The role of small structures for stoats in agricultural landscapes

• Small structures like branch and stone piles enhance farmland habitat conditions. • Although often recommended for small mustelids, their effects remain understudied. • Stone piles benefit stoats in the agricultural landscape. • Larger piles and higher number of piles in a 100 m radius positively affect stoats. The installation of small structures such as branch and stone piles has been recommended by experts for enhancing habitat conditions for biodiversity in intensively used agricultural landscapes, particularly for stoat ( Mustela erminea ) and weasel ( Mustela nivalis ). However, quantitative evidence regarding the effectiveness of such structures is lacking. In this study we investigated the influence of small structures and other surrounding landscape elements on these two mustelid species across the Swiss lowland agricultural landscape. Over the course of two years (2022 and 2023), we used scat-detection dogs, visual scat surveys, and camera traps to sample populations of these species in 420 plots distributed across 28 study sites. Of these plots, 187 harboured a branch pile, 94 a stone pile, while 139 had no small structure. Overall, when considering both scat and camera trap data, stoats were detected at 26 of 420 (6.2%) plots, but only one weasel was recorded, indicating a low mustelid occurrence across our sampling sites. Multi-scale linear models revealed a significant positive effect of small structures on stoat abundance and a preference for stone piles over branch piles. Forest negatively affected stoat occurrence, possibly reflecting a preference for open habitat where small rodents thrive, notably water voles and common voles. Our results underscore the importance of retaining or reinstating small structures, in particular stone piles, in the agricultural landscape to support stoat populations. Nevertheless, we call for ensuring the presence of both stone and branch piles to provide habitat features benefitting a diverse array of species.