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Hibernation

1/21/2014

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Hibernation

During the winter months in the UK food such as green plants and insects is in very short supply and have very little energy value, so many animals solve this problem by hibernating or going into a torpor.

So what is the difference between torpor and hibernation? Torpor is a short term reduction of body temperature on colder days. Hibernation is an extended torpor and is a deep sleep where the animal's body temperature drops much lower and its breathing slows down and its heartbeat drops. This is so that the animal can survive winter by not using much energy. For example the heartbeat of an active hedgehog is between 200 and 280 beats per minute but only 5 beats per minute during hibernation. The body temperature of a hibernating hedgehog falls to 4ºC and if the outside temperature drops to zero, the metabolic rate increase so that the hedgehog doesn't freeze to death.

Animals that go into hibernation have to work hard to prepare for this time by eating extra food and building up their fat reserves. They do this by storing body fat which they can use as energy while they are sleeping. There are two types of fat – the regular white fat and brown fat. The brown fat forms patches near the vital organs – the brain, heart and lungs. It sends a burst of energy to warm these organs first when it is time to wake up again in Spring.

Insects will hibernate under logs, in houses or under the bark of a tree. Sometimes you may find a hibernating butterfly or moth in your cellar or outhouse so don't disturb it.

Fish and water insects tend to hibernate under leaves and even burying themselves in the mud at the bottom of ponds and lakes. If you have a pond in your garden float a ball or plastic bottle on the top of the water so if the top of the pond freezes you can remove it and allow air to reach the creatures living under the water. Toads and frogs hibernate under logs and large stones so even if you think you should tidy up the garden, leave them alone as there may be amphibians hibernating under them.

Most mammals do not hibernate but will become less active in cold weather. Small animals such as shrews have to eat every 2 to 3 hours to survive. Moles have winter nests and as they live underground they rely on food stored near their nest. Other small mammals such as wood mice and voles will be less active in the cold weather and will go into a torpor for short periods but will awake to eat .

Hedgehogs hibernate under leaves and logs so it is very important to leave that log pile in the corner of the garden and be careful to check bonfires before lighting them. Hedgehogs rarely stay in the same nest for the whole winter and tend to move if the temperature falls too low, or if the nest is exposed to heavy rain or they are disturbed by humans or other animals. They wake up for a few hours every 7 to 11 days.

The dormouse is well known for sleeping most of the year. In fact the name 'dormouse' is an Anglo Saxon name meaning 'sleepy one'. Dormice can hibernate for 6 months of the year and even more if the weather remains cool. They store body fat during the summer months ready for the long hibernation period in holes in trees often hazel. They will sometimes wake up for a short time to eat the food that has previously been stored nearby in their nest.

Bats are another species that hibernate. In October, bats are looking for suitable places to hibernate and begin periods of torpor. By November, these periods of torpor are lasting longer and by December the bats are hibernating in disused buildings, old trees and caves where they won't be disturbed. Even so British bats will wake up for a few hours every 20 days to leave their roost to find food and to drink water.



Most animals will start to come out of hibernation around March if the weather starts warming up.




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    Carol Carter, Ecologist

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