Versions of this article have appeared in:
The Montreal Gazette
Image courtesy of Carolyn Hall
The mother of all hangovers
by Ian Popple
So you thought you were hung over after New Year's celebrations? As many of us recover from the effects of excessive holiday cheer, spare a thought for the poor chipmunk. For the past three months, chipmunks have been hiding about one meter beneath our very feet in a deep form of hibernation called torpor. These animals may appear to have discovered the easy route to spring - who hasn't thought of climbing into bed and sleeping away the winter? Recent research by a team of scientists from McGill University and the University of Sherbrooke however, suggests that torpor is more of a nightmare than a pleasant dream. The hangover that follows a six-month torpor is far worse than any overindulgence in Christmas egg-nog.
Simply put, torpor is a coma-like state that involves a severe reduction in both body temperature and metabolism. Hibernation, on the other hand, is a more general term for a lull in activity that many animals express during the cold winter months. Technically, humans that spend more time indoors, reading the newspaper or watching television on cold winter days can be considered hibernators!
"Torpor is commonplace in many animals, including bears, bats and squirrels", explained Dr. Murray Humphries, a biologist at McGill University and principal author of the study investigating chipmunk torpor. Chipmunks spend as much as half their lifetime in torpor, but the relative benefits and dangers involved remain unclear and much debated among scientists.
"Previous research has suggested that a deeper torpor is a better torpor for hibernating animals such as the chipmunk", said Humphries. It is not difficult to see why; energy (in the form of food) is very hard to come by during the winter. There is little point in getting out of bed in the morning when the amount of energy expended in searching for food becomes greater than the amount of energy gained by that food. In order to survive winter, chipmunks store food rather than gain weight. During the late summer and early fall, when food is plentiful, chipmunks attempt to hoard their energy requirements for entire winter. They fill their underground burrow with so much food that they literally sleep on a mountain of acorns. But even with frantic gathering during this period, chipmunks are still unable to accumulate sufficient food to last the six-month winter. By reducing metabolism, torpor reduces the energy demands of chipmunks by more than 75%. In this state, the food stores that a chipmunk has accumulated in its burrow can last much longer. Additionally, by saving energy over the winter when it is not needed, chipmunks emerge in spring with energy to spare for the much-anticipated mating event.
It is hardly surprising that scientists have been under the impression that deep torpor is a chipmunks' best strategy for winter survival. Humphries' research however, shows that in reality, chipmunks are placing one paw in the grave during torpor.
"Torpor is a necessary response to food scarcity during the cold winter months", explained Humphries. "But there are serious risks involved". During torpor, sensory and motor capabilities are severely reduced. Chipmunks fall into a near brain-dead state where their body temperature drops to within a few degrees of freezing. Heart rate plummets from a 400 beat per minute drum roll, to a 23 beat per minute crawl. Many basic body functions cannot be supported and are shut down, resulting in a dangerous build up of toxins. Brain activity is arrested to such a degree that chipmunks lose their ability to sleep. Torpor is definitely a strange process to get your head around. "It is hard to conceive of a sleep so deep that it no longer involves sleep", mused Humphries. Sleep deprivation may be one of the reasons that chipmunks rouse periodically from bouts of torpor - they literally have to wake to sleep! Needless to say when chipmunks arouse from torpor they carry a hangover of epic proportions. Temporary brain damage, resulting in disorientation and memory loss is commonplace and may take days to recover from. In order to survive a Canadian winter you need to be tough - as tough as a chipmunk!
The stress that torpor can cause on both the body and mind suggests that
given the choice, chipmunks might prefer to reduce, rather than increase
their use of torpor. When the researchers provided chipmunks with an unlimited
supply of food, this is exactly what they found. Humphries captured wild
chipmunks and attached radio tags capable of transmitting geographic location
and body temperature to a handheld receiver. This information allowed
the researchers to determine that chipmunk torpor was of much shorter
duration and shallower depth when food was ubiquitous. An unlimited supply
of food is a situation that is very unlikely to happen in reality however;
so despite the obvious dangers of torpor, it is often the only option
for winter survival. Torpor is definitely no picnic for a chipmunk, but
then life is not so bad when you consider the alternative.