An adult gerbil spends up to 30% of its “active time” doing stereotypic digging in the corner of its cage. That would never happen in nature, and many researchers have hypothesized that the reason captive gerbils develop stereotypic digging is that they have a biological need to dig that they can’t express inside a cage.

On the other hand, in nature gerbils don’t dig just to be digging. They dig to create underground tunnels and nests. Once they’ve hollowed out their underground home, they stop digging. Maybe what the gerbil needs is the result of the digging, not the behavior itself. A Swiss psychologist named Christoph Wiedenmayer set up an experiment to find out. He put one set of baby gerbils in a cage with dry sand they could dig in, and another set in a cage with a predug burrow system but nothing soft to dig in. The gerbils in the sand filled box developed digging stereotypies right away, whereas none of the gerbils in the cage with burrows did.