Andy C. Highfield
A typical 'Tortoise Table' setup with overhead basking lamp
'Overwintering' is a term that is used to describe keeping awake, active and feeding a species that normally brumates (hibernates) over winter. This may be necessary for a number of reasons - typically because a tortoise is sick or underweight where allowing the 'winter sleep' would carry a higher than acceptable degree of risk. For successful overwintering a combination of environmental factors must be provided. There must be:
Adequate light.
Adequate heat.
We normally recommend a 12-hour cycle of adequate light and heat per day, with a cool, dark period overnight.
In addition:
Humidity must be maintained within appropriate parameters for the species.
It should be noted that our advice is very clear. Healthy tortoises that would brumate in nature should do so in captivity. There are numerous advantages to this, including limiting excessive growth rates and time under potentially damaging artificial heat sources. In addition, there are profound effects upon their natural hormonal cycles. In multiple studies with other species, those species that brumate (or hibernate) have extended life expectancy vs. those that do not. If managed correctly, the process is very safe indeed and there are a number of different methods, each with their own pros and cons. All of them, however, under the right conditions, and with adequate preparation and care have excellent track records as far as safety is concerned. This process did (justifiably) get a poor reputation many, many years ago, but that was before more was known, and before publications such as the Tortoise Trust's own 'Safer Hibernation and Your Tortoise' (1986) became widely available and taught keepers how to manage this safely. However, there are certainly occasions where non-hibernating (brumating) is justified and in such circumstances there are a number of well-established methods to accomplish this.
Housing during overwintering
We categorically do not recommend glass aquarium or vivarium ('fish-tank') type accommodation for overwintering tortoises. These tanks are heavy, expensive for the very restricted floor space offered (which is what matters most to a tortoise), and tend to be very poorly ventilated (the sides are unnecessarily high) and 'stale' air builds up rapidly in the lower areas.
They are also heavy and dangerous to handle, offer poor access, and most critically, entirely fail to provide adequate basking temperatures, temperature gradients or suitable microclimates. Wooden enclosed vivaria perform similarly poorly in all of these parameters. With most designs, correct placement of light and heat is practically impossible. In the unit shown above, for example, the lighting and heat source is, according to the instructions, placed on top of a very fine mesh screen. This instantly reduces the already inadequate UV-B and visible light levels from the lamps by 60%! The overall result is that no useful UV-B reaches the tortoise at all. The supplied accessories (heat mat, cheap plastic thermometer and substrate) are also disastrously inadequate and unsuitable (in controlled tests the thermometer was misreading ambient temperatures by as much as 13ºC) . Sadly, units and 'tortoise kits' similar in design to this continue to be widely marketed to beginner keepers by 'experts' in pet stores or via social media.
There are very high long-term mortality rates from tortoises kept in such enclosures including high rates of metabolic bone disease, excessive growth syndrome, bladder stones and respiratory disease.
Option 1: Greenhouses
Tortoises can be overwinted in outdoor greenhouse units provided these are set up correctly and have a secure electricity supply to provide adequate heat during daytimes and also frost-protection heating overnight. Be aware, however, that should there be an unexpected interruption to the electricity supply on an extremely cold (sub-zero) night there is a real danger of potentially fatal frost damage. As a minimum, install remote sensing thermometers with audible alarms (to a smartphone, etc.) that will alert you immediately to any such problems.
Greenhouses do offer a lot of floor space, but equally tend to be quite costly to heat adequately due to their height. This very much depends upon your location and how open to clear skies (or shaded) the site is.
Some typical examples of greenhouse systems being used to accommodate tortoises.
Two forms of heat are required to create an adequate thermal environment.
Background heat.
Direct radiant heat from overhead in a basking zone.
Overnight background heat does not need to be excessive (see link below). In fact, excessive overnight temperatures can be harmful. For Mediterranean species overnight ambient (air) temperatures of 8-10ºC are entirely satisfactory. Indeed, as long as the greenhouse does not actually freeze, no harm will occur. During daytimes, ambient temperatures between 18-24ºC are ideal. These temperatures need to be measured at or near to ground level in order to accurately reflect what the tortoise is experiencing. Temperatures measured higher up in the greenhouse will be very different.
It is definitely worth investing in some low cost data-loggers, plus an ambient temperature thermometer and a non-contact (infra-red) thermometer to understand exactly what is happening in the enclosure. Don't rely on guesswork.
The regular use of a non-contact infra-red thermometer will prove very helpful in understanding exactly what is happening within an enclosure, and how tortoises are responding to the conditions provided. Mediterranean tortoises need to be able to reach an all-over body temperature of approximately 30ºC to feed and to engage in normal activity.
