Beyond the enclosure: A decade of monitoring reveals altered traits in a European ground squirrel colony with implications for a recovery program

Effective integrated conservation programs critically depend on high-quality animals from ex situ breeding, specifically those that are genetically diverse and physically healthy, yet insufficient scientific rigor in husbandry protocols can lead to unintended, detrimental consequences that compromise reintroduction success. Drawing on over a decade of long-term monitoring data for the European ground squirrel (Spermophilus citellus), we compared a semi-captive, predator-free and supplementary-fed colony with an adjacent free-ranging population to assess the effects of enclosure management on key population traits such as body mass and female reproduction. We found that the semi-captive system, despite one of its goals of producing animals for release, unintentionally altered traits in ways that could negatively impact its long-term viability and condition of released animals, particularly in terms of body mass and reproductive success While males tended toward higher body mass (though not significantly), only non-lactating females exhibited a statistically significant difference, with a mean increase of 28.4% compared to free-ranging counterparts. Conversely, juveniles born inside the enclosure were significantly lighter, suggesting they might be outcompeted by adults for limited resources such as food and space. Furthermore, a high proportion of non-lactating females inside the enclosure suggests that either high density or surplus food resources may negatively affect breeding success, though the distinct ecological impacts of these factors require further investigation. Practitioners need to implement science-based husbandry protocols and develop feeding strategies that minimize adult-juvenile competition, emphasizing that these recommendations are derived from empirical evidence presented in this study. A rigorous, integrated approach including systematic long-term monitoring must be adopted to mitigate unintended negative consequences, thereby maximizing conservation outcomes and preventing resource waste, with particular attention to adaptive management informed by ongoing scientific evaluation.