The area of cottage country, and for that matter, all of North America, has experienced some unusual changes in weather this past winter.
A den buried deep in snow at Aspen Valley is where bear cubs sleep the winter away, waiting for their internal alarm to wake them when spring has arrived.
Some days the temperature has been considerably below 0 degrees Celsius, while other days are much warmer, even into double digits in southern Ontario, encouraging certain species to come out of their winter homes. Even a garter snake was recently observed crossing a sidewalk in Cambridge, Ontario on one of these warmer days.
As a result, staff has received inquiries about whether or not bears have come out of hibernation.
Black bears are not true hibernators. They do not greatly lower their body temperature or lower their heart rate. They begin their preparations for winter in summer when they begin to gorge on berries and other food to gain a considerable amount of weight. In early autumn a bear (and any cubs with her) will gather up leaves, twigs, plant materials into a den to create a nest. An unidentified signal tells them in late fall that it is time to bed down for the winter.
They do not need to eat, drink, urinate, defecate or exercise during this period of time, but depend upon their body’s fat tissues to break down and supply water and calories and their muscle and organ tissues to provide protein. A pregnant black bear will wake up in January just long enough to give birth, then goes back to slumbering, awakening up occasionally to lick the cubs and tend to them. The cubs do not hibernate. but suckle their mother when hungry and stay warm cuddled up against her warm belly. And so, a slumbering bear has no need to awaken during the warmer days of winter, as it has all it needs within itself until some unknown cue awakens the bears in late April to come out and resume their lives when their food supply will again be plentiful.
An interesting result of research on hibernating bears is the possibility of benefits to humans. Studies are indicating a break-through in many areas, from organ preservation to kidney disorders, to long-distance space travel.
True hibernators such as squirrels, bats or groundhogs, can reduce their body temperature to almost the same as that of the outdoors, so that they can avoid having to find food. But if there is a warm period during the traditionally cold days of winter, they will come out searching for food. This can lead us to believe that animals enter hibernation to avoid the cold weather. These hibernators can suppress their metabolism so that they can avoid having to find food on bitterly cold days, but it is not the inability to deal with cold weather that drives these animals to stay in their nests, but rather an adaptation for the lack of food available in winter (Gavan Watson, U. of Guelph).
Bernd Heinrich has written an interesting book entitled Winter World: The Ingenuity of Animal Survival, which explains in depth the various strategies used by animals to prepare for winter. For instance, chipmunks’ “availability of stored food affects whether it remains active or enters hibernation, meaning that in years with lots of available food, they can be active the entire winter and don’t need to suppress their metabolism”.
Researchers from the University of Toronto have discovered that groundhogs appear to enter and leave hibernation based on their internal clock, some time in February independent of external conditions.
And when the air temperature remained above 30 degrees C, they did not enter hibernation at all.
Given the ongoing changes in our climate, we still won’t see black bears in winter, but we can expect to see some of the smaller Ontario mammals – the true hibernators – out and about on warmer days.
(These weekly articles are contributed by staff at the Aspen Valley Wildlife Sanctuary. The sanctuary rehabilitates orphaned and injured wildlife with a mandate to educate the public towards a better understanding of local fauna.)