It is also possible to replace some or all of the glass panels with UV-B transmitting plastics. Note that 'normal' glass blocks 100% of UV-B. If you do use normal glass, however, you can easily add in some vital UV-B by simply installing one or more T5 fluorescent tubes on an overhead support at a suitable height. One big advantage is that even in rainy areas, they can maintain a really dry substrate. If background or overnight ambient heat is required, tubular greenhouse convection heaters are (unsurprisingly) well-suited. These tend to be very well made, water-resistant and last for ever. We have had some for 30+ years and they still work perfectly.
Another big advantage is that you will get far better visible light levels in a greenhouse compared to under artificial sources (test it yourself with a LUX meter). This can have a big impact upon health and behaviour.
Using a LUX meter (visible light intensity meter) in the natural habitat. Typical levels during periods of tortoise activity range from 80,000 LUX to 160,000 LUX. This should be compared with levels measured under artificial light sources. Indoor habitats are especially poor in this respect, often by as much as 10 to 20 times lower levels of illumination than the tortoise would experience in nature.
Because they offer protection from wind-chill, tortoises can raise their body temperatures far more quickly and easily in a greenhouse than is often possible outdoors in cooler climates, even without heat lamps. However, if a heat lamp is needed (as it will be if overwintering), these are easy to add and because greenhouses offer a lot of height, you can use more powerful lamps, but at a greater distance, which is both safer for the tortoise and creates a better basking zone. As always there is no 'universally' correct or 'best' solution here - you need to carefully assess and weight up the 'pros' vs. the 'cons'.
It is a very good safety measure to line the insides of the greenhouse with wooden boards high enough to prevent tortoises coming into direct contact with the outer glass or polycarbonate. Tortoises can be very strong, and can also dig. This provides an extra level of security against accidents or escapes. This is especially important in the case of large tortoises.
There are two reasons to use a strong raised base that tortoises cannot see through (as here) or to line the sides with a strong wooden barrier: 1) If tortoises can see through glass they will constantly attempt to walk through it 2) If the glass breaks for any reason it is a serious safety hazard.
There are various options available for providing additional basking sources: HID (High Intensity Discharge) lamps that combine bright visible spectrum light with UV-A, UV-B and infra-red output and halogen flood lamps. The latter provide visible spectra light and infra-red, but do not provide any UV-B. The UV-B element can easily be added separately, however, via a T5 'desert reptile' fluorescent tube, as noted above. Both of these approaches have proven track records and are used by many keepers.
A wide range of 'basking lamps' are available. Each type has both advantages and disadvantages. It is important to understand these. In most cases the 'best' solution is to combine various types of lamp to provide the broadest possible spectra of visible light, UV-A, UV-B and infrared-A.
Mercury vapour lamps have been heavily promoted over the years as they combine heat, visible light, and ultraviolet radiation in the form of both UVA and UVB in one single fixture. On the surface, this may appear to be a good thing, but in practice it removes any individual control you that you would otherwise have as to the balance between infra-red vs. UV vs. visible light in the basking zone. They also tend to produce a very intense and concentrated beam. Finally, because they include highly toxic mercury compounds there are serious environmental and disposal concerns. They do have their uses, but in general terms most people will find that a halogen basking lamp (either with or without an ancilliary HID lamp) combined with a separate UV-B tube is a far better solution.
We do not recommend infra-red dull-emitter 'ceramic' heaters. These emit very high levels of Infra-Red-C, whereas Infra-Red-A is preferable. IR-C tends to overheat the skin, while IR-A is much more penetrating and delivers a far more biologically 'useful', effective and safe form of heat to reptiles.
In terms of the type of basking lamp and the power (wattage) you need to look for a wide-beam 'flood' coverage rather than a concentrated 'spot'. The exact power requirement is hard to assess, as there are so many variables, but in our own experience with greenhouse setups, a minimum of 150W is usually required, and as much as 250W might be needed in some situations. In large units, more than one basking zone might be required, especially so if the area is occupied by more than one tortoise.
You can also combine a standard high-power halogen basking flood lamp with an HID lamp to produce a far wider, more natural overall spectrum of visible light, UV-A, UV-B and direct infra-red heating targeted into the same basking area.
A natural UV-B index is measured close to wild tortoises in the natural habitat with a Solarmeter. Typically, levels of between UVI 2.0 to UVI 3.5 are recorded next to active Testudo graeca. Note that to accurately measure the output of artificial lamps, meters calibrated to a different standard is required (Solarmeter 6.2r Reptile lamp meter and the 6.5r Reptile lamp UVI meter). Unfortunately, all of these meters are rather expensive. Tortoises need both the correct spectra of UV-B PLUS radiant infra-red heat to convert UV-B to vitamin D3 internally.
