Spermophilus parryiiArctic ground squirrel

Geographic Range

Arctic ground squirrels are the northernmost species of ground squirrel. They occupy a Holarctic distribution ranging from the west coast of Hudson Bay to the west cost of Alaska in North America, and into eastern Siberia (Donker and Krebs 2011, Barker and Derocher 2010, Yensen and Sherman 2003, Karels et al. 2000, Buck and Barnes 1999a). Recent phylogeographic studies have identified four geographically divergent clades. The Arctic clade consists of arctic and subarctic populations that occur north of the Yukon River in northern Alaska and Canada. The Southeast clade includes populations south of the Yukon River, spreading into south-central Alaska and western Canada. The Beringia clade inhabits the Alaskan Seward Peninsula and St. Lawrence Island, stretching across the Bering Strait into Siberia. The Southwest clade occurs south of the Yukon River in Alaska, continuing west out onto the Alaska Peninsula and associated islands (Galbreath et al. 2011). (Barker and Derocher, 2010; Buck and Barnes, 1999a; Donker and Krebs, 2011; Galbreath, et al., 2011; Karels, et al., 2000; Yensen and Sherman, 2003)

Most populations of arctic ground squirrels are indigenous, though a recent study has shown that many island populations near the Alaskan peninsula may be introduced, resulting from the presumed introduction by early indigenous peoples who valued them for their pelts. Likely introduced populations include several islands in the Kodiak archipelago, Semidi islands, and Shumagin islands, as well as confirmed introduced populations on Kavalga, Unalaska, and Amaknak islands in the Aleutians (Cook et al. 2010). (Cook, et al., 2010)

Range map at: http://mapservices.iucnredlist.org/IUCN/mapper/index.html?ID_NO=20488

Habitat

Arctic ground squirrels inhabit arctic and tundra habitats at northern latitudes and higher elevations, and boreal forest and alpine meadows at lower latitudes and elevations (Byrom et al. 2000, Donker and Krebs 2011). At their northernmost ranges, they contend with long cold winters where temperatures can drop below -20° Celsius for seven to eight months of the year, and where sub zero temperatures and snowfall are possible in every month of the year. In arctic environments, the growing season is short, lasting only six to ten weeks, and for most of the year arctic ground squirrels must cope with frozen soils, high winds, snow accumulation of 10 to 75 cm, and extremes of light and darkness (Buck and Barnes 1999a,b). (Buck and Barnes, 1999a; Buck and Barnes, 1999b; Byrom, et al., 2000; Donker and Krebs, 2011)

Arctic ground squirrels are colonial and live in shallow, subterranean burrow systems up to 20 m in length (Nowak 1999). In many populations, burrow depth is limited to less than 1 meter due to frozen soils (permafrost) (Buck and Barnes 1999b). Burrows serve as maternal dens, hibernacula, and refuges from predators and climatic conditions (Long et al. 2005, Barker and Derocher 2010). There are at least three distinct burrow types constructed and used by arctic ground squirrels. Duck holes are short tunnels with several exits that are used primarily as escape refuges. Permanently occupied single and double burrow systems consist of many multilevel tunnels, nest chambers, and exits. Double burrow systems are used by closely related breeding females as shared places to raise young. Hibernacula burrows are used during hibernation and can either be connected to existing burrow systems, or constructed separately elsewhere. These often have hidden entrances that are plugged with earth upon immergence for hibernation in the fall, and are not cleared until the animal emerges in the spring (Iwen 1999). Within the burrows they construct nests of lichens and dry grasses, which are 22.5 to 30 cm in diameter (Buck and Barnes 1999b). Habitats with sloped terrains, drained soils, and sparse vegetation, are preferred by arctic ground squirrels. Sites with wet soils are avoided due to their poor suitability for digging, and sites with hummocks or abundant tall or shrubby vegetation are selected against since they reduce the arctic ground squirrels ability to visually detect predators (Gillis et al. 2005b, Barker and Derocher 2010). (Barker and Derocher, 2010; Buck and Barnes, 1999b; Gillis, et al., 2005a; Iwen, 1999; Long, et al., 2005; Nowak, 1999)

