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Refrigerator Hibernation for Tortoises & Turtles Andy C. Highfield Refrigerators have been used successfully to artificially hibernate many animals. Snakes, lizards and even bats have been hibernated in domestic refrigerators. Many tortoise and turtle keepers have also discovered the benefits of this system. Refrigerators
can offer a highly stable temperature in
precisely the ideal range for chelonian hibernation,
which is generally agreed
to be in the 3-5 degree Celsius (37.4 to 41 degrees
Fahrenheit) range
(depending on species). Even if room temperatures rise
to above the level at
which tortoises begin to activate and use up more
energy (around 10 Celsius or
50 degrees F.) the temperature in the refrigerator
will remain at safe levels. What a refrigerator will NOT DO, however, is protect the animals if external temperatures fall BELOW the desired levels. In other words, just because 5 Celsius is the setting on the refrigerator, if the room temperature falls to -3 degrees, or even -1 degree, the TORTOISES WILL STILL FREEZE TO DEATH. It is therefore ABSOLUTELY ESSENTIAL that refrigerators used for hibernation purposes are situated in a room where above-freezing temperatures are guaranteed. A warm room is fine. A cool room is also fine - but a cold room or garage, or similar, is certainly NOT safe. I would recommend placing the refrigerator in a room that gets NO COLDER THAN 10 Celsius or 50 degrees F. Use a reliable maximum-minimum thermometer to survey the room where the refrigerator is to be placed, and monitor it regularly throughout the hibernation period. While it may be thought that a garage or outbuilding would be fine provided it is equipped with a ‘frost-protection’ heater, this is not in fact recommended, as a simple power failure, even for a few hours, could very well result in temperatures within the refrigerator plummeting to lethal sub-zero levels very rapidly. Choice of refrigerator: Despite the temptation to use an old or surplus unit, it is firmly advised that instead a new, modern refrigerator should be employed. Old refrigerators often have unreliable thermostats. It is also best to choose a unit without an ‘icebox’ or freezer facility, as temperatures right next to the icebox or freezer section can be considerably lower than in other areas of the unit. In addition, in the event of a thermostat failure, it is a remote (but real) possibility that any refrigerator which can actually attain freezing point might actually do so… therefore, refrigerators that do not have that capability are inherently safer. The most suitable types of refrigerators for hibernation purposes are those often described as ‘fridge-larder’ models rather than as ‘fridge-freezer’ models. The size required will of course vary depending upon how many tortoises or turtles you intend to hibernate - for small numbers you may well find that a ‘table-top’ or ‘counter-top’ mini-refrigerator (such as seen in many hotel rooms) will be quite adequate. In fact, the ‘drinks chiller’ type refrigerator (usually supplied with a glass front door) is probably the best of all if you only have to hibernate small numbers of tortoises. These units are specifically designed never to attain freezing point on their own (although they will still freeze if placed in a sub-zero external environment, of course). Setting up the refrigerator First
of all, TEST the refrigerator thoroughly when
empty. Use a separate thermometer of known accuracy to
establish a set
temperature and to monitor fluctuations from this
point. If using an electronic
thermometer with a separate probe, place the probe in
FREE AIR (not in contact
with any object) to see how much the air temperature
varies within the
refrigerator. Make a note of the results. Do not be surprised if there is quite a
bit of variation, or if stability
is not quite what you expected. We deal with this problem next! The
second test should be to establish how stable the
refrigerator is when fully ‘loaded’. It is a simple
rule of physics that the
more mass an object has, the more resistant it will be
to external changes in
temperature (it will equalize more slowly than an
object of lower mass). To
maximize temperature stability within the
refrigerator, then, it is preferable
to introduce extra mass within the unit. One easy way
to do this is to fill
some 2 litre plastic drinks bottles with water, seal
them, and position these
to fill ‘dead’ space. This will add considerably to
the mass within the
refrigerator, and hence will dramatically improve
overall temperature
stability. One other source of mass when
the unit is in use will be the actual hibernation
boxes, complete with
substrate. For the moment, half fill a 30 X 30 X 10 cm
(12 X 12 inch X 4 inch)
plastic food store, lunch box, or large
ice-cream/margarine type contained with
a 50/50 soft sand and topsoil mix. Position this on
the middle tray within the
refrigerator. Rest the thermometer (or thermometer
probe, if an electronic
type) on the surface of the substrate. Now repeat the
monitoring test for at
