CHAPTER 1 INTRODUCTION
5. FAUNA
2.5 Species-specific mitigation recommendations
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were less successful in the long-term (Waring et al. 1991; D’Angelo et al. 2006).
However, they may be effective when combined with other structures, such as fencing and the recommended lip bent at right angles at the top of the fence (Waring et al. 1991; FHWA 2003), roadside vegetation management (Smit & Meijer 1999;
Kociolek et al. 2010) and increased active signage (Bertwistle 1999).
Figure 5.4: A photograph of a deer reflector (Strieter-Lite ® 2002).
A further recommendation is to make antelope species more visible, particularly those species prone to browsing at night. Two-thousand reindeer were fitted with antler tags over the festive period in December 2010 in Norway, in the hope that the reflective collars increased visibility and therefore protected against collisions. A test exercise with a snowmobile showed that the marked reindeer were much easier to spot in the dark (The Telegraph 2010), but no further data are available. This could be a relatively cheaper method to trial than upgrading fences.
Of the mammal roadkill, scrub hare had the highest levels of road mortality in the GMTFCA, with a total of 118 observed across all three seasons. Of these, 67 were sexed, and more males (69%) were detected as roadkill than females (Appendix B).
Despite a peak during hot/wet summer months, scrub hares are aseasonal breeders (Skinner & Chimimba 2005). When a female is in oestrus, she is often accompanied by more than one male (Skinner & Chimimba 2005) which may explain the higher ratio of male to female roadkill. Additionally, scrub hares are nocturnal and my data showed that nocturnal species were more likely to become roadkill than diurnal species. Whilst population figures were not available for scrub hare, they appear to be an abundant and prolific species (Skinner & Chimimba 2005) and road mortality is
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unlikely to impact populations. However, dead carcasses often result in a cascade effect along the trophic hierarchy where scavenging animals seek out roadkill and often become roadkill themselves (Antworth et al. 2005; Dean & Milton 2009).
Mammal body size is often an excellent indicator of vulnerability to becoming roadkill (Fagan et al. 2001; Cardillo 2003; Ford & Fahrig 2007; Barthelmess & Brooks 2010).
Over one third of rodent species (Rodentia) were found to have a high incidence of roadkill in total numbers in the GMTFCA (Appendices B & G), but the impact on the population may be less than for a large mammal species, such as the African civet (that had 16 road mortalities recorded; Appendices B & G) where reproductive rates are much slower and litter size is smaller (Feldhamer et al. 2007).
Whilst more effective fencing may assist with preventing these species from crossing the road, the barrier that is then created may actually impact the species more than the threat of roadkill as populations become more divided and fragmented (Dodd et al. 2004; Taylor & Goldingay 2010). A solution therefore, would be to not prevent species from crossing roads but to use fencing to direct them to wildlife crossing passages (Forman et al. 2002). Groot Bruinderink & Hazebroek (1995) suggest identifying locations at which wildlife may cross to create a wildlife crossing. Fencing can then be added to prevent animals from crossing everywhere, and instead funnel and guide the individuals towards the passages (Figure 5.5).
Figure 5.5: Two photographs showing how mesh fencing can be used to guide animals towards wildlife passages (a) small mammal wildlife passage leading to a culvert, Australia (van der Ree 2012), (b) Gopher Tortoise wildlife passage, Texas, USA (Lake Jackson Feasibility Study; Sewell 2004).
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This may be effective not just for small mammal species but for all small terrestrial taxa. For example, Flap-neck Chameleon suffered the highest road mortalities for Reptilia with 45 roadkill detected (Appendices B & G) with a further 80 observed crossing the road (Appendix D). Flap-neck Chameleon are largely arboreal, but are found on the ground during the breeding season which occurs from March to May (during the hot/wet season; Branch 1998). Males will actively seek out females, often crossing roads to their detriment, whilst females seek damp soil to lay their eggs (Branch 1998). Due to its size (120-140 mm) and being one of the larger chameleon species, the Flap-neck Chameleon is feared by many tribal people and is the subject of much folklore (Branch 1998). This may result in purposeful killing of them on the roads (Bonnet et al. 1998).
Few amphibian species (n = 3) were detected during my roadkill surveys with a total of 48 road mortalities (Appendix A). Of these, 85% were attributed to the Eastern Olive Toad (Amietophrynus garmani), with 90% occurring during the hot/dry season.
This was over a three-day period when 60% of the rain for the hot/dry season occurred. Many amphibian species are therefore only active for a short and specific period of the year. For example, the endangered Western Leopard Toad (Amietophrynus pantherinus) in the Western Cape (South Africa) is active for ~one week per year in August, when it crosses a major road in search of a mate (Rebelo et al. 2004). Thousands are killed during this annual mating ritual, and consequently, volunteers are on stand-by to physically assist the toads crossing the road. The amphibians detected during my study were not only active at a specific period of the year, but were also found in one particular section of the transect. (Appendix G).
