The Exotic Animal and Wildlife service offers

A. Meredith, MA, VetMB, CertLAS, DZooMed MRCVS
K. Eatwell, BVSc (Hons), DZooMed MRCVS
E. Keeble, BVSc, DZooMed, MRCVS
G. Goodman DVM, MSc, MRCVS
B. Reusch BVetMed (Hons), CertZooMed, MRCVS
S. Hollamby BA, BVSc (Hons II), MS
L. Longley MA BVM&S DZooMed MRCVS
L. Benato DVM, GPCert (ExAP), MRCVS
The Royal (Dick) School of Veterinary Studies
Department of Veterinary Clinical Studies
Hospital for Small Animals
Easter Bush Veterinary Centre
EH25 9RG
Tel: 0131-650 7650 Fax: 0131-650 7652
Tortoise Hibernation
Hibernation is only suitable for those species which would naturally be exposed to adverse weather. Suitable
species include most Mediterranean Tortoises, Horsfield’s and the Desert Tortoise. Do not hibernate
Leopards, African spurred (Sulcata), Southern Turkish spur thighs, Egyptians, Lybians, Tunisians & other
North African variants, Red-foots, Yellow foots and most turtles. Any individuals hibernated should be
healthy and of a sufficient size.
During August and September, as the days grow shorter, the light intensity decreases, the temperature begins
to fall and tortoises prepare for hibernation. Feeding declines: it takes 4-6 weeks for their gut to empty for
winter and before they start this process, in early September, the tortoises need a check over. Make sure there
are no signs of wounds, abscesses, infections internally or externally, also that the mouth is clean and pink,
the eyes alert and bright. If you have any concerns then a health examination by a tortoise vet should be
Historically the Jackson ratio has been used to assess suitability for hibernation in wild caught Herman’s
Tortoises. This ratio defines the minimum weight based on the horizontal carapace length of the tortoise (its
Jackson ratio = wt of tortoise (g) divided by length of tortoise3 (cm)
For an adult Testudo spp., that has been wild caught, the average value should be 0.20-0.22. This has not been
proven to be useful for other species. Values higher than this can suggest the animal has excessive body fat,
excessive fluid, follicles or eggs. Values lower than this can suggest the animal is underweight. The difficulty
is ascertaining that a tortoise at the correct weight is not a thin tortoise with eggs on board! Thus the Jackson
ratio is only a rough guide and a complete health check is required alongside this. Comparing the weight of
the tortoise to previous records is vital.
The Jackson ratio is provided on a graph at the end of this handout.
Any tortoise which is underweight or suffering from an ailment should not be hibernated, but overwintered
in a vivarium. This should have a heat source and full spectrum light (including UV-a and UV-b outputs) for
13-14 hours to prevent hibernation. A basking area is created using a spot bulb, providing a basking
temperature of 400C. This should be kept on all day. The cool end should be maintained at 250C.
Background heat is important with this set up and a stable room temperature is required. Heat can be
provided with a heat mat (on the back wall) a tubular heater, a heat plate or a ceramic bulb. This should be
set on a thermostat so that the overnight temperature does not drop below 250C. The temperatures should
be measured with a maximum/minimum thermometer. During the cold winter months careful checking is
required to ensure the heat sources are keeping the tank sufficiently warm. Heat sources should be guarded
or kept at a height to prevent thermal burns. A simple vivarium can be provided with the light source on one
end and a shelter on the other. Never allow the temperature to go below 15°C (60°F).
Hibernation set-up
 Use a large, wooden, rodent-proof tea-chest or box, with small airholes in the sides. Both the top
and the holes should be covered in wire mesh to prevent vermin entering.
 Line the base and the sides of the box with thick pads of polystyrene or newspaper. Place the
tortoise in an inner box with air-holes and filled for one to three-quarters with polystyrene chips, dry
leaves or shredded newspaper. Avoid hay or straw. Place the smaller box inside the larger one,
making sure you can open it easily for check-ups.
 The tortoise can be carefully weighed individually or complete with inner box on a weekly or twice
monthly basis.
 Weigh the tortoise monthly. An adult tortoise loses about 1% of its pre-hibenation weight per
month, so a l000g tortoise is allowed to lose l0g monthly. A drastic weight loss (>8-10% loss)
indicates something is wrong: the animal should be brought out of hibernation immediately, checked
and disease investigated.
 Make sure the tortoise is hibernated in a frost-free environment, at temperatures of 2-9°C. Tortoises
kept below freezing point can lose their eyesight or at worst their lives. Use a maximum and
minimum thermometer (obtainable from garden shops) to check temperature changes.
 For every drop of 10°C the heart rate drops 50%. At 4°C the respiratory movements are negligible.
If the tortoise is kept too warm and becomes too active it will use up its fat and of glycogen or
animal starch stored in the liver, the latter is needed on emergence from hibernation.
 Persistent temperatures below 15°C and decreasing day length and light quality are inducing factors
for hibernation.