least 24-48 hours. You
should see a dramatic improvement over the first
test. This second test more accurately reveals the temperatures and temperature variation that a hibernating tortoise or turtle will experience within the unit. Using
the results from this test, make any adjustment
to the refrigerator thermostat that are necessary to
ensure a stable
temperature of 5 Celsius, or 40 °F. Only
when the refrigerator has demonstrated that this
temperature can be maintained
with no more than a +/- variation of 2 degrees should
it be regarded as suitable
and safe for actual use. Hibernation boxes: You can use cardboard, plywood or plastic boxes as containers for tortoises and turtles within the refrigerator. Obviously, cardboard and wood are unsuitable for any species that requires a moist substrate. For species that require a dry substrate, they are useable, however. Boxes should not be too small. Allow enough room for the animal to turn around if it wishes to. Sides should be deep enough to prevent easy escapes (although it is strongly recommended that a lid is fitted to completely preclude this possibility). I prefer to use polythene food-grade ‘lunch boxes’ and I drill multiple holes in the lid to assist with ventilation. The only purpose of the lid is to prevent escape and injury - so I drill as many holes in it as I can without weakening it too much. Substrates: Most
of the comments in our article on ‘Vivarium
Substrates’ apply equally in this context, as do
the comments in our
‘Microclimate’
article. For arid habitat species, a dry substrate is
appropriate. We use a 50/50 mixture of soft (play)
sand and topsoil. You can
also use shredded paper, although I personally feel
that the advantages of a
natural sand/soil substrate are considerable.
Certainly, such a substrate does
tend to reduce ‘scratching and scraping’ and appears
to allow the tortoise to
‘settle in’ rather faster than when shredded paper is
used. For moist habitat temperate species, such as American box and Wood turtles, I would recommend a hibernation substrate composed of one third soft sand, one third peat-based compost, and one third moist sphagnum moss. This substrate should not be too deep - just deep enough to permit the animal to bury itself. This a) helps to stabilize temperatures around the tortoise and b) helps to prevent excess fluid loss from respiration and cutaneous (skin) evaporation. The humidity within a refrigerator can fall very low indeed - it is worth monitoring this, especially with sensitive species. If it gets too low, a shallow tray of water with added sponge material can help restore it to acceptable levels. For most species humidity in the 50-60% range is fine. Some very arid species such as Testudo horsfieldii can do well at a Relative Humidity of 40% or less. Box turtles tend to require RH to be maintained in the 65-75% range or higher. Ventilation: This topic probably causes the most concern to those unused to the concept of refrigerator hibernation. The first thing to be aware of is that hibernating tortoises and turtles have a very low oxygen demand. Many species completely bury themselves to a depth of a foot (30cm) or more in the earth to hibernate, where available oxygen is pretty low. In practice, provided the following guidelines are followed, there will be no problem due to anoxia within a refrigerator hibernation environment:
Both methods have proven entirely successful. In most other respects, refrigerator hibernation is the same as for other methods (hibernation pits, hibernation boxes in uncontrolled environments, etc.). All of the same general considerations apply. See our article ‘Safer Hibernation and Your Tortoise’ for further details. A member of the Tortoise Trust Mailing List discussed his method of hibernating Russian tortoises (Testudo horsfieldii) using refrigerators. As this is a personal account of this method in use, you may find these comments very helpful: “I have used a refrigerator to hibernate my Russians for the past 3 years. I stop feeding them about 4-6 weeks before hibernation and shorten the time the lights are on. They have weekly soaks in warm water. About 3 weeks before hibernation I turn off the heat lamp resulting in cooler daytime temperatures. During the last week I soak them multiple times until they no longer void in the water About 2-3 weeks before hibernation I get the fridge setup. I use a small aquarium air pump with 2 air hoses that are feed into the fridge. I tape the door shut as the air tubes tend to cause the door to want to open (note: this can be avoided if you cut away the door seals where the tube enters) . I have a min-max thermometer and keep track of temperatures so I know the setting for 5 degrees C. Then I turn the temp back up to about 15 degrees C for the start of hibernation. I put each tortoise in it's own box. The box is slightly bigger than the tortoise and I place lots of shredded blank newspaper on top. Once they are in the fridge at 15 C I slowly turn down the temp over the 1st week of hibernation until it reaches 5 C. Throughout hibernation I open the door of