Juveniles and adults live in the same locations, in the same habitat, and experience exactly the same environmental conditions. They therefore both brumate when winter temperatures fall to a certain level.
The brumation (hibernation) of juvenile Mediterranean tortoises is a much-vexed issue and causes many keepers a great deal of concern. To brumate or not, that is the question....
In the wild the vast majority of Mediterranean tortoises do brumate for varying periods over winter. There are some exceptions, however. These include populations which live in regions which experience very mild winters, such as certain coastal sites in southern Morocco, or the coastal regions of Tunisia and Libya. In these areas, winter daytime temperatures may exceed 20ºC, and can reach 28ºC. Here, tortoises may remain fully active and feeding all winter. This does vary, however, according to seasonal fluctuations and precise location. During colder periods the tortoises will become inactive, and may enter a short cycle of brumation. The environmental cues or 'triggers' for this behaviour are discussed here. These same regions also experience exceptionally hot and dry summers. In southern Morocco, for example, daytime temperatures in July can exceed 48ºC. These high temperatures, and the almost total lack of plants suitable for grazing, result in aestivation. The tortoises bury themselves underground and sit out the unbearable heat expending as little energy as possible. Although superficially similar to brumation/hibernation, aestivation is biologically a very different process and the two should not be confused. They are only similar in the sense that they result in a seasonal period of inactivity. This naturally affects the rate of growth and the total food intake over a 12-month period. See our recent detailed report on this, and some implications for growth and health.
In the wild, this tortoise will gradually become less active as winter approaches, before digging down (usually under a bush or shrub) to brumate until warm weather returns in spring.
Most tortoises from around the Mediterranean do brumate. The basic facts on how to manage this for adults are explained in the classic Tortoise Trust publication 'Safer Hibernation And Your Tortoise'. Juveniles can also be brumated, and in general this period of inactivity is beneficial as it results in much more natural rates of growth than does continual activity.
There are two vitally important facts which must be understood:
Juveniles require the same safe temperature range as adults for a safe brumation, i.e., 4ºC-6ºC, but their gut pass-through time is very much shorter, typically no more than two to three weeks during which gradual cooling down should be undertaken.
Because of their low body mass juveniles are very susceptible to rapid changes in the local temperature. In other words, they can freeze or become too warm very quickly indeed. For this reason, some extra precautions are necessary.
There are two approaches to the hibernation of juveniles, both of which have proved successful. These approaches have some similarities, especially in respect of the induction period.
For the first method the tortoises should be maintained as for overwintering, ie with light and heat, until at least mid-November. In very mild winters when inducing hibernation can be difficult, it may be necessary to keep them active until December. Begin the induction process by gradually reducing the hours of artificial light daily. At the same time, gradually begin reducing the temperature until the juveniles become inactive. During this period provide access to water daily. A small bath with slightly tepid water is the most effective method of encouraging drinking.
After two or three weeks during which no feeding has occurred, the juveniles are ready for hibernation and can be packed into well insulated boxes, and placed in a room with a stable temperature of approximately 5ºC. USE A RELIABLE THERMOMETER AT ALL TIMES TO CHECK TEMPERATURES! Remember that juveniles can freeze very quickly, so take all necessary measures to guarantee that this cannot happen. By the same token, check regularly if temperatures begin to approach 10ºC, when the juveniles may reactivate.
Most juveniles can be safely hibernated (brumated) for a period of between eight and twelve weeks, The boxes should be placed in a warm room and as the tortoises begin to move they can be transferred to a brightly lit and warm terrarium or (if weather permits) directly outside to a warm and sunny location.
The second method uses identical induction procedures but allows the juveniles to bury themselves in a large earth tray. This tray is then transferred to a cool room or refrigererator. No boxes are therefore used. This method has two theoretical advantages:
The surrounding additional thermal mass of the earth tray reduces the danger of sudden core temperature fluctuations being experienced by the juvenile.
There is significantly less danger of dehydration occurring during brumation.
Both methods have proven safety records and have been used with hatchlings only a few months old. The use of a refrigerator is discussed in depth in several separate articles on this website.
The precise depth of soil required will vary according to the size of the animals involved, but for small juveniles and hatchlings we found that about 50mm worked well. Obviously larger animals will require additional depth. Standard plastic seed or storage trays make suitable containers.
When using the earth tray method, we strongly suggest using at least two separate and reliable digital thermometers, one with a remote probe that can be buried at the same depth as the tortoises, the other measuring ambient (air) temperature in the immediate surrounding environment. Preferably, these should have audible alarms if a temperature exceeds a preset point, either high or low. You will notice that the buried probe is far more stable than the ambient sensor, which is a good thing, and demonstrates just how effective this method is. These days, you can also get entirely remote thermometers that transmit wirelessly and connect to a computer or mobile phone app. These are very useful, but be aware that if used inside a metal-cased refrigerator or similar unit, this could block the signal. Additionally, the use of data loggers for long-term monitoring is also highly recommended.
It might be tiny, and only hatched a matter of weeks previously, but in the wild this juvenile will bury down and brumate alonside adults in the same location.
Certainly do not believe internet 'myths' and advice from people who do not really understand these animals that juveniles cannot brumate until they are a certain size, or certain age. That is complete nonsense. In the wild, Testudo species typically hatch in mid-September to early October, and can be buried down, brumating, by December. They typcally emerge in late March or April, depending upon precise location and altitude.
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(c) 2024 A. C. Highfield/Tortoise Trust
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