Populations of arctic ground squirrels are at their highest densities in arctic tundra and alpine environments, where they are mostly limited by food and burrow availability. In boreal forest populations, densities are lower, and they are limited mainly by a combination of predation and food supply. Boreal forests are considered suboptimal habitat due to an increased number of predators, and the reduced ability of the squirrels to detect predators. Not surprisingly, these areas have been shown to be a population sink for the species (Karels et al. 2000, Gillis et al. 2005b, Donker and Krebs 2011). (Donker and Krebs, 2011; Gillis, et al., 2005a; Karels, et al., 2000)

  • Range elevation
    sea level to 900 m
    to 2952.76 ft
  • Average depth
    burrows average 1 meter below the surface m
    ft

Physical Description

All arctic ground squirrels have a cylindrical body shape with short, powerful forearms and sharp claws adapted for digging, and short, strong hind limbs for propelling forward movement. They have four digits on their forefeet and five on their hind feet. Their feet have soft pads on the bottom surface that allow them to grip and manipulate food and earth (Nowak 1999, Yensen and Sherman 2003). Their dental formula is: I 1/1, C 0/0, P 2/1, M 3/3, and P3 is one-third to one-half the size of P4 (Hall 1981, Forsyth 1999). Arctic ground squirrels molt twice per year; in the spring after emergence from hibernation, and in the fall prior to hibernation. They have tawny or cinnamon dorsal pelage that is flecked with white spots. Their underparts are lighter in color, largely buff tawny in the summer and turning an even lighter buffy color with the fall molt. Their tail color matches their pelage at the base, fading toward darker colors at the tip (Hall 1981, Iwen 1999). The range of length for their skull, tail, and hind foot is 50.7 to 65.8 mm, 77 to 153 mm, and 50 to 68 mm, respectively (Yensen and Sherman 2003). They also have large internal membranous cheek pouches that are used to store and carry food. Females have four to six pairs of mammae (Nowak 1999). (Forsyth, 1999; Hall, 1981; Iwen, 1999; Nowak, 1999; Yensen and Sherman, 2003)

Arctic ground squirrels are the largest of the ground squirrels with a mass of 524 to 1500 g, depending on sex and season. They range from 332 to 495 mm in length, with an average length of 390 mm (Woods 1980, Yensen and Sherman 2003). They are sexually dimorphic in size, and males average 740 to 1000 g and are longer in length, while females average 600 to 1000 g and are shorter in length (Buck and Barnes 1999b, Yensen and Sherman 2003, Hayssen 2008). They also have an enhanced ability to store fat, and for five to seven weeks preceding hibernation they will increase their fat stores to 30 to 41.5% of their total body weight (Frank et al. 2008). (Buck and Barnes, 1999b; Frank, et al., 2008; Hayssen, 2008; Woods, 1980; Yensen and Sherman, 2003)

Arctic ground squirrels are the northernmost hibernating terrestrial mammal and can achieve wide ranges of body temperatures and metabolic rates. This plasticity is an adaptation for surviving extended seasons of extreme temperatures and no food availability (Sheriff et al. 2011). Their upper critical body temperature is 36° Celsius, their lower critical body temperature is 18° Celsius, and their basal metabolic rate is 0.40 to 0.61 ml O2/g/h (Withers et al. 1979, Long et al. 2005). During hibernation they can drop their body temperature to -2.9° Celsius. They also have the lowest known minimum metabolic rate of any endothermic hibernator, reaching levels of 0.012 ml O2/g/h during torpor at ambient temperatures of 4° Celsius (Buck and Barnes 1999b, 2000). (Buck and Barnes, 1999b; Buck and Barnes, 2000; Long, et al., 2005; Sheriff, et al., 2011; Withers, et al., 1979)

  • Sexual Dimorphism
  • male larger
  • Range mass
    524 to 1500 g
    18.47 to 52.86 oz
  • Average mass
    Males-800 Females-700 (Woods 1980) g
    oz
  • Range length
    332 to 495 mm
    13.07 to 19.49 in
  • Average length
    390 mm
    15.35 in
  • Average basal metabolic rate
    0.40-0.61 ml oxygen/g/hour cm3.O2/g/hr

Reproduction

Arctic ground squirrels exhibit a female defense polygynous mating system (Yensen and Sherman 2003). Mating occurs in late April shortly after emergence from hibernation and lasts for approximately two weeks. Females are at maximal estrous three days following emergence and they are only receptive for a short, less than 12-hour period (Buck and Barnes 1999a, Lacy and Wieczorek 2001, Yensen and Sherman 2003, Donker and Krebs 2011). (Buck and Barnes, 1999a; Donker and Krebs, 2011; Lacy and Wieczorek, 2001; Yensen and Sherman, 2003)

