Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [36]
In Jack London’s story “To Build a Fire,” the newcomer to the North was ultimately killed because he got his feet wet. He broke through thin ice under a thick insulating layer of snow on Henderson Creek. His fire that was snuffed by the avalanche of snow under a spruce only made it impossible for him to correct his initial bad luck, or mistake. Ironically, in an insulated sock, mitten, or a squirrel’s nest, a tiny bit of moisture is far more dangerous than deep cold; because wetness destroys insulation. Thus rain, at near 0°C, can be lethal, while snow at -30°C can ensure comfort because it won’t wet and destroy insulation. Without dryness, all lifesaving insulation is for naught, and nest construction or placement must provide for it. Nowhere was this more evident to me than when examining a gray squirrel’s nest in winter.
Gray squirrels’ nests, or dreys as they are often called, appear as haphazard brush-piles of leaves and twigs when we see them piled up high up in trees. All fall and winter I saw one in the branches of an oak tree along our driveway. In mid-January after a heavy rainstorm, the nest blew down, and when I examined it I found it to be anything but haphazard in construction. It was a functionally crafted thing. The outside layer of the 30-centimeter diameter globular nest was of red oak twigs with leaves still attached. The twigs had therefore been chewed off the tree during the summer. Inside this rough exterior I found layer upon layer (twenty-six in one spot where I counted) of single flattened dried green oak leaves. The multiple sheets of leaves served as watertight interlocking shingles, because the nest was dry inside. The leaf layers sheltered a 4-centimeter-thick layer of finely shredded inner bark from dead poplar and ash trees. This soft upholstering enclosed a round, cozy 9-centimeter-wide central cavity. I could not imagine a more efficient functional design from simple common materials. However, not all gray squirrels’ nests are as natty as this. Many that I have inspected were mere piles of junk, as though they might have been fake nests to distract predators so that the real nest could escape being raided.
Gray squirrel nests incorporate leaves, unlike hawks’ nests.
Nests require effort to build, and not all squirrels bother to build one, as I found out with a little help from four of my friends. In the winter of 2000 we saw fresh signs of red squirrels almost everywhere we looked in the spruce forests of Maine where these squirrels live. Yet, we found few red squirrel nests. I wondered if (as is reported in the literature) their winter nests are underground, since I found many red squirrel tracks leading into underground tunnels. I saw numerous tunnels leading under roots of a big rotten pine stump and thought that if a red squirrel nest is anywhere, it should be here. Would this nest be less insulated than that of a flying or a gray squirrel?
Inasmuch as biology is a sterile undertaking until one gets hands-on experience, five of us armed ourselves with spades, pickaxes, plain axes, saws, and a digital thermometer, and then after a good breakfast approached the stump that was in the spruce thicket opposite my swimming hole in Alder Stream. The three entrances going into the ground under the stump had been used within the last day. Bracts of red spruce cones lay in piles on the top of the stump and had been recently chewed. All signs were promising.
It was 8 A.M. and a brisk -14°C on the morning of December 21, 2000, when we started excavating. After only five minutes of work, following tunnels in the spongy duff and soft rotten wood, we were apparently getting somewhere because a red squirrel shot out from one of the three exit holes. We dug deeper and also farther around the periphery of the stump, pulling off huge chunks of frozen humus that, like a carapace, covered the almost dry duff and soil underneath.