When Yukon placer miners remove frozen organic "muck" to get to the underlying gold-bearing gravel, they sometimes expose fossils of ice age animals. Few discoveries are more interesting than the nests of ancient Arctic ground squirrels. Radiocarbon dates and other geological dating methods suggest that some of the nests are more than 90 000 years old!

These ancient nests contain nesting grasses, seed caches, droppings and even skeletons of Arctic ground squirrels or other small rodents, such as lemmings or voles. Analysis of the nests has documented more than 60 different plant species, thereby providing valuable information on ice-age environments of the Yukon. Arctic ground squirrels evolved in, and were ideally adapted to, the cold, dry tundra-grasslands of the ice age.

Arctic ground squirrels are found today across the mainland Arctic tundra and in open habitats of the Subarctic boreal forest. The Inuit name for the Arctic ground squirrel is siksik. Siksiks live in large colonies, and, in order to survive in such a harsh climate, they hibernate for about seven months each year. Their colonies are generally restricted to raised, dry habitats where they are able to dig extensive tunnel systems and hibernation chambers.

After waking up from hibernation, male Arctic ground squirrels feast on the underground seed cache that they collected during autumn. This helps them build up body mass and get ready to mate with females in spring. Although Arctic ground squirrels are herbivores, they occasionally prey upon smaller rodents and other animals.

The Arctic ground squirrel is one of the largest species of ground squirrels. The length of its head and body ranges from 22 to 35 cm (9 to 14 in.). The tail ranges from 8 to 15 cm (3 to 6 in.). Arctic ground squirrels that live in the northern end of their range are generally larger than those further to the south.