SAFER HIBERNATION & YOUR TORTOISE
New Updated Edition
Andy C. Highfield & Nadine Highfield
In order to survive hibernation in good condition, tortoises need to
have built up sufficient reserves of body fat; this in turn stores energy
and water. Without fat and water tortoises die of starvation or
dehydration. Adequate reserves of body fat are vital to tortoises in
hibernation; they live off these reserves whilst asleep, and if the
reserves run out too soon then the animal's body will begin to use up
the fat contained within the muscles and internal organs, eventually
these too will become exhausted. Should this occur the tortoise will
simply die in hibernation.
Very long hibernations are inherently dangerous. The smaller the tortoise,
the more dangerous they are, as such animals have far fewer reserves than
larger ones. In the past, many keepers used to give hibernation periods of up
to four or even five months. This is one reason why so many tortoises used to
die during hibernation. They simply ran out of energy reserves, or suffered
dehydration. The other main cause of death in hibernation is freezing. Both of
these hazards can be avoided if care is taken. This brief guide explains the
steps you should take. Today, educated keepers intervene much more in
the hibernation process and monitor everything closely. This is why a properly
managed hibernation today is far safer than it used to be using the old
methods. There is a simple method of checking to see if your tortoise is of
adequate weight for hibernation.
This is known as the Jackson Ratio graph. This graph must ONLY be used
with the Hermann’s tortoise (Testudo hermanni) and Mediterranean Spurthighed tortoises (Testudo graeca and Testudo ibera). It must not under any
circumstances be used with Horsfield’s or Russian tortoises (Testudo
horsfieldii) or Marginated tortoises (Testudo marginata) as it will produce an
entirely misleading result with them. If you are not sure what species you
have, please consult a specialist vet or ask an expert from a tortoise
organisation. It is extremely important to realise that whether or not a
tortoise can safely hibernate depends on what species it is, and its
geographical origin. This is why an accurate identification is so critical. Pet
shops often sell tortoises that cannot be hibernated; common examples
include Leopard tortoises (Geochelone pardalis), African Spurred tortoises
(Geochelone sulcata), and Hingeback tortoises (Kinixys sp.). If you have such
a tortoise, you will need to provide heated facilities throughout the year,
especially over winter. Please visit our website and advice forum for further
information on the special needs of tropical tortoises. There is only one way
to take meaningful measurements for the purpose of computing the Jackson
Ratio, and that is in a straight line. Any measurements taken ‘over the curve’
of the carapace will invariably produce a false result which will indicate that
the tortoise's weight/length ratio is lower than it actually should be.
This is the WRONG way to measure the length:
This is the RIGHT way to do it:
It is essential that measurements (and weights) are taken accurately,
otherwise the result of the exercise will be meaningless, and may well
endanger the tortoise.
If the tortoise has a full bladder, you may not get an
accurate weight reading. If you get an unexpected result, weigh it again a few
days later.
If you have a female tortoise which is not eating, but still seems very heavy,
she may be carrying eggs. A tortoise which appears considerably overweight
should be checked by a vet, and in the case of a female, this check should
include an x-ray. On no account ever hibernate an underweight
tortoise, or any tortoise which is ill or has recently been ill. Such animals
are unlikely to survive. If in doubt, do not hibernate but keep awake and
feeding over winter using artificial light and heat. We also do not recommend
hibernating recently acquired tortoises. It is important that you are completely
sure that the tortoise is 100% fit and healthy with no underlying problems.
Pre-Hibernation Health Check
It is wise to check your tortoise carefully, several times, in the run-up to
hibernation. A few simple checks are recommended:
CHECK BOTH EYES: for signs of swelling, inflammation or discharge. If there
is a problem, consult a veterinary surgeon with extensive experience of
treating reptile patients.
CHECK THE NOSE: For signs of discharge; a persistently runny nose
requires urgent veterinary investigation. Tortoises with this symptom must
also be isolated from contact with others, as some varieties of RNS (’Runny
Nose Syndrome’) are highly contagious. The presence of excess mucus also
encourages bacterial growth, and hence places the tortoise in additional
danger from diseases such as necrotic stomatitis (’mouth rot’).
