Tortoises have evolved for millions of years to deal with seasonal fluctuations and thrive in periods with less food availability and lower temperatures. These changes in climate naturally slow metabolism in ectotherms and thus hibernation or a ‘winter period’ is an integral influence on tortoise physiology. Although hibernation was a risky process several decades ago, keepers today are much more aware of the potential problems involved in hibernation. Combine this with more reliable fridges, insulated homes and affordable thermometers and the benefits of a dormant period massively outweigh the associated risks. Although it can be a scary prospect, keepers should understand as much as possible about the hibernation process to ensure optimal success.

“All tortoise keepers should seriously consider providing a cooler period for their tortoises and there are a lot of reasons for this” explains Chelonia Specialist and Founder of Tortoise Matters, Eleanor Tirtasana-Chubb. “A big problem in captivity is that young tortoises are growing too quickly, which can be problematic and cause health issues. Tortoises can also be reluctant to feed, as they expect to hibernate. Giving them a short, controlled hibernation can help re-set their body clock and encourage them to feed better and reduce their stress.”

Which species should be hibernated?

Some of the most popular species of pet tortoises have reached their status because of their tolerance to the UK climate. Many of these come from areas across southern Europe and North Africa and fair extremely well outdoors through most of the year. These are the Hermanns (Testudo hermanni), Horsfield (Testudo horsfieldii), spur-thighed (Testudo graeca) and marginated tortoises (Testudo marginata). All four of these species should be hibernated or at least experience a dormant period. Tropical species such as red-footed (Chelonoidis carbonarius) and yellow-footed tortoises (Chelonoidis denticulatus) will not experience such drastic temperature drops and therefore should not be hibernated. The same applies to popular desert species such as sulcata (Centrochelys sulcata), leopard (Stigmochelys pardalis) and pancake tortoises (Malacochersus torneiri).

Typically, Hermann’s, Spur Thigh "dark-shelled" Ibera and Horsfield tortoises will hibernate extremely well. If they are healthy, they are very hardy species and hibernation is considered beneficial, if not essential for their wellbeing. This would typically happen when temperatures drop below 10°C, with optimal conditions being around 5°C. Eleanor continued: “Horsfield tortoises are some of the most northernly ranging tortoises and therefore require a slightly cooler temperature to hibernate. Anything much higher than about 6°C and the keeper may find that they will scratch away in the box and not go to sleep straight away. In the case of Horsfields', the keeper should aim for 3°C – 5°C. They are also extremely intolerant to dampness, so be mindful that the box must not be damp.”

“Marginated tortoises are not very popular in the UK as they were not imported for very long. However, there are still some out there. Although they inhabit warmer climates than Hermann’s and Horsfield tortoises, they will hibernate. They are also prone to a natural pinkness when they are cooled down. Unfortunately, many marginated tortoises end up on antibiotics unnecessarily as an inexperienced owner or vet may think they have sepsis.”

Pale-shelled spur-thighed tortoises are the most delicate of the popular species. Coming from North Africa, they should only have a period of cooling and not a full sleep. This can apply to Tunisian spur thighs and Western dwarf Hermann's (T. hermanni hermanni) also. There are several other, less popular subspecies which may be more or less tolerant to cooler temperatures and thus require slightly different hibernation periods. If a keeper is unsure of what species they are keeping, it should be a priority that they get absolute clarification before deciding on the length of hibernation, or whether to just offer a cooler winter period.

Getting into a healthy condition

Although each species and subspecies will experience different seasonal fluctuations, in captivity a rough estimate on timings can be made. For the three most hardy species (which will be referred to most frequently throughout the feature), Hermann’s, Horsfield and Spur thigh Ibera, hibernation can last anywhere from eight to twelve weeks. Eleanor continued: “At the end of the day, the final decision lies with the keeper. Very elderly and young tortoises should hibernate for a shorter period. This is around two to six weeks. If the tortoise is less than a year old or has never hibernated, the keeper may want to just provide a short one-to-two-week hibernation. This will allow both the tortoise and the keeper to get used to the process. A healthy adult tortoise should be hibernated for anywhere from eight to twelve weeks. I sometimes hear of people who think tortoises should be hibernated for six months and this is not true. They only require a short rest during the coldest months of the year.”

The length of time that a tortoise needs to be hibernated will also vary based on other factors, namely their health. A change in environment or an unclear medical history can produce stress or underline health conditions which may cause problems during hibernation. If a tortoise has recently been de-wormed, it is also worth waiting a while for the gut flora to regenerate before putting them into hibernation.

Ultimately, the keeper must be able to make an informed decision on how long they wish to hibernate their tortoise, based on the animals’ health, breed and age. This will require a good understanding of the tortoise and therefore regular weight checks and health inspections are necessary. “The tortoise should have nice bright eyes, a pink tongue, no sores around its tail or swollen joints” explains Eleanor. “It might sound weird, but the keeper should smell their tortoise and make sure there are no foul smells which would indicate a problem. A healthy tortoise should have clear nostrils and eyes. If someone spends plenty of time getting to know their tortoise, they will have a much better understanding of how to hibernate it.”

