You might not see them in winter, but they are here – the Yukon’s most widespread rodent, the arctic ground squirrel or sik-sik. Commonly called gophers, arctic ground squirrels inhabit tundra and forest clearings from eastern Siberia to Hudson Bay. They are the largest and most northerly ground squirrel, ranging from meadows in the southern Yukon to the tundra of the Beaufort Sea coast and up into the alpine 2000 metres above sea level. And they have been around a long time. Not long ago, a 190,000-year-old ground squirrel nest was discovered in the permafrost of Dominion Creek in the Klondike, with the remains of the ancient animal still curled up in it.
Modern arctic ground squirrels spend their winters just as their ancestors did, curled up in nests of dried grass, lichens, and caribou hair a metre below ground in specially excavated dens called hibernacula. When entering hibernation, a ground squirrel rolls itself into a ball by crouching on its haunches, tucking its head down between its legs, and tossing its tail over its head. A true hibernator, it then allows its body temperature to fall to near that of its hibernaculum for weeks at a time. Periodically it warms itself up to near its normal temperature of 36.4 degrees Celsius, then re-cools within 24 hours. Arctic ground squirrels can even survive when the temperature in their hibernacula drops below freezing, the only mammals known to have this capacity.
The squirrels hibernate for eight to ten months of the year, emerging as early as April for a hectic round of mating, raising young, and stocking up for the next long sleep. With a mating season of only three weeks, male ground squirrels start fighting for breeding territories as soon as they emerge from hibernation. To mark territories, males rub scent from glands on their cheeks and backs onto surfaces along boundaries. Encounters with other males sometimes escalate into a chase or a scratching-and-biting brawl. Territory winners earn the right to mate with the females residing inside their hard-won space.
The young are born in May and early June, blind and naked, weighing about the same as two quarters. Within two weeks, they wear coats of tawny-grey fur with white spots on their backs, and at 20 days their eyes open. Female ground squirrels produce a single litter of five to ten young each year. Arctic ground squirrels eat the seeds, leaves, flowers, and berries of a variety of low-growing plants. They also climb up into willow bushes to stuff their cheeks with new leaf buds and catkins, or scavenge freshly killed animals, including other ground squirrels. In the southern Yukon, adult females start to retreat to their winter dens in late July, and all are hibernating by mid-September. Juvenile females start hibernating in late August. Male ground squirrels remain above ground the longest, but most are below ground by the end of October, though an occasional male has been seen as late as early December.