Studies like this remind me of the simple joys and knowledge science can bring. Researchers in the Netherlands wanted to test whether animals in the wild would run on an exercise wheel, or if that behavior is limited to those in captivity. To test this, they set up running wheels in locations with wild mice, along with infrared sensors, a camera, and food to entice the critters.

Not only did a find that wild mice would run inside the wheel, but various other critters such as shrews, frogs, and slugs. A summary of their results (Figure 2 of their paper):

While most mice ran for a short amount of time (see video), 20% of mice ran for more than 1 minute, with one mouse running up to 18 minutes.

In case anyone was concerned about the food affecting the results, the researchers removed the food and still found animals running in the wheel. With no obvious rewards for the animals, it remains open why they run voluntarily on a wheel. Is it enjoyment? A need for speed? Either way, it's comforting to know that pet rodents running on a wheel are still behaving naturally, and not acting out some neuroses from captivity =P.