Males typically defend a territory where multiple females reside. During this time, males are highly territorial and will act aggressively to all other males that enter their territory. Severe confrontations can occur where males will severely wound or even kill each other in defense of females (Lacy and Wieczorek 2001, Buck and Barnes 2003). Males will mate with multiple females, and extra-pair copulations between females and multiple males also occur. Evidence of copulatory plugs in females has been observed. The first male a female mates with is generally the one that sires the most young in her litter (over 90%), though multiple paternity in litters is common, and females have been observed to mate with up to four males (Lacy et al. 1997, Lacy and Wieczorek 2001, Yensen and Sherman 2003). (Buck and Barnes, 2003; Lacy and Wieczorek, 2001; Lacy, et al., 1997; Yensen and Sherman, 2003)

During and after the breeding season, males experience a trade-off between reproduction and survival. During breeding, males compete for territory ownership and access to females. During this period of intense competition, the males are highly active and often do not feed, resulting in high levels of stress, and body mass losses of up to 21%. Many males will die after the breeding season as a result of compromised immune systems and poor body condition (Barnes 1996, Boonstra et al. 2001, Lacy and Wieczorek 2001). (Barnes, 1996; Boonstra, et al., 2001; Lacy and Wieczorek, 2001)

After the breeding season, sex ratios become skewed towards females. Females are highly philopatric and display nepotism, resulting in groups of closely-related, cooperative females living together in close or connected burrow systems (kin clusters). They often clump their litters together and share in the maternal responsibilities. This is thought to serve two main functions: the first being shared duties in watching for predators, the second being to protect the young from infanticidal males (McLean 1982,1983, Nowak 1999, Yensen and Sherman 2003). The incidence of infanticide by males in arctic ground squirrels is high. Immigrant males that are looking to establish new territories are most likely to engage in infanticide. Males target young that they have most likely not sired, and litters are attacked both pre- and post-emergence from the burrow. Females will fight to protect their young, and it is suspected that a function of intense male territoriality is to protect the young that they have most likely sired from other infanticidal males (McLean 1983). (McLean, 1982; McLean, 1983; Nowak, 1999; Yensen and Sherman, 2003)

Arctic ground squirrels breed in April during a two-week period shortly following emergence from hibernation (Donker and Krebs 2011). Females give birth to one litter per year in mid-May following a 25 to 30-day gestation period (Hayssen 2008, Donker and Krebs 2011, Williams et al. 2011). Litters range from two to ten altricial pups that are born hairless, toothless, blind, with unopened ears, and incapable of thermoregulation (Yensen and Sherman 2003, Williams et al. 2011). After two days hair begins to appear, and they are fully furred by the tenth day (Iwen 1999). Lactation lasts for 28 to 35 days, and pups come above ground around the 27th day in mid-June. Weaning mass is approximately 199 g (Hayssen 2008, Williams et al. 2011). Within five to six weeks, the pups undergo a six to ten fold increase in body size, reaching 80% of their adult weight (Yensen and Sherman 2003). At eight to ten weeks, sexual dimorphism becomes apparent, and the juveniles disperse at this time (Byrom and Krebs 1999, Yensen and Sherman 2003). A rapid growth rate of the young is necessary to ensure that they are able to survive the coming hibernation season (Yensen and Sherman 2003). The young are reproductively active by the following spring (Lacy et al. 1997). (Byrom and Krebs, 1999; Donker and Krebs, 2011; Hayssen, 2008; Iwen, 1999; Lacy, et al., 1997; Williams, et al., 2011; Yensen and Sherman, 2003)

  • Breeding interval
    Arctic ground squirrels breed once yearly
  • Breeding season
    Arctic ground squirrels breed in April for a two-week period.
  • Range number of offspring
    2 to 10
  • Average number of offspring
    4
  • Range gestation period
    25 to 30 days
  • Average gestation period
    28 days
  • Range weaning age
    28 to 35 days
  • Average weaning age
    30 days
  • Average time to independence
    6-7 weeks
  • Average age at sexual or reproductive maturity (female)
    1 years
  • Average age at sexual or reproductive maturity (male)
    1 years