CHECK THE TAIL: For inflammation or internal infection; tortoises with
cloacitis ‘leak’ from the tail and smell strongly. Any signs of abnormality
should be investigated by a veterinary surgeon. It will help if you take a fresh
sample of cloacal excretion for a veterinarian to examine under the
microscope.
CHECK THE SHELL: Look for any signs of fluid under the shell, or any soft or
bad-smelling areas that could indicate ‘shell rot’ or necrotic dermatitis.
CHECK THE LEGS: Look for any unusual lumps or swellings; abscesses are
common in reptiles and if left untreated can result in loss of limb or even
death. Report any unusual findings to a competent veterinary surgeon for
further investigation.
CHECK EARS: The membranes covering the inner ear should be either flat
or slightly concave; ear abscesses are very common and can have fatal
consequences if treatment is not obtained. The ear scales, the tympanic
membranes, are the two large 'scales' just behind the jaw-bone.
CHECK INSIDE THE MOUTH: Look for any sign of abnormality; necrotic
stomatitis or ‘mouth-rot’ is a highly contagious disease of captive reptiles. It is
characterised by the appearance of a yellow ‘cheesy’ substance in the mouth,
or by a deep red-purple tinge, or by the appearance of small blood-spots.
Sometimes all three symptoms are present. Expert veterinary treatment is
called for as a matter of urgency if the animal is to be saved.
These basic checks form your essential pre-hibernation examination.
Provided your tortoise is up to weight and no other abnormalities can be
detected, then you may begin preparation for hibernation. The golden rule,
however, at all times is if in doubt seek expert advice. Not all vets are tortoise
experts. Most tortoise organisations, however, do keep lists of vets with
special experience in this area.
Pre-Hibernation Fasting Period
The key factors that initiate hibernation behaviour begin in late summer or
early autumn. These environmental triggers include:
Reduced ambient temperatures.
The days become cooler with lower peak temperatures.
Shorter day lengths.
Reduced daylight intensity due to the lower position of the sun in the
sky.
As these conditions take effect, the tortoise will become less active, and less
interested in feeding. We call this the ‘hibernation induction period’. If the
weather is very poor in mid to late summer, then the tortoise may stop feeding
too soon - if this looks like it is happening, you need to provide extra light and
warmth to encourage continued feeding for a while longer. The further north
you are situated, the more often this problem occurs.
We suggest using indoor ‘basking pens’, or outdoor greenhouse-type
accommodation where this is a problem. The main thing is to detect the
problem early - it's too late to do anything about it after September. By then,
the ‘winding down’ process will be well advanced. If a tortoise is underweight
at this stage you will not be able to hibernate it safely, but must overwinter it in
warm, light conditions indoors where it can continue to feed without being
hibernated at all. This ‘fasting’ period may last for 3-4 weeks quite safely.
We would recommend keeping the tortoise above 55º F (13º C) for at least 2
weeks after the last meal to allow time for food in the digestive tract to be
processed properly; the most dangerous thing to do is to put a tortoise into
hibernation (i.e. below 50º F (10º C) immediately after keeping it somewhere
warm where it feeds normally. If this occurs, the digestive tract will contain
large quantities of semi-digested food and the tortoise is in grave danger. In
essence, the food can ‘rot’ internally producing dangerous gasses and
toxins.
Important points:
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. All of these periods are temperature dependent. At low
temperatures, the digestive tract slows down and it will take longer to digest
the food in the stomach. At higher temperatures, the process is faster. That is
why we recommend the temperature above, because it is low enough to
suppress feeding, but high enough to permit continued digestion.
Keeping the tortoise outside (if temperatures are safe) for the first half of the
induction period, and then in an unheated room (again, provided temperatures
are suitable) for the last half of the ‘winding down’ period is usually very
effective. It will become less and less active, and more and more ‘sleepy’.
