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Spermophilus saturatusCascade golden-mantled ground squirrel

By David Timmer

Geographic Range

The distribution of Spermophilus saturatus lies exclusively within a limited area of the Pacific Northwest region of North America. This species is unique to the Cascade Mountains of Washington and southern British Columbia, where it occupies a narrow band between the Columbia River in the south and the Nicola River in the north. The northern extent of its range is fragmented and not well documented. ("Inventory Methods for Pikas and Sciurids: Pikas, Marmots, Woodchuck, Chipmunks and Squirrels", 1998; Leung and Cheng, 1994; Nagorsen, 1990; Wilson and Ruff, 1999)

Habitat

Spermophilus saturatus occupies alpine habitat most often within the transition zone on the drier eastern side of the Cascade Mountain range. It is uncommon on the damper west side of the range. This species occurs in alpine talus, meadows, and in mixed coniferous forests. It prefers habitat that provides plenty of cover, with brush, logs, and trees. Spermophilus saturatus is often found in the open yellow pine (Pinus ponderosa) stands of the eastern Cascades among sagebrush and grassland, but rarely away from the cover of logs and trees. (Ingles, 1965; Trombulak, 1988; Wilson and Ruff, 1999)

Physical Description

Spermophilus saturatus is a handsome ground squirrel. It has a sturdy build with a chipmunk-like pelage. The head and shoulders are characterized by a poorly defined russet-colored mantle, and its eyes are bordered by a light buff colored ring. The dorsum of this species is grayish-brown with a white stripe on each side. The white stripe begins behind the shoulders and extends most of the way down the back. This white stripe is bordered on each side by two black stripes, which are sometimes poorly defined. The underside, feet, and tail are buff colored.

Spermophilus saturatus is distinguished from chipmunks (Tamius spp.) in that its dorsal stripes do not continue onto its face. Cascade golden-mantled ground squirrels are also larger than any of the chipmunks. These ground suirrels measure from 287 to 315 mm. Weigh varies seasonally, between 200 g at emergence from hibernation in the spring and 300 g, a whopping weight reached when fat reserves are at their pre-hibernation maximum. There is no significant sexual dimorphism.

Of the three species in the subgenus Calospermophilus, S. saturatus is the largest. Spermophilus lateralis, its closest relative, is smaller and has a more developed mantle. The other, Spermophilus madrensis, is much smaller and almost completely lacks the mantle of the others. (Ingles, 1965; Trombulak, 1988; Wilson and Ruff, 1999)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    200 to 350 g
    7.05 to 12.33 oz
  • Range length
    287 to 315 mm
    11.30 to 12.40 in
  • Average length
    305 mm
    12.01 in
  • Average basal metabolic rate
    0.849 W
    AnAge

Reproduction

Cascade golden-mantled ground squirrels are polygynous. Males emerge earlier from hibernation and then guard a territory waiting for the females to emerge and begin estrous. Males will mate with females who reside within theor territory.

Somewhat atypically, in the fall males usually enter into hibernation later than females. This is thought to be a mating strategy. In other species of ground-dwelling sciurids, males typically enter into hibernation before females, because, lacking the high energy demands of lactation, they are able to achieve adequate fat reserves early, and are less prone to heat stresses if they begin hiberation soon. In species where males enter hibernation after females, it is generally because it takes males longer than it does females to store enough food winter snacking. Spermophilus saturatus is not known to store food. It is thought that the reason for the later immergence of males is that it allows them to see where the females are hibernating, then following spring they remember where the females will be emerging when they are ready to mate. (Trombulak, 1987; Trombulak, 1988; Wilson and Ruff, 1999)

Reproduction in this species is timed to coincide with emergence from hibernation. In the early spring (early April to late May), adult males emerge from hibernation. They defend territories and wait for females to emerge. Adult females emerge less than 15 days after males. Mating begins a few days after the females emerge and lasts up to two weeks. The mating season is highly synchronous, and females will birth one litter/year.

Gestation lasts only 28 days, after which the female gives birth to as many as five pups. Juveniles weigh only 6 grams and are highly altricial at birth. They develop rapidly, and first appear from the burrow about 36 days after birth. Usually three pups survive to emergence, at which point they weigh around 85 grams.

Juveniles are weaned at least one week after they emerge. For a short time after their first emergence, the mother keeps a close eye on the young and will help them back into the burrow if there is any sign of danger. However, usually by mid-July they are on their own to leave the burrow. Both sexes disperse from their natal burrow and establish their own home range. They have been found to disperse up to 300 meters from the natal burrow.

