Urocitellus armatus

Geographic Range

Uinta ground squirrels are restricted to a small area in the west of the United States, from southwestern Montana to southern Utah, including eastern Idaho and western Wyoming.

When the species was first described in 1863, the known rage was at the base of the Uinta Mountains in southern Wyoming. The Green River canyon forms a barrier for dispersal to the east into neighboring Colorado. The Snake River is a dispersal barrier to the north and to the west.

A large number of the studies of Uinta ground squirrels from 1960 to 1980 focused on the population northeast of Logan, Utah. In 2006, a population was studied in the northeastern range of Wyoming. The existence of a precise shift in the range of this species since it was first described to today is unknown.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Uinta ground squirrels have a small geographic range that encompasses open areas. They have been observed in open meadows and fields and on the edge of forests and are usually found in areas of moist and abundant vegetation such as shrubs and grasses. They are found at elevations ranging from 1,219 to 2,438 m. Uinta ground squirrels typically burrow in loose or soft soils.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• savanna or grassland savanna or grassland

Physical Description

Uinta ground squirrels are medium-sized squirrels, with body length that ranges from 280 to 303 mm. They have a grayish-brown or buff pelage with a lighter underbelly and black on the upper side of the tail. The sides of the head are light brown with grey and can be a tone of light yellowish-brown. The eyes have a lighter contour than the rest of the head. Melanistic individuals have been observed as well. The tail is short (approximately 65 mm) and bushy. The dental formula is 1/1, 0/0, 2/1, 3/3 = 22. The cranium ranges from 45.6 to 48.5 mm in length. Males have slightly larger cranial measurements than females.

Mean body mass upon emergence from hibernation is 300 g for adult males. Upon emergence from hibernation, males typically weigh more than females. Recorded body weights range from 201 g in yearling females upon emergence from hibernation to 635 g in adult males upon entering hibernation. Uinta ground squirrels have a body weight approximately 15 to 16% lower in males and 4 to 5% lower in females upon emergence from hibernation. Body mass is positively correlated with litter size and survival rates.

Uinta ground squirrels are endothermic. During warmer periods, when the ambient temperature is approximately 30⁰C, the basal metabolic rate ranges from 137 to 177 cubic centimeters of oxygen/hour. During colder periods, when the ambient temperature is approximately 10⁰C, the basal metabolic rate ranges from 500 to 570 cubic centimeters of oxygen/hour.

• Other Physical Features
• heterothermic heterothermic

• Sexual Dimorphism
• male larger

Reproduction

Uinta ground squirrels mate once per year in the spring, from mid April to early May. They emerge from hibernation prepared to reproduce. Male testes are at their maximum weight and are scrotal at this time. Some female yearlings may mate but male yearlings are usually not ready and may even emerge after the mating timeframe has passed. Females come into estrus within 2 to 4 days of emerging from hibernation and are only in that condition for a few hours in the latter part of the day. Uinta ground squirrels are polygynous (one male mates with more than one female) and mate underground. Around 1 to 3 days after mating, females repel males and may become aggressive towards them due to changes in their hormone levels from pregnancy.

• Mating System
• polygynous polygynous

Uinta ground squirrels breed once per year, in the spring, after emerging from hibernation. Emergence from hibernation occurs from late March to mid April and consequently mating occurs from mid April to early May. The gestation period ranges from 23 to 26 days. Litter size ranges from 4 to 6 offspring, with an average size of 5.4. Young are altricial. The timing of the mating can affect the litter size, offspring weight and survival as these are correlated with the mother’s weight at the emergence from hibernation. Similarly, juveniles that are weaned later in the season tend to have higher body mass than those that are weaned earlier. Males reach sexual maturity at 2 years on average and females reach sexual maturity at 1 or 2 years of age.

Juveniles emerge from the burrow after about 22 days and have their eyes open and weigh on average 60.3 g. The young gradually leave the burrow and become independent over the 2 to 3 weeks after emerging from the burrow for the first time. The mother may become aggressive towards the young after maternal care has ended.

The average birth mass is unknown. Richardson’s ground squirrels ( Spermophilus richardsonii ) have an average birth mass of 6.5 g. Richardson's ground squirrels have similar hibernation patterns as Uinta ground squirrels and have similar adult body mass, although the average adult mass is approximately 20% higher.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• viviparous viviparous

Males do not participate in the care of the young. Females care for the young until weaning, at which point they dig access holes around the burrow from which the young may emerge. Females practically ignore their young after emerging. Approximately two to three weeks after leaving the nest in which they are born, Uinta ground squirrels become intolerant of each other.

