Hibernation in Northern Climates

Another candidate for the title of the world's marathon sleeper is the Barrow ground squirrel, living around Point Barrow, on the northern coast of Alaska. There the snow persists for most of the year and the ground is permanently frozen to a depth of many hundred feet. During the short summer the earth may thaw to a depth of a few inches, at most, a few feet. The best thaw is in areas of good drainage, where the soil is sandy and raised in hillocks. On these "islands" where the risk of spring flooding is low, the ground squirrels have their burrows. There is nothing unusual in the appearance of the Barrow ground squirrel, but there is in its habits. It sleeps for nine months in the year, and must pack everything else into the remaining three. In early May the ground squirrels leave their burrows to look out on a world still snow-covered, and in which the dead, dry vegetation of last year is hidden under the mantle of white. At first they do not go far from the burrows, perhaps 4 ft. at most, and they feed on the stores accumulated in the burrow last year. As the air warms up and the snow recedes the vegetation springs into life, and for the ground squirrels the season has begun in earnest. There is a good deal of fighting, of running from burrow to burrow, and this continues until the time comes again for hibernation. But over and above this general activity, mating takes place towards the end of May and the young ones are born some twenty-five days later, in litters of five to ten.

The young are born naked and blind. Hair starts to grow on the second day, and by the tenth day the body is entirely covered with short hair. The eyes open at twenty days. In July, about twenty-two days after birth, and two days after the eyes have opened, the young leave the burrow and start foraging. At first they stay close to the burrow, but gradually go farther afield, and within the fortnight may have gone as much as two miles away to occupy a deserted burrow or excavate a new one. With her family gone, the female starts to feed herself to repair the loss from feeding her young. The males, which are polygamous and move about a good deal in search of mates, also start to feed heavily, and by the end of August or beginning of September the adult squirrels have laid in the necessary fat for hibernation, have repaired and cleaned-up the burrows, have accumulated nesting materials and a food-store, and are ready once more to hibernate.

The behaviour of the squirrels throughout is as if they were aware of the urgent need to use every available minute. Bad weather does not deter them, neither rain, nor bitter wind. They will return from feeding on the scanty vegetation with the cheek-pouches stuffed with food and a bunch of grass for the nest held in the teeth. They will feed on leaves, stems, flowers, roots, seeds, carrion and offal of any kind, including carcases of other squirrels. Yet for all the urgency they do not work all hours of daylight. The sun is above the horizon for twenty-four hours from the second week in May to the first week in August, yet the working day of the ground squirrel is only seventeen hours or so at the peak period. Burrowing does not absorb much time apparently. Although not obviously equipped for this work, a squirrel has been seen to make a tunnel 37 feet long inside twenty-four hours, and the longest burrow found was only 68 feet. The maximum depth of a burrow is 8 feet.

If the activity and achievement of the adults is remarkable, that of the young is even more so. Born in early June, they achieve adult weight in about forty-two days, and, having also made provision for the long sleep, they enter hibernation a month after the adults, in late September or early October. Barrow ground squirrels have practically no enemies, yet their populations remain more or less static, in spite of the litter-size of five to ten. There are several probable causes. First the female will eat any young she cannot adequately suckle. Then there must be heavy casualties among the young after weaning. Some are doubtless forced to move farther afield to find living-space. This will take them to grounds with even more scanty vegetation and less chance of survival. Even if not forced on to inhospitable ground, they may fail to find enough food, fail to store enough, fail to burrow sufficiently deep. They may be frozen in the burrow, if the weather turns unusually cold in the period of hibernation. And it seems that cannibalism cannot be ruled out, the first to awake eating the others as they sleep. This, at least, has happened in experimental hibernacula provided by man. Cramming a year of life into three months may be strange but it is true.