Species of rodent
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The Arctic ground squirrel (Urocitellus parryii) (Inuktitut: "ᓯᒃᓯᒃ, siksik") is a species of ground squirrel in the squirrel family Sciuridae that is native to the Arctic and Subarctic regions of the Northern Hemisphere, mainly in North America and Asia. For some people in Alaska, particularly around the Aleutian Islands, the rodents are known as "parka" squirrels, likely due to their pelts being used for the ruff on parkas and other cold-weather clothing.
Taxonomy.
Subspecies listed alphabetically.
Description.
The Arctic ground squirrel typically has a beige-tan pelage with a lightly-spotted backside. Similar to the related prairie dog, it has a shorter face than the typical arboreal squirrels–due to its lifestyle of burrowing–as well as smaller ears, with a dark tail and white markings around the eyes. 
During the brief boreal summer, Arctic ground squirrels undergo an annual molting (coat shedding/re-growth) cycle in preparation for the onset of colder weather; this is seen in other Arctic species, as well, such as the white winter coat of the Arctic fox, Arctic and snowshoe hares, ermine (stoat), and even some birds, such as the rock ptarmigan. Summer coats include reddish and yellow colorations along the cheeks and sides of the body; in the fall, these red patches are shed and replaced by a more silvery color. The lighter coloration in winter helps the ground squirrels to camouflage against the often snow-white ground and better evade predators, such as snowy owls or foxes. The average length of an Arctic ground squirrel is approximately . Since Arctic ground squirrels undergo drastic seasonal changes in body mass, it is difficult to give an average mass; adult females are close to , while males may weigh nearly heavier.
Distribution and habitat.
The Arctic ground squirrel can be found in parts of western Northern Canada, from the Arctic Circle to the Yukon, northern British Columbia and the Northwest Territories; west into Alaska, the Aleutian Islands archipelago, and across to the Russian Far East (Siberia), including the Kamchatka Peninsula. The St. Lawrence Island subspecies ("U. p. lyratus") of Arctic ground squirrel is found on its namesake island in the Bering Sea; the Kodiak Island subspecies ("U. p. kodiacensis") is found on the Alaska Peninsula, namely Kodiak.
The Arctic ground squirrel has evolved with and is found on the North American Arctic tundra; depending on the subspecies, its preferred habitats are typically hillside or mountain slopes, riparian areas (such as river flats, banks or lake shores) or tundra ridges. Arctic ground squirrels prefer to live in sandy soil due to its ease of manipulation for burrowing, and its superior drainage as opposed to richer soils. Arctic ground squirrels make shallow tunnels and burrows in locations where the permafrost will not prevent them from digging. The more southerly subspecies typically inhabit open meadows and open tundra habitats.
Fossil record.
The Arctic ground squirrel has an extensive fossil record from the Pleistocene. During the Last Glacial Maximum, it was abundant in areas such as the Klondike region where it is currently rare or absent. Fossilised Arctic ground squirrel nests and caches have also been used for palaeoenvironmental reconstruction; "Calamagrostis canadensis", "Carex albonigra," and "Koeleria" sp. are common in caches from Late Pleistocene Alaska, indicating the presence of an aerially extensive mammoth steppe ecosystem in the region at this time.
Behaviour.
The diurnal Arctic ground squirrel lives on the tundra, where it may fall prey to the Arctic and the red fox, wolverine, Canada and Eurasian lynx, brown bear, snowy owls and eagles. It is one of the few Arctic mammal species which hibernates in the winter, similarly to the little brown bat and the closely-related marmot. In the summer, it forages for tundra plants, seeds, and fruit to increase body fat for its winter hibernation. By late summer, the male Arctic ground squirrel begins to store food in its cache so that, come springtime, it will have a food source until the any new vegetation has grown. Their burrows are lined with lichens, leaves, grasses, and muskox hair, amongst other animal fibers they may find.
Communication between squirrels is done through both vocal and physical means. When they meet, nose to nose contact is made or other body parts are pressed together. The "tsik-tsik" calls are made in response to threats and vary as between different predators. Deep guttural sounds are used to indicate land-based predators while short "band whistle" chatter indicates danger from the air.
Hibernation.
The Arctic ground squirrel hibernates over winter from early August to late April in adult females and from late September to early April for adult males, at which time it can reduce its body temperatures from to as little as . During hibernation, its core body temperature reaches temperatures down to and its heart rate drops to about one beat per minute. Peripheral, colonic, and blood temperatures become subzero. The best theory as to why the squirrel's blood doesn't freeze is that the animal is able to cleanse their bodies of ice nucleators which are necessary for the development of ice crystals. In the absence of ice nucleators, body fluids can remain liquid while in supercooled state. This process is being studied with the hope that mechanism present in arctic ground squirrels may provide a path for better preservation of human organs for transplant. The connections between brain cells also wither away in this state. The damage should have resulted in death, but research on related species show that these connections regrow after waking up. In the warmer months, the squirrel is active during the day.
Diet.
This squirrel feeds on grasses, sedges, mushrooms, bog rushes, bilberries, willows, roots, stalks, leaves, leaf buds, flowers, catkins, and seeds. They will also eat insects and, occasionally, even supplement their diet with carrion (such as mice, snowshoe hares and caribou) as well as juvenile Arctic ground squirrels. Sometimes these squirrels carry food back to their den in their cheeks.
Reproduction.
During the mating season, males engage in male-male aggressive encounters for mating rights.
Arctic ground squirrels live individually in burrow systems. Mating occurs between mid-April and mid-May (depending on latitude) after winter hibernation. Mating includes male-male competition for access to females, and litters are typically sired by multiple males. Gestation is approximately 25 days, and results in a litter of 5 to 10, hairless pups. After six weeks, the pups are weaned and this is followed by rapid growth to prepare for the upcoming winter.
Conservation.
Although Environment Yukon has not estimated their population size, their conservation status is currently said to be "secure" (Environment Yukon 2013).
The Arctic ground squirrel is classified as least concern (LC) on the IUCN Red List (Arkive 2013).
References.
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