Eventually, it will not emerge from its sleeping quarters very often at all. This
is when we consider it ready for hibernation. Note that while tortoises should
not be offered food during this period, they should be offered water by soaking
(as described later) at least 3 or 4 times per week.
Drinking is essential not only to ensure adequate hydration in hibernation, but
also to ‘flush’ urates from the bladder.
PREVENTING FROST DAMAGE IN HIBERNATION
Over the last few very severe winters in the UK, very many tortoises that were
hibernated in sheds, lofts, outbuildings or even unheated rooms in the house
have either frozen to death or emerged after hibernation frost-blinded. If you
have a tortoise in a box that has been placed in a shed, for example, to
hibernate and temperatures drop to -26 C as they have done in some
parts of the UK, that tortoise has very little chance of survival.
It is absolutely critical that a tortoise is never exposed to freezing
temperatures, even for a short time.
Hibernating tortoises in ‘warm’ rooms is
not the answer, as high temperatures also cause problems. Once the
temperature rises to around 10 C, the tortoise will begin to use up fat and
energy at a vastly increased rate and may be left with insufficient reserves to
survive hibernation.
The solution is to hibernate at a temperature low enough to conserve energy,
but not so low as to risk freezing. For Mediterranean tortoises, the hibernation
temperature needs to be maintained as close as possible to 5 C at all times,
day and night.
There are three main methods of hibernation. Each has advantages and
disadvantages.
Hibernation underground
This method can work, but is highly dependent upon the locality, and
especially upon the soil texture and consistency. It works best in sandy, welldrained soils. Dense clay soils are not well suited. Major drawbacks are that it
is impossible to inspect the tortoise regularly, it may be vulnerable to rodent
attack, and if the soil is too wet or damp it could die. On the positive side,
buried tortoises rarely freeze. Best results with this method tend to be
obtained when the tortoise buries down inside a dry greenhouse. This is a
method so dependent upon location and soil texture, however, that it cannot
generally be recommended for most keepers.
Hibernation in a box
This is the traditional method. Unfortunately, it is also associated with high
levels of frost damage unless monitored extremely carefully. Tortoises that
are hibernated in sheds, attics, unheated rooms and outbuildings can be
subject to wide fluctuations in temperature. These temperatures can easily
rise above 10C for extended periods, or drop to (or below) the lethal freezing
point.
Refrigerator hibernation
Many keepers now use temperature-controlled hibernation environments
based upon refrigerators (not freezers). Full details of how to do this are
available on the Tortoise Trust website. If set up and monitored correctly, it
has proven to be very safe and effective. If considering this method, it is
essential that you follow the instructions carefully, and take expert advice. It is
our view that this is presently the safest of all methods currently available.
Never place the chiller or refrigerator in an unheated room or outbuilding
where temperatures could fall below freezing. The temperature inside the unit
will fall as well, and will not protect the animals within it from freezing.
Dangerously low temperatures may be found on inside surfaces above
refrigerant pipes or cooling surfaces towards the rear of the unit. Containers of
animals should always be placed on the centre of shelves, well away from
anything containing refrigerant. It is a very good idea to put a spacer made out
of insulation material, such as thick polystyrene, between the tortoise
container and the cooling surfaces of the refrigerator to prevent accidental
contact.
Most people who use this method place the tortoise in a plastic container filled
with a natural type substrate of light soil and sand (a sealed container must
not be used). The tortoise will naturally burrow into this substrate. It provides
additional mass to help stabilise temperatures, and also helps to prevent
dehydration. The top of the container needs to allow for air circulation, but at
the same time, should prevent the tortoise escaping. If the tortoise did get out
of the box in the refrigerator, it may fall and injure itself, or get too close to a
dangerously cold area containing refrigerant. Controlled hibernation in a chiller-type refrigerator has proven consistently
safe and effective. Do not rely upon old and unreliable units, however. Double
check the accuracy of the thermostat before using an accurate electronic
thermometer. Ideally, use two separate thermometers with remote probes.
