Understanding the influence of nutritional drivers on the habitat use of African elephants (Loxodonta africana) living in a semi-arid, anthropogenic landscape
Creators: name: Troup, Georgia
Publisher: name: The Australian National University
Year: 2021

description: An individual's nutritional status plays a key role in its health and reproductive success. For herbivores, adequate nutrition is largely dependent on forage quality, which is heavily influenced by the amount of rainfall. Accordingly, large herbivores may travel long distances between seasons in search of forage, so to ensure their nutrient requirements are met. The African elephant (Loxodonta africana) is a wide-ranging herbivore whose movement is largely driven by the availability of water and forage. Elephants require adequate nutrition for growth, reproduction, energy metabolism and immunity. For those living in anthropogenic landscapes, the search for sufficient forage may lead movement into cultivated areas, often resulting in human-elephant conflict. With rising temperatures and the occurrence of extreme weather such as droughts, in addition to rapid conversion of wildlife habitat into agricultural land, it is increasingly important to understand how the spatio-temporal distribution of resources affects the foraging behaviour of mega-herbivores. Over 22 months between December 2016 and September 2018, I explored how nutritional drivers influence spatio-temporal patterns of African elephant habitat use in Kenya's Tsavo ecosystem. Tsavo is prone to drought, home to the largest population of elephants in Kenya, and comprising large areas of farmland experiences wide-spread crop-raiding by elephants. I used nitrogen (N), specifically Available N, as an indicator of forage quality as it provides an estimate of protein, and protein is limiting in herbivores. Protein is a particularly important component of a nutritious diet, essential for the growth of elephants. I analysed variation in the nutritional quality of forage (wild and cultivated) consumed by elephants, and found that they are able to meet their nutritional demands during wet and dry seasons, hence crop-raiding at these times is probably an extension of their optimal foraging strategy. However, elephants may find it challenging to meet nutrient requirements during drought periods without supplementing their diet with crops, and therefore crop-raiding during this time is likely out of necessity to meet nutritional demands. I also explored differences in elephant nutritional status (as indicated by faecal N, Nf) between Tsavo East N.P. and adjacent farming areas, and found that Nf is an appropriate indicator of temporal variation in elephant diet quality, although employing Nf as an indicator of spatial differences in diet quality may lead to misleading conclusions. Results also emphasise the important contribution of elephants to nitrogen cycling in Tsavo through their faeces. In addition, I investigated the trade-offs of crop-raiding for elephants through analysis of their fine-scale movement behaviour (as indicated by speed and tortuosity) around farmland, and found that GPS-collared crop-raiding elephants increase their intensity of anti-predator behaviours with closer temporal proximity to farmland, and move in a way that is indicative of intensive foraging on crops while in farmland. Further, I assessed the physiological stress response (using faecal glucocorticoid metabolites as a proxy for stress) of elephants between wet and dry seasons in Tsavo East N.P., as well as between Tsavo East N.P. and nearby Rukinga Wildlife Sanctuary during the dry season, and found that elephants appear to be physiologically unaffected by decreasing forage quality between seasons, which is promising for their ability to adapt to increasingly prevalent drought periods. Results also highlight the success of Rukinga in providing a safe refuge for elephants when travelling outside the national parks and into areas of human disturbance. Ultimately, the findings of this thesis highlight how the habitat use of elephants in Tsavo is influenced by nutritional drivers, specifically protein.