Hedgehog hibernation: what wakes it, what saves it — and when you need to step in

In November the garden goes quiet. The hedgehog that came to the feeding spot every evening all autumn stops coming. Most people wonder at that moment whether something has happened to it. Usually the opposite is true: it has done exactly what it spent all autumn eating for. It is asleep. And from now on, the most important thing you can do for it is not to wake it.

When hedgehogs settle down to sleep

Hibernation is not triggered by a date but by the weather. When the nights turn cold for good and there are hardly any beetles, caterpillars and earthworms left to find, foraging no longer pays. The hedgehog withdraws into its nest and curls up. In Switzerland, Germany and Austria that usually happens in November, in mild years not until December.

Not all hedgehogs go at the same time. The males go to sleep first, often as early as October. The females follow later, because after raising their young they first have to put weight back on. The young from late litters stay out the longest. They are under time pressure in late autumn, and that is exactly why you still come across small hedgehogs in November when the big ones have long since disappeared.

The hedgehog wakes in spring, usually between March and April, once it stays warmer. So the whole hibernation lasts around four to five months.

What happens in its body during hibernation

A hibernating hedgehog is not simply tired. Its body shuts down almost everything that costs energy. Its body temperature drops from around 35 degrees to close to the temperature around it, often to just a few degrees above zero. Instead of beating around two hundred times a minute, its heart beats only a few times, and it breathes so rarely that you can barely see it from outside.

It lives on this energy-saving programme for months, without eating at all. Its energy comes from the fat it built up by eating in autumn. By spring it loses up to a third of its weight. That is why its autumn weight matters so much, and why there is the rule of thumb that a young hedgehog should go into winter at around 500 grams. How to weigh an animal and what the numbers mean I have described in my article Found a hedgehog: when it needs help.

That is why a sleeping hedgehog feels cold and barely reacts. In a hedgehog in its nest, that is no sign of illness. In a hedgehog lying out on the lawn, it is.

Waking up is part of it, but it costs a lot

Many people are surprised that hedgehogs wake up now and then during winter. That is normal. They wake in mild spells; some then change nests, drink a little and go back to sleep. A single hedgehog out briefly on a warm January night is therefore not automatically an emergency.

It is costly all the same. To wake up, the hedgehog has to bring its body back from a few degrees to its normal temperature under its own steam. Every waking uses up a large share of the reserves that were meant to last for weeks. And in January there is nothing out there it could replace them with.

A hedgehog that wakes once of its own accord usually copes. A hedgehog that is disturbed several times starves in February, even though it weighed enough in autumn. That is exactly why the most important thing a garden can give in winter is peace.

The greatest danger is not the cold

A healthy hedgehog with good fat reserves copes surprisingly well with frost, as long as its nest stays dry and undisturbed. What really endangers it in winter is us. The most common disturbances come from the garden:

• Clearing leaves and leaf blowers. Hedgehogs sleep under leaves, under hedges and in leaf piles. A blower exposes the nest or tears it apart.
• Turning the compost. A compost heap is warm and sheltered, which makes it a popular winter quarters. The garden fork often hits the hedgehog before you see it.
• Burning brushwood and log piles. Anything that has lain stacked for weeks is inhabited. If you want to light a pile, restack it first.
• Grubbing out hedges and clearing undergrowth. Winter is when many people tidy up the garden. For the hedgehog it is the worst time of all.
• Dogs. A dog digging in a leaf pile is sure to wake the hedgehog, even if it does not hurt it.

The rule that follows is simple: whatever was left lying in autumn stays there until April. If you really have to work, do it by hand, with a rake instead of a blower, and look under every pile first.

If you find a winter nest

A hedgehog nest is a ball of tightly packed leaves, often under a hedge, a woodpile or a garden shed. If you come across one while you are working, there is no need to worry, as long as you respond the right way:

• Do not check whether anyone is inside. Every opening is a disturbance.
• Carefully lay the leaves back over it so that the nest is closed and dry.
• Mark the spot and leave it in peace for the coming months. Keep dogs away from it.

If you have accidentally uncovered the hedgehog completely and it lies there cold and curled up, put it back, nest material and all, in a sheltered spot nearby as quickly as you can. If it is injured or stays awake and restless, call a hedgehog rescue before you do anything else.

When a hedgehog needs help in winter

A hedgehog that is awake in winter does not always need help. But there are situations in which you should not wait:

• It is out in daylight in frost or snow, seems disoriented or is lying in the open.
• It is still very small in December or January. A young animal well under 500 grams has little chance of getting through the rest of the winter on its own.
• It staggers, is injured, coughs or no longer curls up.
• It was in a nest that has been destroyed and cannot find new shelter.

In all of these cases: do not overwinter it yourself, call a hedgehog rescue or a veterinary practice instead. Until then, the hedgehog goes into a tall cardboard box lined with newspaper, in a quiet place in the house. If its belly is colder than your hand, it needs warmth first and only then food. And please, no milk. Hedgehogs cannot tolerate lactose.

The feeding spot in winter

If you fed a hedgehog in autumn, you will be wondering in November when to stop. The hedgehog gives you the answer itself: once it stops coming, it is asleep. Leave the feeding spot out for about two more weeks after that, in case a straggler or a youngster comes by. Then clear it away.

A shallow dish of water can stay out all winter, especially in mild spells. A hedgehog that is awake is often thirstier than it is hungry. Do not feed all the time, only when an animal really does turn up, and then with cat food without sauce, never with milk, bread or fruit.

By the way, this does not only apply to hedgehogs. Other animals in your garden have their own rules in winter too. With squirrels, for example, which do not truly hibernate, feeding looks quite different. I have written about that in my article on feeding squirrels (in German).

In spring: thin, thirsty and very welcome

When the hedgehog wakes in March or April, it is a different animal from the one you knew in autumn. It is thin, thirsty and needs a few weeks until the ground offers enough insects again. During this time a dish of water helps it more than anything else, and for the first few weeks a small feeding spot does too.

And even then: do not clear away the leaf pile on the first warm weekend in March. Not all hedgehogs wake at the same time, and there may still be sleepers in a pile. If you wait until the end of April, you are on the safe side.

What a quiet garden achieves in winter

What I like about the hibernating hedgehog is how clearly it shows how much help lies in holding back. You do not have to buy anything or build anything. You only have to leave what is lying there where it is, and not look.

A garden where nobody tidies up in winter is worth more to a hedgehog than any well-meant rescue. That is also why I gave the garden so much space in my special booklet „Bevor du eingreifst“ (in German): most wild animals do not need care, they need room.