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

Lifespan/Longevity

Uinta ground squirrels live on average 4 years but are known to live up to 7 years. The main cause of mortality is predation.

Behavior

Uinta ground squirrels are social animals. Females and males typically mate in burrows underground. Females burrow with their offspring until they are independent, at which point offspring disperse to other burrows and engage in social encounters with other individuals. Groups of related individuals (mother and offspring) that burrow together are typically composed of 4 to 7 individuals.

Feeding is the most common behavior of Uinta ground squirrels during periods in which they are active. Uinta ground squirrels are active for approximately 3.5 months of the year, from mid-April through early September, and hibernate in burrows for the remaining 8.5 months.

A study conducted from 1964 to 1971 measured the impact of behavior on population density and regulation. The densities of certain populations of Uinta ground squirrels were purposely reduced by approximately 50% for the experiment. It was found that juveniles tend to disperse more at higher population densities and that yearlings tend to breed more at low population densities.

Uinta ground squirrels only walk when taking a few steps around the burrow or when feeding. For all other distances they tend to run. Their walking is quadrupedal and foot posture is plantigrade with the opposite fore and hind limbs moving together when taking a step. They have three different postures when walking or feeding: they are “body-on the ground”, “hunched” and “body-off the ground.” The “body-off-the ground” movement is characterized by the head being held low and the legs are flexed so that the body is close to the ground. The “body-off-the-ground” movement is generally observed when Uinta ground squirrels are tense and strongly correlated to when the animal will attempt to escape. This movement may also be observed when animals are feeding. At this time, movements are slower and more relaxed. In the “hunched posture”, Uinta ground squirrels have their limbs partially stretched and the spine hunched. This posture is associated with feeding, cold temperatures and when the animal is outside of familiar areas, or in subordinate animals. The “body-off-the-ground” posture is characterized by extended limbs and an extended back. This occurs mainly when Uinta ground squirrels are feeding and can be associated with dominance and animals that are not in an alarmed state. When running, Uinta ground squirrels alternate between having both forelimbs and both hind limbs on the ground. The posture typically changes according to the situation that the animal is in. For example, the tail is typically off the ground or upright when they are in familiar territory, such as its home range. When outside of this area, Uinta ground squirrels hold the tail closer to the ground and hunch the lower part of the spine.

Feeding behaviors of Uinta ground squirrels are correlated with the appearance of the sun and with temperature. They are diurnal and have more intense feeding activity during the first 1 to 3 hours after the sun rises and also during the 1 to 3 hours before the sun sets. On colder or cloudier days,feeding patterns become more uniform throughout the day or may start later and end earlier in the day. Uinta ground squirrels hold food with their fore limbs and stands on their hind limbs to reach food.

Uinta ground squirrels do not present any particular distinguishable behavior or posture when eliminating. They dust and groom themselves. When dusting, Uinta ground squirrels lie in loose dirt and move in order to cover the body in the dust. They then shake their bodies to remove the dust. Grooming consists of several complex movements that include washing, scratching and biting the fur. The head, neck and portions of the trunk can be scratched with the hind feet.

Both sexes engage in digging activity to either build new burrows or expand existing ones. They use the fore limbs for digging and the hind limbs for pushing the dirt back and out of the way. The muzzle may be used to help loosen dirt. Alertness is also a key behavior as it decreases the probability that the animal will be preyed upon. When Uinta ground squirrels are approached by an unknown object or animal, they display a more tense and elongated posture.

Uinta ground squirrels are quite intolerant of each other even though they live in groups. Aggressive behavior towards one another is observed when they come in close contact.

• Key Behaviors
• terricolous
• fossorial fossorial
• diurnal diurnal
• sedentary sedentary
• hibernation hibernation
• social social

Home Range

Uinta ground squirrels have a preference for large open areas in which it is easier to see predators. During a high-density year, population density varies between 23 and 28 animals per hectare. During low-density years, yearling females may increase their reproductive rates.

The territory size of Urocitellus armatus is unknown. Richardson's ground squirrels ( Spermophilus richardsonii ) have an average territory size of 240 m^2.

Communication and Perception

Although Uinta ground squirrels prefer to maintain a distance from each other, they exhibit altruistic behavior that is reflected in their communication. Communication consists mainly of alarm calls to warn other squirrels of the presence of predators or other threats.

