Bridging the gap between lab and field sleep studies: a proof-of-concept for studying wild rats in semi-captive environments

Sleep is a vital and universal behavior distinct from mere inactivity, yet its ecological role remains poorly understood due to methodological limitations in recording sleep in the wild. Using a small, low-power biologger, collecting brain activity, body movements, and physiology, we recorded key sleep parameters in wild black rats (<i>Rattus rattus</i>) under semi-captive conditions. We developed a rapid (<1 h) surgical procedure using a custom subdermal flexible electrode, providing signal quality comparable to standard cortical electrodes. Our validated semi-captive setup allowed animals to remain in their natural environment with ad libitum food and social contact while minimizing interactions. This protocol enables the study of sleep's ecological role and the influence of environmental factors on sleep expression, offering insights into its evolution. Additionally, it can help clarify sleep's central role in the context of global environmental change. By monitoring general behavior and sleep patterns in four wild rats for up to 10 days post-surgery, as well as feeding behavior for over a month, we observed no signs of pain or stress, with sleep patterns stabilizing within 2 days. This approach provides a unique tool to assess sleep variability and flexibility, demonstrating its feasibility for studying sleep in small (<200 g) wild animals.