High Tech Hibernation
In order to keep the hibernation temperature more stable many owners have resorted to using a dedicated
fridge. This is good in principle as a hibernation temperature of 2 - 40C is achieved. However the
temperature is variable depending on the position in the fridge (higher is slightly warmer). The inclusion of a
thermal probe or max/min thermometer is required to ensure the correct temperature is achieved. Fridges
will also tend to dry out the air inside them and the humidity will be too low. The ventilation is also poor.
The solution to the short comings is to open the door daily (just for 30 seconds) to allow for ventilation and
assessment. Placing a bowl of water in the bottom of the fridge and keeping it topped up will allow for the
humidity to be maintained. A chiller cabinet does have some advantages over a fridge as direct visualisation is
possible through the glass door. Many are fan assisted and this improves ventilation. There is no need to
insulate tortoises hibernated in this way, although many people prefer to provide some substrate to allow the
tortoise to bury itself.
Hibernation plan
 Tortoises will appreciate climate change over the year and as the days reduce in length and the
temperature drops (overnight and during the day) the tortoise will start to prepare for hibernation.
 1st week in October allow the tortoise to spend increasing time outside (in out house/ cold frame
ect), as this will allow exposure to a shorter day length and decrease in environmental temperature.
Aim for a decrease of 50C core body temperature per week. Still bring the tortoise in overnight but
do not provide a basking site.
 For tortoises maintained inside, the temperatures and lighting provided should mimic the natural
levels to encourage hibernation. Typically the basking site is left on (but only for nine hours) for the
first week and then turned off for the next three weeks. Any thermostatically controlled heat sources
should have the temperature reduced slowly.
 Stop feeding and bathe for 20 minutes a day to encourage good hydration, defeacation and urination.
Make sure the temperature of the bath is the same as the core body temperature.
 Once body temperature is around 130C, the tortoise can be moved to a refrigerator or hibernation
box and maintained between 2-90C. This is usually around early November. Above 100C they will
loose weight and may die of starvation. Below 20C they get blindness and frostbite.
 Hibernation periods can run until as late as April given our weather conditions but this longer than
tortoises would naturally be exposed to. Horsfield tortoises probably hibernate for longer than some
species for four months.
 The decision to wake the tortoise up may be as soon as six weeks (for juveniles just learning the
process) or up to four months after going into hibernation.
 For adult tortoises wake up from hibernation in February.
Emergence from hibernation
 Start checking your tortoise from the end of January onwards. When the animal starts moving take it
out of its hibernation quarters or remove it at the allocated time based on species, size and any
veterinary recommendations.
 Bring it out of hibernation slowly, check for discharges from the nose, eyes and tail end. Inspect it
carefully, bath the face and eyes and wash the mouth.
 Leave the tortoise at room temperature for the first few hours.
 Then the tortoise can be given a warm bath for at least half an hour. This can be repeated twice
daily. It is important that the tortoise empties its bladder to get rid of the toxic waste accumulated
during hibernation and that it replenishes its water supply by drinking. Monitor urination and
defeacation. If this does not occur then a visit to the vet is required so the tortoise can be rehydrated
and further investigations performed as required.
 Keep the animal warm (in vivarium or heated enclosure), until the days get sufficiently warm for the
tortoise to go outside. Keep the tortoise indoors overnight until the nights get warmer.
 Feed succulent foods (cucumber initially then back to 80% fibrous grass/weeds, 15 % veg and 5%
 Once out of hibernation and eating, keep it active (as for overwintering) if the weather becomes cold
again. Warm spells in February breaking hibernation are a hazard of the British climate
 Any tortoise that is not feeding or has not urinated with in seven days of emergence from
hibernation, or if it appears ill, should be taken to a veterinary surgeon with an interest in tortoises
without delay.
Avoiding hibernation
Hibernation does pose some risk and there is a natural mortality associated with it in the wild. In captivity
where we can control hibernation this risk is reduced. Hibernation is a reaction to adverse weather in the
wild, but it is natural and is part of a tortoise’s life. It also helps to reduce rapid (and potentially abnormal)
growth. It may also increase the longevity of your tortoise although you personally will never reap the
benefits of this! There are times when hibernation should be avoided. This may be due to your tortoise being
too small to hibernate, due to poor husbandry identified at a health check or due to ill health. Whatever the
reason it is important to know how to prevent the tortoise entering hibernation if it is considered to be to
high a risk.
The Exotic Animal and Wildlife service offers
 We offer pre-hibernation sessions
 All our vets are very experienced and have extra qualifications in reptile medicine and surgery and
can offer your pet a high quality standard of veterinary care
 All reptiles are hospitalised in appropriate accommodation
 First opinion consultations
 For the more unusual and complex cases you can be referred to us
 For emergencies, 24 hours a day, 7 days a week, 365 days a year, please ring our veterinary hospital
on 0131-6507650
 our website providing up to date information on our services.
 the latest information on UV light sources.
 a good source for information sheets, husbandry advice and a vet
list detailing local vets who treat tortoises.
 a good source for husbandry sheets.
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