How free-ranging ungulates with differing water dependencies cope with seasonal variation in temperature and aridity

We compared the behavioural and physiological flexibility of two sympatric species with different water dependencies to seasonal variation in temperature and aridity. Both species coped relativelywell with current fluctuations, but as water sources become less reliable under future climate change scenarios, the water-dependent species may risk extirpation. Large mammals respond to seasonal changes in temperature and precipitation by behavioural and physiological flexibility. These responses are likely to differ between species with differing water dependencies. We used biologgers to contrast the seasonal differences in activity patterns, microclimate selection, distance to potential water source and body temperature of the water-independent gemsbok (Oryx gazella gazella) and water-dependent blue wildebeest (Connochaetes taurinus), free-living in the arid Kalahari region of Botswana. Gemsbok were more active nocturnally during the hot seasons than in the cold-dry season, while wildebeest showed no seasonal difference in their nocturnal activity level. Both species similarly selected shaded microclimates during the heat of the day, particularly during the hot seasons. Wildebeest were further than 10 km from surface water 30% or more of the time, while gemsbok were frequently recorded >20 km from potential water sources. In general, both species showed similar body temperature variation with highmaximum24-h body temperaturewhen conditions were hot and low minimum 24-h body temperatures when conditions were dry, resulting in the largest amplitude of 24-h body temperature rhythm during the hot-dry period. Wildebeest thus coped almost as well as gemsbok with the fairly typical seasonal conditions that occurred during our study period. They do need to access surface water and may travel long distances to do sowhenlocal water sources becomedepleted during drought conditions. Thus, perennial water sources should be provided judiciously and only where essential.