You might not see them in winter when they are hibernating deep beneath the ground, but the arctic ground squirrel is the Yukon’s most widespread rodent. Commonly called gophers, or sik-sik, after a call they make to warn each other of predators, they are the largest and most northerly of ground squirrels. They inhabit tundra and forest clearings from eastern Siberia to Hudson Bay and have been around for a long time. A 750,000-year-old squirrel nest was discovered in the permafrost of Dominion Creek in the Klondike, with fecal pellets and seeds still in it.
Arctic ground squirrels depend on an elaborate network of burrows, with up to 50 entrances and multiple layers of tunnels for protection from predators and winter survival. They spend their winters curled up a metre below ground specially excavated dens within their burrow called hibernacula. Here they make nests of dried grass, lichens, and caribou hair. 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 zero degrees Celsius. Periodically it warms itself up to near its normal temperature 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, with males emerging as early as April. Spring and summer are spent 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 onto surfaces along their territorial boundaries. Encounters with other males can escalate into a chase or a scratching-and-biting brawl. Winners earn the right to mate with the females residing inside their territory.
The pregnant female digs a specially protected natal burrow where she has her young. The litter of 5-10 young are born in May and early June. They are blind and naked and weigh the equivalent of two quarters. Within two weeks, they have grown fur coats and at 20 days their eyes open. 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, An occasional male has been seen in early December though.