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Providing evidence to improve practice

Action: Dig trenches around culverts under roads/railways Terrestrial Mammal Conservation

Key messages

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  • One study evaluated the effects on mammals of digging trenches around culverts under roads and/or railways. This study was in South Africa.




Supporting evidence from individual studies


A replicated, randomized, controlled, before-and-after study in 2015 along a road through dry savanna in Limpopo, South Africa (Collinson et al. 2017) found that digging trenches alongside culverts did not reduce the number of mammals killed on roads. Results were not tested for statistical significance. One mammal (a South African pouched mouse Saccostomus campestris) was detected as a roadkill near culverts after trenches were dug and one (a red veld rat Aethomys chrysophilus) was found before they were dug. Over the same period, near culverts where no trenches were dug, two multimammate rats Mastomys sp. were detected as roadkills after trenches were dug at treatment sites and one was found before trenches were dug. The study was conducted in January–February 2015 along 400-m-long road sections with 2-m-wide culverts. In three sections, a 30-cm-deep trench, 2 m from the road verge, was dug for 200 m on either side of the culvert. Three road sections had no trench. Roadkills were counted at all sites over 20 days before the trench was dug and 20 days afterwards, by an observer in a car moving at 40–50 km/h.

Referenced papers

Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.