One should rest on the substrate next to the tortoise, the other should hang in
free air within the unit. Check temperatures regularly. It is normal for the
sensor in free air to show more fluctuation than the probe that is positioned
next to the tortoise.
Be aware that the possibility of a power supply failure needs to be taken into
account if using such systems. Avoid refrigerators that include a freezer
section, as in the event of a thermostat failure these can easily attain fatal
sub-zero temperatures. The ‘drinks chiller’ type is preferable.
Temperature stability within the unit will be improved by packing empty space
with full water bottles to increase thermal inertia. The door should be briefly
opened every couple of days to flush carbon dioxide and maintain oxygen
levels. A small aquarium air pump tube can also be inserted through a break
in the door seal to achieve the same objective. Check the air pump regularly
to see that it is operating properly and that the air tube is in place. You can
best ensure that adequate oxygen levels are maintained within the refrigerator
by using both of these methods. If you do hibernate in an uncontrolled
environment, however, your only defence against freezing or excessively high
temperatures (resulting in too much energy loss) is to monitor the
temperatures constantly, and be prepared to move the tortoise to a safe place
immediately if temperatures stray outside the safe, permissible band.
For practical purposes, we recommend taking action without delay if
temperatures approach 2.5 C or if temperatures rise above 10 C for
extended periods
There is very little room for error at the lower end. If the tortoise’s body is
exposed to 0 C even momentarily it will suffer frost damage and death in a
very short time indeed. If temperatures threaten to fall to freezing point - move
it immediately to a safe place. Short periods above 10 C will not do
immediate harm, but extended periods above 10 C will rapidly deplete the
tortoise’s energy (glycogen) reserves and put it in danger. It is quite safe to
check a tortoise in hibernation for excessive weight loss, or for signs of
dehydration.
Most keepers agree that if much more than 1% of total weight is lost over a
month, hibernation should be terminated. Any tortoise that has urinated in
hibernation should also immediately be awakened, rehydrated, and
overwintered in warm and bright conditions for the rest of the usual
hibernation period. These animals are at extreme risk of fatal dehydration.
Be especially alert for sudden and severe over-night temperature drops
in December, January and February. The best way to check temperatures
is by using two, totally independent thermometers positioned outside of the
hibernation box. The reason we recommend two, not one, is that some
thermometers are not very accurate, and to guard against failure. The best
low cost thermometers we have found are the small electronic type. These
can be readily obtained from many gadget, gardening and DIY stores. They
run on a small battery that lasts for months. Some have a separate probe for
easy positioning and others also feature built-in audible high and low
temperature alarms.
There are now also remote sensing’ thermometers that work by placing a
sensor with transmitter in one location, and the readout (with receiver) in
another - in the house, for example. These can work well, but it is vital to
check them regularly. If the battery in the transmitter fails, or the signal is
weak, they may fail to alert you to dangerous temperatures. We feel that while
they are a useful addition to a standard thermometer, their risk of failure is too
high to recommend them completely. It can also be helpful to monitor the
temperatures inside the hibernating box, right next to the tortoise. For this,
you need a thermometer with a remote probe. However, this should not be the
main thermometer you rely on to judge hibernation safety. By the time this
thermometer responds to a dangerously low temperature, it could already be
too late! Use external thermometers, outside of the box, to maintain a safe
environment.
Never - ever - try to hibernate any tortoise without constantly monitoring
temperatures using reliable thermometers. Remember, years ago few
tortoises survived hibernation in captivity, these days losses are rare if the
correct methods are used. This is entirely due to keepers adopting the
methods described here. Juveniles, with their low body mass, are extremely
vulnerable to rapid changes in temperature. One method of improving the
temperature stability of juveniles is to allow them to bury into a dense, high
mass of substrate just as they would in nature, but within a tray or container
that can be placed in a temperature controlled environment. This will also
assist with limiting fluid loss via the skin and respiration.
