Which Tortoises Hibernate and Which Do Not
Not all tortoise species hibernate, and attempting to hibernate a tropical species can be fatal. The three species most commonly kept in the UK and Europe that do hibernate are Hermann's tortoise (Testudo hermanni), the Spur-thighed tortoise (Testudo graeca), and the Horsfield's or Russian tortoise (Agrionemys horsfieldii). These are Mediterranean and Central Asian species that experience cold winters in the wild and are physiologically adapted to withstand a period of dormancy.
Tropical species such as the Leopard tortoise (Stigmochelys pardalis), Red-footed tortoise (Chelonoidis carbonarius), and Sulcata tortoise (Centrochelys sulcata) should never be hibernated. These species are not equipped to handle the cold and will suffer organ damage or death if temperatures drop too low. If you are unsure which species you own, consult a reptile vet before making any decisions about hibernation.
Pre-Hibernation Health Check
Before allowing your tortoise to hibernate, a thorough health assessment is essential. A visit to a reptile-experienced vet in late summer or early autumn is strongly recommended. The vet will check for respiratory infections, mouth rot (stomatitis), eye problems, nasal discharge, and internal parasites. Any of these conditions make hibernation extremely dangerous and must be treated before the tortoise is allowed to enter dormancy.
At home, examine your tortoise regularly in the weeks leading up to hibernation. Clear, bright eyes with no swelling, a clean and dry nose, and a mouth free from mucus or discolouration are all signs that your tortoise is fit to hibernate. A tortoise that has been unwell, undergone surgery, or received antibiotic treatment recently should not be hibernated that year.
The Jackson Ratio: Is Your Tortoise Heavy Enough
The Jackson ratio is a weight-to-length formula used to assess whether a tortoise carries enough body reserves to survive hibernation safely. It compares the tortoise's weight in grams to the cube of its straight carapace length in centimetres. A ratio below 0.16 is considered dangerously underweight, 0.17 to 0.21 is borderline, and 0.22 or above is generally considered safe for hibernation.
You can find Jackson ratio calculators online, or your vet can calculate it during the pre-hibernation check. An underweight tortoise should not be hibernated. Instead, continue feeding it well throughout the winter under artificial lighting and heating, and aim to improve its condition before the following autumn. Never hibernate a tortoise that does not meet the minimum weight threshold.
The Wind-Down Period
Approximately four to six weeks before the intended hibernation start date, begin reducing your tortoise's feeding. The gut must be completely empty before hibernation begins, because food left in the digestive tract will rot rather than digest during dormancy, causing serious internal harm. Stop feeding entirely during this wind-down phase.
Continue to bathe your tortoise in warm, shallow water for around ten to fifteen minutes every few days throughout the wind-down period. This encourages the tortoise to empty its bladder and bowels and helps maintain hydration before the long sleep. Reduce the number of hours the basking lamp is on each day to mirror the natural shortening of daylight.
Hibernation Methods
Fridge Hibernation
Fridge hibernation is widely considered the safest and most controllable method. Place your tortoise in a well-ventilated box filled with dry topsoil or shredded paper, then place the box in a dedicated or second-hand refrigerator set to between four and six degrees Celsius. Check the temperature inside the fridge with a minimum-maximum thermometer. Check on your tortoise at least once a week, offer a brief warm bath every three to four weeks, and keep a log of its weight throughout hibernation.
Cool Room or Garden Hibernation
Some owners use a cool, frost-free shed, garage, or outbuilding. The temperature must remain between three and seven degrees Celsius at all times. A garden cold frame or insulated box buried in the ground are traditional methods, but both carry a higher risk of temperature fluctuation. Install a thermometer alarm that alerts you if temperatures fall below three degrees or rise above ten degrees. Never allow the hibernation environment to freeze.
Common Risks During Hibernation
Too warm an environment is one of the most common dangers. If temperatures rise above ten degrees Celsius, the tortoise will wake and begin burning through its fat reserves without being able to feed, leading to starvation. Too cold, and ice crystals can form in the tortoise's tissues, causing fatal damage. Freezing temperatures must be avoided at all costs.
Hibernating for too long is another serious risk. Most tortoises should hibernate for no longer than sixteen weeks, and many owners aim for ten to twelve weeks. Weigh your tortoise at the start of hibernation and check weight weekly. A weight loss of more than ten percent of the starting body weight is a warning sign — wake the tortoise immediately and seek veterinary advice.
Waking Your Tortoise Safely
When the hibernation period ends, bring your tortoise to a warm room gradually. Do not place it directly under a basking lamp. Allow it to warm up slowly over several hours. Once it is showing signs of alertness — moving its head and limbs — offer a warm bath. Bathing for fifteen minutes once or twice daily in the first week helps rehydrate the tortoise and stimulates the kidneys to begin functioning again.
Do not offer food until the tortoise is actively moving around and showing interest in its surroundings. Most tortoises will not eat for the first few days after waking. Once feeding has resumed and the tortoise is alert and active, monitor it closely for any signs of post-hibernation anorexia, which is a failure to resume eating within two weeks of waking and requires veterinary attention.
Record-Keeping and When Not to Hibernate
Keep a detailed hibernation log for each tortoise, recording the start date, weight at the start, weekly weights during hibernation, temperature readings, and the wake date. This record is invaluable for spotting problems early and provides your vet with useful information if health issues arise after hibernation.
Do not hibernate a tortoise that is underweight according to the Jackson ratio, that has been unwell in the months prior to hibernation, that has intestinal parasites, that has had surgery recently, or that is a juvenile under three years old. When in doubt, it is always safer to overwinter your tortoise indoors under controlled heating and lighting than to risk a dangerous hibernation.