the fridge about once a day just to let fresh air in. I weight them at least 2 times during hibernation to ensure that they are not losing too much weight. I also take them out and examine them about once a week. The most amazing thing for me is when they come out of hibernation. I follow Andy's recommendations from his guide and place them in bright light immediately after taking them out of the fridge. I soak them multiple times over the first few days until they have voided and start drinking. I feed them immediately and they typically eat the same day or next day after hibernation. Airpumps Let me clarify what I use. It is a simple pump used for aquariums. Cost is about $10-20 here. The pump sits outside on the floor and I just open the door, run the air tubes, in and tape the tubes onto the back and sides of the fridge to stop them from moving. As for boxes, I have used sturdy cardboard boxes with a piece of thick indoor-outdoor carpet on the bottom. I fold the tops over just to make sure they can't climb out. With the tops folded there are still large spaces open. So far this has worked. I usually need new boxes each year as they do tend to scratch almost right through the box. This is where weekly checks are important. This year I am going to build boxes out of plywood. I place only 1 tortoise per box. They can be active (some scratching etc.) even at less than 10 C and I would be concerned that if one animal was active it might disturb another if in the same box. I try to cool the turtles down gradually rather than taking them from room temp right into the fridge. To do this you need to test the fridge before the turtles go in to know what the fridge temp setting should be for 5 degrees. Thus, when you first put the turtles in at say 10 C they will still move about. Just wanted to mention this as it might be distressing to hear them scratching around if you haven't hibernated Russians before. Russian tortoises are also more cold tolerant than other tortoises and are more active at lower temps. If unaware of this, some might be tempted to pull the turtles out of hibernation thinking that it wasn't working when in fact some activity even at 5C is normal. Graham Reid, Ontatrio, Canada. REFRIGERATOR HIBERNATION Q&A Q.
Can I hibernate aquatic turtles using this system? A.
In terms of temperature, yes - but there is a real
possibility of problems arising from lack of oxygen in
the water, or from other
chemicals building up in the water around the turtle.
The fact is that unless
the refrigerator being used is extremely large, the
water volume around an
aquatic turtle is likely to prove inadequate to ensure
safety. WE
THEREFORE DO
NOT RECOMMEND YOU SHOULD ATTEMPT TO HIBERNATE
AQUATIC TURTLES UNDER WATER IN A
REFRIGERATOR. We would
be interested to hear from anyone who has had success
(or failure) in this regard. Certain
species of aquatic turtles do hibernate out of water,
however, often buried in
river banks or under tree roots. These species may be
candidates for
refrigerator hibernation in the same kind of moist
substrate used for
semi-terrestrial species. Q.
Can I hibernate semi-terrestrial turtles, such as
American box turtles this way? A.
Yes, certainly. No problems have been reported. Use
a substrate as described above. Q.
How does this system work with very small juveniles
or hatchlings? A.
Perfectly. They should be treated as for adults. Do
be sure to use a suitable substrate to avoid undue
risk of dehydration when
hibernating juveniles. Q.
Can I go away on vacation if I use the airpump
method of ventilation? A.
We absolutely do NOT recommend
leaving the animals
in a refrigerator unattended for any kind of extended
period. What if there was
a power failure? Q.
What kind of thermometer should I use to check
temperatures? A. We recommend using two: one should be a mechanical (old fashioned!) minimum-maximum horticultural type, and the other can be a modern LCD electronic type with remote sensing probe. These are useful in that the internal temperatures within the ‘fridge can be seen constantly without having to open the door. Many models can also be switched between two probes (one of which is usually built into the thermometer body) to provide indoor/outdoor readings. In this application, the ‘indoor’ reading will reveal the ambient temperature around the refrigerator, and the ‘outdoor’ reading (remote probe) should be resting in contact with the substrate in the tortoise’s box to reveal the actual temperature in the hibernation container. You can even get models with programmable high-low audible alarm points. If available, we recommend these highly. Try aquarium supplies or electronics stores for a complete range of suitable thermometers. Q. Can I use the same refrigerator I use to keep food in? A. No. Absolutely not. There is a SERIOUS danger that food could become contaminated with potentially LETHAL pathogens, including salmonella. No refrigerator used for tortoise hibernation should EVER be used to keep food or drink in. More useful hibernation information on this site: Safer Hibernation and Your Tortoise |