COS 140-3 - Interfering the resource tracking of three southern African antelopes: Insights into animal-fence interactions from high resolution movement data

Abstract: In semi-arid environments characterized by erratic rainfall and scattered primary production, migratory movements are a key survival strategy of large herbivores to track resources over vast areas. Veterinary Cordon Fences (VCFs), intended to reduce wildlife-livestock disease transmission, fragment large parts of southern Africa and have led to limited wildlife movements for over 60 years. Consequently, wildlife-fence interactions are frequent and often result in fence breaches. However, we lack detailed knowledge about the resource tracking of antelopes in southern Africa. This knowledge is crucial to assess how fences may alter migratory movements and what consequences for populations could emerge.

We studied over two-year ungulate movements in three common antelopes (springbok, kudu, eland) across a perforated part of Namibia's VCF separating a wildlife reserve and Etosha National Park. Baseline data included GPS telemetry, accelerometer measurements, and satellite imagery. We identified over 3,000 fence interaction events which we used to evaluate times of encounters and direct fence effects on motion patterns. Using vegetation type-specific greenness dynamics, we identified resource tracking and quantified which resources antelopes of diverse movement types gained from crossing the VCF.

Our results showed that the perforation of the VCF sustains herbivore-vegetation interactions in the savanna system. Permeability led to seasonal peaks in crossing numbers and direct fence effects differed between individuals with varying movement patterns. While the use of space of sedentary kudus was less affected by the VCF, migratory springbok and nomadic eland benefited from gaps. They gained vegetation type-specific food quality and quantity after crossing. For instance, springbok groups traveled to small shrub and grass patches with local green-up, and eland groups tracked large shrub or grass patches of high biomass. Our findings highlight the importance of access to vast areas for ungulates to track vital vegetation patches. This access can prove crucial to sustain wildlife populations, since the spatio-temporal variability of resource availability will increase under climate change.