Tortoise hibernation: the decision, the wind-down and the wake-up

Quick answer

The decision starts with a health check, not a calendar. A tortoise that is not fit to hibernate is not made fit by the season arriving.

Two questions come before anything else. Is your tortoise a species that hibernates at all, and is this individual healthy enough to do it this year.

Mediterranean species such as Hermann's, Greek, marginated and Horsfield's hibernate. Tropical species such as sulcata, leopard, red-footed, yellow-footed, Indian star, elongated, pancake and hingeback do not, and cooling one of them is not hibernation, it is hypothermia. If you are not certain which species you have, that is the first thing to establish, not the last.

• Never hibernate a tortoise with any nasal or eye discharge, mouth lesions, recent injury, or unexplained weight loss.
• The gut must be empty before the temperature drops. Food left in a cold gut ferments instead of digesting.
• The tortoise must be well hydrated going in. Dehydration during hibernation damages the kidneys, and that damage often shows up after waking.
• Temperature must be measured continuously with a maximum and minimum thermometer, not assumed.
• A tortoise that wakes must eat within about a week. If it does not, that is a veterinary case.

:::danger
Freezing kills tortoises and blinds the ones it does not kill.

A tortoise held below freezing suffers permanent damage to the tissues of the eye, and post-hibernation blindness in animals overwintered in a shed or garage during a cold snap is a recognised and preventable outcome. Deaths are common.

At the other end, a box that drifts warm keeps the metabolism running so the tortoise burns reserves without eating, and may become semi-active without being able to feed or drink. Both failures come from the same cause: no continuous temperature measurement. A maximum and minimum thermometer inside the box, read every day, is not optional.
:::

Decide in 60 seconds

Which tortoises hibernate, and why it matters so much

Hibernation is not a general reptile behaviour. It is an adaptation of species whose native range has a cold season, and the animals that have it are physiologically built to survive months at low temperature with a shut-down metabolism.

Species that hibernate include Hermann's tortoise, the spur-thighed or Greek tortoise, the marginated tortoise and Horsfield's, also called the Russian or Central Asian tortoise. Horsfield's in particular hibernate long and deep in the wild, and also aestivate through hot summers.

Species that must not be hibernated include the African spurred tortoise or sulcata, the leopard tortoise, red-footed and yellow-footed tortoises, Indian star tortoises, elongated tortoises, pancake tortoises and hingebacks. These come from climates without a cold season, and cooling them produces immune suppression and pneumonia rather than dormancy.

The reason to be pedantic about this is that species identification is genuinely difficult for owners, tortoises are frequently sold or inherited with the wrong name attached, and a mistake here is fatal. If there is any doubt, a photograph of the shell from above, from the front and of the underside, shown to a reptile vet or a specialist tortoise group, resolves it quickly.

Why the gut must be empty

A tortoise's digestion runs on temperature. Warm, it breaks food down. Cold, it does not.

Food left in the gut when the temperature drops does not sit inert. Gut bacteria continue to act on it, fermenting rather than digesting, producing gas and metabolic by-products that the tortoise cannot process or expel. The result can be gut distension, toxaemia and death, and it is one of the classic causes of a tortoise that goes into hibernation looking well and does not come out.

That is why the wind-down exists, and why it cannot be rushed. The sequence is: stop offering food while keeping the tortoise fully warm and lit, so that it can finish digesting and pass what is left, and only then start reducing temperature.

Warm baths through this period do two jobs. They encourage the tortoise to drink, which is the hydration it must carry through the winter, and they stimulate defecation, which empties the gut.

The tortoise should be passing normal droppings during the wind-down, and then nothing, before the temperature starts to fall. If it is still producing faeces, it is not ready.

Preparing: the checks that decide the answer

Weight in grams and shell length recorded on the same day each week through autumn. The trend is the evidence, and it is the thing owners most often do not have.

Weight and length, written down.

Weigh weekly from late summer onwards on a gram scale and record it, along with shell length measured straight across rather than over the curve. Weight alone means little without length, and neither means much without a trend.

