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A Guide to Hibernation

Hibernation is possibly the most worrying part of owning a tortoise. In the past, many tortoises which went into hibernation died as a result of lack of knowledge or inadequate housing/temperature control.

There is still some ambiguity regarding hibernation with regards to methods, timescales and preparation. It is important to remember that hibernation is an important and natural part of a healthy tortoise’s life in the wild, and if we are to emulate natural conditions as closely as possible, hibernating your tortoise is not an option but a necessity.

This guide will hopefully clear up some of the myths and confusion surrounding the hibernation of tortoises and will make sure that your tortoise is hibernated safely.

What is Hibernation?

Hibernation is the time when your tortoise or turtle will ‘sleep’ through the cold weather of winter. This is not a normal sleep where the brain is still active and noise or movement can easily awaken the sleeper, but is a torpor through which metabolic activity is very, very low.

In the wild, as they are poikilothermic (cold blooded), tortoises begin to prepare for the winter hibernation period as the temperature starts to drop. As these tortoises are native to the Mediterranean where the winters are shorter and milder than in the UK, it is necessary to artificially prolong the summer of your tortoise indoors to avoid excessively long hibernation periods.

Hibernation is part of a tortoise or turtles natural yearly cycle and so it is important to allow hibernating species the opportunity to hibernate and this seems to improve their natural behaviour patterns throughout the year (for instance tortoises which are hibernated tend to breed more readily and successfully).

What is Aestivation?

It is important not to confuse winter hibernation with aestivation. Aestivation is torpor or hibernation due to high temperatures or lack of water and occurs during hot and rain-free summers. There may be several reasons for aestivation such as a lack of food and water or excessively high temperatures.

During aestivation tortoises bury themselves below ground in burrows. These burrows have temperatures which are much lower than those above ground and the relative humidity is very much higher. This microclimate combined with little or no activity, result in a vastly reduced rate of fluid loss and therefore the need to eat or drink is vastly reduced.

Is Your Tortoise a Hibernating species?

The first thing to be sure of when it comes to hibernating your tortoise is that you have a species of tortoise which would naturally hibernate in the wild. If you try to hibernate a species of tortoise for which this is not natural behaviour, you will end up with only one result: a dead tortoise.

A general rule of thumb, Mediterranean tortoises do hibernate, and tropical tortoises don’t hibernate. Most of the commonly available species in Britain will fit into one of these two categories which are more clearly broken down in the table below.

Hibernating Species

Hermanns tortoise - Testudo hermanni

Spur-thighed tortoise - Testudo graeca

Marginated tortoise - Testudo marginata

Horsfields tortoise - Testudo horsfieldi

Common Non-Hibernating Species

Leopard tortoise - Geochelone paradis

Sulcata tortoise - Geochelone sulcata

Indian Star tortoise - Geochelone elegans

Red footed tortoise - Geochelone carbonaria

It is vitally important that you know the exact species and subspecies of tortoise which you own as the list in the above table is not by any means complete and only contains information for the commonly available British tortoise species. Many other more unusual tortoise and terrapin species may hibernate (for instance many box turtles do so) and their requirements may be different. Also some of the African subspecies of the spur thighed tortoise may not hibernate due to the hot nature of the climate in which they live.

This guide is aimed at safe hibernation of Mediterranean tortoise species only and we cannot urge you enough to make sure that you know exactly what species of tortoise you own (many forums or the Tortoise Trust will help you with identification if you are unsure) and exactly what its hibernation/overwintering needs are if it is to be kept safely in this country.

What If I Own A Tropical Tortoise?

If your tortoise is a species which does not hibernate, but stays awake and feeding all the year round, then you need to make adequate arrangements to see your tortoise safely through the winter months. Due to the damp and cool climate in the UK and the regular fluctuation of temperatures between night and day (especially as it drops below freezing), it is totally inappropriate to keep a tropical tortoise outside at all during the winter months.

The only way to keep these tortoises for the cooler six months of the year is to have them in an indoor area where the daytime background temperature is above 20 degrees centigrade and the night time temperature does not drop below 10 degrees centigrade. Neither is it possible to rely on the background temperature of the room in which the tortoise is kept as the only source of heat and light even if it meets the above temperature criteria. Tropical tortoises need to be able to regulate their body temperatures. This means having a temperature gradient across their enclosure with a hot basking area and a cooler area with somewhere to hide. To achieve this your enclosure needs adequate basking lamps at on end/corner. Tropical tortoises also need a source of full spectrum light containing both UVB and UVA rays to enable them to maintain normal behaviour patterns and to absorb the vitamins/minerals from their food. The enclosure should be cooler and dark through the night time period.