Juveniles reach adult size and sexual maturity the following spring, which is slightly less than a year after they are born. Although sexually mature, yearling females and males reproduce at lower rates than do full adults. Reproduction for adult females and males is nearly 100%, whereas it varies from 50 to 100% for yearling females. Only about 10% of yearling males breed. (Banfield, 1974; Trombulak, 1987; Trombulak, 1988; Wilson and Ruff, 1999)

  • Breeding interval
    Cascade golden-mantled ground squirrels breed once yearly.
  • Breeding season
    Breeding occurs from April to May.
  • Range number of offspring
    3 to 5
  • Average number of offspring
    4.16
    AnAge
  • Average gestation period
    28 days
  • Average gestation period
    28 days
    AnAge
  • Average weaning age
    6 weeks
  • Average time to independence
    2 months
  • Average age at sexual or reproductive maturity (female)
    10 months
  • Average age at sexual or reproductive maturity (female)
    Sex: female
    335 days
    AnAge
  • Average age at sexual or reproductive maturity (male)
    10 months
  • Average age at sexual or reproductive maturity (male)
    Sex: male
    335 days
    AnAge

Males are not involved in the parental care of this species. Females give extensive parental care to their altricial young until they are weaned. She provides the young with milk, grooming, and protection. After the young emerge from the burrow, the mother keeps a close eye on them for protection and warning, until it is time for them to disperse. (Banfield, 1974)

  • Parental Investment
  • no parental involvement
  • altricial
  • female parental care
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Individuals of S. saturatus are known to have lived at least 4 years in the wild. Their average lifespan is not known, nor is their maximum possible lifespan. (Trombulak, 1988)

  • Range lifespan
    Status: wild
    4 (high) years

Behavior

Spermophilus saturatus, like other ground squirrels, is diurnal and semi-fossorial. They are primarily ground-dwellers and will only occasionally climb trees and shrubs. Individuals construct a simple burrow for hibernation, shelter, and sleeping. Females also use their burrows for raising young.

The most commom above-ground behavior of this species is sitting on a stump or log. Other time is spent foraging, eating, and grooming. These animals prefer warm sunny days and often remain in their burrows when conditions are cool and rainy.

Spermophilus saturatus spends the majority of the year in a state of hibernation. Individuals are active above ground for only 4 to 5 months during the summer. They enter their burrows to hibernate in mid-August to late-September and emerge from hibernation in late-April to mid-May. As is common for most ground squirrels, males and females have different hibernation schedules. Unlike other species of their genus, male S. saturatus enter hibernation after females, apparently as a means of assuring themselves of the location of potential mates in the spring.

Spermophilus saturatus is not known to store food for hibernation. Late in the active period these squirrels begin to fatten themselves to get ready for the winter. During this time individuals get noticeably larger and can dramatically increase their weight. During hibernation their metabolic rate decreases to 5 percent of what it was during the summer. Body temperature drops to just above freezing. Because they are not known to store food, this decrease in metabolic rate and body temperature allows these animals to survive for up to 8 months on only their body fat. During this period of hibernation, they will arouse every few days to 2 weeks likely to urinate.

This species constructs burrows which are relatively simple, although they often have multiple entrances hidden under rocks, stumps, or bushes. They leave no tell-tale sign of a mound that would give away the entrance to the burrow, preferring to keep them cryptic. The tunnel is usually more than 1 meter long and opens into a nesting chamber. The nesting chamber has multiple entrances. The nest within the chamber is constructed of leaves, grasses, and pine needles. (Banfield, 1974; Trombulak, 1987; Trombulak, 1988; Wilson and Ruff, 1999)

Population density differs by habitat. Adult and yearling density is greater than 4.5 individuals per hectare in meadow habitat and 2.0 individuals per hectare in closed coniferous forest. Juveniles are known to disperse from their natal burrow to at least 50 meters and to more than 250 meters. (Trombulak, 1988)

Home Range

Precise measurements of individual home ranges are not documented. It is known that individuals will range between forested and meadow habitat during the breeding season. (Trombulak, 1988)

Communication and Perception

Spermophilus saturatus has both a very good sense of sight, and hearing. It perceives danger primarily by spotting approaching predators. Individuals often scan for predators from a prominent perch on a stump or log. Given their good vision, it is likely that members of this species use some visual means of communication, such as body postures. Individuals often give an alarm call as they dive into their burrows.

Very little is documented about the methods of communication between individuals of S. saturatus. Banfield wrote about the communication of Spermophilus lateralis, which he considers to be the same species. He describes three calls: a high-pitched two-noted whistle, an explosive alarm call, and a buzzing chatter that individuals make when they are cornered.

