Life in the Cooler

BCG Newsletter 2001

  Having started my chelonia interests some 25 years ago with  water turtles, box turtles and tropical tortoises, it was some time before the peculiarly ritualistic autumn events of boxing up one’s tortoise for the winter came to my attention, or indeed, required me to take part in the ceremony. I am of course talking about hibernation.  As an ‘outsider’ therefore, I can perhaps cast a fresh insight into an event so steeped in tradition and dogma that often the reason for hibernation has been completely overlooked or misunderstood.

  All tortoises have survival mechanisms to get them through adverse times in their life cycle. Essentially, these rough periods will either consist of cold, heat, and (or) drought.  If a tortoise is too cold, its digestion will not work, and, its ability to move will be slowed to a painful crawl. This is because nearly all reptiles are endothermic- they obtain energy from the surrounding heat. Under these conditions the tortoise will attempt to stabilise its temperature at a such a level at which energy loss is at a minimum. This usual requires the tortoise to dig below the topsoil into  cool but frost free soil. Here its internal systems will slow to imperceptible levels. It becomes comatose- but not asleep as such.

Similarly, under conditions of extreme heat and subsequent drought, the tortoise behaves in the same fashion, burying itself in the cool to conserve energy until conditions improve, when it can revive, and continue with its life. It is this revival stage which is the most critical time, in which the waiting environment should match the tortoises expectations, and in which captive husbandry should match conditions in the wild.

  The abilities, expectations and capabilities of tortoises to survive the cold (hibernation), or to endure the heat (aestivation) vary wildly from species to species, and from one part of a single species’ range to another. The horsfield’s tortoise for instance, plays both cards- living in burrows to survive the long fierce Siberian winters, and using these same burrows to avoid the searing heat of the arid summertime. They emerge in bursts of mild weather, mornings and evenings, to conduct their frantically compressed lives. In complete contrast, the Yellow Footed tortoise from Brazil suffers terribly from drought, and will die overnight if left to experience an autumn chill in the back garden- they seem to have little ability to hibernate or aestivate at all.

  Our most common captive tortoises have ranges stretching from the South of France, through to Yugoslavia (T.hermanni), and from the plains of Libya and Egypt, through to the mountains of Iran and Turkey (T. graeca). Despite these vast differences in climate, conditions and habitat, the traditional wisdom for hibernation has been the same for all- place in a box of straw for 5 months. No wonder that everyone has developed their own recipe for success in hibernating these species of tortoises. What we must realise is that for every one tortoise alive in this country today, nine died in their attempt to survive. The primary cause of death has been hibernation related. The survivors are here today because of a series of chance factors- genetic (a little more cold hardened), luck (in a garden with plenty of natural food) or, amazingly, having their owner select by chance some bizarre method of hibernation that matched that of their natural habitat and climate. How would your tortoise fare if hibernated in a warm airing cupboard, being fed only once in four months (on Christmas Day!)? I know of one such who has done perfectly well for 20 years with this treatment- clearly by chance a T.g.graeca who is adapted to aestivate for long periods.

  Considering all of this, how was I to proceed with my own plans for tortoise hibernation. Traditionally, dogma says that tortoises should end up in one of four places- the garden shed, the garage, under the stairs, or in the loft.  Unlike the home of my childhood, when tortoises were common pets, my house is double glazed, cavity filled, and centrally heated (there goes the loft), with open plan stairs (enough said), and a garage turned into a tropical house (no help there). The garden shed was there, but it was not frost proof, and early attempts to correct this with lights and thermostats simply did not work- the temperature fluctuations were severe enough to leave my poor tortoises confused and exhausted.

