Winter World_ The Ingenuity of Animal Survival - Bernd Heinrich [81]
The potential implications of the knowledge of freezing-tolerance do not seem to be lost on the agencies that fund research. One researcher with whom I talked had at one time worked on frost-tolerance in insects. He told me that after switching to work on vertebrate animals, “they practically threw the money at me.” I would probably have taken such money as well, if offered. But I confess to unease. The promise to make us immortal and the specter of frozen bodies in vats horrifies me. The unintended implications alone are all too obvious to need reiteration here. It is pure research, that which has no practical implication whatsoever, that enlivens the human spirit the most.
15
MICE IN WINTER
Even before I finished building my cabin in Maine, I could see that it had potential. Bubo, my tame great horned owl, chose to perch on the rafters rather than out in the woods, where he or she was harassed by the blue jays. Similarly in June the hordes of bloodsucking blackflies and horseflies left off their hot pursuit as soon as I crossed the doorstep. The cabin was a sanctuary for me in the summer. When winter came to the Maine woods, however, it suddenly became appealing to the wild local fauna, and many adopted my haven as their own.
Masked shrews and red-backed voles, my occasional winter visitors from the subnivian zone, were only transient visitors. In contrast, white-footed mice took up permanent winter residence. For some reason they find the cabin congenial. But before I tell you more about them, I need to describe and identify them. According to Mason A. Walton, the so-called Hermit of Gloucester, who in 1903 wrote about them in his book, A Hermit’s Wild Friends or Eighteen Years in the Woods: “The white-footed mouse, unlike the house mouse, is a handsome fellow. He sports a chestnut coat, a white vest, reddish brown trousers, and white stockings. His eyes and ears are uncommonly large, causing his head to resemble a deer’s in miniature. This resemblance has bestowed upon him the name of ‘deer-mouse.’” (p. 118)
Deer mice juveniles have lead-gray pelage and white bellies. Unlike meadow voles or field mice, they also have long legs that allow them to bound like deer. There are, however, two species of closely related deer mice, and only one of them is the official deer mouse, Peromyscus maniculatus. The other is the white-footed mouse, Peromyscus leucopus.
Differences between the two species are subtle. One field guide I consulted indicated that in white-footed mice the tail is longer than the body, while in the deer mice it is shorter. But those that I measured at my cabin had tail lengths about equal to their body length. Only experts can distinguish the two, and the defining characteristic used for differentiating them is a molecular variation in their salivary amylase, an enzyme in their saliva that helps digest starch. Bill Kilpatrick, the mammologist I consulted, told me that mine were indeed deer mice, Peromyscus maniculatus. This information makes a difference to me, because here in the East, only Peromyscus leucopus is known to carry the Hanta virus, which is lethal to humans. (However, I’m not convinced that a virus capable of jumping from P. leucopus to H. sapiens would be incapable of transmission to P. maniculatus.)
Even with Hanta virus out of the picture, deer mice can be objectionable in a cabin, and in the winter they enter in droves. I can’t blame them, though. The fault is mine. I should have used dry, nonshrinkable ceiling boards to foil these partly arboreal mice. Nor should I have used Styrofoam panels for ceiling