A4 Motorway Wildlife Crossings — Camera-Trap Monitoring in the Lower Silesian Forest (Poland)

The A4 motorway's Zgorzelec–Krzyżowa section cuts through the Lower Silesian Forest, a large tract in western Poland recently recolonised by grey wolves (Canis lupus). To assess whether the road fragmented this recovery, researchers monitored 6 overpasses (30–45 m wide), 5 large underpasses (33–114 m) and 4 small underpasses (15–19 m) using track-beds and camera traps over three years (2010–2013).
Wild species accounted for 51.5% of all recorded crossings (versus 34.8% human and 13.7% livestock/pet use); among wild animals, ungulates made 77.4% of crossings, lagomorphs 15% and carnivores 7.6%. Researchers from the Association for Nature "Wolf", led by Robert W. Mysłajek and Sabina Nowak, documented the first hard evidence of regular, repeated overpass use by three distinct wolf packs – direct proof that wide vegetated overpasses, not just underpasses, support large-carnivore recolonisation.
Species richness and crossing frequency of wild mammals were consistently higher on overpasses than underpasses, and use by wild species, domestic animals and people all increased over the three study years as vegetation matured and animals habituated to the structures.
Poland's road authority (GDDKiA) has since scaled this approach nationally: by the end of 2018 it had built roughly 2,960 wildlife crossing structures across the country's road network, and it reports that fitted with the guiding fencing, animal-vehicle collisions on equipped sections fall by several tens of percent – though this national aggregate figure is GDDKiA's own reporting rather than independently peer-reviewed.

Read the full analysis: https://www.archiwum.gddkia.gov.pl/pl/a/35554/Budujac-nowe-drogi-zapewniamy-swobode-migracji-zwierzat