Does voluntary wheel running exist in Neotropical wild mammals?

Running wheels are frequently used to improve the welfare of captive animals, increase environmental enrichment, and, by doing so, reduce stereotypic behaviors. It is, however, still debated whether or not wheel running itself is a stereotypy. New evidence emerged when Meijer and Robbers (2014, Proc. Royal Soc. B) reported voluntary wheel running of wild animals in the Netherlands. Since stereotypic behaviors are exclusively attributed to captive animals, the occurrence of wheel running in the wild suggests that this behavior is non-stereotypic. Our study explores that same line of investigation, examining whether wild animals will voluntarily use running wheels in a natural area in Paraguay in comparison to the urban and semi-urban settings in the Netherlands. Of the 1857 small mammal visits we recorded, only two occasions showed evidence of what could be considered as wheel running behavior; over hundredfold fewer than previously reported. The potential reasons for the observed difference in wheel running activity, such as different species pool or seasonality, are discussed. The difference, however, is likely to be due to the much lower probability of Neotropical mammals in a remote natural site encountering man-made objects and experiencing urbanization-related behavioral patterns. Additionally, in the light of our findings, we review the definition of wheel running as a stereotypic behavior.