An omen of spring was sprawled on the railing of our deck this morning: a groundhog. His appearance was rather surprising after only two days of mild weather following six weeks of ice, snow and frigid temperatures. While he seemed to be enjoying his respite in the morning sun, this early riser may have to return to his winter slumber; the ground is still mostly covered with snow and there is little greenery to sustain him.
Groundhogs are one of our true hibernators; others include ground squirrels, marmots, many bats and some bears. These mammals "sleep" through the winter, sustained by layers of brown fat that they put on during the warmer months. They are also able to greatly reduce their metabolism, entering a coma-like state with a minimal pulse and respiratory rate. Should their energy stores run out before spring arrives, the animal will die. For the latter reason, arctic mammals cannot hibernate; the winter at their latitude is too severe and prolonged to permit survival. Even at temperate latitudes, some mammals, such as chipmunks, store food in their winter dens, awakening at intervals to restore their fat pads.