The Jackson ratio is a weight-to-length index developed for Mediterranean tortoises and is still used as one input into the decision. It is a screening tool with known limitations, it was not designed for Horsfield's, and it does not replace a clinical examination. Treat it as one piece of evidence alongside body condition and a vet's assessment, not as a pass mark.

Body condition, physically assessed.

The limbs should feel muscular and fill the shell openings. Skin that looks loose and baggy around the neck and legs, or a tortoise that feels unexpectedly light for its size, is not ready.

A veterinary check.

Eyes clear and open, with no swelling or discharge. Nostrils clean and dry, with no bubbling, crusting or streaking down the face. Any nasal discharge means respiratory disease, and hibernating an animal with a respiratory infection is one of the most reliable ways to lose it, because immune function falls with body temperature.

Mouth pink and clean, with no plaques, redness, ulceration or smell. A beak that is not overgrown. A shell with no soft areas, pitting or damage. No wounds and no recent injuries.

Ask about a faecal test, particularly for a tortoise that is new, has come from an unknown source, or has had loose droppings.

Reproductive status.

A female that has been with a male, or that has been restless and digging, may be carrying eggs. Hibernating a gravid tortoise is dangerous. Raise it with the vet.

Age.

Adults are the straightforward case. Hatchlings and first-year juveniles are debated: some experienced keepers give them a shortened hibernation, mirroring what happens in the wild, and others overwinter them warm for the first year or two. Both approaches have support. What is not in doubt is that a small tortoise has a smaller reserve and a smaller margin for error, so a juvenile hibernation needs a vet's involvement and shorter duration rather than an owner's guess.

The two methods

The fridge.

A dedicated refrigerator, not the one holding food. It holds a stable temperature regardless of the weather outside, which is the single biggest advantage and the reason it has become the recommended approach.

Set it up and run it empty for a week or more first, with a maximum and minimum thermometer inside, so you know what it actually does rather than what the dial says. Fridges have cold spots and thermostat swings, and a bottle of water in the fridge alongside the box helps buffer the temperature.

The tortoise goes in a ventilated box with substrate, inside the fridge. Open the door daily for air exchange, because a closed fridge is close to airtight and the tortoise still needs oxygen, and because it makes you look at the animal every day.

A box in an unheated space.

The traditional method, and much less controllable. If you use it, it must be an insulated box inside a second box, in a place that never freezes and never warms, and it must be genuinely rodent-proof. Rats and mice chew hibernating tortoises, and the injuries are severe.

Whichever method you use, the requirements are identical: continuous temperature measurement, daily checks, weekly weighing, and clear thresholds at which you stop.

Running it

The commonly recommended holding range is roughly 4 to 8 degrees Celsius. Below freezing causes permanent eye damage and death. Above about 10 degrees the tortoise's metabolism picks up, it burns reserves it cannot replace, and it may become semi-active without being able to feed or drink.

Check the maximum and minimum thermometer every single day and reset it. That reading is the whole safety system.

Weigh weekly. A small, steady loss is expected. Guidance in general use puts acceptable loss at around one per cent of body weight per month, and a faster loss than that is a reason to investigate rather than to wait. Excess loss usually means the box is too warm or the tortoise went in dehydrated.

Look at the tortoise when you weigh it. It should be still, with limbs and head drawn in, and should resist gently if you tug a leg. Complete flaccidity, an open mouth, discharge, or a tortoise moving around the box are all reasons to stop.

Duration varies by species, by age and by the keeper's plan, and is a decision to make with your vet rather than from a fixed rule. Shorter is safer than longer, and there is no requirement to run to any particular length.

Waking up

The first target after waking is drinking, then eating. A tortoise that is browsing and passing droppings has come through it.

Bring the tortoise up to room temperature first, then put it under full basking heat and UVB the same day. The animal needs to reach its normal operating temperature quickly, because everything else depends on it.

Bathe in shallow warm water immediately and daily. Drinking is the first priority, not eating. Through hibernation the tortoise has accumulated waste products it cannot excrete without water, and rehydration is what allows the kidneys to flush them.

