To cross or not to cross? The effects of fences around Etosha on large carnviore movement.
Fencing represents one of the most common linear infrastructures in the world and is used for a variety of reasons, including wildlife management. In particular, fencing is widely used to mitigate human-wildlife conflicts, reducing the risk of disease transmission between wildlife, livestock, and humans, preventing poaching of endangered species, and restricting encroachment of human settlements on protected areas. Large parts of Africa are composed of complex landscapes, where protected areas are interspersed within human-dominated regions, and thus fencing is often used as a tool to mitigate human-wildlife conflict in these regions.
Southern Africa still supports substantial megafaunal populations and low human densities compared to other developing regions, and fencing is widely used to separate wildlife, livestock, and humans. Despite its benefits, large-scale fencing has implications on animal movements, especially within arid ecosystems where resources are seasonal and limited, and wildlife needs to move across large areas to access them. Fencing also disrupts migratory movements, fragments habitats, and restricts the use of corridors connecting free-ranging wildlife populations. Fencing can be especially detrimental to large, wide-ranging mammals that need to move across extensive areas to access food, water, and mates. Although fences are commonly used across Southern Africa, our understanding of their effects on large carnivores is limited.
We evaluated the impact of the perimeter fence surrounding the Etosha National Park (Etosha) in northern Namibia on the movement behaviour of Africa’s two most widely distributed apex predators: lions (Panthera leo) and spotted hyaenas (Crocuta crocuta). This work is part of the Greater Etosha Carnivore Programme, a collaborative research effort between Namibian (Etosha Ecological Institute, Ministry of Environment, Forestry and Tourism, Ongava Research Centre) and international institutions. Etosha is one the largest protected areas of sub-Saharan Africa and is enclosed by an 834 km long perimeter fence erected in 1974.
Considerable amounts of funds, labour and time are spent by the Etosha management to maintain the fence. Etosha supports the largest population of lions and spotted hyaenas in Namibia and provides substantial benefits to the government through tourism. A complex matrix of private game reserves (such as Ongava, Onguma and Etosha Heights), commercial freehold farms (used for livestock and/or game farming), village lands and communal conservancies surround Etosha.
Despite the dedicated efforts of the park’s management, incidents of human-carnivore conflicts regularly occur in the periphery of Etosha, impacting the livelihoods and well-being of local communities, and often resulting in retaliatory killing of carnivores. Consequently, approximately 10% of the Etosha lion population is lost to human-carnivore conflicts every year and unknown numbers of other carnivores.
Three Namibian organisations (Etosha Ecological Institute, Ongava Research Centre, and the Namibian Lion Trust) joined forces along with the University of Georgia to compile GPS movement data collected over a 14-year period (2007-2020) from 89 lions and 22 spotted hyaenas. Using this extensive dataset, we quantified the impact of the Etosha fence on carnivore movements, calculated the likelihood of fence crossings, and evaluated the spatial-temporal characteristics of these crossings.
We found that both species moved faster in the vicinity of the fence, which could be due to the fear of persecution by humans within farmlands bordering Etosha. Lions showed no variation in path straightness, whereas hyaenas had straighter and more directional movements closer to the fence. This suggests that hyaenas were aware of the holes/gaps in the fence and moved in a uniform pattern towards the fence. The permeability of the fence differed between the two predators, with hyaenas being twice as likely to cross the fence compared to lions when within the vicinity of the fence (18% versus 9%), despite the overall likelihood of crossing being low. Fence crossing predominantly occurred at night, which is not surprising for nocturnal species. Lions and hyaenas had contrasting seasonal patterns regarding fence crossings, with lions more likely to cross the fence during the cold dry season (May-August) and hyaenas more likely to cross during the warm wet season (December-April). These differences could be related to specific behavioural traits, such as greater tolerance of hyaenas towards anthropogenic features, habitat preference and effects of wild prey and livestock distribution on carnivore movements. Female and adult lions were more likely to cross the fence than males and subadults. Both species travelled long distances to cross the fence, which could have energetic costs and requires further investigation.
We documented numerous fence crossings between Etosha and the surrounding shared landscape, highlighting the potential for human-carnivore conflicts, especially at the protected area-farmland interface along the southern periphery of Etosha. Most of the lion fence crossings occurred on the southwestern, south-central, and south-eastern periphery of ENP in the vicinity of commercial livestock farms, game reserves and wildlife concession areas. Most hyaena fence crossings occurred on the southern-central and north-eastern periphery of ENP, in the vicinity of where these individuals were collared. These findings could be useful in the development of appropriate strategies to ensure human-carnivore coexistence and manage large carnivores within the Greater Etosha Landscape. Further research is needed to better elucidate the impact of perimeter fences on a broader suite of carnivores and other large mammals, including species-specific variation in the response to fences, fence structure, and the economic benefits of fencing provided to local communities. It is also necessary to conduct research on the interactions between carnivores, wild prey and livestock, as well as the effect of environmental conditions and land management on their movements and habitat use along the periphery of Etosha.
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The graphical abstract was designed by Rhys Medcalfe, our UGA outreach intern, with the support of Dipanjan Naha, Jim Beasley and Stéphanie Périquet.