Escaping
from the cold
Hibernation allows a long winter's sleep
By Callan Bentley
Flat Hat Variety Editor
Two hundred years ago, a scientist at the Royal Society of London performed an interesting experiment. His name was Charles Blagden, and he asked two friends to help him one afternoon. Blagden took his two friends, a dog, and a raw steak into a room that was gradually heated to a sweltering 260 degrees Fahrenheit.
When the men and dog stumbled out after 45 minutes, they were exhausted, dehydrated, and dripping with sweat. The dog was panting hard. After a while, they recovered from the heat, and looked back in the room to find that the steak was completely cooked.
What prevented the flesh of the living mammals from cooking? The experiment showed that homeothermic animals, such as mammals, adjust to temperature changes with some sort of built-in system. Since Blagden's experiment in the 1700s, science has learned that a certain region of the brain called the hypothalamus acts as the body's thermostat. It is also the hypothalamus that controls hibernation.
Hibernation is an energy-saving way for animals to survive through the winter, when food is scarce. They enter a period of dormancy that can be seen as a deep sleep.
Physiological changes occur in hibernating animals. The body temperature drops, sometimes close to freezing. Its heart rate slows, breathing rate drops, and the animal lives off of its fat reserves.
Along with the normal white fat, hibernating mammals have a special supply of brown fat, which is concentrated across their shoulders and back, close to the animal's brain, heart, and lungs. If needed, the brown fat gives a quick energy burst to the animal so it can get going. For instance, if a hibernating squirrel wakes up to find itself in imminent danger, the brown fat will enable it to escape before the ordinary white fat would.
Not all animals hibernate, however. Groundhogs (a.k.a. woodchucks), along with ground squirrels and bats, are referred to as "deep sleepers." Armed with a three-quarter inch thick layer of fat, the groundhog curls up into a ball and falls into a deep sleep. Its body temperature drops from 100 degrees to 45 or 50. Its heart beats only four or five times per minute, as opposed to the usual 80.
The groundhog is so asleep that, according to Do Not Disturb: The Mysteries of Animal Hibernation and Sleep, you could "roll a dormant woodchuck like a bowling ball across a field, and it would not wake up." This is in contrast to a hibernating bear, who will wake up instantly (due to its brown fat reserves) if disturbed even slightly.
Every few weeks, though, the deep sleepers wake up to much on some stored food, drink some water, use the bathroom burrow, and go back to sleep. Through periodic replenishing, they are able to maintain their equilibrium until spring arrives.
Hummingbirds and pygmy mice represent another group, the "daily dormants," who have periods of 'mini-hibernation' each night, but regain their ordinary body temperature at the beginning of each new day. It takes several minutes to warm back up, but once they do, they're off and running. Our local squirrels are a good example of daily dormants: you will see them in the daytime sniffing out buried food reserves.
Even some birds, such as the poorwill, can hibernate. This was only verified in the 1940s, though the Hopi Indians have long spoken of a bird called "the Sleeping One." Most birds, though, including most of the ones in this region, adopt one of two strategies: they either simply go about their business or they fly south to warmer climes.
Not all organisms are homeothermic, though. Reptiles and amphibians also enter a state of dormancy in the winter, but as they are 'cold-blooded' (poikilothermic), their body temperature drops to that of their surroundings. Special molecules prevent their blood from freezing, so they can even stay underwater. Frogs and turtles manage this, for instance, by burrowing down into the mud. Snakes find crevices in rocks, and frequently nest in large numbers through the winter.
Insects are usually killed
off by the harsh winter, but leave behind protective egg cases that can weather
the snow and ice. Praying mantises, for instance, do this. Come spring, their
egg cases break open and release hundreds of baby mantises to the blooming world.
At the same time, the woodchuck crawls out of his hole, the bear wakes up, the
snakes slither out of their caves, the Canada Geese fly back into the 'Burg,
and the students return to William and Mary.