Combined with seasonal, species-specific signage, existing features (such as culverts) could be modified to create wildlife passageways to assist species such as the Flap-neck Chameleon and amphibians in crossing the road. A variety of animals are known to use wildlife crossings and movement patterns of many wildlife species are often associated with drainage lines (Sagastizabel 1999; Smith et al. 1999; Smith 2003; Caltrans 2003). Drainage culverts (Figure 5.6a) beneath roads can be modified with mesh fencing to encourage small vertebrate species and amphibians to cross (Figure 5.6b; Boarman & Sazaki 1996; Jackson 2000), whilst modified culverts with add-on shelves, slightly above the water surface, may be incorporated for small mammals and reptiles accessing the culvert (Figure 5.6c; Evink 2002). The
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additional cost is minimal in comparison to the overall cost of the structure (FHWA 2003).
Figure 5.6: Three photographs showing different types of underpass design for small mammals, reptiles and amphibians (a) amphibian underpass using existing road features (FHWA 2012b), (b) fine mesh fence and culvert for small mammals in Europe (Evink 2002), (c) small mammal wooden plank crossing in a drainage culvert (Cramer 2004).
Bridges can also be modified with the addition of a shelf pathway going under the bridge to create a wildlife passage (Figure 5.7a and b), whilst more permanent verge shelving can aid directing wildlife towards crossings (Figure 5.7c).
Figure 5.7: Photographs showing (a) and (b) a modified shelf pathway under a bridge for small mammals, The Netherlands (van der Ree 2012), and (c) a wall with a lip and culvert to prevent amphibians and small reptiles from crossing the road. The wall also directs them towards the culvert (bottom left of the photograph). (FHWA 2012a; Photograph © Forsyth, D).
These small underpasses are not appropriate for larger mammal species (i.e.
antelope) and therefore larger underpass structures would need to be incorporated in the future planning of roads. However, this may be a challenge for South African road ecologists, as many landowners who own wild game do not want their property
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linked with adjacent properties, and prefer to keep their wildlife separated by fences.
Any proposed wildlife passages such as overpasses and underpasses, as used in other countries (Figure 5.8), are likely to be met with resistance. Therefore, these larger wildlife crossing structures may be more applicable to protected areas and wildlife conservancies that are divided by roads, such as Hluhluwe-iMfolozi Game Reserve (KwaZulu-Natal, South Africa). However, these structures are expensive to build and also require monitoring and extensive maintenance.
Figure 5.8: A photograph showing the Mount Elephant Corridor in Kenya with elephants utilising the underpass beneath the Nanyuki-Meru Highway (Mount Kenya Trust 2012). The underpass cost US$1 million to build.
Avian roadkill was the most impacted taxa (43%) in my study. A total of 69 Helmeted Guineafowl roadkill were detected with the majority occurring during the hot/wet season (Appendix D). These birds were commonly seen feeding on roadside verges (pers.obs.). A total of 63 nightjar roadkill were recorded with the majority being during the hot/wet season. In addition, nightjar species are generally more prevalent in the GMTFCA from September to March (Hockey et al. 2005), which would explain why high roadkill numbers were observed for this bird family during this period (Appendix C). Signage erected during this time alerting drivers to nightjar on the roads may reduce mortality rates.
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Global mitigation efforts for birds are limited due to the very nature of bird behaviour.
Birds react to traffic by flying away, and this very act is often what results in their mortality as the down-draught from traffic ‘sucks’ them in and results in a collision (Dreyer 1935). Unlike terrestrial species, they are unable to use wildlife passageways, although Orlowski (2008) suggests constructing high embankments (Figure 5.9) on either side of the road to force birds to fly higher, and therefore avoid being pulled into the down-draught of vehicles. This may be an effective deterrent to implement in certain areas of the GMTFCA where large flocks of birds are likely to occur.
Figure 5.9: A photograph showing a dual-carriageway in Australia with raised roadside embankment either side of the road (van der Ree 2012).
Two snake species also suffered high roadkill numbers with a total of 22 Brown House Snake and 24 Mozambique Spitting Cobra accounting for 31% of snake (Squamata) roadkill. Snakes are often resented and misunderstood by people with the attitude of ‘kill first’, identify later’. Consequently, this may result in the deliberate killing on roads (Bonnet et al. 1998). Both the Mozambique Spitting Cobra and the Brown House Snake are nocturnal species with the former much feared due to its highly venomous bite (Branch 1998). If snakes are deliberately killed on roads, then it is easy to understand why the Mozambique Spitting Cobra was targeted. However, this does not explain why the Brown House Snake may be deliberately targeted above the other 22 snake species detected as roadkill. One possible suggestion may be due to the similarity in appearance of the Brown House Snake to the juvenile
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Mozambique Spitting Cobra which are both brown in colour and may easily be mistaken for one another at night. Alternatively, it may just mean that both the spitting cobra and the house snake are the two most abundant snake species in the area.
Mitigation measures for snakes may involve modifying culverts for their use, but it is my opinion that understanding snake behaviour may motivate some motorists to alter their driving behaviour to avoid encounters with animals on roads. This may be done through the publishing of information in popular media channels, such as newspapers and magazines, thus portraying certain species more positively, providing information about their conservation status, and why it is important to protect them.
Of the 162 vertebrate species detected as roadkill, 88 were arboreal and 74 were terrestrial. The majority of the arboreal species were from the taxon group, Aves (81), with five from Mammalia and two from Reptilia. No cluster areas were identified for either of these two taxa nor did they occur in high roadkill numbers (apart from the Flap-neck Chameleon). Therefore, no mitigation measures are proposed for these seven species in the GMTFCA.