Gently into Brumation: Temperature Reduction, Moving into the Refrigerator and Refrigerator Brumation

Talk · Temperature Reduction and Refrigerator Brumation

This page accompanies my talk „Temperature Reduction and Refrigerator Brumation“, for reading up on and linking to. European tortoises do not enter brumation overnight. In the Mediterranean, autumn cools down very gradually – and we reproduce this slow transition in the heated cold frame. This page summarises the entire process: from the climate in the habitat and the four-week temperature reduction to safe checks during refrigerator brumation.

The slides from the talk are available here: Temperature Reduction and Refrigerator Brumation (PDF, in German)

1. The Mediterranean climate sets the pace

Our European tortoises come from the Mediterranean subtropics – a winter-rain climate with damp, mild winters and hot, dry summers. In Greece, average temperatures over the year range from about 5 to 33 °C; in Germany, from 1 to 23 °C. Ambient temperatures here are therefore generally too low. Then there is the light: Athens has around 2,700 hours of sunshine a year, the Antalya region around 3,000 and Palma de Mallorca around 2,850 – whereas North Rhine-Westphalia has only about 1,500 (climate normal period 1991–2020).

Everything else follows from this annual rhythm of light, warmth, drought, rain and wind. In spring, warmth and fresh wild plants start activity. In summer, heat, drought, shade and microhabitats become central. Autumn brings rain, a second growing season and preparation for brumation. Winter is the cooler, damp phase – for Testudo, the basis of brumation. In the habitat, it lasts about 12 weeks, from December to March. Technology in cooler regions should therefore make basking, warm microclimates, retreat, dry phases and safe brumation possible.

End of October: habitat and Germany compared

In the habitat, the reduction only begins at the end of October or beginning of November – as soon as there are fewer than 150 hours of sunshine a month, daytime temperatures fall below 20 °C and nights below 15 °C. Here, it cools down much earlier and faster. Without technology, our tortoises would be forced too early and too abruptly into a resting phase that is too long.

2. Why not overnight?

Tortoises are not machines that we can send into brumation at the push of a button. Simply switching off the heating or bringing the tortoise into the warm house creates exactly the condition we want to avoid.

Genuine brumation only sets in at temperatures permanently below 8 °C. Metabolism and muscle activity decrease, and heartbeat and breathing are reduced to a minimum. Brumation is important for the immune system, growth, hormonal balance and life expectancy. The target range is 4.5 to 7 °C. There is a clear lower limit: temperatures must not fall below 4 °C – 3.7 °C proved fatal for Hermann’s tortoises of the subspecies THH (Testudo hermanni hermanni) (Bonin et al. 2007). Hatchlings also brumate from the very beginning, and for just as long as adult tortoises.

3. The schedule at a glance

The process is the same for refrigerator and pit brumation. The temperature reduction and the first 1–2 weeks of brumation always take place in the heated, safeguarded cold frame. Only after that do the two methods differ.

1. Sept. – end Oct.
   Staying activeMediterranean late summer: about 20 °C at night, 25–27 °C during the day (2–3 °C more for spur-thighed, or Greek tortoises).
2. End Oct. – end Nov.
   Reduction over about 4 weeksNo more than −1 °C per day, basking spot reduced from 8 to 5 hours, always 35 °C at shell height.
3. End Nov. – early Dec.
   1–2 weeks of brumation in the cold framePermanently below 8 °C, target range 5–6 °C, never below 4 °C.
4. around St Nicholas’ Day (6 Dec.)
   Moving into brumation quartersInto the refrigerator (4.5–7 °C) or the secured pit – only tortoises in deep brumation.

4. Week by week to brumation

The example begins at the end of October. We lower day and night temperatures and the hours of sunshine over four weeks until brumation temperatures are reached. Greek tortoises (TGI) from southern regions of origin are brought down somewhat more slowly, following their original climate – for them, only the night temperature is lowered at first.

No more than −1 °C per day · basking spot always 35 °C at shell height · *lamp off only once all the tortoises have been inactive for a week · move into brumation quarters after 1–2 weeks permanently below 8 °C

5. The tortoises prepare themselves

If we provide the right parameters, the tortoises prepare for brumation entirely on their own. They know best when to eat, bask or bathe – we just have to create the conditions for it.