Keepers can also do a ‘Bone Density Formula’ which can be applied to Hermann’s, Spurthighs and Horsfield tortoises. This involves taking the weight (in grams) of the tortoise and dividing it by the length (in centimetres cubed). If the bone density ratio is in the range of .20 and .25, the tortoise is a healthy size and possibly ready to be hibernated. Shell deformities can skew this slightly. Eleanor continued: “The bone density formula is a great indicator, but certainly not the deciding factor. I have heard people choose not to hibernate their animals because the formula suggest they are underweight, even though they are healthy and fed well. In this case, it might be a better idea to just hibernate for a slightly shorter period. If the tortoise is really heavy, make sure there is no egg retention. If it is really light, maybe it’s worth a consultation with a vet. But that shouldn’t become an instant reason not to hibernate.”

When to hibernate?

Choosing when to hibernate a tortoise can be confusing. The weather in the UK can naturally become cooler as early as September, but just because it reaches 8°C in the UK does not mean that it will be reaching these temperatures in Southern Europe and Western Asia. Keepers should try to keep their tortoise awake for as long as possible with artificial heating and lighting indoors once the UK climate falls below 10°C at night and becomes too cold for full-time outdoor keeping. Many keepers aim to keep their tortoises awake until late November. This time frame means it’s usually easier to find natural plants right up until the tortoise needs to hibernate and they can also be greeted with warmer Spring temperatures and lots of fresh weeds when they awaken.

In September/October when the weather starts to cool down a tortoise should be given an indoor enclosure. As this is only temporary, this can be made of a whole host of materials or tortoise tables, vivariums (with the glass removed) and large tubs work great. A basking lamp that provides UVB such as a metal halide or incandescent flood will be necessary to provide heat and light. It is important that the keeper checks their bulbs, or replaces old bulbs at this time. A bulb that has not been used all summer may appear bright, but its UV and IR output may have diminished. Once the tortoise has been brought inside and housed in its new temporary enclosure, it should be maintained at a comfortable 16°C ambient temperature at night and a 30°C basking area for daytime should slowly be reduced. Daylight cycles should also be gradually reduced. For example, if the bulb is on for 12 hours once the tortoise has been brought inside, the keeper should reduce this by a few hours every couple of days down to 6 hours a day. The final few days can be no daytime lighting at all.

The tortoise should be contained during this period, to allow the keeper to monitor the animal and supplementary calcium and vitamins are essential. Gradually changing the tortoise's diet to more fibrous dried flowers and grasses will ensure that they have less nutritious, high-fibre food in their system. Avoid feeding treats or “junk food” options such as veg, fruit or a lot of salad in the month before hibernation fasting. Richer foods are more likely to rot and cause infection if any remains in the gut during hibernation. It can take up to four weeks of fasting for a tortoise to have an empty gut. During this time, ambient and basking heat is essential for the tortoise to clear its gut and good quality heating/light bulbs are a necessity. Extra fluids should also be provided. “Frequent baths are a really important part of the hibernation preparation process” explains Eleanor. “Extra fluids will help clear their gut and detox them. They should be soaked every 2-3 days for about 15-20 minutes in warm water at around 36°C. Although the keeper can just provide more water, bathing allows them to take on more liquids and the warmth of the water will also encourage them to go to the toilet as well.”

“A few days before hibernation, a more thorough clean with an antibacterial and fungal iodine-based soap is advised. This will reduce the chance of the tortoise picking up an eye infection, skin infection or developing shell rot during hibernation. Giving them a once over with Tamodine and using a soft toothbrush to get the entire shell, tail and limbs is great. Tamodine is also worth just keeping in the cupboard year-round. It can be used as a soap or as first aid if the tortoise gets any grazes or cuts.”

Where to hibernate?

There are a few methods of hibernating tortoises with the most popular being the ‘fridge method’. Modern housing is typically very well-insulated, so finding a location in the home with a steady 5°C temperature can be challenging. A fridge, on the other hand, can be a more predictable option if it is in good condition. The most important thing to consider when choosing a location to hibernate a tortoise is ensuring a steady, consistent temperature. A fridge that has a freezer compartment is extremely risky as a damaged fridge may lead to part of the fridge freezing. Eleanor explains: “There are a few things that keepers must consider if they choose to use the fridge method. Firstly, remember to open the door every few days to make sure that there is always enough oxygen. Secondly, check the temperatures several times in the run-up to hibernation to ensure that the temperature is steady. Finally, the addition of a few large bottles of water will add mass, which should then support the stability of the temperature.” The tortoise should be placed in a plastic container, with a deep layer of soil-based substrate to allow it to dig into a comfortable position (leaflitter can also be added for extra security) and placed into the fridge. Soil should not be soggy and should be able to crumble and fall off the keeper’s hand. Alternatively, the keeper could place the tortoise on a towel with dried leaves or shredded paper on top. If this method is chosen, a bowl of water should be added to the fridge to allow some ambient humidity.

