Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [39]
The most common, conspicuous, and noisy of the local squirrels is the little red Tamiasciurus hudsonicus, also called pine squirrel in parts of its range. It is the “sentinel of the taiga” as William O. Pruitt Jr. calls it in a little book titled Animals of the North that I have long treasured. It leaves signs of its presence everywhere: cone bracts of pine and spruce freshly strewn over the surface of the snow, cone cores discarded on a log where tunnels enter the base of an old pine stump. Almost every fresh snowfall is quickly followed by a new sign, and the perpetrator of that sign will likely be perched on a branch next to a trunk above your head. The cheeky little chicoree (still another name for T. hudsonicus) will let loose with a loud sputtering chatter or a churrrrrr that resounds throughout the forest. This will usually be sequenced to a long series of harsh staccato chatter, accompanied by flicks of its fluffy tail over its head and thumping with its hind feet for emphasis. Red squirrels are emphatically active at any month of winter. They appear not to hibernate at all. However, during periods of extreme cold, the woods are silent, and they hole up for days at a time in their subterranean burrows under a stump or tree roots.
Once underground they are almost fully protected from the cold. At least some of their populations, particularly out West, make large caches of seed cones, and with that food they can presumably continue to be active. Yet, cone crops are not reliable every year, and in Maine there are many years, such as the winter of 2001–2002, when I’ve found no caches at all. At these times they feed on the buds of spruce and fir (see Chapter 3). Although there is no guarantee that they do not become inactive with lowered body temperature for a few days, if need be, their emphasis is on fighting the cold by storing food if they can, finding alternate food if they have to, seeking shelter, and growing a thick, rich-rust-colored, insulating fur coat in winter.
The red squirrels’ temporary retreats into tunnels and dens in the winter at subzero temperatures contrasts with the behavior of the other four local squirrel species. Of these, the larger-bodied gray squirrel (Sciurus carolinensis) and the much smaller northern flying squirrel (Glaucomys sabrinus) stay above ground the whole time. Two others, the eastern chipmunk (Tamias striatus) and its very much larger cousin the woodchuck or groundhog (Marmota monax) absent themselves from the cold snowy world above ground for weeks, months, and even to half the year. In general, most ground squirrels hibernate all or most of the winter, whereas tree squirrels, which can still find food on trees, don’t. The stark differences in overwintering biology within this one group of related animals shows that hibernation is less a strategy of avoiding the cold than of what they eat, of weathering famine.
Hibernating chipmunk.
The local squirrel showing the least tendency to hibernate is the now-often suburban gray squirrel. It is active through all months of winter. In the absence of the largess of sunflower seeds at bird feeders, these squirrels will dig through shallow snow to recover acorns, nuts, and maple seeds stored in the fall. If seed crops fail them, they then feed on tree buds and sometimes bark. Food storage, snug leafy well-insulated nests, and large body size give them enough energy resources and means to conserve body heat so that they do not need to hibernate.
Chipmunks are “true hibernators.” Like other ground squirrels, they spend most or all of the winter in a subterranean nest where they curl up, cool down, and become torpid. However, they are not torpid all winter long. If they were, then they would not need to lay up food stores to fuel body heating. Torpid animals don’t eat. The chipmunk’s large cheek pouches indicate an ancient evolutionary commitment to storing food. I do not know how many seeds a chipmunk usually packs into each of its two pouches—I easily inserted sixty black sunflower seeds through the mouth into