Putting a tortoise into hibernation: what matters

In a few weeks the time comes, and in many households the same question is asked: box in the cellar or in the fridge? With tortoises, more hangs on that decision than most people realise — and on a few numbers you have to know.

I am regularly asked whether I “do reptiles too”. Yes — and on the subject of hibernation I become unusually blunt, because more animals die here of well-meant mistakes than of hibernation itself.

The most common of those mistakes, incidentally, is leaving it out altogether.

First the one question that decides everything: which tortoise do you have?

Before a single word about fridges, temperature or weight, one question stands right at the beginning — and it is so important that I put it first: do you know for certain which species you actually have? Because “tortoise” is not an answer. It is about as precise as “four-legged animal” — that covers the chihuahua as readily as the pony, and nobody would feed, house or care for the two the same way.

The reason this is not pedantry but a matter of life and death: the handling differs completely from species to species — right down to the exactly opposite rule.

• European tortoises — Hermann’s, spur-thighed and marginated tortoises, the typical animals in German and Swiss gardens — must hibernate. Everything in this article applies to them.
• Tropical and subtropical species — red-footed and yellow-footed tortoises, for instance, and many aquatic turtles from warm regions — know no winter at all in their homeland. They do not hibernate. Put such an animal in the fridge “to overwinter” and you kill it.

The same action — putting the animal in the cold — is correct care in one species and a death sentence in the other. That is exactly why the species is not step five but step zero. If you are not certain: check the receipt, ask the previous owner or breeder, or send a photo to a reptile-experienced practice. Only once the species is established beyond doubt does the rest of this text apply — and everything that follows refers to European tortoises.

Hibernation is not an option, it is biology

European tortoises — Hermann’s, spur-thighed, marginated — are animals with a firmly built-in yearly rhythm. Hibernation is not a state they endure but one their body needs. Metabolism, hormone balance and reproduction all depend on it.

Keeping a healthy tortoise warm “to be safe”, to spare it hibernation, is well meant and still harms it. Over the years these animals show growth disorders, shell problems and a shorter life expectancy. Hibernation is not the risk. Badly done hibernation is.

And here comes the part that surprises many: this also applies to the tortoise that sits warm in its enclosure in the living room all year and never meets real cold. Indoor conditions do not “domesticate” it and it does not lose the rhythm — the rhythm sits in the genes, it is not trained in and cannot be heated away. What winter triggers in nature has to be deliberately recreated by the keeper for an indoor-only animal. If the cold stimulus is missing entirely, the hormone balance is thrown off, the immune system suffers, and over the years the animal becomes more prone to illness. Put differently: the warm flat is no substitute for winter but precisely the reason why winter has to be created artificially — and that is exactly what the fridge is for.

That is exactly why the rest of this article is so detailed: it hangs on a few numbers, and you have to know them.

Who must not hibernate

This is the most important section, so it comes early. A sick tortoise must not go into hibernation. In the cold the immune system powers down — an infection that would be manageable in summer then has three months of free rein. A great many animals that come out of the box dead in spring were already ill in autumn.

So before hibernation comes a look at the animal, and a searching one:

• Eyes — watering, gummed up or swollen rules it out.
• Nose — discharge or bubbling points to a respiratory infection. No animal goes into the box with that.
• Mouth — coatings, redness or an odour need investigating.
• Shell — soft patches are a warning sign of disturbed bone metabolism.
• Skin — reddish discolouration is an alarm signal.
• Weight — clearly too light means: too few reserves for three months.

If anything is off, the animal belongs at a reptile-experienced practice, not in the fridge. And “reptile-experienced” is not a figure of speech here: not every small animal practice works with tortoises routinely. Do ask directly.

Preparation: the gut needs a run-up

Before hibernation, feeding is stopped so that nothing stays behind in the digestive tract. The reason is unpleasantly concrete: leftover food in a cold gut is no longer digested but decomposes. That can poison the animal from within.

How long that run-up takes depends on size and temperature — which is why no fixed number of weeks is given; instead the temperature is lowered step by step while the animal empties out. Warm baths support this and at the same time make sure it enters hibernation well hydrated.

