On February 2, the country’s most famous groundhog, Punxsutawney Phil, was once again pulled out of hibernation to ask whether we can expect six more weeks of winter. His verdict: an early spring, though according to some reports, his predictions are not very reliable.
One thing that is for sure, however, is that winter is particularly tough for smaller mammals. Because small mammals have proportionally large body surfaces for their overall body size, they lose body heat quickly in a cold environment. They have to burn extra fuel to maintain a body temperature of around 98 degrees Fahrenheit when temperatures drop below freezing. Fewer available high-quality food sources make it more difficult for animals to find the fuel needed to produce more heat. Rather than struggle to stay warm and find food throughout the winter months, many species conserve energy by hibernating.
Hibernation patterns vary among species. Ground squirrels, chipmunks, marmots and woodchucks have a strong yearly rhythm that separates hibernation season from their reproductive, growth and fattening phases. In late summer and fall, these animals prepare for hibernation by accumulating fat and doubling their body weight. They will not eat or drink again until the weather turns warmer and hibernation ends, relying on stored fat to survive.
Throughout late fall and winter, these hibernators save energy in the cold weather by entering a state called torpor. Torpor saves energy by slowing metabolism, heart rate and breathing. This allows the animals’ body temperature to drop to near freezing, slowing all life processes. Periods of torpor can last a few days to a few weeks. Animals that go into torpor can turn metabolism back on and rewarm to normal body temperature for a few hours when they need to, although scientists are not exactly sure why this happens. Torpor and rewarming can occur several times each hibernation season.
By spring, animals have lost their excess fat and their reproductive hormones begin to surge. These two events prevent them from hibernating longer. Their reproductive and growth phases complete by fall, and the cycle begins anew.
This ability to safely turn metabolism off and on has potentially huge implications for human medicine and space travel. If people could lower their metabolism and use less oxygen after a heart attack or stroke, blood flow could be restored without harming the body’s tissues. Torpor could also help astronauts withstand long-duration space flight and protect them against harmful radiation.
So, though Punxsutawney Phil might never make it as a weather forecaster, he and other small mammals could hold the key to how energy-saving torpor and hibernation can help humans survive and thrive in harsh environments, too.
Sandy Martin, PhD, is a professor in the department of Cell and Developmental Biology at the University of Colorado School of Medicine.