Tortoise Hibernation Guide
This guide is written for Mediterranean species, such as Spur Thigh, Hermanns and Marginated Tortoises, and is also suitable for Horsfield (Russian) Tortoises.
Do not hibernate tropical tortoises.
Hibernating Young Tortoises
There is much debate over whether a young tortoise needs to be hibernated from their first winter or whether to wait until they are 3-4 years old or over 400g. There is no right or wrong answer; there are benefits to each approach.
Hibernating from the first year
Naturally tortoises would hibernate from their first winter. This is due to the environment changing; a drop in temperature and reduction in food supplies.
Hibernation helps to slow the growth rate and helps keep the shell nice and smooth.
Extra care needs to be taken when hibernating a juvenile tortoise due to their lower body weight.
Hibernating from 3-4 years, or 400g
Waiting until the tortoise is 3-4 years or over 400g is considered safer as they have more fat reserves, making hibernation less risky.
Why not just keep them warm all winter?
The Tortoise Trust has found that tortoises which would naturally hibernate but have not been hibernated have an increased incidence of liver disease and a definite decline in fertility.
Pre Hibernation Checks
It is very important to ensure that your tortoise is healthy and in good condition before you decide to hibernate it. If the tortoise is underweight, has a skin condition, respiratory disease or you have any other worries regarding its health then it is safer not to hibernate it. Tortoises which are not being hibernated must be kept under UV lighting and heat with a reduced food supply so it doesn’t gain too much weight. It is also important to check they are not infected with internal parasites/worms prior to hibernation. We would recommend a pre-hibernation check with an experienced reptile veterinary surgeon, especially if you have any concerns at all about your tortoise or have not had the tortoise very long and don’t know the history. A faecal sample would be very useful as this can be checked for parasites.
Preparing for hibernation
Preparation for hibernation is very important, in the wild the onset of autumn and winter will trigger the tortoise to start preparing for hibernation.
This can be replicated by
Reducing daylight hours
Reducing the intensity of the UV light
This can be achieved by turning the basking light thermostat down by a few degrees or raising the height of the light. If the UV light is a strip light this can be raised to lower the intensity or by offering more shade.
The temperature under the lamp should be reduced to around 13-17 C.
The tortoise will become less active and less interested in food.
A period of fasting is very important, to allow the contents of the stomach to be digested and passed. If there is any undigested food left in the tortoise this can rot producing dangerous gases and toxins.
THE LARGER THE TORTOISE, THE LONGER THE TIME REQUIRED TO DIGEST FOOD IN THE STOMACH
Large tortoises, in the 2-3Kg range will require about 1 month fasting period.
Medium-sized tortoises, in the 1-1.5 kg range will need about 3 weeks
Small tortoises (less than 1 Kg) typically require a fasting period of 2 weeks
We would not recommend fasting for less than 2 weeks even for very small animals.
The low temperature will slow down the digestive system and it will take longer to digest food. The temperature is also low enough to suppress appetite.
Food should not be offered in this period but water is very important, so bathe the tortoise 3 – 4 times a week to ensure it is fully hydrated. The tortoise should have stopped passing faeces prior to starting hibernation.
This is the preferred technique as the temperature is fully controlled. The older technique of putting the tortoise into a cold area of a garage or shed is more risky as the temperature cannot be controlled. Weather changes and fluctuations in the ambient temperature can lead to the tortoise waking prematurely. The tortoise is also more at risk of attack by rodents, especially if a suitably secure hibernation box is not used.
The ideal temperature for hibernation is between 3-6 C, which will shut the body down so very little energy is needed. A normal household fridge can be used but there are limitations; if the external temperatures drop below 3c the fridge cannot heat itself, so it’s possible the tortoise could freeze. For this reason never use a fridge in a garage or shed.
Temperatures must always be checked with a maximum-minimum thermometer to ensure that the temperature range is safe.
Ensure that you use a new fridge as the thermostats can be unreliable on an old fridge. It is best to use a fridge without an ice box as these can create cold spots, considerably colder than the other areas of the fridge.
Be sure to test the fridge for a few weeks in advance, using a maximum/minimum thermometer to be sure the temperature is safe. The sensor for the thermometer must be in free air (not touching anything) for a more accurate reading. Keep notes of the temperatures. If you find there is a variation in temperature place some bottles of water in the fridge as this will help stabilise the temperature.
The box used must be large enough for the tortoise to turn around comfortably; plastic boxes are great for this but must be well ventilated.
Use a deep layer of loose substrate such as coco fibre, or similar which will allow the tortoise to bury it self. This will help stabilise the temperature. It should be slightly damp (drier side of damp) to help prevent fluid loss from breathing or through the skin.
Ventilation is greatly reduced in a fridge, but fortunately the tortoise will have a low oxygen demand! However, the fridge should be opened at least 3 times a week for around a minute to allow the air to change.
Length of hibernation
Although in the wild all sizes and ages of tortoise would hibernate for roughly the same amount of time, in captivity it is considered safer to hibernate a young tortoise for shorter periods.
We would suggest the first hibernation should be 4 weeks long and add a week for each year until the tortoise is hibernating for 12 weeks.
Year 1 4 weeks
Year 2 5 weeks
Year 3 6 weeks
Year 4 7 weeks
Year 5 8 weeks
Year 6 9 weeks
Year 7 10 weeks
Year 8 11 weeks
Year 9 + 12 weeks
Checking the tortoise during hibernation
Tortoises need to be checked regularly during hibernation to ensure everything is going well. Weigh the tortoise weekly, making notes of the weight. We expect the tortoise to lose up to 1% of their body weight per week. If the tortoise is rapidly losing weight something must be going wrong. The tortoise will need to be brought out of hibernation as soon as possible. Also if a tortoise urinates in hibernation this must be woken immediately, as it is at risk of fatal dehydration. The tortoise must be re-hydrated and kept awake. Do not attempt to put it back into hibernation.
Waking the tortoise
When it is time to wake the tortoise, take the box from the fridge and allow to warm up naturally for a few hours. Then bathe the tortoise in warm water and put into their enclosure. The following day switch the UV and basking light on for a few hours and gradually the increase heat and light over a few days until the normal heat and light cycle are resumed.
The tortoise should start feeding and drinking within a week, if it doesn’t a trip to the vets is recommended.
Weigh the tortoise when it comes out of hibernation and every couple of months through spring/summer/autumn to ensure it is putting on weight and if it has not put on a good amount by the time of next hibernation, then it shouldn’t be hibernated (and should see a vet).