According to a recent study, wild African elephants sleep for the shortest time of any mammal.
The elephants sleep for only two hours, mainly at night.
Elephants in zoos sleep for four to six hours a day, much longer than the elephants in the wild that sleep mainly at night for only two hours.
Sometimes elephants stay awake for several days when they travel long distances, perhaps to escape lions or poachers.
They only fall into dreaming sleep every three or four days, when they sleep lying down rather than on their feet.
How elephants survive on so little sleep is a mystery.