Increased vigilance of plains zebras (Equus quagga) in response to more bush coverage in a Kenyan savanna

Climate change-induced bush encroachment into grasslands has profound impacts on herbivores in African grasslands through changing their food and water supplies and influencing their perception of predation risk, and thus modulating the trade-off between resource acquisition and predator avoidance. For plains zebras (Equus quagga), bush is usually viewed as risky because it provides cover to predators to ambush prey. Projected climate change and increase in bush coverage may elevate perceived predation risk for zebras and influence their behaviors. However, direct evidence of bush coverage impacts on herbivores’ behavioral trade-off remains scarce. We conducted field observations and counts of plains zebra behavioral investments in vigilance, grazing and other routine activities across a variety of bush densities in Kenya's Laikipia Plateau. Results suggest that increasing bush density reduces the distance at which zebras detect the approach of a potential predator. After controlling for group size, zebras are more vigilant in dense versus open habitats. Increase in bush coverage has little impact on grazing time allocation, however it does reduce bite rate. Zebras spend less time on activities other than vigilance or grazing in bushier habitats. Our finding implies that increases in bush encroachment will increase the perception of predation risk by zebras, and reduce efficiency on food uptake and other essential behaviors. Maintaining sufficient area of open grasslands, in part by protecting elephants as ecological engineers, will help sustain populations of zebras and other large herbivores wherever climate change and land use change increases bush density.