The hibernation box
We recommend ‘double boxing’ tortoises. This means using first an outer,
larger box, then a smaller inner box positioned right in the middle with the
intervening space filled with insulation material. Suitable material is shredded
paper or polystyrene packaging chips. Hay or straw is not recommended as it
often contains mould spores. Tortoises do move in hibernation (they will often
try to ‘dig down’ as temperatures drop), and this prevents them digging too
close to the outer side of the box where they lose the benefit of any
insulation.
Insulation only slows down the time it takes for severe cold to reach a
tortoise. It does not stop it completely. So, no matter how well insulated
your tortoise is, if your shed, attic or outbuilding is subjected to freezing
conditions, your tortoise is in real danger. Move it.
Do not make the fatal mistake of believing that because it is well insulated it is
safe. It is not. Only by keeping ambient temperatures within a safe range can
injury or death be prevented. This is why using thermometers and checking
them frequently is so absolutely critical.
Tortoises can be safely moved in hibernation. There is no truth to the belief
that this is dangerous or harms them in any way. If temperatures threaten to
go outside safe limits, the correct thing to do is to get them to a place where
temperatures are suitable without delay.
Be aware that rodents, and possibly other predators, will attack dormant
tortoises. It is essential that all areas where tortoises are kept are rodentproof, and preferably, that any box containing animals is placed within a
strong welded-wire cage. Animals placed in outbuildings or attics are at
extreme risk. Severe injuries to the tail and limbs are commonplace if rats or
mice gain access. Such attacks often prove fatal.
All methods of hibernation require careful consideration by the keeper, and
regular monitoring. You cannot simply put a tortoise away for the winter and
forget about it. If you do that, it is very unlikely to survive. Hibernation today
is much safer than it was, because keepers take it more seriously and
check things on a continuous basis. Years ago, few tortoises survived
even their first hibernation. Today, if correct procedures are followed, fatalities
are rare.
Hibernation period
We recommend a minimum of 8-10 weeks for small tortoises, and no more
than 16 weeks even for very large animals. This will require some intervention
on your part and you will need to provide some artificial light and heat in early
Spring.
Post-Hibernation Care
Tortoises only enter or remain in a biological state of hibernation (which is
characterised by a depressed metabolic rate) while temperatures are within a
certain range. The optimum range for the hibernation of terrestrial tortoises is
in the range 4-6 degrees Celsius. As temperatures rise towards 10 degrees
Celsius, the animal’s metabolic rate begins to return to normal, energy use
increases, and the biological state of hibernation comes to an end. As the
average mean ambient temperature begins to approach the critical 10
degrees C or 50 degrees F point, a tortoise’s metabolism will begin to
reactivate in readiness for waking.
Certain complex chemical and biological processes are initiated as the animal
prepares to emerge into the spring sunshine. At this point, unfortunately, it
often runs into its first problem. In Northern Europe, spring can be cold, wet,
and miserable. For us, this sort of weather may be merely unpleasant. For
tortoises it can present rather more serious problems. Upon first emerging
from hibernation a tortoise is depleted in strength, has a low White Blood Cell
(WBC) count, and is very vulnerable to infection. Glycogen (energy) reserves
will also be very low at this time.
Unless it receives adequate quantities of heat and light it will simply ‘not get
going properly’, and instead of starting to regain weight and strength lost
during hibernation, will refuse to eat, will use up its existing fat and energy
reserves, and will begin to decline quickly.
Do not make the fatal mistake of
believing that ‘he does not want to come out of hibernation yet, it must be too
early’ and put the animal back into hibernation. You will not be putting the
animal into hibernation - in all probability you would be killing it. Hundreds of
people do make this very mistake each year, and hundreds of tortoises die as
a consequence. If the tortoise wakes up, and temperatures are approaching
or above 10 C or 50 degrees F keep it awake. Do not return it to hibernation.
Also, if you detect that the tortoise has urinated in the hibernating box, get it
up and keep it awake too .
