When do hedgehogs hibernate? In the UK hedgehogs typically go into Hibernation in October or November. They come out in late March or April. Timings vary depending on the weather and the supply of suitable food. Hibernation is a hazardous time for a hedgehog. Hogs that are underweight going into Hibernation may not survive the winter.

Hedgehogs are one of only 3 UK mammals that hibernate. The other two being bats and dormice. Hibernation is a fascinating behaviour and an ingenious response to the inherent challenges of winter.

But it can also pose challenges and dangers for our much-loved hedgehogs. So it's vital that we understand hedgehog hibernation and what we can do to help hedgehogs before, during and after.

In this article, we are going to answer some of your questions about hedgehog hibernation.

• When do Hedgehogs Hibernate?
• Why do Hedgehogs Hibernate?
• Where do Hedgehogs Hibernate?
• What Happens to the Body During Hibernation?
• Is Hibernation Dangerous for Hedgehogs?
• How to Help a Hibernating Hedgehog?
• 5 Things to avoid during Hibernation.

When do Hedgehogs Hibernate?

Exactly when Hibernation happens varies a lot depending on the weather and the food supply.

In England Hibernation generally lasts from October or November to March or April. In Scandinavia, Hibernation is much longer, and in New Zealand's North Island, which has very mild winters, Hibernation barely happens at all.

Warm autumns or mild winters will delay Hibernation. Just as the early onset of spring may bring hedgehogs back out earlier.

Males hibernate earlier than females. Females, especially those who have had a late litter, need time to build up their fat reserves which have been depleted by breeding and raising young. Males, who do not contribute to the breeding process other than the act of mating, have all summer to get fat. They are often ready to go into Hibernation by mid-September.

Why do Hedgehogs Hibernate?

Hibernation is an energy-conserving mechanism evolved to get hedgehogs and other animals through the winter.

All animals need energy to live. We get that energy by eating. In the case of hedgehogs by eating beetles, caterpillars, earthworms and the like.

But foraging for food also uses energy. As winter draws near the things that hedgehogs eat become scarcer and more difficult to find. It gets to the point where the hog is using more energy trying to find food than it is getting from eating the food.

An active mammal must also keep its body temperature at a certain level to survive. As the air temperature drops lower, heating the body, uses up more and more energy. So the "energy in v's energy out" balance sheet looks even worse as the weather gets colder.

At around the same time the year, many of our garden birds fly south for better supplies of food. Hedgehogs can't do that, so they shut up shop and hibernate instead.

Scientists still don't fully understand what triggers Hibernation and "waking". But it seems to be some combination of temperature, daylight hours and food supply.

Where do Hedgehogs Hibernate?

Hedgehogs like to hibernate somewhere quiet and out of the way. Thick undergrowth, a log pile, underneath a shed or even down an old rabbit hole are favourite places.

They are solitary creatures and will hibernate alone in the wild. Strangely, hedgehogs kept in captivity will often choose to share a nest.

Once they have chosen their spot, they will start to build a nest.

The hedgehog will bring back nesting materials a little at a time and wedge them into its chosen corner.

They may use grass and bracken, but leaves are a favoured material. Leaves are easy to form into the correct shape and offer excellent insulation and weatherproofing.

Once the hedgehog has enough nesting material gathered together, it will get into the middle of the pile and start to shuffle around in circles. This shuffling has the effect of pressing the leaves together to form walls.

The finished nest will be circular, anything from 18 inches to 3 feet across. The walls will be at least 4 inches thick, and it will have a short, narrow entrance tunnel at one end.

Nest building takes practice, and it's easy to recognise the nest of a young hog from its flimsy construction.

Even though a lot of effort goes into nest building hogs don't stay in the same nest or hibernaculum (great word!) all winter. Most hogs will use at least two nests during the winter.

Hedgehogs won't move into a nest that's been vacated by another hog. They will always build their own new nest.

The empty nests don't go to waste though; they are poplar homes for other small animals like mice, who might be looking for shelter.

What Happens to the Body During Hibernation?

