Game fence presence and permeability influences the local movement and distribution of South African mammals

Abstract

Fences are utilized throughout the world to restrict the movements of wildlife, protecting them from threats and reducing human-wildlife conflict. In South Africa the number of privately-owned fenced game reserves has greatly increased in recent years, but little is known about how fencing affects the distribution and movements of target and non-target mammals. We surveyed 2m either side of the complete fence line of a recently established commercial game reserve in South Africa, identifying signs of animal presence (spoor, scat, foraging or other field signs) while also recording damage (holes) to the fence. Every 250m we carried out 100m perpendicular transects either side of the fence, recording vegetation cover and height at 10m intervals along the transect. We found that livestock (largely cattle) were excluded from the reserve. However, 12% of records of large animal species were recorded outside of the fence line. These species had been introduced to the reserve, strongly suggesting that they had crossed the boundary into the surrounding farmland. Sixteen naturally present wild species were found on both sides of the fence, but we found more evidence of their presence inside the reserve. Observational evidence suggests that they were regularly crossing the boundary, particularly where the fence was damaged, with hole size affecting species recorded. We also found evidence that the construction of the fence had led to a difference in vegetation structure with plant richness and percentage of non-woody plant cover significantly higher inside the fence. While fencing was highly effective at preventing movement of livestock, introduced and wild animals were able to cross the boundary, via holes in the fence. This work shows that the efficacy of the most common approach to preventing animal movement around protected areas depends on the species being considered and fence condition.

Quantifying wildlife responses to conservation fencing in East Africa

“…Of the 27 mammal species we recorded crossing the fence, carnivores and primates crossed most frequently, and crossing behaviors were strongly predicted by microhabitat at the crossing point, body size, and adjacency to the nearby Soysambu Conservancy. This result supports other studies that have shown primates and carnivores frequently move over, under, and through fence lines (Pirie et al, 2017). Most ungulates, on the other hand, faced difficulties crossing.…”

“…Our methods offer a novel approach for quantifying wildlife responses to fencing, and our findings are consistent with surveys and frequent observations that report wildlife regularly passing in and out of the park (Kassilly et al, 2008, but see also Elliot et al, 2020). Our findings also echo indirect assessments that have shown fences are permeable to many wildlife species elsewhere in Africa (e.g., Pirie et al, 2017).…”

“…Extrinsic factors affecting fence ecology include fence construction as well as patterns of fence maintenance, surrounding habitat and soil types, human disturbance, hydrology and season. The intrinsic factors that best predict species' response to fences are often as simple as mode of locomotion, body size, agility, strength and adaptations to dig or break through or under fences (Karhu and Anderson, 2006;Pirie et al, 2017). Capacity for problem-solving and searching can also be useful predictors.…”

Assumptions about fence permeability influence density estimates for brown hyaenas across South Africa

“…In many parts of the world, wildlife is confined to fenced areas, and this is especially true in South Africa where it is a legal requirement to fence an area containing dangerous game species 8 , 12 . Although fences are often successful at confining cattle and large herbivores, fences are semi-permeable for many mammals including some large predators 13 – 15 . Holes under fences are created by erosion and by digging species 16 , and when a fence line is breached, species detect and exploit holes quickly 17 .…”

Fence Ecology: Frameworks for Understanding the Ecological Effects of Fences

“…nature and the difficulty in quantifying their extent and impact. The level of maintenance or decay of a fence is essential to its effectiveness at its intended purpose and may drastically change its ecological effects (Pirie et al 2017). Keeping fences maintained has long been a central occupation of pastoralists, but now other fence builders have come to understand its importance.…”