Tortoise - Hibernating

Not all tortoises hibernate. The advice on this sheet pertains only to those of the Testudo genus that will hibernate in the wild. This includes Hermann's Tortoise (T. hermanni), Horsfield's Tortoise (T. horsfieldi) and some of the Spur-Thighed Tortoise group (the Asia Minor and some of the North African species). If in doubt, it is important to have your tortoise accurately speciated before hibernating it.

Is it necessary to hibernate a tortoise?

In general, no. Most will be fine kept awake all year but you must have a suitable vivarium and be able to keep the environmental temperature between 25-30°C during the day and 20-25°C at night. It is also important not to overfeed during this time as obesity may result. For growing tortoises keeping awake overwinter may result in too rapid a growth rate and shell deformities.

It is advised not to feed overwintering tortoises every day and to give them lots of fibrous plant material. Hay can be useful at this stage as a lower calorie food.

As an exception, breeding females do require a hibernation period. This is because the drop in temperature followed by a rise is necessary to stimulate ovarian activity.

What pre-hibernation checks should be made?

It is important that tortoises are checked before hibernation. The body weight and condition should be checked as underweight individuals should not be hibernated. Female tortoises should receive an ultrasound and/or radiograph to assess reproductive function. Unlaid eggs should be induced prior to hibernation as they will affect bodyweight interpretation.

A faecal sample may be assessed for parasites and the tortoise dewormed if necessary. Alternatively, as larval worms may also cause disease and will not show in a faecal sample, some believe in routine deworming.

How should tortoises be hibernated?

It is important to remember that these species come from areas where there is a short cold winter. The British climate with its long mild autumn and Winter is not the same, so the old 'Blue Peter' method of putting the tortoise in a box in the loft for 5 or 6 months is inappropriate and will result in excessive weight loss in this period.

Tortoises should be hibernated between 5-8 degrees C. Below this, changes in water density may affect the eyes resulting in blindness. Above this they will become more active resulting in overusage of body stores.

It is therefore important to control temperature in a special unit - a fridge or canned drink cooler provides the correct environment.

This should be set up a few weeks before hibernation and contain a maximum-minimum thermometer. This means that the fridge thermostat can be adjusted to ensure correct running temperature before the tortoises are placed inside.

It is important to provide a cooling-off for the tortoises before hibernation. Ideally this should start immediately after the pre-hibernation check:

• In the first 7-10 days the tortoise should be maintained at normal vivarium temperatures, be bathed each day and fed as normal.
• For the next 7-10 days the tortoise should be brought down to room temperature. Feeding should stop but daily bathing continued.
• For the final 7-10 days the tortoise may be kept in a garage or outhouse and should not be bathed or fed.

It should then be ready to enter the hibernation unit! It is weighed, placed in a plastic tray (eg cat litter tray) and placed in the fridge.

During hibernation the tortoise should be weighed at weekly intervals. This enables monitoring of the animal and also an opportunity for a change of air in the fridge.

There will usually be a small weight loss in the first week or two. If this continues beyond the third week then the tortoise should be brought out of hibernation and a vet consulted.

Similarly if at any stage total weight loss exceeds 5% of starting weight the tortoise should be brought out of hibernation.

How long should hibernation last?

This partly depends on the age of the tortoise. Most sources do not recommend hibernating tortoises during their first winter and first hibernation should be during their second to fourth winter depending on size and body condition.

The first hibernation should be only 6 weeks long.

Thereafter periods of 2-3 months are appropriate.

3 months should be the absolute maximum.

After hibernation

At the end of the hibernation period the vivarium should be prepared, brought up to correct temperature and the tortoise placed in it.

It should be bathed daily in warm water and offered food from the second day after warming.

Most will eat within a few days of hibernation ending although some take a little longer. If not eating within two weeks or if appearing lethargic and ill, a vet should be consulted.

Even if doing well, a formal post-hibernation check should be performed in the spring. This will be similar to the pre-hibernation check described above.