‘Remote’ behavioural ecology: do megaherbivores consume vegetation in proportion to its presence in the landscape?

Abstract

Examination of the feeding habits of mammalian species such as the African elephant ( Loxodonta africana) that range over large seasonally dynamic areas is exceptionally challenging using field-based methods alone. Although much is known of their feeding preferences from field studies, conclusions, especially in relation to differing habits in wet and dry seasons, are often contradictory. Here, two remote approaches, stable carbon isotope analysis and remote sensing, were combined to investigate dietary changes in relation to tree and grass abundances to better understand elephant dietary choice in the Kruger National Park, South Africa. A composited pair of Landsat Enhanced Thematic Mapper satellite images characterising flushed and senescent vegetation states, typical of wet and dry seasons respectively, were used to generate land-cover maps focusing on the forest to grassland gradient. Stable carbon isotope analysis of elephant faecal samples identified the proportion of C ₃ (typically browse)/C ₄ (typically grass) in elephant diets in the 1–2 days prior to faecal deposition. The proportion of surrounding C ₄ land-cover was extracted using concentric buffers centred on faecal sample locations, and related to the faecal %C ₄ content. Results indicate that elephants consume C ₄ vegetation in proportion to its availability in the surrounding area during the dry season, but during the rainy season there was less of a relationship between C ₄ intake and availability, as elephants targeted grasses in these periods. This study illustrates the utility of coupling isotope and cost-free remote sensing data to conduct complementary landscape analysis at highly-detailed, biologically meaningful resolutions, offering an improved ability to monitor animal behavioural patterns at broad geographical scales. This is increasingly important due to potential impacts of climate change and woody encroachment on broad-scale landscape habitat composition, allowing the tracking of shifts in species utilisation of these changing landscapes in a way impractical using field based methods alone.