Assessing the importance of field margins for bat species and communities in intensive agricultural landscapes

Landscape simplification and degradation through agricultural intensification is widely recognized as a main driver of biodiversity loss. In intensively used agricultural landscapes, patches of semi-natural habitats and particularly connections between them are of high importance for many taxa. Vegetated connections like hedgerows are especially important for foraging and commuting of mobile taxa such as bats. However, the interest of another treeless linear habitat - herbaceous field margins - remains unstudied for insectivorous bats. Field margins are nevertheless known as an important habitat for other taxa, including bat prey. Here we assessed the importance of field margins for bats compared to other landscape variables. We measured bat activity based on a repeated passive acoustic monitoring during 17 complete nights in summer on 112 study sites in an intensively used agricultural landscape. Each night, we sampled bat species activity and community metrics (i. e. species richness and community habitat specialization index) at different distances to field margins, and along a gradient of relative density of field margins. To compare field margin effects with other landscape variables, the sampled sites were selected by keeping a large variability in these other variables (land-cover Shannon diversity index, forests, hedgerows, water bodies, main roads, urban areas, grasslands, number of crops and rapeseed percentage). Only Myotis sp. were affected by herbaceous field margins. Specifically, the Myotis group activity decreased with the distance to herbaceous field margins (i.e. towards field crop cores), and positively correlated with relative density of herbaceous field margins, for which the effect size was comparable to other landscape variables. However, other landscape variables such as the proportion of and the distance to forests, the relative density of and the distance to hedgerows or land-cover Shannon diversity index, affected species richness, community specialization index, and bat activity of species from open, edge and narrow-space foragers, including the Myotis group as well. Our results highlight that herbaceous field margins have a positive effect on the activity of narrow-space bat foragers as Myotis species, but do not replace other landscape variables that drive the activity of the whole community.