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Hibernation and Aestivation
Hibernation is a process of adaptation necessary for the survival of most tortoises in south-east Australia during the winter months. The temperature at which hibernation begins varies considerably. Tortoises in a particular area usually settle down for the winter months within two or three weeks of each other.

When tortoises hibernate, they do so either on land or in the water. No set depth in water appears to be selected; it can range from a few centimetres below the surface to the bottom of the waterhole where they settle among debris. Tests carried out overseas have shown that tortoises hibernating in water absorb oxygen through their cloacal cavities, which enables them to remain underwater for several months.

Most species occurring in eastern Australia south of the Queensland border hibernate or become inactive, but in July 1968 Emydura in the Macleay River (NSW) were still active, although the water temperature was 5ºC. In this temperature a diver would need the insulation of a rubber diving suit, but tortoises show little signs of slower reflexes when being pursued.

Western Australian tortoises apparently do not hibernate. Vincent Serventy reports that in Western Australia the Oblong Tortoise (Chelodina Oblong) does not. Experience with this species in captivity tends to confirm his opinion - they have been observed basking under overcast conditions in mid-June.

In some areas where heat causes surface water to completely evaporate, or where the water temperature rises far above the norm, tortoises will leave the water and aestivate. Aestivation is a state of torpor generally regarded as a parallel to hibernation. After drinking as much as they can tortoises leave the water to seek a damp place where they bury themselves (usually until their carapace is at lease level with the ground) beneath foliage, fallen timber, in rocky crevices, or in holes made by crustaceans. Some tortoises burrow into the mud at the bottom of their pool when the water drops to a dangerously low level, and remain there long after the water has disappeared. Here they stay until rain restores the water level; or if the drought is protracted, they will die.

It would appear that there are other unknown factors that trigger a state of reduced activity in tortoises. Over a period of five years, tortoises were very common in a particular section of the Macleay River and it was usually possible to see large numbers with minimal effort. However, on one occasion a concentrated search failed to locate the tortoises in their usual numbers. Only a few specimens were discovered, usually concealed among algae, weed or sediment. The water temperature was normal 22ºC and although the water level was slightly lower than at any other time during the five year period, some holes still contained water to a depth of 3m and the level did not seem to pose a threat to the tortoises' survival.