Are you ready for the science bit? It's fascinating!

Before Hibernation, a hedgehog must stock up on its fat reserves. The hedgehog stores two distinct types of fat for Hibernation. White fat, like the fat on bacon, is stored all over the body. It is used to keep the hedgehog alive during Hibernation. There are also pockets of brown fat in specific locations on the body, like behind the shoulders. These are held in reserve and used when the hedgehog needs to wake from Hibernation.

During Hibernation, most of the hedgehog's bodily functions slow down to almost stopping point.

The heart rate slows to less than 10 beats per minute.

Body temperature drops from 35 degrees centigrade to less than 10.

Breathing slows to the point that a hibernating hedgehog may only take a few breaths once an hour.

Brain activity pretty much shuts down, apart from one small area of the hypothalamus which stays alert to monitor vital signs and potential threats. (New Scientist)

In fact, all bodily functions shut down to the extent that a hibernating hedgehog has a tiny percentage of the daily energy requirements of an active one.

So fat reserves which would keep an active hedgehog going for just 16 hours can sustain a hibernating hog for 170 days. (Wildlifeonline)

Is Hibernation the Same as Sleep?

No, Hibernation is definitely not the same as sleep. Hibernation and sleep are two very different biological processes.

Sleep is a physiological necessity for most animals. It's a period where a lot goes on in terms of repair and regeneration of cells.

During Hibernation or torpor, by contrast, not much goes on at all. The body is shutting down processes to conserve energy and not engaged in any repair or regeneration work at all.

In fact, Hibernation is so different from sleep that one study of lemurs suggests that one of the reasons that Hibernation is interrupted, might be so that they can get a bit of sleep!

Is it Harmful to a Hedgehog to miss out on Hibernation?

With enough food and if the weather isn't too cold, then there is no reason for it to hibernate.

If you have rescued a young, underweight hog in the autumn and keep it indoors in the warm and well-fed, it will remain active throughout the winter with no ill effects.

Hedgehogs in the wild, in warmer countries, with year-round food supplies will also often skip Hibernation altogether.

Is Hibernation Continuous?

No, Hibernation is not continuous. Hedgehogs will usually wake several times during the winter. Periods of activity during the winter are a perfectly natural occurrence.

Some individuals become active for a short period every few days; others may not rouse for months.

They may remain in their nests during these active periods, or they may venture out for a walk and a drink, or to build a new nest.

So, seeing a hedgehog out at night during the winter is no cause for concern.

However, if you see one out during the day in the winter, it is probably in trouble, and you should take it in and contact your nearest hedgehog rescue. You can find your local hedgehog rescue project by clicking here.

Can Hedgehogs Get Too Cold During Hibernation?

Hedgehogs can survive in Hibernation with body temperatures as low as 1-degree centigrade, or just above freezing point.

Their nests are also very well insulated and keep out the cold.

But, if the temperature outside drops to below -8 degrees for an extended period there is a danger of the hedgehogs' body temperature falling to freezing point.

If this happens, ice crystals may form in there, which would kill them.

Hibernating hedgehogs are aware of icy conditions which may be threatening to them. If the weather becomes so cold that they are in danger of freezing they willfully or partially rouse from Hibernation, raising their body temperatures.

Is Hibernation Dangerous for Hedgehogs?

Yes, Hibernation is a dangerous process for hedgehogs. They only do it if they have to.

Apart from the danger of freezing which we've discussed earlier, there are other hazards for a hibernating hog to contend with.

It will take a hibernating hog several hours to fully "come round" so they are a sitting target for predators like badgers. And being disturbed by humans, foxes, dogs and cats can also cause problems.

The biggest threat though comes from being underweight. A hedgehog who is underweight going into Hibernation will not make it through the winter. And a hog that is very underweight on rousing in the spring is in danger too.

This is one of the critical areas where we humans can help.

How to Help a Hibernating Hedgehog

Feeding for Hibernation

One of the critical challenges for a hedgehog heading into Hibernation is putting on enough weight to survive the winter.

We can help by providing extra food.

