Friday 18 October 2019

Hibernation time for hedgehogs as winter looms

HEDGEHOGS ARE going into hibernation about now. There isn't a precise date on which they all go into their winter state together; timing is an individual matter and it depends on both the weather and the condition of individual animals.

Before entering the hibernation state, Hedgehogs need to lay down enough fat to carry them over the winter. A severe winter followed by a late spring is a life or death issue.

Furthermore, if winter weather sets in early Hedgehogs born in late litters may not have enough fat to survive the long months ahead and may be doomed before they start hibernating.

While there are many variables, nature will ensure that the strongest and the fittest survive and the weakest and the least fit will be weeded out. In the wild, the needs of the individual are of little importance; it is the survival of the species that is paramount.

A Hedgehog entering hibernation builds a ragged, ball-shaped nest made from grass and autumn leaves. A well-built nest may be vital to survival as is choice of nest site. Ideally the nest site should be sheltered and safe. A site deep in a thick hedge or under a garden shed brings obvious benefits.

Hibernation is not sleep. During sleep Hedgehogs maintain their normal heart rate and body temperature. During hibernation the heart rate drops about ten-fold and body temperature drops to that of the surroundings. Being the same temperature as the surroundings ensures that the animal prevents heat loss.

However, if the outside temperature drops below 4°C water in the Hedgehog's body is in danger of freezing and the animal suffering from frostbite. To prevent that happening, the hibernating Hedgehog burns some fat to generate enough heat to protect itself from severe conditions. A well-built nest and a well-chosen nest site obviously reduce the need to tap into fat reserves.

Hedgehogs do not remain in hibernation continuously. During mild spells they come back to life to urinate and to take stock of how things are going. They may carry out some adjustments to their nests or may decide to move house altogether. When the mild spell comes to an end they go back into their strange state of suspended animation and weather it out until the end of March.

Who knows if humans will someday copy Hedgehogs and use a hibernation-like state to aid space travel to distant parts of our solar system and beyond?

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