Wheel in the Wild
Lab mice and rats run on wheels in captivity, but researchers wanted to know if the behavior is natural. To find out, they set out exercise wheels in wild areas.
Although the wheel looks like a cage, animals can come and go freely. [Read More About the Wild Wheel-Runners]
A wild mouse hops on one of the outdoor exercise wheels and takes a spin.
Frog on a Wheel
It wasn't only mice who appreciated the exercise wheels. Frogs, shrews and voles used the equipment, too.
Slug on the Wheel
Even slugs and snails enjoyed taking the exercise wheels for a spin.
Lead researcher Yuri Robbers (center) and associates set up an outdoor exercise wheel.