The temperature in this basking zone is controlled by physically raising or lowering the lamp fixture as necessary. Unfortunately you cannot use standard temperature controllers with discharge lamps (HID or Mercury Vapour) and even though you can use 'dimmer-stats' with halogen type lamps this greatly affects their colour temperature and rendering. Hence, raising or lowering the fixtures is by far the most practical and effective means to arrive at a suitable temperature in the basking zone.
HID lamps (High Intensity Dischage) are often used in combination with halogen flood lamps to 'extend' the spectra. Be sure to factor in the additional cost of the matching electronic ballast unit required to operate them, however. Note that HID lamps used alone will not normally provide adequate infra-red (warmth) for basking purposes. They need to be used in conjunction with a more efficient infra-red radiator, such as a halogen lamp.
Quick Summary: For a simple, but effective, source of basking heat + UV-B combine a halogen 'flood' lamp of adequate power with a T5 UV-B fluorescent tube (either 10% or 12%). You can, if you wish, improve this further by adding an HID lamp to boost overall brightness and UV levels.
Size of the basking zone
Very small, highly concentrated basking zones are very problematic. They will fail to provide adequate 'all over' warmth, but will, instead, overheat the parts of the tortoise closest to the lamp. Combine this with the fact that no lamp commonly available today precisely matches solar infra-red, but is instead far more active on water molecules within the body (and especially the keratin and epidermis) then the result is a) A failure to heat the tortoise evenly and b) A very high risk of localised tissue damage (burns) in those areas closest to the heat source. Sadly, we routinely see many tortoises that have suffered such burns due to precisely these effects.
From all the available evidence, tortoises and turtles perceive and evaluate heat differently than do mammals. Some studies suggest that their receptors for heat and pain might be separate, and that they might also be 'attuned' to evaluate natural combinations of infra-red and UV-B, which are quite different from the IR and UV-B generated under artificial sources. As such, they may be 'mislead' by the conditions in captivity under artificial heat sources and as a consequence fail to move away from heating sources that are injuring them.
The basking area should be as large as possible, In nature, it is incredibly large, and because the sun is also so large, and is at such a great distance from the surface of the earth, the infra-red is very evenly distributed over a very wide area. It is totally different when the heat source is only a matter of mere cm from the animal.
It must be understood that as yet, there is no 'perfect' solution to this problem. This is why we advise making as much use as possible of unfiltered natural solar radiation and minimising exposures to artificial sources.
Where the use of heat lamps are necessary, however, a higher powered, physically larger and more distant lamp is likely to prove more effective and relatively safer than a lower powered, smaller lamp used in close proximity.
It is generally agreed that the basking zone needs to be at least equal to the size of an animal beneath it, and preferably, much larger.
Basking zone temperatures
It is actually quite difficult to specify an 'ideal' basking zone temperature. Indeed, it is equally difficult to measure such temperatures. What exactly are you measuring? The air temperature? The surface temperature on the ground? The temperature on the top of the carapace? The temperature half-way up the carapace? The skin temperature at the neck?
All of these will produce wildly differing readings..... which is 'correct'?
Answer: They all are. However, they need to be understood in context.
This is why simply citing 'ideal' temperatures in absolute terms can be so misleading.
The 'ideal' temperature might better be understood in terms of the animal's behaviour and only using readings as a general guide. There are so many variables to readings, even with precise instruments. Think of the difference between a white rock, a grey rock and a white rock under the exact same heat source.... this is why apparently 'authoritative' directions that the "basking zone should be 38 (or 35, or 34)ºC", for example, are so undefined as to lack any real meaning.
We strongly recommend using a non-contact infra-red thermometer to gather multiple readings, but then also to OBSERVE the tortoise carefully over an extended period. That will reveal precisely how these readings relate to behaviour, and how to meaningfully interpret them in your own individual situation. Even individual tortoises will vary in this respect. A very melanistic individual, vs. a very pale or 'yellow' individual, for example. Body mass and size will also affect this. For comparison, here are some actual UV-B and temperature readings taken from a wild Testudo graeca graeca here in Spain, in March (a peak activity period). This is a useful indicator of what happens in the wild, and of conditions (light intensity and UV-B levels, etc.) in the natural environment.
As a very general guide, we usually find wild Testudo most active when their carapace temperatures are between 28-34ºC, and when ambient (air) temperatures are in the 20-24ºC range.
Option 2: Tortoise Tables
The primary concept behind this type of design is that they offer improved airflow and convection possibilities, and allow for the use of deeper substrates. Although they can be purchased ready made from various suppliers, they are very easy to make at home for minimal cost and without requiring advanced woodworking skills. The general advice is to make them as large as possible. Large units, of all designs, will typically give the best performance while smaller enclosures tend to produce the least satisfactory results.