Arctic ground squirrel females spend the majority of their time underground with their young during lactation. They will emerge several times a day for short foraging bouts before returning to their young (Williams et al. 2011). Females will form kin clusters with other closely-related females, where they will clump their young together and share in the maternal responsibilities of watching for predators and defending the young against conspecifics (McLean 1982, 1983, Nowak 1999, Yensen and Sherman 2003). Mothers will care for their young for another one to two weeks following weaning and emergence from the burrow (Iwen 1999). Paternal parental investments are minimal and may be restricted to territory defense surrounding their females and sired young (McLean 1983). (Iwen, 1999; McLean, 1982; McLean, 1983; Nowak, 1999; Williams, et al., 2011; Yensen and Sherman, 2003)

  • Parental Investment
  • altricial
  • female parental care
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female
  • post-independence association with parents

Lifespan/Longevity

Arctic ground squirrel mortality sources include predation, disease, starvation, freezing, and death by conspecifics. Mortality during the first year of life is 54 to 74%. Survival is dimorphic, with females living longer than males. Increased male mortality is due to several factors. Males experience higher mortality rates that are associated with increased dispersal demands and risks, and aggressive interactions between males. Males also experience increased predation during the mating season due to their increased visibility associated with their increased activity. They also experience a higher overwinter mortality that is associated with competition for optimal hibernacula sites with females (Yensen and Sherman 2003). In contrast, highly philopatric individuals (mainly females) have a 73% survival rate, and dispersants (mainly juvenile males) have a 20 to 40% survival rate (Byrom and Krebs 1999). (Byrom and Krebs, 1999; Yensen and Sherman, 2003)

Survival also varies depending on habitat and season. In the summer, survival is lower in the boreal forest than in the alpine habitat, due to greater predation rates in the boreal forest habitat. In winter, survival is higher in the boreal forest than in the alpine habitat, due to increased hibernation demands in the alpine habitat (Gillis et al. 2005b). Burrow site is also important for survival: burrow sites with good visibility, and deeper warmer burrows, result in increased survival (Buck and Barnes 1999b, Yensen and Sherman 2003). (Buck and Barnes, 1999b; Gillis, et al., 2005a; Yensen and Sherman, 2003)

Regulation of arctic ground squirrel populations is both density-dependent and density-independent. Annual mortality depends on: individuals obtaining variable or limited resources such as food and burrow sites, predator abundance and success, presence of infectious diseases, and climatic conditions such as temperature and snow depth (Yensen and Sherman 2003). Arctic ground squirrels will survive to a maximum of eight to ten years in the wild (Forsyth 1999). (Forsyth, 1999; Yensen and Sherman, 2003)

  • Range lifespan
    Status: wild
    8-10 (high) years

Behavior

Arctic ground squirrels are a colonial species. Communities are based around kin clusters of closely-related adult females and their offspring, with a single territorial male (McLean 1982, Yensen and Sherman 2003). Adult males establish territories in the spring that are 0.14 to 2.2 ha, and may encompass several kin clusters (Nowak 1999). Adult females make use of existing burrows, or excavate new burrows, that they use as refuge, and to birth and wean their pups (Yensen and Sherman 2003). Home range size varies with sex, life stage, and resource density, but is generally 0.2 to 4 ha (Hubbs and Boonstra 1998, Nowak 1999). After weaning, young are independent and will likely disperse. The females are highly philopatric and will likely remain in the area and kin cluster. Females will only disperse if there is already a high population density, and competition for resources is high (Byrom and Krebs 1999). Males are highly likely to disperse, and 57 to 100% of juveniles will disperse in their first year, and 41 to 68% of adult males will disperse after the breeding season. This dispersal behavior is thought to function to reduce the chances of inbreeding, and to minimize competition for mates (Byrom and Krebs 1999, Yensen and Sherman 2003). Dispersal comes with a cost, and disperses tend to lose body mass and experience increased mortality as a result. One study demonstrated a positive correlation between mortality and dispersal distance, likely as a result of predation (Buck and Barnes 1999a, Yensen and Sherman 2003). (Buck and Barnes, 1999a; Byrom and Krebs, 1999; Hubbs and Boonstra, 1998; McLean, 1982; Nowak, 1999; Yensen and Sherman, 2003)

