As the snow piles up and daylight is at a minimum for the year, many of the animals we regularly see have vanished. We imagine them sleeping peacefully in their burrows, dreaming of endless supplies of pine cones, green leaves, berries or whatever their favourite food is.
The true picture is a little more complicated though, hibernation is more of a continuum of responses to environmental factors, rather than a set 'on and off' switch.
While some animals are down and out for up to six months, others carry on as if the cold and snow weren't there. As well, within the same species, some individuals may hibernate while others don't, even in the same locale.
Gender, age, and physical condition of individuals play a role in influencing an animal's tendency to hibernate or not. True hibernators are animals that go into a deep, deep sleep. It would probably take them several hours to wake up even if they were interfered with and placed in a noisy environment. This is because their body core temperature has fallen to near freezing and their heart rate is at only a few beats per minute.
True hibernators consume less than 5 per cent of their normal metabolic rate. Animals like woodchucks, jumping mice, little brown bats, and some ground squirrels are true hibernators. Marmots, including our Whistler Marmot, are considered to be 'model' hibernators. They were the first (1896) animals to be studied for the physiological adaptations of hibernation.
Even though researchers have devoted years to studying hibernation, there are still many unanswered questions. For example, why do animals in true hibernation have different set points for the lowest temperature they will tolerate? The lowest on record is the arctic ground squirrel, whose body temperatures can fall below 0º C. Why animals have diverse hibernating temperatures and what controls the set point are some of the questions which have many variables at work.
Another interesting aspect of true hibernators is that they wake up every few days to void wastes and eat stored food. Again, the mechanism causing them to awake (no, it's not a full bladder, it's been tested) is complex and involves a combination of hormones and increasingly toxic body chemistry.
This brings us to those animals not considered to be true hibernators. Either they are active all winter because of particular adaptations or they go into partial hibernation of varying degrees of intensity depending on environmental factors. Beavers, skunks and racoons congregate in dens and either live off of stockpiles of food accumulated during the summer or periodically emerge in search of food. Mid-winter sightings of racoons are not uncommon and they will return to homes for handouts or to clean out Rover's food bowl.
Voles are unusual in that they are predominantly solitary in summer but congregate in dens in the winter to keep warm. They exploit the sub-nivean (nival = in or under the snow) space; the gap between the earth and the snow. Heat from the earth melts the snow directly in contact with its surface, resulting in a crawlspace small mammals like voles can wander around in. They can forage for plant food under the snow, somewhat safe from the predators that usually hunt them. Their tunnels are visible in spring when the snow melts, especially on ski runs where the summer grasses grow in abundance.
Bears have been studied extensively and are very peculiar in their hibernating adaptations. These peculiarities may affect space travel, organ transplants and warfare and will be the topic of an upcoming Naturespeak.
Monthly Bird Walk - Attention all local birders: the bird walk on Saturday, Jan. 3, 2004 has been cancelled. Sorry about the mix-up. The next bird walk will take place on Saturday, Feb. 7, 2004. Join Whistler experts in the monthly update of our feathered locals and migrants.
Written by: Dan McDonald