Activity patterns of African elephants in nutrient-rich and nutrient-poor savannas

Abstract

The Jarman-Bell principle states that small herbivores feed on the high quality forage in nutrient-rich, eutrophic savannas, whereas large herbivores tolerate the lower quality forage in nutrient poor, dystrophic, savannas. The African elephant, Loxodonta africana, is a large herbivore occurring in both savanna types, where it meets different quality and quantity of forage and different competition from small herbivores. Activities of elephants are comparatively well studied, but little emphasis has been on contrasting time allocation on different activities in eutrophic and in dystrophic savannas. We studied elephant activities in eutrophic Serengeti and dystrophic Mikumi, in Tanzania in order to explain differences between the savannas which differ in nutrient availability and herbivore densities. The two parks had similar, mean annual precipitation. We drove along all accessible roads in our study areas, and once an individual or a group of elephants was sighted the car was stopped for observation. We used group activity scan sampling methods to record number of individuals grazing, walking, resting, browsing, interacting with other group members or vigilant in a group. We also recorded group type, group size, and habitat. The study revealed that activity patterns of elephants differed between the eutrophic and the dystrophic savanna, between females and males, and between the wet and the dry season. Grazing was a dominant activity in both sites, particularly in the wet season, when nutritious grasses were available. There was more browsing in the eutrophic Serengeti compared to the dystrophic Mikumi and in bachelor compared to family groups, probably due to differences in availability of grass and browse, and in palatability of plant material between the sites. Resting was affected by interaction effect between site and season, where proportions of individuals resting in a group was higher in Mikumi in the dry season and in Serengeti in the wet. Walking was affected by group type, where bachelor groups walked more than family groups, probably searching for estrous females, and by interaction between season and site, where elephants walked more in Serengeti in the wet season and in Mikumi in the dry. The dry season has limited forage quantity and quality and shortage of water, thus animals face a tradeoff between resting to save energy and walking to search for water and food. We conclude that, the differences recorded between the sites might be attributed to differences in quality and quantity of grazing and browsing, as well as to differences in nutritional and reproductive demands between females and males.