Is Your Tortoise Old Enough to Hibernate?

Many tortoise authorities suggest that you do not hibernate your tortoise for the first 2 or three years of its life or until its plastron length exceeds 10cm. This is not necessarily detrimental to your tortoise provided that you can provide it with the correct conditions and food over the winter months and indeed any tortoise which is sick or underweight should not be hibernated under any circumstances. To overwinter your tortoise, you must create for it an artificial summer throughout the winter months complete with heat, light and food (see ‘What If I Own a Tropical Tortoise’ above). If a tortoise is of a hibernating species however, it would, in its natural environment, hibernate from birth without any ill effect. This is what these tortoises are designed to do. We feel that hibernating all tortoises, regardless of age, is the more natural way to proceed and is better for the tortoise in the long run. Some people hibernate their younger tortoises for shorter periods of time, which would seem to be an effective compromise.

Some people advocate hibernating tortoises for as much as six month of the year. This does fit in better with the British climate, but would seem to be done more for the benefit of the tortoise owner than for the benefit of the tortoise or turtle itself as they would never naturally hibernate for this length of time in the wild(with the possible exception of some Horsefields. We feel that it is not advisable to hibernate any tortoise for more than twenty weeks maximum.

It must be stressed again, that any tortoise which is underweight or ill in any way should not be hibernated but should be overwintered safely indoors.

What are the Benefits of Hibernation?

Hibernation for tortoises is an important biological process and we strongly feel that all Mediterranean species of tortoise require some form of winter hibernation to remain healthy in captivity (unless they are already sick).

Tortoises which are not hibernated can become lethargic and are less likely to breed successfully. Due to the fact that they are fed through the winter tortoises which are not hibernated can also grow too quickly which can potentially cause them health problems in later life. There is also more difficulty in obtaining a natural tortoise diet of weeds and grasses during the winter months as these do not grow well outside at this time of year.

Feeding 'salad' type foods which are high in phosphates (most supermarket grown food has high levels of phosphates) and often low in calcium and fiber can exacerbate or cause further health problems for your tortoise.

In short tortoises are designed to hibernate. It is part of their natural yearly rhythm. We feel that any tortoise which is well enough and heavy enough to be hibernated should be hibernated.

Is My Tortoise Fit to Hibernate?

There are two main issues which need to be addressed when you are deciding whether or not your tortoise is fit to hibernate. Firstly, your tortoise needs to be heavy enough for its length. Secondly, your tortoise needs to be fit and well and free from any signs of illness, injury or disease. You need to begin deciding whether your tortoise is fit for hibernation some weeks before you are going to hibernate in order to be prepared for either eventuality.

To assess your tortoise’s health you can use the following checklist:

  • Has your tortoise been eating well?
  • Is its nose dry and its breathing free from wheezing?
  • Are your tortoise’s eyes clear with no stickiness or discharge?
  • Are its ears flat and free from discharge?
  • Check that your tortoise does not have a discoloured or spotty mouth.
  • Are there any swellings or lumps around the tail or legs?
  • Is your tortoise’s faeces moist but firm without any diarrhoea/slime/offensive smell?
  • Is your tortoise free from any other external injuries?

If your tortoise is showing any of the above signs it should be isolated from any other tortoises and taken to a vet who specialises in tortoises/turtles.

Probably the most popular method of calculating safe hibernation weights in Mediterranean tortoises is to use the Jackson ratio.

This ratio is only suited to Hermann's tortoises and Testudo graeca sub-species as these species have a 'normal' body shape. It is not suitable for Horsfield's tortoises as they are too short and appear overweight, or Marginated tortoises which are too long and appear underweight. It is definately not suitable for any other species of tortoises, turtles or terrapins which hibernate. The Jackson Ratio is usually expressed as a graph which can easily be found on the internet.

Tortoises which fall either side of the ‘mean weight for length’ ratio can be safely hibernated. Tortoises which are on or below the ‘Dangerously low weight for length’ ratio (or are even approaching it) should not be hibernated but should be safely overwintered in an artificial indoor environment.

Hazards and Mistakes of Hibernation

There are numerous hazards and mistakes which face tortoises and turtles during hibernation and these are increased by the fact that you are hibernating your tortoise in an artificial environment.

There are three main natural errors which affect hibernating tortoises and three main problems which occur due to mistakes in husbandry either before or during hibernation.

Probably the biggest killer however, is attempting to hibernate a sick or underweight tortoise. Make sure you read the tortoise fitness section above and follow the guidelines given there.

