Balancing Food, Heat and Predation Risk: Seasonal and Diel Movement Strategies of African Herbivores.

Understanding how large herbivores adjust their movement patterns in response to seasonal environmental variation is important for wildlife management. We investigated how sympatric African herbivores with contrasting body size, digestive systems and forage specialisation adjust their movement across seasons and the diel cycle. Using high-resolution GPS data from 16 plains zebra (Equus quagga; hindgut fermenter) and 8 tsessebe (Damaliscus lunatus; ruminant) between 2014 and 2016 in the Okavango Delta, Botswana, we quantified 24 h range size, 24 h displacement distance, as well as displacement distance and tortuosity across 4 h time blocks, and evaluated these movements in response to season, maximum daily air temperature and vegetation greenness. Zebra occupied 24 h ranges double that of tsessebe during the rainy and early flood seasons, but 24 h range size converged during the late flood season. Zebra travelled twice the distance of tsessebe over 24 h during the early flood season, whereas travelling distances were similar during the rainy and late flood seasons. At finer temporal scales, both species showed pronounced but seasonally variable diel movement patterns. Movement paths were generally less tortuous in zebra than tsessebe, although interspecific differences diminished during the late flood season and midday. Movement patterns also changed with environmental conditions: increasing maximum daily air temperature was associated with a stronger reduction in movement in zebra than in tsessebe, whereas increasing vegetation productivity was associated with larger 24 h ranges and increased tortuosity, with the latter response stronger in zebra. Overall, our findings demonstrate that movement differences between zebra and tsessebe are strongly context-dependent rather than constant across seasons. Movement convergence during the late flood season suggests that seasonal conditions can reduce otherwise pronounced interspecific differences in movement patterns. These findings improve our understanding of large herbivores' responses to seasonal environmental variation and may help predict species-specific responses to future climate change.