Good quality meaty or dry dog or cat food is an excellent choice for hedgehogs.  Ready-made hedgehog food is even better, providing the exact balance of nutrients your hedgehogs need.

Putting out food and water in a feeding station each evening will help to give your hedgehogs the best chance of making it through the winter.

Keep feeding into November or December, when the food stops being taken stop leaving it out.

There is no need to leave food out during the hibernation period. But it is a good idea to keep leaving out a dish of water. Water will help any hedgehogs that are about, as well as other birds and animals.

In March or April start leaving out food again. Hedgehogs emerging from Hibernation may be skinny and weak. They need all the help they can get to put on weight before the breeding season.+

Weighing Hogs in Autumn.

A hog that weighs less than 600gms going into Hibernation will probably not survive the winter.

So while we would generally advise you to leave healthy-looking hogs alone, in the autumn, we would suggest you weigh any that look a little undersized.

Handling a hedgehog is going to be a prickly business, so wear a pair of thick gardening gloves.

Other than the prickles though, there is no need to worry, hedgehogs are quite docile creatures. They are very unlikely to try to bite you and even if they do, they have such weak jaws they can't do any real damage.

If your hog is over 600gms its okay, place it back into the garden and let it go about its business.

If it's under 600 grams, the hog needs help. Place it in a secure box, lined with newspaper or a towel and contact your local hedgehog rescue.

Creating a Better Hedgehog Hibernation Habitat

Next to feeding, giving hogs in your garden safe and warm places to hibernate is the best thing you can do to help them through the winter.

They love to nest in well-hidden corners.

So making sure your garden is not too tidy will be a great help. Leave a log pile, or an overgrown border and hedgehogs will thank you for it.

Leaves are a favourite nesting material. So make a leaf pile for your hedgehogs to use.

Providing a hedgehog house as a nesting site is also a great idea, particularly if you don't have old trees, rabbit holes or any of the other nesting sites they favour in your garden.

You can buy a range of ready-made hedgehog houses. 

When choosing your hedgehog house, be sure to opt for one that is fully predator-proof and allows your hog enough space to build her insulating nest inside.

You could give your hedgehog a head start by adding some bedding or leaves to the house. Providing bedding can help if there aren't a lot of bedding materials for the hedgehog to gather nearby.

Place the house in a quiet area of your garden in the undergrowth. Try to avoid placing near a boundary as these are often highways for all sorts of animals and the hog may get disturbed.

Don't put food in the house, but do leave a dish of clean water somewhere nearby.

Once the hedgehog house is set up, you must resist the urge to check inside to see if you have guests.

Leave the house undisturbed until well into the spring, when any hibernating hog will have moved out.

5 Things to Avoid During Hibernation

1. During Hibernation, don't look inside or move your hedgehog house. Though hedgehogs naturally become active several times during the winter, they do not like to be disturbed.
2. If you find a hedgehog in your garden, don't move it. If it's in an inconvenient place, maybe where you want to do some work, just wait a few weeks, and it will be gone.
3. If you accidentally disturb a hibernation nest, replace the leaves and bedding as carefully as you can and leave it alone.
4. Never light a bonfire, fork through your compost heap, or strim undergrowth without checking carefully for hibernating hogs first.
5. Never leave out milk to drink, always water. Despite the old-wives tales, milk is very bad for hedgehogs.

Conclusion: Successful Hedgehog Hibernation

Winter hibernation is a perilous but necessary behaviour for hedgehogs when food is scarce, and temperatures drop.

Hedgehogs that make it through the winter are ready to embark on the next mating season and doing their bit to build up the numbers of this fragile species.

By understanding Hibernation, its purpose and its pitfalls, we can help hedgehogs to successful Hibernation.

We hope you've enjoyed this post and have learned a little more about the when, where and why of hedgehog hibernation.

If you have more questions, please leave us a comment.

If you want to find out more about helping hedgehogs, please visit:

The British Hedgehog Preservation Society.

Hedgehog Street.

And if you spot a hedgehog in trouble, you can find your local hedgehog rescue project by clicking here.