We are at the beginning of the traditional hibernation period for tortoises.

It is an enormously complex subject and much depends on the particular species, the geographical variation of species, health and age, and the experience of the keeper.

In the wild, certain species may hibernate in parts of their range but may remain active throughout winter in other parts. These tortoises are considered to have the biological capacity to hibernate. This applies to most North African tortoises, for example, the Greek Spur Thigh (Testudo graeca graeca). In Morocco, those that inhabit the north of the country and live at high altitude will hibernate. Those from the south of Morocco or the warmer coastal areas may remain active throughout the winter.

Anecdotal evidence, however, suggests that it is better to hibernate tortoises and that there is an increased incidence of liver disease and a decrease in fertility in long-term, over-wintered tortoises.

Which species can be hibernated?

Certain species should not be hibernated, so don’t be afraid to check the species with the owner.

The four commonly seen species that may be hibernated are the Spur Thighs (Testudo graeca, Testudo ibera and Testudo whitei), the Hermann’s (Testudo hermanii), the Marginated (Testudo marginata) and the Horsfield’s (Testudo horsfieldii).

Other tortoises that may be regularly seen and that should not be hibernated include the Leopard tortoise (Geochelone pardalis), the African Spurred tortoise or Sulcata (Geochelone sulcata), the Redfoot (Geochelone carbonaria) and the Yellowfoot (Geochelone denticulate).

What stimulates a tortoise to hibernate?

Decreasing temperatures – especially once they get below 15°C (59°F) – together with decreasing day lengths, are the stimulus for tortoises to hibernate.

What checks should be performed prior to hibernation?

It is a good idea for all tortoises to be checked by a vet prior to hibernation. They should be weighed with gram scales and the straight carapace length (SCL) measured in centimetres.

A lot of books quote the Jackson’s ratio, which is the graph of length (cm) versus weight. This is no longer accepted to be as accurate as previously thought. The original data were taken from a small population of recently imported tortoises, which is extremely different to today’s captive populations. Female tortoises may be carrying large numbers of eggs and ova, which may give the impression that the tortoise is a good weight. These structures may frequently add up to 20 per cent of the entire body weight of an individual. Bladder calculi are also frequently seen and can weigh a substantial amount (Figure 1).

Figure 1: Large bladder stone that was successfully removed prior to hibernation

A general physical examination should be performed; with particular attention being paid to the mouth and ears, looking for stomatitis and aural abscesses (Figure 2). Any wounds, infections, shell damage and the like should be noted and may affect the decision to hibernate an individual (Figure 3). Any tortoise that has not fully recovered from surgery should not be considered for hibernation.

Figure 2: Swollen tympanic membrane with underlying aural abscess

Figure 3: Leg abscess that had been present for about 10 years

I like to perform a faecal examination looking for flagellated organisms and worm eggs. It is useful to take radiographs, especially of female tortoises, as it is interesting to know whether they are carrying eggs (Figure 4). If there is any doubt about the physical status of a tortoise, it would be prudent to err on the side of caution and not subject it to hibernation.

Figure 4: Clutch of eggs including damaged eggs

Is it safe to hibernate?

There appear to be genuine health and fertility benefits to hibernation. That said, the majority of tortoises in the UK are kept in conditions that are far from ideal and are certainly very different to the conditions they would experience in the wild. Typically these would include hibernations that have been too long, unsuitable temperatures and diets, and the inadequate provision of UV light.

This leads to a population of tortoises that are hanging on to life and are metabolically and immunologically challenged. In my opinion, these are some of the reasons why tortoises may die during hibernation or awaken with the so-called ‘post-hibernation anorexia’.

Is it safe to hibernate young tortoises?

The answer has to be “Yes” if they have been well fed and cared for. Hibernation in the wild will be dictated by the prevailing climatic conditions. No doubt some of the wild ones may die if conditions are severe. There is good evidence to show that those that are hibernated from a young age have a smoother growth rate, which tends to equate to those in the wild.

How should tortoises be prepared for hibernation?

The stomach should be devoid of food because anything that remains in the stomach may ferment and lead to bacterial problems. This will involve a three- to four-week fast under controlled conditions. Smaller tortoises should probably only be fasted for about two weeks. During the starvation period, the temperatures should be gradually reduced. If not, individuals may lose up to five per cent of their body weight per week, which would have seriously implications for hibernation.

