Changes in mammal crossings in less than 10 years after the construction of Estonia’s first wildlife overpass

Wildlife passages aim to improve connectivity between habitats fragmented by heavily trafficked roads. However, their effectiveness must be monitored. Kolu ecoduct, Estonia’s first wildlife overpass, was built in 2013 during the reconstruction of the Aruvalla-Kose section of the T2 (E263) road. To evaluate its usage, we analyzed camera trap data from two periods: initial monitoring (March 12, 2015 – October 31, 2016), which recorded 1,585 crossings, and follow-up monitoring (November 6, 2020 – October 25, 2022), which recorded 1,308 crossings. Over this period, the distribution of mammal species using the overpass changed significantly. The proportion of domestic animal crossings declined from 36–9.4%, while large game crossings increased from 19–58%. Small game crossings slightly decreased from 37–31%. Unidentified crossings dropped from 3.6–0.5%. Human presence was rare, decreasing from 4.2% in the initial period to just 0.2% in the follow-up monitoring.