A wooden overhead gantry arrangement to permit the fixture of flexible heating and lighting options is all that is required to complete the unit.
This type of overhead lighting support beam offers a high degree of flexibility to install alternate forms of light and heat, however. Whichever form of heat and light is used, it is important that it is selected to match the requirements of the species being maintained. The comments on lighting and heating (above) in greenhouse setups apply equally to tortoise table setups, incidentally, although because these are normally used in a house and are substantially smaller, you are unlikely to require basking lamps that are quite as powerful. Often a 100-150w lamp will be adequate vs 175-250w in an outdoor greenhouse installation.
Safety
Each year we hear of cases where fires have been caused by the careless use of basking lamps for tortoises. This is entirely preventable:
Always use heavy duty ceramic (not plastic) lamp holders for heat lamps.
Never - ever - place anything flammable close to the lamp or where it could fall or be blown onto the lamp.
Make sure all lighting fixtures and fittings are fully secured. Keep other pets or children away from them (see our 'Constructing a Simple Open topped Tortoise Enclosure' article for some practical ideas on securing such units).
For heat lamps, heat resisting cable is highly recommended.
Use the correct fuses and avoid trying to run too many 'daisy chained' heat sources from extension cables.
Always fit an RCD (Residual Current Detector) to enhance electrical safety and a smoke alarm - just in case.
A temperature-resistant, high-power-handling (200w) ceramic heat lamp holder.
HYDRATION
Beware of over-drying tortoises accommodated indoors. Provide clean, fresh water and all times and we strongly recommend regular soaking also for tortoises that are exposed to heat lamps. See our recent separate article on this topic, 'Hydration and your Tortoise'.
HUMIDITY
As we are typically referring to Testudo species here, an ambient room (or greenhouse) RH in the 45-55% range at 18-24ºC is suggested. Be aware, however, that directly under basking heat sources this will be very much lower, hence the need for extra attention to hydration levels.
OVERNIGHT
Lights should be switched off overnight to avoid stress and to provide a natural light cycle. In very cold situations some additional heat will be required overnight, especially where greenhouses are used. If accommodation is based indoors, in a house, normal overnight room temperatures should be more than adequate. See our article on temperatures actually experienced by Testudo graeca graeca in the wild. They are probably quite a lot lower than you might expect!
FEEDING
Be sure to provide a nutritious, well balanced diet over the winter period - try not to rely upon bland supermarket produce!. Even in winter some weeds and other 'wild-foods' can be found. See our detailed guide to 'Winter Feeding'.
POST-HIBERNATION USE
These exact same housing and heat-light combinations can also be used to provide extra help to tortoises that have brumated (hibernated) yet which emerge into a very long, cold, wet spring instead of into a warmer, brighter Mediterranean spring as experienced in their natural habitats. We receive numerous calls for help each year 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”. Even people who have read our advice in “Safer Hibernation and Your Tortoise” often make this mistake. Maybe they think that these basic biological rules do not apply to their particular tortoise? We don’t know. We do know, however, that every year animals die unnecessarily because this simple and low-cost step is ignored. There really is no excuse. Tortoises need adequate light and heat. The methods we describe here are the easiest and most effective way of providing it.
It is very important to note that standard 'infra-red' lamps that put out a red coloured light are TOTALLY unsuitable for use with tortoises. Tortoises need DAYLIGHT spectrum lighting. These lamps are equally unsuitable for overnight heating, as tortoises need DARKNESS at night.
The basic procedure is to remove the hibernating box from its winter quarters and warm it up by placing it close to a heater. After an hour or so, remove the tortoise from its box (or the refrigerator if that method has been used) and place it in a warm, bright environment. A 150 Watt reflector lamp as described above is then suspended about 40-50cm above the tortoise and will make a huge difference. The next thing to do is to ensure adequate hydration. This is far more important initially than feeding. Always concentrate on getting the tortoise drinking first.
Do not expect a tortoise to begin feeding easily without some kind of assistance in the U.K. – British and northern European spring weather is totally different from that in the Mediterranean. Tortoises must have adequate light and heat at this sensitive time. Keeping the tortoise in a normal house, even if well heated, is still not likely to be sufficient unless a basking lamp is also provided. They need to be able raise their body temperature to around 30ºC. A simple basking lamp can make a huge difference – use one always (unless you have access to a greenhouse system or 'Climate Frame' system that can achieve similar body temperatures). See also our article on 'Post-Hibernation Anorexia' if you do encounter problems.
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(c) 2024 A. C. Highfield/Tortoise Trust
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