Population densities of arctic ground squirrels are controlled by interrelated factors such as resource density and predation. Most of the limitations are seen through changes in reproductive success. In the boreal forest, predation and food availability interact to form an additive limitation on litter size, body condition, percent of lactating females, and number of successfully weaned litters. In arctic and tundra environments, populations are often limited by food and burrow availability (Karels et al. 2000). (Karels, et al., 2000)

Even though in the summer months there is almost constant sunlight, arctic ground squirrels are diurnal and are most active between 5 am and 11 pm, at temperatures of 17 to 33 degrees Celsius. They retire to their burrows at night and during inclement weather to minimize their thermoregulatory costs (Long et al. 2005). Arctic ground squirrels are obligate hibernators; they are active only three to five months of the year and spend the rest in hibernation. Hibernation is an essential physiological adaptation they employ to survive the extreme climatic conditions and extended period of fasting that they experience in their winter arctic habitat (Buck and Barnes 1999a, Williams et al. 2011). Beginning in July for females, and mid-August to September for males, individuals will start to increase body mass and fat stores in preparation for hibernation. Females will enter hibernation first in August, and males will follow over a one-month interval. They will remain in hibernation for 215 to 240 days, females remaining longer than males, and adults remaining longer than juveniles. Males will emerge before females in mid-April and adults will emerge before juveniles (Buck and Barnes 1999a,b). Burrow site plays an important role in the costs of hibernation. Burrows with shrubby vegetation over them will accumulate more snow and have warmer soil temperatures than burrows located on clear, windswept sites. Competition for favored burrow sites can be intense, and males will become particularly fierce in late summer defending their hibernacula. Adult females appear to inhabit the favored burrows more than males and juveniles, and juveniles are often left with the least-favored sites (Buck and Barnes 1999b, 2003). (Buck and Barnes, 1999a; Buck and Barnes, 1999b; Buck and Barnes, 2003; Long, et al., 2005; Williams, et al., 2011)

During hibernation, arctic ground squirrels will drastically lower their body temperature and metabolic rate. They will supercool their body temperature to -2.9° Celsius and remain in this state of torpor for up to three weeks at a time. Even at this low temperature, they must still thermoregulate since the ambient temperature and soil temperature in their burrows will drop down to -18.8° Celsius. In between bouts of torpor they will experience arousal episodes where they rewarm their body temperature to euthermic levels (34 to 36° Celsius) for one to two days. These rewarming episodes are the most energetically expensive cost of hibernation. They accomplish this rewarming through shivering and non-shivering thermogenesis. Non-shivering thermogenesis uses brown adipose tissue and fatty acids as a fuel source to achieve rewarming. During the endothermic arousal, high energy costs are incurred through increased metabolic rate, and elevated activity levels of major organs, like the heart and brain. This incurred costs depletes glucose levels in the body, which are replenished through gluconeogenesis of protein (lean mass) tissue. It is hypothesized that they require the endothermic arousal episodes to maintain certain homeostatic processes that are inhibited by the colder temperatures, like brain function. It is also thought that they arouse simply to sleep, as severely reduced body temperature during torpor prevents this (Buck and Barnes 1999b, 2000). (Buck and Barnes, 1999b; Buck and Barnes, 2000)

Males become euthermic four to six weeks earlier than females, but will remain in their burrow for an additional 10 to 21 days. Males must arouse from hibernation earlier in order to achieve sexual maturation. Spermatogenesis is not possible at sub-zero temperatures and males must become euthermic to allow gonadal development. During this time, they consume food they have cached in their hibernacula from the previous season. Only males cache food in their hibernacula, and their ability to cache an adequate supply of food from the previous season will impact their reproductive potential and survival. When males arouse, they have lost close to 30% of their body weight. By feeding on their cache, they will regain that mass and emerge from their burrows the same mass they were at immergence the previous fall. Females, on the other hand, will emerge from hibernation with a greater than 30% loss in body mass from the time of immergence (Barnes 1996, Buck and Barnes 1999a). (Barnes, 1996; Buck and Barnes, 1999a)

  • Average territory size
    0.14 to 2.4 ha km^2

Home Range

Arctic ground squirrels have home ranges between 0.2 to 4 ha.

