This imprint in the sand was left by a sleeping Sundara, an eight-year-old Asian elephant at Chester zoo. Elephants lie down on their sides to sleep for around four hours a night and usually turn over once, meaning they sleep for approximately two hours on each side.
All of the zoo paddocks are covered in a thick layer of sand which gives the elephant herd a nice, soft surface to sleep on. The elephants prefer to sleep on a slight slope, so every couple of days the sand is turned over and banked up into piles for them to lean against.
Every night zoo staff record what happens and review the footage the next day. This allows them to note where the elephants have slept, who they have been sleeping next to and how long they have slept for.
They can therefore check that everyone is getting enough sleep, that the babies aren't keeping the older girls awake all night, and keep an eye on the social dynamics of the group.