Natural hazards which can kill or damage your tortoise during hibernation are freezing, drowning, or predators.

Tortoises need to be hibernated at a temperature of between 3 and 7 degrees centigrade (these are the outside limits 5-6 degrees centigrade is the optimum temperature to maintain your tortoise at). If you allow the temperature to fall below 3 degrees centigrade you risk your tortoise starting to freeze. Because tortoises are poikilothermic (cold blooded) they are totally incapable of maintaining their own body temperature and can easily freeze to death. Even if your tortoise doesn’t die, freezing temperatures can cause blindness or tissue damage leaving you with a permanently maimed tortoise.

Do not hibernate your tortoise anywhere where there is a remote possibility of frost. Always monitor the temperature of your tortoise during the hibernation period. Do provide insulation (described below) to help protect your tortoise from temperature fluctuation.

Drowning is a hazard for tortoises which are hibernated naturally outside. Try to encourage your tortoise to hibernate on higher or well drained ground. If your tortoise gets wet it will not dry out as it is poikilothermic and generates no heat. Also, if you hibernate your tortoise in an outhouse/greenhouse make sure it doesn’t leak or flood.

Predators are another hazard of hibernation. Your tortoise is totally defenceless whilst hibernating and if you’re not careful, your tortoise could be partially eaten resulting in lost limbs or even death. As long as your tortoise is in a secure box then the risk from larger predators such as foxes is minimal. Rats and mice are the main hazard in the UK. Ensure that your tortoise is hibernated in an area which is totally secure from rats or mice. If you hibernate your tortoise in an outhouse/garage etc. then you need to make sure that there is no access to the box in which your tortoise is hibernating. Fine gauge wire mesh around the box is possibly the safest option available.

It is important to minimise the risk of other hibernation hazards which are usually caused by poor or incorrect tortoise husbandry prior to or during hibernation.

Dehydration kills many tortoises in hibernation. It is essential to ensure that your tortoise has regular baths and opportunities to rehydrate itself prior to being hibernated. Tortoises must be hibernated with a full bladder. If, when you are inspecting your tortoise during its hibernation, you find that it has urinated, it should be removed from hibernation immediately and slowly warmed in a lukewarm bath to ensure adequate rehydration. Such tortoises will need to be kept awake in an artificial summer environment for the rest of the winter.

It is also important to weigh your tortoise at least every other week whilst it is hibernating to ensure it is not losing too much weight. If your tortoise is losing more than 1% of its initial hibernating weight in a month it may be becoming dehydrated and again should be awoken for the rest of the winter period.

Allowing your tortoise to get too warm whilst it is hibernating is another common mistake. When a tortoise awakens from hibernation, its body releases a store of glycogen which gives the tortoise enough of an energy boost to enable initial foraging for food and water. If a tortoise is repeatedly brought up to temperatures approaching 10 degrees centigrade, it will have used up these reserves and will be in a poor condition come spring. It is vital to monitor the temperature of your tortoise whist it is hibernating to ensure they remain between 3 and 7 degrees centigrade. If your tortoise has been repeatedly awakened then it will need to be taken out of hibernation and overwintered indoors. Note that briefly handling a hibernating tortoise (for weighing for example) will not wake it up and tortoises so move slightly during hibernation. The only way to be absolutely sure if you may have a problem is to accurately monitor the temperature of your hibernating tortoise using a minimum/maximum thermometer (available at garden centres) throughout the hibernation period.

Another problem which can potentially kill your tortoise during hibernation or just after it is hibernating your tortoise with a full stomach. During hibernation the food in the stomach ferments creating gases and toxins which in turn can cause internal damage and trauma to your tortoise. Specific conditions caused by hibernating your tortoise with a full stomach are tympanic colic and numerous bacteriological infections inside the tortoise. We recommend not feeding your tortoises for at least four weeks before you hibernate them to ensure that they have an empty stomach when thy commence hibernation. It is important that regular water is available and that your tortoises are bathed prior to hibernation to ensure a full bladder (see above).

Preparing for Hibernation

For a couple of weeks, slowly reduce the amount of food your tortoise is given by feeding more occasionally and in smaller quantities.

Four weeks before hibernation, stop feeding your tortoise completely and gradually reduce the temperature and the amount of daylight over the four weeks prior to hibernation.

Continue to provide water for your tortoise and give him a weekly bath. This will ensure adequate hydration and may encourage defecation.

Once your tortoise has had nothing to eat and has been slowly cooled for four weeks he is ready to be hibernated.

Hibernation Methods

There are 3 main ways to artificially hibernate a tortoise.

