Overview
The Arctic Ground Squirrel (Urocitellus parryii), celebrated in indigenous Inuit lore as the Sik-Sik, is an extraordinary physiological marvel of the polar tundra. Enduring winter temperatures dropping past minus 40 degrees in the permafrost landscapes of Alaska and northern Canada, this plucky rodent performs the most extreme hibernation of any known mammal on Earth, supercooling its internal body temperature below the freezing point of water without freezing solid.
Biology and Physical Characteristics
Urocitellus parryii has a stout, cylindrical body with short, muscular limbs and a relatively short, flat tail. Its coat is tawny-brown to cinnamon-rufous, beautifully speckled across the back with white frosty flecks that blend seamlessly into lichen-encrusted tundra. Its small, rounded ears are tucked close to the skull to minimize heat loss, and its cheeks feature large internal pouches used for hauling seeds and winter nesting moss.
Behavior and Ecology
To hibernate, it excavates complex burrows down to the permafrost layer, packing a deep hibernation chamber with dry cotton grass and caribou hair. During its eight-month winter sleep, its core body temperature drops to an unbelievable -2.9°C (26.8°F), its heart slows to just one beat per minute, and its blood supercools, periodically shivering for a few hours every three weeks to maintain vital brain function.
Conservation and Human Impact
Assessed as Least Concern by the IUCN, the Arctic Ground Squirrel is abundant across undisturbed polar biomes, serving as a keystone prey species that sustains Arctic foxes, snowy owls, gyrfalcons, and grizzly bears. Indigenous peoples historically harvested their pelts to craft traditional, lightweight winter parkas.
Interesting Factoid
The Arctic Ground Squirrel is the only mammal on Earth whose body temperature drops below freezing during hibernation: its blood supercools to 27°F (-2.9°C) without turning into ice crystals.