Offer food once the tortoise is properly warm. Strongly scented favourites work best, and many tortoises will drink before they show any interest in eating.

Expect the tortoise to be slow for a few days. Expect it to drink a great deal.

The critical rule: a woken tortoise should be eating within about a week. Post-hibernation anorexia is the classic problem of the spring and it is a genuine emergency, not a phase. A tortoise that will not eat is drawing on reserves it has already spent, and the liver and kidneys are the organs that pay.

Also check the eyes on waking. Swollen, closed or cloudy eyes after hibernation raise the question of cold damage, and they need seeing.

What goes wrong, and what it looks like

Read that table before you set the box up, not afterwards. Every row is prevented by something done in the preparation phase.

Choosing not to hibernate

Deciding to overwinter a Mediterranean tortoise awake is a legitimate choice. Vets often recommend it for a tortoise that is underweight, ill, very young, newly acquired, or where the owner cannot provide controlled conditions.

The important point is that overwintering has to be done properly, and the half-hearted version is worse than either alternative.

Properly means full basking temperature, a correct thermal gradient, working UVB, and a long day length maintained artificially, so the tortoise stays genuinely active, feeding well and digesting normally throughout the winter.

The failure mode is a tortoise kept in a cool room with a bit of heat and a short winter day. That animal is neither hibernating nor properly active. It stays semi-dormant, eats poorly, does not digest what it eats, and loses condition through the season. This is where a large share of spring problems in non-hibernated tortoises actually come from.

A tortoise that is not hibernated does not become unable to hibernate in future years. Skipping a year is not a permanent decision.

The routine that keeps this safe

What the vet will ask for

Species and how you identified it. Age, or how long you have had the tortoise and its size when you got it.

The weight and length history, with dates.

Where the tortoise lives, what heat and UVB it has, the lamp type and age, and whether it goes outdoors.

The diet, including whether it eats mainly weeds and leafy plants or mainly shop-bought salad and fruit, and what supplement is given.

Previous hibernations: how long, by what method, and how the tortoise came out of each.

For a problem after waking: the wake date, how much it has drunk, whether it has passed urates or faeces, what it has eaten and when, and whether the eyes look different.

What never to do

Do not hibernate a tropical species. Not briefly, not "just a bit cooler", not at all.

Do not hibernate a tortoise with a runny nose, a bubbling nostril, an eye problem, a mouth lesion, a wound, or unexplained weight loss.

Do not start cooling before the gut is empty.

Do not use the family food fridge. It is opened constantly, its temperature swings, and reptiles carry Salmonella.

Do not hibernate in a sealed airtight container.

Do not bury a tortoise in a garden or leave it to hibernate outdoors where you cannot control temperature, flooding or predators.

Do not use a heat pad, a hot water bottle or a hair dryer to wake a tortoise quickly. Warm gradually to room temperature, then to basking temperature.

Do not assume a tortoise that woke slowly and has not eaten will "come round in its own time". The week rule exists because the ones that do not eat are the ones that die.

Do not skip the daily temperature check because the last ten days were fine. A single cold night is enough.

When to get help

A tortoise that comes out of the winter walking well, drinking, eating and passing normal droppings is what a successful hibernation looks like.

Before hibernation, see a reptile-experienced vet for the pre-hibernation check, and for any tortoise that is new to you, has lost weight, has had a discharge at any point in the year, or whose species you cannot confirm.

During hibernation, contact a vet if the tortoise has urinated in the box, is losing weight faster than expected, has become active, has any discharge, or has been exposed to temperatures outside the safe range.

After hibernation, contact a vet if the tortoise has not eaten within about a week of waking, is not drinking, has swollen or closed eyes, has swollen limbs, is passing thick gritty urates, has any nasal discharge, or is weak and cannot walk properly.

None of these is a wait-and-see situation. A tortoise coming out of hibernation is at the low point of its year, and the conditions that follow a bad winter progress quickly in an animal with nothing left in reserve.