Rise and shine

Research on hibernating squirrels may explain why they wake for short periods

source: Stephen Leahy,
New Scientist May 4 2002 p16

Research on ground squirrels has helped to explain a mystery relating to hibernation, why chipmunks, marmots, ground squirrels, and other true hibernators wake up regularly. This is difficult to understand since waking up costs the hibernators a lot of stored energy. They apparently need to wake up as a way of boosting their immune systems, and checking themselves for pathogens and parasites.

Hibernation is a way of conserving energy at a time when there is little food about. Badgers and bears have short drops in temperature, while true hibernators can have temperatures at five deg C for several consecutive weeks. The golden-mantled ground squirrel from California hibernates for some five to six months, and its heart beat slows, beating only twice a minute. This squirrels wakes up around once a week, and undergoes a temperature rise to 37 deg C during 12 to 16 hours. These periods of wakefulness can account for some 80% of the squirrels’ energy budget for a winter.

Ohio State University’s Brian Prendergast and his team studied 31 squirrels, some of which were injected with a lipopolysaccaride, the constituent of dead bacterial outer cells. The squirrels did not react with a temperature rise until they awoke, indicating that their immune systems were not operational while they hibernated. The temperature rise only occurred once the animals awoke, and then their bodies responded as if they had only just received the injection.