1. The Box Method

This is the traditional way to hibernate a tortoise and has several variations.

It basically involves putting your tortoise into a reasonably tight fitting box (cardboard is best but a tupperware type box with air holes in the lid will suffice) with some insulation material (we prefer nearly dry soil or compost as this keeps the tortoise better hydrated, but shredded newspaper will do) inside a second box (preferably wooden) filled with tightly packed newspaper or polystyrene chips.

An improvement on the original method provides better insulation and therefore better protects your tortoise from extremes of temperature. The main difference is the use of a large polystyrene box usually used for transporting fish (which can be obtained from a good aquatic retailer) instead of the outside box. These boxes are designed for insulating fish during transport and therefore provide a much better level of insulation than a standard wood or cardboard box. The tortoise itself is put in a cardboard box not much bigger than the tortoise itself which is half filled with nearly dry compost or soil. This box is placed in the centre of the insulated polystyrene box (not on the bottom) and completely surrounded with packed newspaper or polystyrene chips. Make sure that neither box is completely sealed as although tortoises don’t use a lot of air whilst they are hibernating, they do need some! Small air holes are the best way of achieving this without losing too much insulation.

With the box method it is essential to monitor hibernation temperatures throughout preferably with a digital thermometer. Place the probe the thermometer probe in the inner box with the tortoise and the control panel on the outside to enable you to check the temperature daily without disturbing your tortoise. The entire box setup can then be placed in an outhouse, garage, shed or cool spare room.

2. The Fridge Method

This method is a more recent phenomenon and usually allows more secure and accurately controlled hibernation for your tortoise. With this method a fridge is used to control temperatures throughout hibernation. It is essential to check that your fridge is functioning properly with a digital high/low thermometer for a couple of weeks prior to hibernation. It is also necessary to ensure adequate air supply within the fridge. This can be achieved by opening the fridge door for a few moments daily, or by cutting out part of the fridge door seal and running a small air pump into the fridge.

The tortoise is placed in a cardboard box just slightly larger than itself which is half full of nearly dry soil/compost or shredded newspaper in the same way as for the box method. The box is then placed in the fridge set at 5C. A digital thermometer needs to be placed inside the fridge and the temperature checked on a daily basis.

3. The Natural Method

This is as the name suggests the most natural method of hibernation for your tortoise, but it is not really recommended in the UK due to the temperamental weather, damp and difficulty in monitoring your tortoise during hibernation.

In the wild tortoises bury themselves in soft, dry sandy soil usually under bushes or at the foot of trees. The soil protects the tortoise from the elements and also from predators whilst maintaining humidity and the correct microclimate for the tortoise. If this method is to be used in the UK then it should be strictly within the confines of a greenhouse, with a soil base.

The tortoise needs to be starved in the usual way and its weight checked. Tortoises should only be allowed to hibernate in this way if they are extremely healthy since it is much more difficult to check on them during hibernation. They should then be allowed to burrow into the soil and the exact location should be noted. The soil should be dry and well drained. If your greenhouse leaks then this method is not appropriate as your tortoise will become too wet or even drown. The area where the tortoise has buried itself can then be covered with leaves as a further level of insulation.

How do I Wake My Tortoise Up?

When it’s time to wake your tortoise or if it has woken itself or needs to be brought out of hibernation for health reasons, the following procedure should be followed:

  • Place your tortoise at room temperature for 2-3 hours and allow its temperature to rise slowly.
  • Perform all of the same health checks which you carried out before hibernation.
  • Put your tortoise somewhere warm and bright until it is fully awake (for instance its tortoise table/indoor enclosure with the lamps and lights on). This should take 30 minutes to an hour.
  • Offer your tortoise a drink.

It is vitally important to get your tortoise drinking within the first few hours of waking up from hibernation. Sometimes getting a tortoise to drink is difficult after hibernation. Putting him in a bath of lukewarm water is more likely to stimulate a response. Once your tortoise is drinking, you can offer him food. It is important that your tortoise eats within the first week after hibernation.

If your tortoise is not eating after a week, will not drink, or has any other health problems, immediate veterinary attention from a vet who specialises in tortoises/reptiles is required. There is a lot of conflicting advice about the hibernation of tortoises and the best method of hibernation.

Possibly the most important thing to be sure of is what species of tortoise you have and whether this species of tortoise would naturally hibernate in the wild.

As a general rule of thumb, Mediterranean tortoise species do hibernate, and tropical species don't.

This page discusses hibernation and the best methods of hibernating your tortoise successfully. It also aims to explode many hibernation myths by answering all of the important hibernation questions.