Another study describes the relationship between S. lateralis and yellow-bellied marmots Marmota flaviventris . Each species responds to the alarm calls of the other, and will take appropriate cover upon hearing such calls. These squirrels distinguish alarm calls from other loud noises, and will seek refuge at the sound of an alarm call from the other species even though the animals of the two species do not normally interact. (Banfield, 1974; Ingles, 1965; Shriner, 1998)

Although not specifically mentioned in the literature, it is reasonable to assume that these animals use some forms of tactile communication. Mothers communicate with their young through touching, as do mates. Males may have some tactile communication with one another while defending their territories.

Food Habits

Spermophilus saturatus is primarily a mycovore and herbivore. Individual diet is variable, and depends on the specific habitat in which an animal resides. One study showed that in meadows, the diet consisted of 44% hypogeous fungi, 21% vetch leaves, 10% bark, 6% grasses, and 1% conifer seeds. In forested habitat, the diet was 63% hypogeous fungi with a proportionately smaller amount of plant material.

Spermophilus saturatus often forages on the ground for pine cones that have been dropped by Douglas squirrels Tamiasciurus douglasii.

Other items found in the diet of S. saturatus include: dandelion flowers, tubers, lupine seeds, and the berries of salal, huckleberry, and mountain ash.

Finally, this species has been known to forage on road-kill, even that of conspecifics. (Trombulak, 1987; Trombulak, 1988)

  • Plant Foods
  • leaves
  • roots and tubers
  • wood, bark, or stems
  • seeds, grains, and nuts
  • fruit
  • flowers
  • Other Foods
  • fungus

Predation

Spermophilus saturatus is a prey species for many raptors and carnivores. Anti-predator behaviors include scanning for predators from prominent logs or stumps, then diving for cover at the first sign of danger. Burrows often have multiple entrances to escape digging predators and so they have more access to safety from above.

Female ground squirrels keep a close eye on offspring for a time after they first exit the natal burrow and will assist juveniles back into the burrow if danger has been spotted.

Alarm calls likely warn other individuals and kin if predators are approaching. This species is known to respond to the alarm calls of Marmota flaviventris. (Banfield, 1974; Trombulak, 1988)

Ecosystem Roles

Spermophilus saturatus is a primary consumer, converting plant energy into body mass, and therefore making it available to upper level consumers. As listed above it is a prey species for many raptors and carnivores.

As a seed and fungus eater, S. saturatus decreases plant and fungus regeneration but is also likely responsible for dispersing seeds and spores throughout its range.

The digging of this species can facilitate soil mixing and aeration, and abandoned burrows can become home to other underground nesting animals.

Spermophilus saturatus has an interesting relationship with other rodents that live in close proximity to it. It often lives near and tolerates yellow-pine chipmunks, Tamius amoenus. They seems to avoid aggressive interactions by occupying different feeding niches. T. amoenus eats more plant seeds, whereas S. saturatus eats more leaves and stems. The two species have been known to forage non-aggressively within 5 cm of each other, and nest within 10 meters of each other. They also live in close proximity to Douglas squirrels, Tamiasciurus douglasii. T. douglasii generally climbs pine trees for cones and seeds, whereas S. saturatus forages for pine seeds on cones that have dropped - often by Douglas squirrels. (Ingles, 1965; Trombulak, 1988)

Commensal/Parasitic Species
  • Rocky Mountain spotted fever

Economic Importance for Humans: Positive

Spermophilus saturatus has little economic importance to humans. Its limited distribution reduces human contact, though it often provides much entertainment to campers and hikers who venture into its habitat. (Ingles, 1965)

  • Positive Impacts
  • research and education

Economic Importance for Humans: Negative

The lifestyles of ground squirrels are often in conflict with human economic interests because of their food choices and digging habits. Much research, expense, and effort has been put forth to control ground squirrel populations. Spermophilus saturatus is fortunate because its limited range most often keeps it away from human economic interests. It seldom inhabits agricultural areas, where most conflicts occur. One potential conflict may be with the timber industry which has extensive tree plantations within the range of S. saturatus. This species eats conifer seeds and can damage planted seedlings. However, the actual cost to the timber industry is likely negligible. Futhermore, this damage is likely countered by the number of seeds and spores these animals disperse.

Finally, being an intermediate host to Rocky Mountain spotted fever can cause concern because of its potential transmission to humans by infected ticks. (Banfield, 1974)

  • Negative Impacts
  • injures humans
    • carries human disease
  • crop pest

Conservation Status

Spermophilus saturatus is fairly common where it occurs. Due its limited range and relative rarity there has been some interest in determining its overall status. This is the case in British Columbia, where the ground squirrel is only found in a small portion of the province. In 1998, this species was on the provincial blue list for species that are vulnerable or sensitive. A 1999 report found that it appears to not be at risk though further information is required to determine its overall status. Not much is confidently known about its population trends and threats. It is still on the provincial blue list. Some potential threats could be timber harvesting, road construction, and competition with other rodents, specifically the Columbian ground squirrel Spermophilus columbianus.

