Study

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.

Actions

This study is summarised as evidence for the following.

Action Category

Dig trenches around culverts under roads/railways

Action Link
Terrestrial Mammal Conservation

Install fences around existing culverts or underpasses under roads/railways

Action Link
Terrestrial Mammal Conservation

Install tunnels/culverts/underpasses under roads/railways

Action Link
Reptile Conservation

Install barriers and crossing structures along roads/railways

Action Link
Reptile Conservation
  1. 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)

  2. 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)

  3. 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)

  4. 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)

Output references
What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 19

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.


Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape Programme Red List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Bern wood Supporting Conservation Leaders National Biodiversity Network Sustainability Dashboard Frog Life The international journey of Conservation - Oryx British trust for ornithology Cool Farm Alliance UNEP AWFA Butterfly Conservation People trust for endangered species Vincet Wildlife Trust