Linking habitat composition, local population densities and traffic characteristics to spatial patterns of ungulate-train collisions.
Abstract
The total length of railways worldwide exceeds 1 million kilometres and recent railway development directly impacts wildlife because of animal-train collisions. Few studies, however, have analysed factors driving ungulate-train collisions. We analysed over 3,500 ungulate-train collisions including roe deer, red deer, wild boar, and moose collected in 2012-2015 in Poland. We compared train traffic characteristics (e.g. traffic intensity, speed, rail curvature), land-use and habitat characteristics (e.g. share of forests and build-up areas) and local ungulate population densities at collision sites and random sites distributed along the rail network. Forest coverage generally increased, while urban areas decreased ungulate collision risk. Local density of ungulate species had a strong positive relation to the relative collision risk in all four ungulate species, but above certain densities, the risk levelled off for all four species. Train speed and train traffic intensity were positively associated with elevated collision risk in all four species, but the latter in a nonlinear manner reached an asymptote at the level of c. 10 trains per day. Rail curvature also increased probability of collisions with roe deer and red deer and possibly also wild boar. Mortality rate of ungulates on railways in Poland is estimated to be 0.13%-0.42% of annual hunting bags of studied species assuming that only one individual is killed at each occasion and ignoring undetected collisions. These values are expected to increase in the near future due to increasing train speed in Central European countries. Synthesis and applications. Ungulate-train collisions spots are characterized by surrounding forest, rail curvature, high train speed, and a moderate to high train traffic intensity. To reduce collision risk in a cost-effective way, we suggest prioritization of mitigation actions at sections of the railway characterized by those factors, for example, by fencing and various warning devices. Due to nonlinear correlation between collision risk and population density, reducing density of ungulates will most likely reduce collision risk only marginally, and only in regions of low population densities where collision risk is relatively low anyway.