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Providing evidence to improve practice

Individual study: Do dry ledges reduce the barrier effect of roads?

Published source details

Villalva P., Reto D., Santos-Reis M., Revilla E. & Grilo C. (2013) Do dry ledges reduce the barrier effect of roads? Ecological Engineering, 57, 143-148


This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.

Install ledges in culverts under roads/railways Terrestrial Mammal Conservation

A replicated, controlled study in 2008–2009 of 32 culverts under roads in southern Portugal (Villalva et al. 2013) found that under-road culverts with ledges were used more by two mammal species, less by two species and to a similar extent by one species compared to culverts without ledges. Culverts with ledges were used more by stone marten Marte foina and genet Genetta genetta (data reported as model results). However, red fox Vulpes vulpes and badger Meles meles used culverts with ledges less than they used those without ledges (data reported as model results). The use of culverts by European otter Lutra lutra was not altered by the presence of ledges (data reported as model results). In January–March 2008, wooden ledges, 50 cm wide, were installed in 15 culverts and no ledges were installed in 17 culverts. Two video cameras with movement and heat sensors were placed at one entrance of each culvert. Marble dust was spread covering the width of the culvert for monitoring footprints. Each culvert was monitored for seven consecutive nights, in each season, for a year after ledge installation.

(Summarised by Phil Martin)

Install fences around existing culverts or underpasses under roads/railways Terrestrial Mammal Conservation

A replicated, before-and-after, site comparison study in 2008–2009 of 64 culverts under roads in southern Portugal (Villalva et al. 2013) found that fences connecting to existing under-road culverts did not alter mammal road mortality. After fence installation, there was a similar number of mammals killed by traffic (19 road-kills) compared to before (20 road-kills). There was also no significant difference in mammal road-kills between road sections where fences were installed (19 road-kills) and those that were not fenced (13 road-kills). In April 2008, 100-m-long fences with 2.5-cm mesh, buried to 50 cm deep and extending 50 cm above ground, were installed alongside the road at each side of 32 under-road culverts. These were in addition to existing livestock fencing. Another 32 culverts in the same area that were unfenced were selected for comparison. The number of mammals killed by traffic was recorded by highway maintenance staff for 10 months before and 10 months after fence installation.

(Summarised by Phil Martin)