Historically, many keepers opted for the ‘box’ method. This sees the animal placed inside a box with some newspaper shredding and placed in the coolest room in the house. Hay/straw should be avoided as it can bind around the tortoise’s joints. The addition of more mass will help stabilise temperatures, therefore having a box within another box is going to be much more reliable. A temperature probe should be inserted into the inner box, housing the tortoise. The box should also be labelled clearly and placed somewhere secure. Eleanor continued: “The tortoise may rustle around, so make sure the box isn’t anywhere up high. It should also be away from any potential predators. Lofts, conservatories and wooden sheds will also experience major temperature shifts. Unless someone is lucky enough to have a brick shed, the box method is not a great option.”

In mainland Europe, many keepers will opt for the ‘natural method’. This involves creating a brick-lined pit in the garden for the tortoise to hibernate in at their leisure. It is not advisable to do this in the UK due to a much wetter climate. The keeper also has less control and if the hibernation pit is damaged or poorly constructed, one frost could cause the animal to perish. Some UK keepers are extremely successful at keeping European species outdoors year-round by producing impressive hibernacula, but for the average pet owner, this can be tricky to navigate. For all methods, the keeper must ensure that the box is secure and predator-proof. This applies not just to cats and foxes, but to rats and mice which can also attack a hibernating tortoise.

Peace of mind

Leaving a beloved pet to their own devices, asleep in the fridge, can be a daunting prospect for any keeper. They shouldn't be disturbed too much during this period, but there are a few ways that a keeper can check up on their animal. Firstly, a data log of minimum and maximum temperatures is an excellent tool to monitor the conditions of the tortoise, whilst also providing some peace of mind for the keeper. Tortoises will typically sleep with their legs spread out. If the keeper touches the animal's leg, it should move slightly which is a good indicator that the tortoise is still alive, without disturbing its hibernation entirely.

“It is perfectly normal for the tortoise to move around in its box for up to 10 days after being hibernated" Eleanor added. "It might seem odd to the keeper, but a bit of movement is normal. If the tortoise urinates in the early stages of hibernation, there’s nothing to worry about. If it defecates, the keeper may need to remove the tortoise and fast it for a little longer before trying hibernation once again. If it happens at a later stage, this would be a cause to cut hibernation short. Once hibernation ensues, the number one most important thing is to keep the temperature steady. The steadier the temperature, the less stress on the animal and the less chance of it losing excessive weight.”

After the hibernation process, the tortoises can be warmed up to room temperature gradually over 48 hours. Eventually, they can be reintroduced to their indoor enclosure and placed under a basking light which will kickstart their feeding behaviour. If the tortoise does not feed within a week of waking from hibernation the keeper should offer tempting favourite foods, hand feeding opportunities and daily soaks. If these do not work, the tortoise may need to be force-fed with the support of a knowledgeable vet or expert. A slow starter can sometimes benefit from Reptoboost soaks post-hibernation. This is designed to replenish electrolytes, vitamins and probiotics.

In the wild, tortoises will often awake to find plenty of fresh spring shoots to feed on. In this case, feeding crunchy moisture-filled salads such as crunchy romaine, baby gem lettuce, rocket and even some cucumber is great. However, Eleanor warns that “cucumber is mostly filled with water. It is great for a drink, so it is really useful after waking the tortoise up, but it is not very nutritious. Keepers should be aiming to move their tortoises onto more fibrous foods as soon as possible, so going out to collect as many weeds as possible is important. These can be kept in sealable sandwich bags in the fridge. It’s a good idea to ask friends and family with pesticide-free allotments and wild gardens to collect these for you as often as possible. It’s free and they have much more trace elements and nutritional value than store-bought salads.”

Calcium and vitamin supplements are also incredibly important at this time of year. Even the very best natural weeds will have less nutritional content in spring and autumn than they will in summer. Therefore, high-quality calcium and vitamin supplements are essential. These can also expire and lose potency over time, particularly if they have been left open for a long period so keepers should aim to pick up fresh tubs of supplements ready for when the tortoise emerges from hibernation. Eleanor continued: “Most tortoises don’t like the taste of vitamins and they will try to hard-ball the owner. Persevere! Even if that means hiding small amounts in certain foods.”

Extra resources

There are plenty of resources available online to help tortoise keepers do right by their animals. Tortoise keeping has shifted greatly in recent decades. Not only do experts know much more about their wild behaviours, but keepers can now access a whole host of accessible information based on herpetological studies to ensure their animals are receiving the very best care. Eleanor’s YouTube channel @tortoisematters has exceptional advice on many issues relating to tortoise husbandry. Norfolk Tortoise Club are also very useful for asking direct questions about tortoise health and welfare. For those looking to learn even more, the European Turtle Alliance Annual Conference will be held at Writtle University next month. Click HERE for more details.

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Don’t Lose Sleep Over It: Understanding Hibernation