A bathing opportunity is provided in the cold frame, but bathing is never forced. Tortoises that have been bathed „empty“ are prone to problems getting going after brumation, such as post-brumation anorexia, because the gut flora suffers. As long as a tortoise is basking and eating, the basking spot stays on for 5 hours a day. Exception: bathing on the instructions of a reptile vet.

Healthy into brumation

Before brumation, a faecal examination for intestinal parasites and a pre-brumation check-up at a reptile veterinary practice are essential – especially for tortoises brumating with us for the first time or coming from poor husbandry. Brumation should only take place after consultation with the vet. After worming, the tortoise must be kept at high-summer temperatures for a further 6 weeks.

6. In parallel: preparing the refrigerator

While the temperature is being lowered for the tortoises in the cold frame, we run in the refrigerator. If you do not have one yet, get one now.

Running in without tortoises

The refrigerator is placed in the heated room and started on the warmest setting. We then put in the prepared boxes with soil and leaves and gradually set the temperature to 4.5–7 °C. Measurements are always taken at the back of the boxes, the coldest area: with a probe in the substrate under the leaves, or without a probe in the lower layer of leaves. Temperatures outside the boxes are irrelevant. Every day, we note the minimum and maximum in all boxes and reset the values. After a week, a stable pattern emerges. All adjustments to the refrigerator and emergency cut-off are always made without tortoises – changes in steps of 0.1 °C, then observe for a few days.

The life insurance: the emergency cut-off

An emergency cut-off thermostat such as the UT300 switches off the refrigerator before it gets too cold. Its sensor sits in the coldest box, at the back under the leaves, slightly inserted into the substrate. The OFF temperature is 0.2 °C below the measured minimum temperature – OFF never below 4.3 °C, ON never above 5.8 °C. Ideally, the refrigerator is set so well that the emergency cut-off never has to intervene. For calibration, we first let it run alongside without plugging in the refrigerator.

7. Moving into the refrigerator

The tortoises stay where they are until they are in deep brumation. If a tortoise is still looking around, it is not brumating. Tortoises are site-faithful and sensitive: tortoises that are moved while awake or merely resting experience great stress, panic and wake up in the refrigerator – such „forced“ brumation almost always fails. The tortoises should not notice the move at all, and in spring they return to the cold frame in deep brumation and free of stress in the same way. If a tortoise stays awake despite permanent brumation temperatures, we have the cause investigated.

How we recognise deep brumation

The tortoise does not wake during the check-up and weighing, moves only very slightly, as if in slow motion, and keeps its eyes firmly closed. Finally, we lower the temperature in the cold frame to 5 °C – the move usually takes place around St Nicholas’ Day.

Health and weight check

Before the move, we weigh each tortoise and note its starting weight. We check the shell, nose, beak, eyes and cloaca for mucus, discharge and redness, and the limbs for swelling. Only tortoises without abnormalities are moved into the refrigerator. The final check: is the refrigerator running stably and safeguarded? Is the UT300 sensor positioned correctly? Are the tortoises healthy and in deep brumation? Then they can be moved in safely.

How the move works

1. Cool the room down well.
2. Take the boxes out one at a time, remove the leaves and form a small hollow.
3. Health check and weighing in subdued light.
4. Place the tortoise in the hollow – head and front legs slightly raised.
5. Cover the carapace with soil and fill up to the top with leaves.
6. Fasten the mesh lid, slide the box in carefully without knocking it. Close the refrigerator door in between.
7. Measure further back in the substrate; the emergency cut-off sensor stays in the coldest box – check its position.

8. Checks during refrigerator brumation

After the tortoises have been moved in, the refrigerator stays closed for two days. After that, we air it every two days for about 10 seconds – small and fully loaded appliances daily. It is better to air briefly more often. A temperature alarm monitors the values. Every two weeks, we feel the soil under the leaves: it should be slightly moist, but not wet. If it is too dry, we spray a little water onto the leaves from the side. Moistening too much can cause a drop in temperature.

The tortoises are weighed and briefly checked every four weeks, and every two weeks in the last third of brumation. We note the weight with the date and check appearance, movement and smell: does the tortoise respond to touch as if in slow motion? Are the nose, mouth and eyes normal? Emergence follows after about 12 weeks, or after 16 weeks at most for large adult tortoises.