Hibernation
Surviving Winter’s Big Sleep
Some animals survive the cold, winter months by falling to sleep so deeply it’s as if they were dead. This is called ‘ true hibernation’. Insects and cold-blooded animals such as frogs cope with the situation by shutting down their bodies less dramatically – this is called ‘ darmancy’. Either way by hibernating these creatures solve the twins problems of food scarcity and low temperatures.
Slowing down - Hibernations means winding down body processes until they are only just functioning. It is this dramatic slow down of the body that marks out true hibernation from just a deep sleep. As the mammal’s metabolic rate lowers, so its average body temperature plummets to a little above freezing, and the heart beats very slowly. A woodchuck or groundhog for instance , drops its body temperature by over 30 C (60 F). Some hibernators can slow their heart rate to justfive beats a minute, and occasionally a whole hour may pass without a single breath. This tactic does not always work, though. Hibernating animals can either freeze to death or simply stop breathing. Many hibernators have a special substance in their blood called HIT (hibernation Inducement Trigger). This is affected by the amount of daylight every 24 hours and by the surrounding temperature.
Ready for bed – If they are to survive the winter, animals must prepare well for their hibernation. First of all, they must build up the reservesof body fat they will draw on, by feasting heavily in autumn. Secondly they must find the right place to sleep-safe from the worst of the weather and from predators. Usually this means a deeper hole or cave. Many ground squirrels retreat to a special part of their burrow called a hibernaculum where they often have anearby store of food in case they should wake up. Most animals also ensure their home will be warm and snug by adding materials such as grasses and leaves.
Heavyand Light Sleepers - The depth of sleep varies from animal to animal. Ground squirrels, dormice, hedgehogs, various bats and Australia’s echidna are true hibernators whose body temperaturedrops to near freezing point and heart rate falls almost to zero. They do occasionally rouse themselves during winter, if only to defecate. But these brief periods awake are keptto a minimum to save energy. Bouts of sleep tend to be short in the early and late winter but become almost continuous in mid-winter. Other animals such as bears , raccoons and kunks sleep more lightly. Their body processes do not slow down as muchand they emerge often from their dens to feed. Global warming may lead to more frequent awakenings and shorter hibernations.
The Case of the Poorwill - In 1946 zoologists were amazed to find that a bird called the common poorwill, North America’s smallest nightjar, could be cold to the touch and appear neither to breathe nor have a heartbeat. This short-term state of dormancy seems not only to help the bird through cold periods when food is scarce, but also to help it survive times of summer drought. The poorwill is one of the very few birds known to ‘hibernate’ like this and its temperaturedrops to 6 C (43 F ) far lower than that known far any bird. Various tropical animals go through this summer sleep or ‘estivation’, but it is almost unheard of outside the tropics.
A Metabolic Marvel – During hibernation the North American black bear does not wake up to 130 days. Now biologists are studying its amazing metabolism to see if their findings can help with human organ preservation, kindly disorders and even long – distance space travel.
[tags]hibernation,metabolic, human, animal[/tags]
