09/10/2025
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Information Post from Hedgepigs and Hoglets Rescue : Hibernation
Temperatures are warmer than normal for October, but I have had a couple of information calls about hibernation 🦔🥱 ❄
What is hibernation? and what makes hedgehogs go into hibernation?
Hibernation is described by the Open University as a sustained and profound state of torpor, triggered by internal signals combined with external seasonal cues. Torpor is a state of hypothermia combined with whole body inactivity. During hibernation, the hedgehog lowers it's own body temperature to save using up precious body reserves. The hedgehog is very clever because it is warm blooded (endothermic) when active but can also behave like a reptile too (poikilothermic) by cooling down.
There is a charming hypothesis that because hibernation involves a near shutdown of the animal's body functions it naturally follows that the body wears itself out more slowly and so enjoys a longer lifespan. If people weren't responsible for the insurmountable risks to Hedgehogs they might live to be at least 7 years old.
Hibernation is a strategy that hedgehogs use to survive the winter when food is scarce and the only way to save their energy requirements is to go into a state of torpor. A single arousal incident lasting a few hours uses about the same amount of stored energy as several days in hibernation, so it is important that hedgehogs are not disturbed during winter.
What makes hedgehogs go into hibernation?
It is temperature versus food supply that triggers hibernation. The best temperature for hibernation is +4°c because their metabolic consumption of fat will be at a minimum. In freezing weather, hedgehogs increase their metabolic rate without rousing to raise their temperature above freezing, but this uses up their fat reserves.
In hibernation mode, a hedgehog's body temperature falls drastically to just above freezing and their breathing and heartbeats almost stop, falling to 4 or 5 beats per minute. In fact, in deep hibernation, they can actually stop breathing for an hour or two, this is then followed by 40-50 rapid shallow breaths which slow before they sink into another state of torpor, much like a Dormouse.
Their temperature plummets from a normal 35°c to just a few degrees above freezing. It is their metabolic heat production that prevents their tissues from freezing. If the hibernating animal is warmed too much, its chemical reactions will burn up too much fat and this is why it is important for over wintering hibernators to remain cool and not be kept 'nice and warm'.
The winter nest is called a hibernicula and is a compact structure of dead leaves and moss. In its chosen site the hedgehog burrows into the heap and circles around inside creating a centrifugal agitation until the leaves end up like pages of a book. Some well built nests are returned to in the following autumn and simply repaired (Pat Morris (1969). Hibernucula are often also re-used by bumble bees, field and bank voles and wood mice.
Hedgehogs lay down white fat for general tissue maintenance but also lay down brown fat known as BAT fat (brown adipose tissue). BAT tissue is excellent at storing energy in it's cells.
So what do the wildlife rescue experts say about over wintering hedgehogs in rescues? Well The Secret World of Wildlife have this to say;
"Hedgehog rescues shouldn't have large numbers with them in winter, if the hedgehog is a good weight AND shape, healthy and thriving then release it". They use a release weight of 550 grams for 5°c temperatures or 600 grams in 0°c (5 days before and after). They have watched many hedgehogs overnight in their cages via camera and say how heartbreaking it is to watch them scratching to get out. Providing these is no hard and thick frost - get them out there"
I should mention that we as a rescue adopt a policy of winter release based on a MINIMUM weight of 625g as a general guide with temperatures of 5°c for 5 days pre and post release into a hibernation box with support feeding.
If the animal is a hedgehog ring the BHPS number 01584 890801, they will give you your nearest rescues number and should know if they are open too, or for all wildlife go online on www.helpwildlife.co.uk for all rescues.
For more information visit our website
www.hedgepigsandhoglets.org
Please do not take in and attempt to over winter a hedgehog that you find, if you are worried about it because it is out during the day pick it up immediately (please don't delay, time is crucial to his survival) and put it in a box with a hot water bottle wrapped in a fleece then ring your nearest hedgehog rescue. If you are in west Cornwall our tel no is 07506722850.
(BHPS have the national register on 01584 890801).
Your rescue are experts, they should be trained and experienced. They should have vet support, meds, evidence based protocols, proper housing and a whole array of resources at their disposal and will test for internal parasites.
Rescues lose many hedgehogs through well meaning people thinking they can just "take the hedgehog in and fatten it up". There are always invisible reasons why the hedgehog is poorly, only to be identified via the microscope and treated via expensive meds.
For more information visit; www.hedgepigsandhoglets.org