Communication and Perception

Arctic ground squirrels engage in a form of altruism by giving alarm calls when predators are in the area. While the individual who gives the call experiences a higher predation risk associated with drawing attention to themselves, they are thought to benefit evolutionarily by protecting their relatives, and assuring their genes will be passed to subsequent generations (Yensen and Sherman 2003). It has been suggested that they have different calls for different predators. They appear to use a high-pitched whistle for aerial predators, which is difficult to pinpoint, and a guttural chatter for terrestrial predators (Woods 1980). (Woods, 1980; Yensen and Sherman, 2003)

Males communicate their territories to other males by marking the boundaries with scent glands in their cheeks and back. Territoriality, as well as other confrontations, is resolved through violent contact that includes biting and scratching. Individuals are often seriously injured through such confrontations, some of which result in death. Initial social contact between individuals involves nose-to-nose contact and pressing against each other in various poses, in which the individuals smell and get a sense of one another. These interactions can end amicably or violently, depending on the situation (Woods 1980). (Woods, 1980)

Food Habits

Arctic ground squirrels are generalist foragers, feeding on everything from plants, invertebrates, small vertebrates (including their own species), eggs, birds, and carrion (McLean 1985, Boonstra et al. 1990, Gillis et al. 2005a, Zazula et al. 2006, Cook et al. 2010). They have been observed to actively prey on the eggs and chicks of birds, as well as collared lemmings (Boonstra et al. 1990, Cook et. 2010). Plant matter makes up the majority of their diet however, and when caching food for winter stores, they use only plant material. They consume all parts of plants, depending on the species, including foliage, roots, seeds, flowers, and fruits. Commonly consumed plant families include: Polygonaceae, Juncaceae, Cyperaceae, Ranunculaceaea, Rosaceae, Brassicaceae, Caryophllaceae, Poaceae, Saxifragaceae, Salicaceae, Gentianaceae, Scrophulariaceae, Poaceae, Asteraceae, Plantaginaceae, Fabaceae, and Santalaceae (McLean 1985, Gillis et al. 2005a Zazula et al. 2006). They are known to selectively choose and cache certain species, dependent on habitat location (Gillis et al. 2005a). (Boonstra, et al., 1990; Cook, et al., 2010; Gillis, et al., 2005b; McLean, 1985; Zazula, et al., 2006)

Arctic ground squirrels have also been shown to select for a diet with moderate levels of polyunsaturated fatty acids (PUFAs). Polyunsaturated fatty acids are essential fatty acids that are incorporated into cell membranes. They play a critical role for hibernating animals that need to maintain certain levels of PUFAs in their diet, in order to maintain flexibility in cell membranes when body temperatures drop to subnormal levels. However, a diet too high in PUFAs results in increased lipid peroxidation, which produces lipid peroxides that damage cells. Therefore, arctic ground squirrels select foods that provide moderate levels of PUFAs in the fall before hibernation (Frank et al. 2008). (Frank, et al., 2008)

  • Animal Foods
  • birds
  • mammals
  • eggs
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • leaves
  • roots and tubers
  • seeds, grains, and nuts
  • fruit
  • flowers

Predation

Arctic ground squirrels are an important prey source for many arctic and boreal predators. Anti-predator adaptations include extreme vigilance while above ground and away from their protective burrows. While foraging, they will frequently sit or stand up on their hind legs to listen and look around them. When predators are in the area, arctic ground squirrels will give alarm calls to alert other family members. When an alarm call is given, individuals will likely run for the protection of their burrows (Yensen and Sherman 2003). Predation is a limiting factor in most populations and can influence their distributions, particularly within the boreal forest habitat. In the boreal forest, they are the third-most abundant small prey species, and during low cycles of the snowshoe hare cycle, many predators switch from hares to arctic ground squirrels, limiting populations even further (Karels and Boonstra 1999, Byrom et al. 2000). The preferred habitat of arctic ground squirrels is open areas with little vegetation, which allow them to see predators coming from greater distances (Yensen and Sherman 2003). Common predators of arctic ground squirrels include lynxes, coyotes, wolverines, red foxes, arctic foxes, wolves, grizzly bears, ermines, northern goshawks, great horned owls, red tailed and Harlens hawks, common ravens, long tailed jaegers, snowy owls, short eared owls, golden eagles, northern harriers, gyrofalcons, rouch legged falcons, and peregrine falcons (Buck and Barnes 1999a, Byrom et al. 2000, Barker and Derocher 2010). (Barker and Derocher, 2010; Buck and Barnes, 1999a; Byrom, et al., 2000; Karels and Boonstra, 1999; Yensen and Sherman, 2003)

  • Anti-predator Adaptations
  • cryptic