An adaptive plan for prioritizing road sections for fencing to reduce animal mortality

Abstract

Mortality of animals on roads is a critical threat to many wildlife populations and is poised to increase strongly because of ongoing and planned road construction. If these new roads cannot be avoided, effective mitigation measures will be necessary to stop biodiversity decline. Fencing along roads effectively reduces roadkill and is often used in combination with wildlife passages. Because fencing the entire road is not always possible due to financial constraints, high-frequency roadkill areas are often identified to inform the placement of fencing. We devised an adaptive fence-implementation plan to prioritize road sections for fencing. In this framework, areas along roads of high, moderate, and low levels of animal mortality (respectively, roadkill hotspots, warmspots, and coldspots) are identified at multiple scales (i.e., in circles of different diameters [200-2000 m] in which mortality frequency is measured). Fence deployment is based on the relationship between the amount of fencing being added to the road, starting with the strongest roadkill hotspots, and potential reduction in road mortality (displayed in mortality-reduction graphs). We applied our approach to empirical and simulated spatial patterns of wildlife-vehicle collisions. The scale used for analysis affected the number and spatial extent of roadkill hot-, warm-, and coldspots. At fine scales (e.g., 200 m), more hotspots were identified than at coarse scales (e.g., 2000 m), but combined the fine-scale hotspots covered less road and less fencing was needed to reduce road mortality. However, many short fences may be less effective in practice due to a fence-end effect (i.e., animals moving around the fence more easily), resulting in a trade-off between few long and many short fences, which we call the FLOMS (few-long-or-many-short) fences trade-off. Thresholds in the mortality-reduction graphs occurred for some roadkill patterns, but not for others. Thresholds may be useful to consider when determining road-mitigation targets. The existence of thresholds at multiple scales and the FLOMS trade-off have important implications for biodiversity conservation.

The identification of wildlife-vehicle collision hotspots: Citizen science reveals spatial and temporal patterns

“…Then, the share of land covered by each land cover class was quantified in the buffer area surrounding road segments, in order to obtain a gradient for each land cover class and road segment length. Buffer extents were chosen to account for uncertainty around crossing sites (Červinka et al 2015;Valerio et al 2019), and the trade-off between identifying hotspots and covering a large area, which is shown to be most effective at a scale between 200 and 2000 m (Spanowicz et al 2020).…”

Contrasting wolf responses to different paved roads and traffic volume levels

“…However, by contrast, wolf mortality was highest on motorways elsewhere in Spain, with fencing being reported as a key predictor in roadkill (Colino-Rabanal et al 2011). Whilst traffic volume is an obvious explanation of mortality, the effects of fencing may not be immediately apparent, as they are usually thought of as an effective mitigation tool in reducing roadkill (Spanowicz et al 2020). However, if a wolf enters a motorway through gaps in fencing, they may be forced to spend more time on the road searching for an exit, thus heightening their chances of being killed.…”

“…An increasing focus should be allocated to identify drivers of wolf mortality on primary roads (class II) in our study area (Fig. 4), in order to identify segments of roads where mitigation efforts should be prioritised (e.g., crossing structures such as bridges, underpasses, or fencing; Grilo et al 2010;Van der Ree et al 2015;Spanowicz et al 2020). Research has indicated that wildlife-vehicle collisions are not random events, but clustered (Clevenger et al 2003;Ramp et al 2006;Morelle et al 2013;Keken et al 2019).…”

Impact of Road Fencing on Ungulate–Vehicle Collisions and Hotspot Patterns

“…Short wildlife fences may not sufficiently reduce the risk of accidents [63][64][65][66]; however, they are economically more affordable. Long fences are less economically efficient, but may perform better [18,63,66] on roads with the highest traffic intensity [67].…”