As an indicator of above ground net primary productivity, the Normalised Difference Vegetation Index (NDVI) has been identified as important tool in understanding the resource requirements and distribution patterns of large herbivores. The efficacy of NDVI as an ecological tool is however, strongly contingent upon the scale of the foraging hierarchy at which data are interpreted. In this study I investigated whether vegetation greenness, as represented by MODIS NDVI 250 m resolution imagery, is a driver of zebra (Equus quagga) foraging patterns at three spatial/temporal scales, namely location within sixteen day home ranges, sixteen day home range within seasonal home range and seasonal home range within total home range, during both wet and dry periods. I also investigated how tree canopy cover influences the ability of MODIS NDVI to see the greenness at which zebra respond. During the wet season, the zebra clearly demonstrated evidence of selecting for greenness and a tendency to avoid areas of high woody canopy at all three scales. Conversely, during the dry season the zebra showed no preference for greenness and no consistent preference for or against woody cover across the three scales. I also noted that despite a positive relationship between ΔNDVI and woody canopy cover, the relationship is not significant and suggests that in savanna ecosystems tree densities may not be high enough to affect overall MODIS NDVI readings. These results indicate that zebra foraging behaviour is complex and differs according to the scale of analysis, season, and even between individual zebra herds. The ability of MODIS NDVI to elucidate zebra movements is therefore limited to specific spatial and temporal scales and should be accompanied by an understanding of non-forage related factors.

MSc., Faculty of Science, University of the Witwatersrand, 2011 / Spatial patterns in topography and forage distribution clearly determine large herbivore movements but our understanding of the foraging strategies that free-grazing herbivores adopt at different temporal and spatial scales is limited. Different foraging response patterns are displayed at different scales. Here fine-scale foraging strategies of Zebra (Equus quagga) were investigated by studying their selection for vegetation greenness in a Southern African savanna. Zebras have high-energy requirements thus the primary productivity and condition of the habitat plays an important role on their movements. Grass greenness was measured by Normalized Difference Vegetation Index (NDVI), a proxy for vegetation productivity and quality. Finer-scale studies are needed to understand the processes leading to a correlation between NDVI and herbivores performance. Data was collected at two different spatial scales, foraging area and feeding station. Food selection was recorded in relation to grass species and grass tuft greenness. Within the foraging area, grass species and greenness within zebra feeding stations were compared with random non used stations. Within the feeding station, species and greenness of grasses eaten by zebra were compared with those of grasses available but not eaten. Zebra selection was not consistent across scales. Although greenness was a factor in selection at feeding station levels and grass tuft levels; feeding station selection was limited to greenness due to season, and selection for species occurred only at the grass tuft level. However, zebra did select for the greener grass tufts within the feeding station even if it meant to eat ‘less palatable’ species (i.e. Eragrostis rigidior) instead of ‘very palatable’ species (i.e. Panicum maximum).