To assess a known mitigation measure for effectiveness in reducing wildlife mortality on roads in the Greater Mapungubwe Transfrontier Conservation Area, northern Limpopo.
South Africa has a legal and moral responsibility to conserve its biodiversity, especially species which are of conservation concern. Mitigation measures have been prompted mainly by the human-safety issue posed by animal-vehicle-collisions rather than the effects on wildlife. A variety of mitigation measures have been proposed globally to reduce the impact of roads on wildlife. However, none are actively practiced in South Africa and many successful global mitigation measures are taxon specific. Many mitigation monitoring studies have examined before and after figures for roadkill rates, but little data are available that examine wildlife crossing structures and their use as an effective mitigation strategy for preventing roadkill.
South Africa is fundamentally different to Europe and North America. There are major differences existing between the species of wildlife, landscapes and geography, the density of roads and humans, and funding and support for road ecology research and mitigation measures. However, the information and lessons learned in these developed countries can be implemented and adapted to the South African situation.
Transport infrastructures are a common presence everywhere humans have settled and it is now becoming widely accepted that roads affect many aspects of ecosystems. Roads and traffic are destructive in two ways to animal populations; directly, roads impact wildlife via mortality (i.e. roadkill), and is of immediate impact, and indirectly, by fragmenting a population’s habitat, with this threat only apparent over a period of time. Roads therefore pose a threat not just to the survival of individual animals but also to populations.
South Africa is a country with a ‘fence culture’ with thousands of kilometres of fencing dividing private farms, national parks and individual properties. The disadvantage of fencing is that it can constrain the movement of animals – usually by preventing access to adjacent habitats and impeding dispersal. Less roadkill were detected in the GMTFCA (2012) when there was an electric or game fence, and more when there was a gate, barrier or cattle fence. This suggests that the higher and more permanent the structure, the more effective it is at preventing wildlife from crossing roads. However, in addition to causing increased population isolation, many South African fences are electrified and animals that do try to move through or under the fences may die. A sister publication, published by the EWT in 2007, examined electric fence mortalities on wildlife in South Africa, with a range of recommended mitigation measures to minimise mortality rates.
Fencing is a favoured method for mitigating against the impacts of roads on wildlife in Europe and America, but it limits landscape connectivity for wildlife. Current mitigation practises across the rest of world are implementing measures that connect wildlife habitats by way of wildlife crossing structures. These potentially prevent collisions between animals and vehicles, and include underpasses for livestock on farms, passenger bridges, culverts, and drainage lines. Although generally not built or erected for the express purpose of being a wildlife passage, they may still fulfill this function, since a variety of animals are known to use wildlife crossings.
To encourage landscape connectivity of amphibians, a study in Holland (Ottburg & van der Grift 2013) examined the effectiveness of road mitigation for a common toad population. It demonstrated that 40% of the toads utilised the culverts and crossed the road successfully. Fences were installed along a 1 km stretch of road, and a total of 789 toads were individually marked with the aid of drift fences and pitfall traps. Use of the tunnels were monitored with the help of a pitfall trap at the tunnel exits. In addition, the road was surveyed to assess roadkill rates of unsuccessful crossings. Similar successful mitigation studies for reptiles, amphibians and small mammals have been conducted in the United States, Europe, and Australia.
Movement patterns of many wildlife species are often associated with drainage lines (Figure 1a), or can be modified with mesh fencing to encourage small vertebrate species and amphibians to cross (Figure 1b/1c).
Figure 1: Three photographs showing the use of an underpass design for small mammals, reptiles and amphibians (a) amphibian underpass using existing road features, (b) fine mesh fence and culvert for small mammals in Europe, (c) turtles in Florida using the fence funnel directed towards an underpass
In 2013, South Africa’s first standardised protocol for the detection of roadkill on South African roads was developed. The protocol assists users in collecting data for multiple species of vertebrate roadkill and was used to collect baseline estimates of roadkill in the Greater Mapungubwe Transfrontier Conservation Area (GMTFCA), Limpopo Province.
This study aimed to contribute to filling several gaps in the understanding of factors that affect roadkill. The study site was selected for several reasons. As a conservation area it is home to a wide range of vertebrates, of which six are considered endangered, 12 are vulnerable, and 11 are nationally protected. Over a 120-day period, 1,121 roadkill carcasses were detected and 166 species identified. Birds were the most commonly detected species (52%), and mammals, reptiles and amphibians comprised 26%, 20% and 2%, respectively. ‘Hotspot areas along the transect were identified, with most roadkill occurring for amphibians, small mammals and reptiles in the south-west corner of the transect on the paved road leading to Venetia Mine (Figure 2).
A pilot study examining the uses of culverts and funnel fencing will be implemented in October of this year to determine if there is a reduction post-erection of funnel fencing. Sampling will be conducted pre/during the rains (October – March) when vertebrate activity is most prevalent.