One widespread misunderstanding I want to clear up here: this is not about forcing the gut completely empty. It is about giving the animal enough time to digest before it gets cold. Panicking and helping things along does more damage than the last remnant in the gut.

And right at the beginning stands: weigh and write it down. That starting weight is, for the whole winter, the only figure by which you can tell whether all is well.

Why the fridge is standard today

Perhaps you know it differently: a box in the cellar, leaves, soil, the garage. That worked for generations — and for generations it also cost animals their lives, because the temperature in a cellar does as it pleases. A warm January and the animal wastes away without waking. A cold snap and it freezes to death.

The fridge has a single, decisive advantage: you can set the temperature and check it. That is why it is the recommended method today, however unromantic that sounds.

Three things matter here. It should be a fridge of its own, not the one with the dinner in it. A thermometer belongs inside, measuring the actual temperature there — not the number on the dial. And it has to be aired regularly, because even a hibernating tortoise breathes. Opening the door briefly once a day is enough, and it is the best opportunity to take a look anyway.

Won’t it suffocate in the fridge?

This is the question almost everyone asks first who has never overwintered a tortoise — and it is entirely reasonable. A living animal in a closed box in a fridge: you think of suffocation at once. But the worry assumes an awake animal. And a hibernating tortoise is exactly not that.

In hibernation the whole body runs on a low flame — the metabolism drops by around 90 per cent. Heartbeat and breathing slow so far that the animal takes only about one to two breaths a minute. A body throttled that far barely uses any oxygen. The whole point of the exercise is that almost everything stands still — which is why the air in a ventilated box is amply sufficient.

So the cold here is not the danger, it is the trigger for exactly this powering down. And so that it is equally clear why airing is nevertheless part of it: opening the fridge door briefly once a day exchanges the air, costs ten seconds and is your daily check anyway. An airtight box with no air exchange at all is neither needed nor wanted — a box with a few small air holes plus the brief daily airing is entirely sufficient.

The temperature: a narrow window

Here are the numbers that matter. Hibernation runs at about 4 to 6 degrees Celsius. Some start at around five degrees and go down later to three or four.

It becomes critical in both directions:

• Too cold — below freezing, lasting damage threatens, among other things to the eyes. Frost is not “a little too cool”, it is the end.
• Too warm — above about 10 degrees the metabolism starts up again without the animal waking and eating. It then burns its reserves in its sleep. That is the more common and more insidious version, because nothing about it is visible.

So you measure not once but daily — and write it down. A fridge that reliably holds five degrees in November can be sitting at seven in February without anyone having changed a thing.

Checking: weigh, weigh, weigh

Weight is your only window into an animal that gives no sign. The usual practice is to weigh about every four weeks, and every two weeks in the final third of hibernation.

As a guide: over the whole hibernation a tortoise should not lose more than around ten per cent of its starting weight. And it is worth looking well before that — at more than about five per cent loss I would consult rather than wait. Weight loss that is too fast almost always means one of two things: it is too warm, or the animal is ill.

Also a reason to intervene: the animal is noticeably restless, it has passed faeces or urine, or it looks sunken. Then hibernation is over for that animal — not “let’s try again”.

Waking up

The end of hibernation is not a switch. The tortoise is brought to room temperature step by step, then under the heat lamp. A warm bath helps with drinking and with emptying out — both belong at the start, before the first food.

That an animal eats little or nothing in the first days after waking is normal at first. If after about a week it still will not eat, will not drink, or seems apathetic, that is no longer an after-effect. Then it needs examining. The same applies if the eyes are gummed up — the classic sign of an infection that grew quietly over the winter.

Why I wrote this article

Because reptile keepers are left remarkably alone online. For dogs and cats you find a thousand guides; for hibernation you find forum posts from 2011 and plenty of opinions that contradict one another.

And yet this is precisely a subject where precision decides between life and death — and where the keeper holds almost everything in their own hands. A thermometer, a scale and a note pad are worth more here than any preparation.

My approach with tortoises is the same as with dogs, cats and horses: first check the conditions an animal lives in, then talk about everything else. What I mean by that is set out in Holistic veterinary medicine: when it makes sense. And how much the surroundings decide over health is shown almost as clearly by coughing in horses — a different animal, the same principle.