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Classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Rodentia
Family: Sciuridae
Genus: Spermophilus
Species: Spermophilus parryii

The Arctic Ground Squirrel (Spermophilus parryii) is the largest, most northern-dwelling ground squirrel in North America. Arctic Ground Squirrels are found from the Arctic Ocean in the north, to about the 60th parallel in the south, and from eastern Siberia west to the Hudson Bay area of Canada.

Ground squirrels are social burrow-dwellers, and prefer open areas with good vegetative cover and low soil moisture. These areas are generally free of permafrost, which prevents burrowing; yet provide ground cover for protection from predators. Consistent with their choice of habitat, ground squirrels eat seeds, berries, grasses, leaves, and pretty much whatever else they can find. They are primarily herbivorous, but have been known to scavenge and eat meat, and even to cannibalize.

Male and female ground squirrels both reach an average length of about 15.5 inches (40 cm), although males usually weigh several ounces more than the females' 1.75 lbs (800 g). Ground squirrels are short in stature and stocky, with a narrow, fully furred tail. (For the purpose of physical comparison, they fall somewhere between a stout prairie dog and a small woodchuck.) They live in family groups of 5 to 50 individuals in burrow colonies, similar to other ground squirrels and prairie dogs.

Due to the long, bitterly cold winters, ground squirrels hibernate in their burrows for the majority of the year - usually from September to April. To survive this prolonged torpor, ground squirrels pack on the fat, doubling their body weight over the course of the short arctic summer. By the time they go underground for hibernation in September, some of the more successful squirrels can barely waddle around. This is the primary reason why they are such favored food for larger hibernators such as grizzly bears. It is common to see grizzly bears in early fall digging up patches of tundra to root out a colony of fattened ground squirrels.

One of the most fascinating things about ground squirrels is the way they have adapted to the harsh arctic climate. For example, the arctic ground squirrel is the only known mammal which lowers its core body temperature below freezing when it hibernates. Let me say that again: the ground squirrel's body temperature drops as low as 26F/-3C, but it somehow does not freeze, and no one knows exactly why.

Depending on the year, male ground squirrels will rouse from hibernation some time in late April or early May when there is still snow cover on the ground. They emerge to stake out their all-important breeding territories for the coming season before the females rouse in mid-May. Since there is still snow on the ground, the males live off the remains of their winter fat supply, or on seeds and berries that they stockpiled in their burrows the previous fall. Males may remain in their current area, or move up to a kilometer away, and mark their territories with scent from glands on their cheeks and backs. Battles over territorial boundaries are fierce, and can result in death or serious injury to the participants.

Once a male has won and defended his territory (or not), the females rouse from hibernation. One male will mate with all reproductive age females in his territory. The 2 to 3 week mating season happens in mid- to late-May, and a litter of 5 to 10 pups is born 25 days later. They grow from their birth weight of 3.5 ounces (10 g) to full adult size over the next three months.

In mid-summer, juvenile males disperse in search of new territories. This reduces the likelihood of inbreeding, but the sparse ground cover and inexperience of the young ground squirrels make them choice targets for bears, foxes, ravens, and other hungry predators.

Ground squirrels are abundant, and are preyed upon by a variety of animals, both terrestrial and airborne. Humans were once a major source of predation for ground squirrels, although this has been reduced sharply in recent decades due to changes in the cultural practices of indigenous peoples living in the ground squirrel's range.

Sources

  • Yukon mammal series, http://www.renres.gov.yk.ca/wildlife/agsquirrel.html
  • U. of Michigan Museum of Zoology, http://animaldiversity.ummz.umich.edu/accounts/spermophilus/s._parryii$narrative.html
  • U. of Alaska Fairbanks Science Forum, http://www.gi.alaska.edu/ScienceForum/ASF13/1378.html
  • Animal Behavior and Biochemistry class notes

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