, K., R. Smith. 1998. Location, structure and contents of burrows of *Spermophulus lateralis* and *Tamias minimus*, two ground-dwelling sciurids. Southwestern Naturalist, 43(3): 352-362.

Encyclopedia Britanica Online, "Colorado tick fever" (On-line). Accessed November 14, 2001 at search.eb.com/bol/topic?eu=25245&sctn=1&pm=1>.

Ferron, J. 1985. Social behaviour of the golden-mantled ground squirrel (*Spermophilus lateralis*). Canadian Journal of Zoology, 63(11): 2529-2533.

Frank, C., K. Storey. 1995. Optimal depot fat composition for hibernation by golden-mantled ground squirrels (*Spermophilus lateralis*). Journal of Comparitive Physiology, 164: 536-542.

Holmes, W. 1995. The ontogeny of littermate preferences in juvenile golden-mantled ground squirrels: effects of rearing and relatedness. Animal Behaviour, 50(2): 309-322.

Iwaniuk, A. 2001. Interspecific variation in sexual dimorphism in brain size in Nearctic ground squirrels (*Spermophilus* spp.). Canadian Journal of Zoology, 79: 759-765.

National Wildlife Federation, Unknown date. "Golden-mantled ground squirrel" (On-line). Accessed November 14, 2001 at http://enature.com/fieldguide/showSpeciesGS.asp?searchText=golden-mantled+ground+squirrel&curPageNum=1&recnum=MA0124.

Shriner, W. 1998. Yellow-bellied marmot and golden-mantled ground squirrel responses to heterospecific alarm calls. Animal Behaviour, 55(3): 529-536.

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