Effect of rainfall on white rhino calf survival depends on home range choice of the mother

Within African savannas, seasonal rainfall influences the survival of mammalian grazers by determining the availability and quality of food. The strength of these effects may, however, vary depending on the availability of reserve and buffer resources within the home range of an individual. From 1999 to 2019, 24% of the white rhino (Ceratotherium simum simum) calves born in Ithala Game Reserve died without a known cause. To explore this, we investigated the impacts of seasonal rainfall on calf survival, and whether these relationships were modified by the availability of woodlands (i.e., reserve resources) and bunch grasslands (i.e., buffer resources) within the home ranges established by the mothers. We found that nearly all of the deceased calves died during their first dry season after weaning had commenced. The likelihood of a calf surviving this period was positively influenced by rainfall during the dry season and negatively influenced by its duration. However, these effects were more pronounced when the availability of woodlands within the home range of the mother was high. Ultimately, calf deaths were caused by a combination of low dry season rainfall, long dry seasons, and the selection of home ranges with insufficient bunch grasslands by some mothers. With climate change models predicting increased dry season durations and a reduction in dry season rainfall, our results highlight future challenges for the conservation of white rhinos and other large herbivores.