Mitigating Road Barrier Effects for Small Mammals: Evidence From Wildlife Passages in the Brazilian Atlantic Forest

Roads significantly impact wildlife through collisions and habitat fragmentation. Wildlife crossing structures aim to mitigate these impacts, but their effectiveness for Neotropical small mammals is largely unknown. During 12 months, we monitored small mammal movements near overpasses, underpasses, and areas without structures (controls) in Rio de Janeiro, Brazil, using capture-mark-recapture. We quantified highway crossings, structure use without crossing, and structure avoidance. Eight small mammal species were recorded, among which were four forest specialists. The marsupials Didelphis aurita and Marmosa paraguayana used overpasses, while the water rat Nectomys squamipes and the four-eyed opossum Philander quica used underpasses. However, only 5%–7% of marked individuals of the latter two species crossed the highway. The remaining four species (Akodon cursor, Metachirus myosurus, Monodelphis cf. iheringi, and Mus musculus) did not use the structures and were uncommon in roadside habitats. The results suggest that locally abundant forest small mammals avoiding roads can use crossing structures, potentially improving population connectivity compared to areas without them. However, rare forest specialists that did not use the passages may require more substantial interventions to enhance their connectivity. This research provides evidence for potential benefits of crossing structures for Neotropical small mammals while highlighting the need for tailored solutions for different species.