Hibernation, unlike traditionally thought, may not be a response to harsh environmental conditions alone, suggests new research published last week in the journal Functional Ecology.
Hibernation is usually regarded as an adaptation that enables mammals to reduce their energy expenditure so that they can survive in unfavourable conditions like low temperatures or during food shortages. For edible dormice (called so because their fat stores made them tasty enough to be considered a delicacy by ancient Romans), such conditions exist for about six months every year.
So scientists found the fact that they choose to hibernate for almost eight months baffling. To solve this mystery, a team from the University of Veterinary Medicine, Vienna, and the University of New England, New South Wales, collected 42 datasets of the energy use patterns of hibernating female edible dormice over four years.
They observed that irrespective of body mass prior to the onset of hibernation, the dormice hibernated for almost eight months every year. One would expect fat dormice to use their surplus energy to shorten their hibernation duration, but this was not happening.
They found out that while the hibernation duration of fat and leaner edible dormice were the same, the former had more bouts of arousal within their eight months than the latter.
It was already known that the period of dormancy of obligate hibernators like the edible dormouse was interspersed with short periods of arousal where their metabolism, body temperature and heart rates boosted before slowing down again. These periods of arousal do not mean the animal is “waking up,” it is uncertain why this was happening.
One theory is that low body temperature during hibernation affects immunity, so these periodic boosts of metabolism rate may counteract these negative effects.
One would expect animals to minimise the time they had to spend hibernating. The fact that even edible dormice fat enough to afford a shorter hibernation period were choosing to doze for the full eight months by increasing the number of arousals, suggests that it might not be just unfavourable environmental conditions that predict hibernation patterns after all.
A possible motive for hibernating longer is to minimise risk of above-ground predators. The study shows survival rates during hibernation periods have been extremely high in dormouse population — over 98 per cent, compared to 80-94 per cent during the active period. “Animals seem to benefit from the torpid state, in terms of predator avoidance, since they are motionless and emit minimal noise and body odour,” write the authors. So hibernation may be more than just an energy-saving mechanism. “It might have other positive effects, which previously were only rarely considered,” they write.