What is the cost of that fence? The impact of fences on the movements of ungulates in a hyper-arid landscape

Abstract

Ungulate movements in arid environments are largely driven by rain events, food resources and surface water availability. In hyper arid areas such as the Namib desert these are patchily distributed, fluctuating and overall sparse. As a result, animals living in these environments need to be highly mobile to exploit the ephemeral and spatiotemporally variable resources. In the past few decades, there has been growing recognition of the importance of wildlife habitat connectivity, and the detrimental effects of linear infrastructure on wildlife and their movements. Barriers, such as roads and fences, block or filter wildlife movements, with severe and sometimes lethal effects on wildlife especially in dry periods or resource-poor environments. In the Greater Sossusvlei Namib Landscape we assessed whether fences impacted ungulate home ranges and movements, and identified particular sections of fences or roads which were most restrictive to ungulate movements. To achieve this, the movements of 12 springbok (Antidorcas marsupialis), 13 gemsbok (Oryx gazella) and 15 Hartmanns mountain zebra (Equus zebra hartmannae) were tracked telemetrically. In general, ungulate home range sizes were smaller in the vicinity of physical barriers. Roads and fences were found to impact ungulate movements considerably in some areas: these included the C14 and C19 main roads that run from the coast to Maltahohe and from Solitaire to Maltahohe respectively, several district roads, parts of the Namib-Naukluft National Park fence, as well as farm fences. While Hartmanns mountain zebra were able to cross some fences, springbok and gemsbok were not as successful, their movements sometimes being completely restricted within farms or along fences until they found a fence gap to cross. The findings highlight which barriers are key to consider for modification to allow for wildlife movement.