Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [37]
We found no food stores and no sign of a nest. Negative data is not considered good evidence, and is generally not reported. However, we had dug all this up so thoroughly that the negative data sure felt like a positive result: No nest. Given the lack of tracks around the stump in the morning, the two squirrels had spent the night in the tunnels under this stump whose spongy humus felt warm to the touch (mostly because it was dry, but measured -0.02°C). The several dry maple leaves that we found in our excavation may have been carried down by the rodents in a weak motivation to build a nest, but in their heavy winter coats they would probably not have needed one.
Flying squirrels may also not bother to build much of a nest when they can snuggle up next to other warm bodies. On November 19, 2000, I was banging yet another tree, this one a dead red maple in the woods near my home, in my continuing quest for birds overnighting in tree holes. I happened to look up in time to see a flying squirrel scamper to the top of the twenty-foot stump and stop there, as if frozen in place. Its flat tail was flush against the bark, and it didn’t move a muscle. I saw then a second squirrel peeking out of the tree hole above me. I looked again, and saw two more scampering up the tree, one behind the other. As my companion and I walked around the tree, the top squirrel jumped off, gliding about fifty feet to the bottom of a live red maple. Seconds later, another squirrel “flew” off in another direction. We left quickly, because we did not want to disturb them further. It had snowed a couple of days earlier, and there were deep nightly frosts. It stayed below freezing all day. Would any of the four return to their shelter?
Flying squirrel in the hole made by a hairy woodpecker in a dead sugar maple.
The next day around 3:00 P.M., after it had snowed hard, I went back to the tree, hoping to see them leave their communal den. I hunkered under the low spreading branches of a red spruce, and there I waited until 4:45 P.M. (forty minutes past sunset), when it was too dark for me to see any more. According to DeCoursey’s experiments, the squirrels should have known it was time to get up, even in the constant darkness of their den, yet I saw no squirrels exit the hole.
Four days later I went to the stump again. This time I lightly jiggled it as I had done before. Nothing came out of the hole. Then I banged the tree hard with an ax. One came out. No more. I banged it again, harder. Three more came out. So—they do come back to the same place. However, a month later, on December 17, when I checked again, no amount of banging raised a squirrel. I climbed up and examined the hole. Surprise! There was no nest at all, and the hole was only three or four inches deep. It contained dry rotted wood and several tiny wisps of dried green moss that must have been carried in. The four squirrels would have nearly filled the whole cavity, and either there was no need for nest insulation or there was no room for it.
From tracks, I knew that these or other flying squirrels were still nearby. My cabin at the edge of a one-acre clearing was within about three hundred feet of where I had seen the four. One seldom sees the tracks of a flying squirrel in the woods, when they land on tree trunks rather than on the snow. But on March 16 that winter I saw where a flying squirrel didn’t quite make it across my acre-sized clearing the night before. The squirrel had hopped out into the field from the south, climbed the maple in the middle, and then twenty snowshoe lengths (sixty-five feet) farther it hit the field again, almost at the edge on the other side. Another, similar flying squirrel track commenced across the clearing from