Influence of caging conditions on captive behaviour and recapture rates of wild wood mice (Apodemus sylvaticus)

Wild animals can be held in captivity for research and released back into the wild later. However, since in most of those cases, the primary goal of the study is not the release of animals, the captivity conditions might not be explicitly designed to support survival after release into their original habitat. This study aimed to evaluate the effects of caging conditions on the captive behaviour of wild wood mice ( Apodemus sylvaticus ), to analyse post-release recapture rate and monitor body mass across different stages: capture, captivity, and recapture. To fulfil our aim, we captured wood mice and assigned them to three different groups: i) FIELD: animals that were captured and immediately released on site, ii) LAB: animals held in captivity under standard laboratorial caging conditions, and iii) NAT: animals held in cages that included natural enrichment elements. All animals were individually marked. For all animals held in captivity, we weekly assessed anxiety (using Dark-Light tests) and behavioural stress-responses (observation of stereotypic behaviours and urine marking behaviour). Additionally, we recorded their body mass. After 30 days, animals were released, and recapture sessions took place over the following month, during three nights per week. Our results showed that caging conditions modulated behavioural stress-responses during captivity. Initially, mice in NAT caging conditions showed lower levels of anxiety in the dark-light test and less urine marking, but over time, animals in the NAT and LAB conditions converged to similar levels. In contrast, the performance of stereotypic behaviour and body mass did not differ between caging conditions and week of testing. Following release, we found no marked differences among groups in post-release trappability. Overall, this study shows that natural enrichment delayed, but did not prevent, the adjustment of wild wood mice to captivity. Although post-release data are limited, this adjustment does not appear to affect the reintegration of these animals into their natural habitats. These findings provide valuable guidance for refining maintenance protocols for wild-caught small mammals, particularly wood mice. • Natural enrichment delayed adjustment but did not affect post-release survival. • Caging conditions had no effect on body mass or short-term survival outcomes. • Enrichment improved welfare and preserved natural behaviours during captivity.