Wildlife roadkill and COVID-19: a biologically significant, but heterogeneous, reduction.
Collisions with vehicles are a major cause of wildlife mortality. During the COVID-19 pandemic, many countries enforced lockdowns that reduced vehicular traffic and consequently wildlife-vehicle collisions. However, no study has yet explored how traffic-related mortality declined across multiple species of wildlife, leaving doubts about the species-specific impact of COVID-19 on wildlife ecology and management. We modelled how two lockdowns (in spring and autumn 2020) influenced wildlife-vehicle collisions throughout Slovenia, in central Europe, by comparing weekly roadkill in 2020 with 2010-2019 time series for European roe deer (n = 53,259), red fox (n = 9,889), Eurasian badger (n = 5,170), brown hare (n = 5,050), stone marten (n = 4,267), wild boar (n = 1,188) and red deer (n = 1,088). During the spring lockdown (16 March-30 April 2020), we observed far fewer collisions than expected for roe deer and badgers. During the autumn lockdown (20 October-31 December 2020), we observed significantly fewer collisions for roe deer and wild boar, but we noted an excess of collisions with badgers. Traffic reduction had a major influence on roe deer, whose roadkill decreased between 156 and 321 individuals. Heterogeneous changes in road mortality across the seven studied species indicate that reductions in human mobility can trigger complex species-specific dynamics in wildlife assemblages, which may generate compensatory effects beyond lockdowns. For some species, such as roe deer, local reductions in the number of roadkill attained a significant fraction of the overall mortality. This could affect local population dynamics in cases where lockdowns are repeated over a number of years. Policy implications. Management aimed at reducing vehicular traffic, and therefore human disturbance and roadkill, can be evaluated using time-series analysis of data on multiple species. During times of restricted human movement, local-scale reductions should be estimated and accounted for in adaptive management, such as for planning culling quotas, to minimize their ecological and socio-economic impacts while optimizing the outcomes of science-based population management.