The photo provided shows two BLACK MOUNTAIN TORTOISES digging down into a large pile of dried bamboo leaves. When finished, they will be completely covered with leaves & will utilize the leaves -- as well as warmth from the earth -- to maintain a comfortable temperature for the night. Their movement will be almost none existent during the night & their movement will not return until the warmth of the morning sun & rising temperatures provide the necessary "heat" to re-charge their body functions.
It will not be too many more days & all the tortoises -- I have a total of six -- will have to be relocated to their indoor, Winter quarters, not to return outside until the warm temperatures of Spring.