As the temperature rises listen carefully to the
hibernating box - you should begin to hear the first sounds of movement. Act
quickly to get the tortoise up.
Remove the hibernating box from its winter quarters and warm it up by placing
it in a moderately warm room. After an hour or so remove the tortoise from its
box and place it in a warm (+25 C), bright environment. A 150 Watt reflector
lamp suspended about 40cm (15’) above the tortoise will make a huge
difference. Do not expect a tortoise to begin feeding without this sort of
artificial assistance in the UK. British spring weather is totally different from
that in the Mediterranean. Tortoises must have extra light and heat at this
sensitive time. Keeping the tortoise in the house, even if well heated, is still
not likely to be sufficient unless a basking lamp of this type is also provided.
They need to raise their body temperature to at least 30 degrees Celsius
– far above normal room temperature. A simple basking lamp can make a
huge difference – use one always!
Both radiant heat and light in
adequate quantity and quality are absolutely vital to get the tortoise
functioning properly. We cannot stress this enough. It is not optional. It is
essential!
We receive numerous calls for help from people who tell us that their tortoise
came out of hibernation ‘several weeks ago’ but ‘is not eating or doing much
yet’. Our first question is ‘Do you have it in a nice warm, bright place with a
basking lamp?’ The answer is almost invariably ‘No’. Every year animals die
unnecessarily because this simple and low-cost step is ignored.
There really is no excuse. Tortoises need light and heat. The method we
describe here is the easiest and most effective way of providing it. It will cost
you less than £15 to provide such a facility. Consider the veterinary costs that
may be incurred if you do not!
Hydration and drinking
Many people experience problems in getting tortoises to drink - in fact almost
all tortoises will drink provided water is offered in a suitable manner. We
recommend placing the entire tortoise in a washing-up bowl filled with about
25 mm of tepid water - less in the case of very small tortoises, a little more for
larger animals. The depth should be about chin height. Simply offering a small
dish of water to the tortoise is not likely to stimulate a good drinking response,
but actually placing it in water is usually successful. Splashing water on the
shell and around the head also often helps.
Drinking is, at this stage, far more important than feeding. Both dehydration
and the presence in the renal system and bladder of toxins dictate that every
effort must be made to encourage drinking first, feeding later.
The tortoise must also be kept warm as described previously - it is absolutely
vital that such temperatures are maintained in order to speed up activation of
the tortoise’s digestive system. As the tortoise awakes, certain biological
changes take place; one of the most important of these is the release into the
bloodstream of a chemical called glycogen, which has been stored in the liver.
This provides extra energy to give the tortoise an initial ‘boost’. Feeding must
take place before this is exhausted, or the animal will begin to decline. The
glycogen level can be artificially boosted by providing water with glucose in
solution daily - about 2 teaspoons per 250 ml dilution, at about l0-20 ml per
day for an average sized animal. Do not continue this therapy indefinitely, or
dangerously high blood-sugar levels may be attained. Four or five days
maximum should be sufficient.
All tortoises should very definitely feed within ONE WEEK of emerging from
hibernation. If they do not there is either:
A health problem
such as frost damage.
A husbandry problem (usually lack of heat and light)
If your tortoise is not feeding by itself within one week of waking up (provided
the correct conditions are present) do not delay any longer - consult a
veterinary surgeon that has particular experience of reptile husbandry
Good diagnostic techniques, combined with an understanding of reptile
metabolism and function, will invariably produce a satisfactory answer.
Whatever you do, please do not delay. A tortoise which refuses to feed
after a week or more of correct temperatures definitely has a veterinary
problem that requires professional investigation. Delay in these
circumstances can result in the loss of your tortoise, as it is especially
vulnerable at this time.
In most cases, however, if you provide suitable conditions, with adequate
heat and light, and ensure adequate hydration, your tortoise will make a very
fast recovery from its winter sleep and will soon begin feeding normally.
Further advice and information can be obtained at www.tortoisetrust.org or
www.britishcheloniagroup.org