Tortuga Gazette 28(10): 9, October 1992

Hibernating Desert Tortoises During Their First Winter

by William G. Watson

The general consensus in southern California seems to be that desert tortoises should not be allowed to hibernate during their first winter. However, I feel that if you choose to hibernate your hatchlings in their first year they can survive and prosper.

In September 1980 I had three hatchlings emerge from a clutch of 6 eggs. Val was measured on 9/18 and weighed 19.5 g. Naomi and Tori were weighed on 9/21 and were 25.4 g and 24.8 g respectively. Through the middle of September to the end of October all three ate and gained weight. On 10/27 Val weighed 24.1 g, Naomi weighed 30.8 g and Tori weighed 29.6 g. All three had been kept in a terrarium in a shop area separated from the house and removed from any central heating system. Sometime in November the temperature dropped and all three tortoises became inactive. Val was in a cement pipe and did not emerge after this cold spell. I decided to leave Val in the shop for the winter, and moved Naomi and Tori into the house and into a glass terrarium with a hot rock.

Each tortoise was weighed once a month. As might be expected, Val dropped in weight by about 1 g each month. Both Naomi and Tori averaged around 30 g during this period. By February of 1981 the temperature increased enough to bring Val out of hibernation; on 1/27 Val weighed 20.7 g and increased to 24.5 g on 2/27. In this month Val regained the weight lost during the hibernation period. Naomi and Tori did not do as well. Naomi weighed slightly less on 2/27 (30.2 g) than back in October; Tori weighed slightly more (30.3 g on 2/27).

Unfortunately, both Naomi and Tori were found dead on their hot rocks shortly after this last measurement. My guess is that the brief cold spell may have stimulated all three tortoises to become inactive, and diminished their appetite. Val was able to survive this period by hibernating. However, Naomi and Tori remained fully active, but with a reduced appetite. This combination may have lead to their deaths. Even though Naomi and Tori maintained constant weights, giving me a false impression that all was well, in hindsight I should have expected monthly gains in their weights.

This had been the first clutch of hatchlings I had reared since moving from the warm San Fernando Valley to the much colder Mojave desert. In the Valley a fifteen gallon aquarium and two 25 watt bulbs were sufficient to rear tortoises over the winter. But, in the colder high desert even the addition of a hot rock failed to provide the proper conditions to bring these tortoises through the winter.

I feel that the ability of a hatchling tortoise to survive the winter depends upon the temperature at which it is maintained. Here in the high desert the winter temperature drops into the 20°s F and 30°s F. In the enclosed shop area the temperature stays in the 40°s F. At these temperatures hatchlings remain inactive and use up little of their reserves. A hatchling fed well in its first month should have the reserves to get through a short hibernation of two or three months. If I were to raise hatchlings in a warmer area such as the San Fernando Valley, I would probably not hibernate them since winter temperatures are too warm.

The decision to let your hatchlings hibernate or not should be determined by the local climatic conditions and from observing the behavior of your tortoises. Should your tortoises stop eating or fail to gain weight during the winter, turning off the heat source and letting them hibernate for one or two months may stimulate their appetites. Young tortoises should also be weighed once a month to track their progress.

Bear in mind that there is no single right or wrong way to raise a tortoise and we must find the methods that work best for each of us and the tortoises in our care.