Hippopotamus population trends in Ndumo Game Reserve, South Africa, from 1951 to 2021

Understanding population trends is important when managing wildlife in protected areas. The common hippopotamus, Hippopotamus amphibius (hereafter hippo), is an iconic African species that, in South Africa, is mainly restricted to protected areas. Ndumo Game Reserve (NGR), South Africa, was established as a sanctuary for hippos in 1924. However, NGR and its hippo population are under increased anthropogenic threat, outlining the importance of long-term and current data on hippo population dynamics. We collated census data from 1951 to 2021 to identify trends in hippo population numbers. We also conducted monthly unmanned aerial vehicle (UAV) censuses from August 2016- July 2017 to identify changes in the distribution of hippos in the most important water bodies in NGR. Historical census data were collected using a variety of methods, and observed trends revealed a decrease in the hippo population in the past 40 years. Monthly census data from 2016 to 2017 revealed that wading locations in NGR hold differing values as wading sites, with 85-95% of the population using the uSuthu and Phongolo Rivers and associated floodplains. Areas in NGR experiencing the greatest anthropogenic land invasions are also the areas that represent the best hippo habitat in NGR. We, therefore, recommend that the conservation management authority, sections of the South African government like the Department of Land Affairs and local communities work together to reinstate the boundary of NGR to protect hippo and other wildlife in this important protected area.

Automated summary

Understanding population trends of hippos in Ndumo Game Reserve is crucial, with data showing a decline in numbers over the past 40 years. Collaboration between conservation authorities, South African government departments, and local communities is recommended to protect hippos and other wildlife by reestablishing reserve boundaries.