Spermophilus saturatus occurs in several protected areas throughout its range. These include Manning Provincial Park, and Cathedral Provincial Park in British Columbia and North Cascades National Park and Mount St. Helens National Volcanic Monument in Washington. ("Inventory Methods for Pikas and Sciurids: Pikas, Marmots, Woodchuck, Chipmunks and Squirrels", 1998; "Rare amphibians, reptiles, and mammals of British Columbia", 1999; Leung and Cheng, 1994)

Other Comments

Spermophilus saturatus has an interesting classification history. It is very closely related to Spermophilus lateralis, and there are some scientists who consider S. saturatus a subspecies of S. lateralis. These two species occur relatively close to one another, but the Columbia River in the south, the Okonagan River in the east, and the Nicola River in the north isolate the range of S. saturatus.

In 1938, Howell classified golden mantled-ground squirrels into three allopatric species (those mentioned in Physical Description). Alternatively, in 1972 Wright proposed that S. saturatus be classified a subspecies of S. lateralis based on cranial and pelage morphology. In 1981, Hall stuck with the traditional classification of the three separate ground squirrels and today the three are most often considered separate species. Additional genetic information from S. saturatus is required from individuals throughout its range to absolutely validate its species status.

One study compared the genetic variability of both S. saturatus and S. lateralis in two nearby populations near the northern limit of the range of S. saturatus. The study showed less genetic diversity in the S. saturatus population. They considered this to be a local occurrence because other unpublished data found S. saturatus to by polymorphic at the same loci in a more southern portion of its range. The authors hypothesized that the low genetic diversity in this northern population is due to founder effects when a small population of S. saturatus extended its range from the south as the Cordilleran Ice Sheet retreated northward 17,500 years ago.

Spermophilus saturatus shows some tough adaptability. It is one of a few small mammal species that quickly recolonized the decimated blast zone area of Mount St. Helen. Perhaps some individuals survived the actual eruption in surrounding areas while hibernating underground. Conceivably, its somewhat generalist diet and an abundance of cover have allowed it to quickly recolonize even the blast zone area. (Leung and Cheng, 1994; Nagorsen, 1990; US Forest Service, 2003)

Contributors

Nancy Shefferly (editor), Animal Diversity Web.

David Timmer (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

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

acoustic

uses sound to communicate

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.

chemical

uses smells or other chemicals to communicate

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

diurnal
  1. active during the day, 2. lasting for one day.
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.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

forest

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

fossorial

Referring to a burrowing life-style or behavior, specialized for digging or burrowing.

herbivore

An animal that eats mainly plants or parts of plants.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

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.

mycophage

an animal that mainly eats fungus

native range

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

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.

visual

uses sight to communicate

viviparous

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

References

Ministry of Environment, Lands and Parks. Inventory Methods for Pikas and Sciurids: Pikas, Marmots, Woodchuck, Chipmunks and Squirrels. Standards for components of British Columbia's biodiversity; no. 29. Vancouver: Resources Inventory Committee. 1998. Accessed January 30, 2004 at http://www.gor.gov.bc.ca/ric.

British Columbia Ministry of Environment, Lands, and Parks. Rare amphibians, reptiles, and mammals of British Columbia. AMAFB05180. Vancouver: Wildlife Branch and Resource Inventory Branch. 1999. Accessed February 10, 2004 at http://srmapps.gov.bc.ca/apps/eswp/reports.do?index=0.

Banfield, A. 1974. The Mammals of Canada. Toronto: University of Toronto Press.

Ingles, L. 1965. Mammals of the Pacific States. Stanford, California: Standford University Press.

Leung, M., K. Cheng. 1994. Genetic variability of the Cascade golden-mantled ground squirrel (Spermophilus saturatus) in British Columbia. Canadian Journal of Zoology, 72: 371-374.

Nagorsen, D. 1990. Mammals of British Columbia: A Taxonomic Catalogue. Vancouver: Royal British Columbia Museums.

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

Trombulak, S. 1987. Life history of the Cascade golden-mantled ground squirrel (Spermophilus saturatus). Journal of Mammalogy, 68: 544-554.

Trombulak, S. 1988. Spermophilus saturatus. Mammilian Species, 322: 1-4.

US Forest Service, 2003. "Teacher's Corner Mount St. Helens National Volcanic Monument" (On-line). Life Returns: Animal and Plant Recovery Around the Volcano. Accessed February 05, 2004 at http://www.fs.fed.us/gpnf/mshnvm/education/teachers-corner/library/life-returns02.shtml.

Wilson, D., S. Ruff. 1999. The Smithsonian Book of North American Mammals. Washington DC: Smithsonian Institution.

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