The aim should be to drop the temperature by 5°C per week, which means that the core body temperature would drop from about 26°C to about 13°C, at which point they can be transferred to the hibernation area. During this period, they should be bathed twice daily for 10 to 15 minutes to promote hydration.

Where should hibernation take place?

My advice these days is to use a refrigerator because the temperature can be accurately controlled and tortoises are kept safe from predators. Many clients will argue that they have successfully hibernated their tortoises outdoors – in the loft, shed or garage – for many years. This may be true, but sooner or later their pets will fall foul to a predator or, after many years of substandard conditions, they may finally expire.

The so-called ‘post-hibernation death. Remember that tortoises take many years to die from poor husbandry.

A small ‘bar’ fridge can be used and the ide
al temperature to aim for is 4°C – 5°C. A minimum/maximum digital thermometer is useful and the fridge should be opened daily for air changes to occur. If temperatures get below 0°C it may lead to blindness and damage to the extremities of limbs. If temperatures rise much above 10°C, weight loss, dehydration and the build up of toxins, such as uric acid and potassium, may occur. Energy stores may also become depleted.

Tortoises that hibernate in the garden or compost heap many eventually fall victim to predators, such as dogs, foxes or badgers. Lofts, garages and sheds may experience frost and temperatures that drop dangerously low, on the other hand, we frequently have very warm days in the middle of winter which means that they may wake up or at least their metabolism will increase dramatically.

You will have fun arguing with the older keeper who is reluctant to change these established habits!

How long should hibernation last?

If left to their own devices, most tortoises will hibernate from approximately late October until March/April, depending on the weather conditions. A five- to six- month hibernation – together with a month’s fast – is way too long. Tortoises will manage this type of prolonged hibernation for a number of years, but eventually it will take its toll.

These days, a much shorter hibernation is recommended – typically six to eight weeks. This may shock many clients. It is pretty well accepted that many of the medical problems we see may have some of their roots in prolonged hibernations with the subsequent catabolic effects on the body.

When should one intervene in hibernation?

Contrary to what a lot of people believe, it is safe to check on tortoises during hibernation. In the event that a tortoise urinates, it should be woken from hibernation, as the bladder is regarded more as a store of water rather than of urine. No tortoise should lose more than eight to 10 per cent of its body weight during hibernation. A good rule of thumb is to make sure weight loss does not exceed one per cent of body weight per month.

So, what happens after hibernation?

Clearly a shorter hibernation will mean waking tortoises up in mid-winter. They should be placed under a UV light and a heat lamp. A temperature of 22°C- 25°C should be aimed for. The Powersun UV heat lamp is a combination bulb and is very useful (Figure 5). If adequate temperatures are not provided, bacterial infection may occur owing to the suppressed immune system that has not had a chance to fully recover. Any tortoise showing signs of disease should be given a full veterinary examination as soon as possible.

Figure 5: Powersun UV heat lamp provides UV light, as well as heat

Those that appear to have come through hibernation without any obvious problems should be bathed twice daily in lukewarm water. This will encourage drinking, defaecation and urination, as well as the absorption of some fluid via the cloaca. It may be useful to stomach tube tortoises at 0.5 per cent of bodyweight, twice daily, with water.

Food is avoided at this stage to prevent the so-called ‘re-feeding syndrome, which may prove fatal.

Initially it may be useful to offer food that is highly palatable and visually attractive, such as cucumber, melon and strawberries. As soon as eating has commenced, every effort should be made to re-introduce the regular diet which ideally should consist mainly of weeds, such as dandelions, clover, vetch, trefoil and bindweed.

Any tortoise that has not urinated or eaten within a week of awakening should be given a full veterinary examination.

Author

William Lewis

BVSc CertZooMed MRCVS

William graduated from Pretoria University in South Africa in 1988 and obtained his RCVS CertZooMed in 2003. He has worked in a number of small animal and exotic referral practices across the UK, and lectures widely in this country and continental Europe.

• VOL 25 • No 1 • January 2010 • Veterinary Nursing Journal