  Surely technology could provide a solution? The optimum hibernation temperature has been worked out to be 5 degrees Celsius. Instead of warming tortoises in a freezing garden, what about cooling them down inside a warm house- by using a refrigerator!  Not sure of the implications, or the techniques involved, I began some research- looking at similar existing schemes. It soon became clear that just as with other methods of hibernation, everyone had their own recommendations on what to use, and what to do. It  became obvious however, that few had looked into the procedure in any depth. In particular, the use of a cheap modern ‘fridge was suggested, and indeed used by many, despite the risks. These risks centered around the operating temperatures of ‘fridges- which by law need to keep food between 0-4 degrees Celsius. This naturally means that temperatures outside this range are on the very extremes of the ‘fridges normal operational boundaries, which for a cheap model, means that its thermostat is operating outside its design parameters to hold a steady 5 degree minimum for tortoises. Having spoken to one distraught owner at a Birmingham health check, whose ‘fridge thermostat stuck ‘open’, freezing to death her hibernating tortoises, I warily steered clear of that solution.

  The very expensive professional ‘fridge is of course another matter. Designed for catering, they have a more flexible temperature capability, and having seen one in operation at friends of ours (Ken and Jackie), this seemed the business- complete with retro-fitted temperature alarms designed to ‘wake the dead’ if electrical failure lead to freezing (or ‘thawing’) of the tortoises. A visit to ‘Currys’ however put me off the idea- 500-800 pounds each, these ‘fridges were not an option for us!

  Other reptile societies were at that time proud to show off  options they were experimenting with- the drinks chiller cabinet, and we visited two such in the Birmingham area. With glass doors to view through, the tortoises literally stacked like coca cola cans within, these seemed the very essence of 21st century hibernation. The advantage of this type of cabinet is the fact that they are not designed to go below freezing point, even on full power- an obvious plus point. The disadvantage was the increased electrical cost- leaking cold through the glass doors. This seemed however to be a viable option, provided that the tortoise was insulated against the temperature fluctuations within the cabinet by providing the usual box-and-shredded-newspaper for each animal (not always provided in the examples that we saw).

  Back at home, we wondered at the cost of such equipment. Not being whole societies, with funds at our disposal, but just ordinary members of the BCG, we had no idea whether we could afford to go along that path. Surveying the wine cooler in our local pub that night (estimating its capacity in tortoises!), we read the logo- ‘Whitbread’, a local firm- and decided to write to them, offering to buy (second hand) one of their coolers. Their reply exceeded our wildest expectations. Yes, you can have some coolers (we said two), no, you owe us nothing, BUT, could we use you in some advertising. We of course agreed, and TV coverage followed, along with national press articles (including the ‘News of the World’), and even a cartoon in the Independent!  The actual firm who provided the coolers (Hereford Coolers) were even more obliging, not only delivering and installing the Whitbread logo’d coolers, but they have even provided free maintenance ever since. Before use, I fitted temperature sensors to the coolers- wired to a laptop, allowing the range of temperature to be recorded in order to oversee any fluctuations. In addition, alarm thermometers were added, to give warning of any equipment failure. The tortoises themselves each enjoy a personal wooden box, filled with shredded newspaper, and with a loose fitting, perforated lid. The sliding glass fronts to the cabinets were fitted with a sheet of polystyrene to reduce the electric bill, and to provide darkness inside.

  With every system there are of course drawbacks. A cooler is vulnerable to power cuts, and to equipment failure. Without adequate ventilation, they can also produce condensation- all forms of damp must be carefully avoided. This is a ‘cold’ hibernation, not suitable for all tortoises, and certainly to be used in moderation with new specimens whose history is not known. There is also an electric bill to pay.

  So what are the benefits? The first is that I can select the exact time to start, and to stop hibernation during the year, giving far greater control over the tortoises well being. I have the cabinets easy to hand, allowing regular inspections (removing the polystyrene, I can see if any lids have been ‘popped’, indicating a restless tortoise). Finally, the temperature inside remains constant, giving a high quality hibernation. This is indicated by very little weight loss at the end of their time- often just a few grams. Indeed, sometimes the tortoise actually seems to gain weight in hibernation. I have it confirmed by other cooler users that this is not just me, but a common phenomenon. This of course is impossible, unless the tortoises know more about the use of Einstein’s Theory of Relativity than we do. (conversion of  mass to pure energy requires travelling at light-speed, so perhaps the opposite is true (energy converted to mass) in our slow moving, hibernating tortoises!!)

Paul Coleman