Uinta ground squirrels produce six different calls: chirp, churr, squeal, squawk, teeth-clatter and growl. The chirp in males is slightly longer than in females (0.08 versus 0.06 seconds). This call is typically done in the vicinity of burrows and occurs more frequently in males before the breeding season than after. This call is not correlated to the approaching of females to males, rather it is to warn males not to approach. As in males, females typically use this call to intimidate others not to approach as they are not tolerant to other animals after becoming pregnant. Other Uinta ground squirrels typically become more alert when they hear this call. The churr is typically used by females when approached by other species. When others hear the churr call, they typically face the caller and stop moving. This call serves to threaten other animals and warn them to not come any closer. The squeal call typically happens in response to an attack by another animal. The squawk call is similar to the squeal in that is a response to an attack by another animal, but unlike the squeal, is associated to physical contact. The teeth-clatter typically happens at the end of an aggressive animal encounter but can also occur during threat posture. The growl occurs when Uinta ground squirrels are encountered by a different species and especially when they are being removed from a trap. The function of the calls is to alert other Uinta ground squirrels and warn both airborne and ground predators not to move closer. Others respond to these calls with alertness and by looking for the predator or danger visually. Alarm calls can carry over long distances, with the churr carrying further than the chirp. Care-giving related calls are not observed in this species.

No specific behaviors have been observed to indicate that Uinta ground squirrels mark burrow entrances, however their anal glands and bodies make contact with the burrow entrance which may leave their scent. Males may mark their territories by wiping their cheeks on the ground.

• Communication Channels
• tactile tactile
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• scent marks scent marks

• Perception Channels
• visual visual
• acoustic acoustic

Food Habits

Uinta ground squirrels are herbivores. The diet pattern changes throughout its active season. Upon emergence from hibernation, they eat mainly leaves and plant material. As the end of the active season approaches, in preparation for hibernation, they consume more seeds. They may also supplement their diet with invertebrates, even eating carrion occasionally.

• Primary Diet
• herbivore herbivore
  • folivore folivore

• Plant Foods
• leaves
• seeds, grains, and nuts

Predation

Known predators are coyotes ( Canis latrans ), weasels ( Mustela ), badgers ( Taxidea taxus ) and raptors. Badgers ( Taxidea taxus ) may prey on Uinta ground squirrels during hibernation. Approximately half of over winter mortality can be attributed to predation by badgers.

Uinta ground squirrels rely on warning calls as signals to be careful with approaching predators. These squirrels have a specific language that details the type of threat in the area and that is adapted to carry over different distances and indicate the proximity of the threat. Predation rates are lower when the population density of Uinta ground squirrels is high, most likely due to the fact that the probability of detecting a predator increases as more squirrels are available to produce warning calls. Uinta ground squirrels are more likely to produce warning calls when other members of the population are closely related to them (of close kin).

• Anti-predator Adaptations
• aposematic aposematic

Ecosystem Roles

Uinta ground squirrels are prey to coyotes ( Canis latrans ), weasels ( Mustela ), badgers ( Taxidea taxus ) and raptors. They host the parasites Heligmosomoides polygyrus , Neopsylla inopina , Opisocrotis tuberculatis , Oropsylla idahoensis , and the fleas Thrasis andorae and Thrasis francisi .

Uinta ground squirrels are burrowing animals, which may help with soil aeration, that is beneficial to vegetation. It is unknown if their burrows are used by other animals.

• Ecosystem Impact
• soil aeration soil aeration

Economic Importance for Humans: Positive

Uinta ground squirrels are cited on the website of the National Park Service as an animal for tourists to watch in Yellowstone National Park. Although it is unlikely that tourists will travel exclusively to see Uinta ground squirrels, they are popular among tourists at campgrounds.

• Positive Impacts
• ecotourism ecotourism

Economic Importance for Humans: Negative

Uinta ground squirrels may damage crops within their geographic range and especially in intermountain regions.

• Negative Impacts
• crop pest

Conservation Status

Uinta ground squirrel populations are not listed as threatened or of any special concern. Population sizes vary according to dispersal and emigration; as population densities increase, individuals tend to emigrate.

Other Comments

Urocitellus armatus has also been known by the names Citellus armatus and Spermophilus armatus .

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Vanessa Santana (author), University of Alaska Fairbanks, Laura Prugh (editor), University of Washington, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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