Effects of culverts and roadside fencing on the rate of roadkill of small terrestrial vertebrates in northern Limpopo, South Africa

Published source details Collinson W. J., Davies-Mostert H. T. & Davies-Mostert W. (2017) Effects of culverts and roadside fencing on the rate of roadkill of small terrestrial vertebrates in northern Limpopo, South Africa. Conservation Evidence, 14, 39-43.
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This study is summarised as evidence for the following.

	Action	Category
	Dig trenches around culverts under roads/railways Action Link
	Install fences around existing culverts or underpasses under roads/railways Action Link
	Install tunnels/culverts/underpasses under roads/railways Action Link
	Install barriers and crossing structures along roads/railways Action Link

Dig trenches around culverts under roads/railways

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.

(Summarised by: Ricardo Rocha)
Install fences around existing culverts or underpasses under roads/railways

A randomized, replicated, controlled, before-and-after study in 2015 along a road through dry savanna in Limpopo, South Africa (Collinson et al. 2017) found that installing fences around existing culverts reduced mammal road casualties. Results were not tested for statistical significance. One scrub hare Lepus saxatilis was detected as a roadkill near fenced culverts compared to two bushveld gerbils Tatera leucogaster detected as roadkills before fencing was installed. Concurrently, two multimammate rats Mastomys sp. were detected as roadkills near unfenced culverts after fence installation at treatment sites compared to one before fence installation. The study was conducted along six 400-m-long road segments with culverts. In three segments, a 70-cm-high fence was erected extended 200 m along both sides of the road on either side of the culvert. The fence was approximately 2 m from the road verge, sloped at 45° away from the road and extended 30 cm below ground. Three segments remained unfenced. Roadkills were counted in all sites during a 20-day period before fences were installed (January 2015) and a 20-day period after (February 2015). Roadkills were counted by an observer in a car moving at 40–50 km/h.

(Summarised by: Ricardo Rocha)
Install tunnels/culverts/underpasses under roads/railways

A site comparison study in 2015 along a grassy verge in Limpopo Province, South Africa (Collinson et al. 2017) found that incidences of reptile road casualties were the same whether or not there were concrete underpasses (‘culverts’) installed. Results were not statistically tested. When there were culverts, numbers of reptiles killed on the road were the same as when there were not (26 individuals found in both circumstances). A road with 17 culverts was selected. Surveys of reptiles killed on the road were carried out at sunrise in a vehicle along a 12.3 km long stretch of road for 20 consecutive days each in January and February 2015.

(Summarised by: Katie Sainsbury)
Install barriers and crossing structures along roads/railways

A randomized, controlled, before-and-after study in 2015 along a grassy verge in Limpopo Province, South Africa (Collinson et al. 2017) found that adding trenches or barriers to direct reptiles to concrete road underpasses (‘culverts’) did not reduce reptile roadkill numbers. Overall numbers of small terrestrial vertebrates killed were statistically similar after trenches or barriers were erected (before: 0.33 roadkill/day/km vs after: 0.04 roadkill/day/km). After trenches or barriers were erected 0–1 reptiles were killed on the road compared to 1–2 individuals before they were put in place. Based on areas of high roadkill, pre-existing concrete culverts on a 12.3 km long road stretch were selected and randomly chosen to be adapted by the addition of a barrier (70 cm high, 30 cm below ground, 3 culverts), or a trench (30 cm deep, 3 culverts), or no changes were made (3 culverts). Trenches and barriers were built parallel to the road (approximately 2 m from the edge), 200 m long either side of the culvert (400 m total length). Roadkill surveys were carried out by vehicle for 20 consecutive days before trenches and barriers were built in January 2015 and afterwards in February 2015 (20 consecutive days).

(Summarised by: Katie Sainsbury)