So, although chipmunks will sleep for days at a time in winter to save energy, when they wake, they need food to stay alive.
Luckily, thanks to that hard shell, nuts store pretty well.
So, they gather nuts throughout autumn and stock-pile them.
Chipmunks make hundreds of trips backwards and forwards to their pantry.
It takes a lot of time and energy.
Flexible cheek pouches make the task slightly easier - - fitting in up to seven nuts at a time.
But there is a problem - other chipmunks that want to steal your stash.
A horde must be defended even if it means fighting for it.
With the thief chased away, the precious stock-pile is safe.
It's everything a chipmunk needs to get through the winter.