The effect of grassland shifts on the avifauna of a South African savanna

Abstract

Two distinct grassland types occur within Hluhluwe-iMfolozi Park (HiP): short stoloniferous grazing lawns and tall, tussock-like 'bunch' grasslands. Grazing lawns are maintained by grazing mammals, among which White Rhinoceros Ceratotherium simum is of major importance. By contrast, tall bunch grasslands are promoted by frequent burning. The extent of each grassland type within the park is highly dynamic and can be altered by changes in mammal numbers and/or fire regimes. Such changes may have cascading consequences for other components of the ecosystem if they show specialisation towards one or other grassland state. This study compared avifaunal assemblages of grazing lawns and bunch grasslands to assess how bird species of the park might change with shifts in the grassland mosaic. Distinct bird communities were associated with each grassland type, including several specialists, and bird distribution was linked to vegetation structure rather than floristics. Post-fire bunch grasslands provided ephemeral habitats for short-grass specialists. Outside HiP, domestic livestock produced structurally-similar grasslands to grazing lawns and bunch grasslands, but heavy predation of birds by people reduced bird densities. Because HiP is surrounded by such communal grazing lands, the park is of key importance in conserving grassland birds on a regional scale, a factor that needs to be considered in managing the park's grassland mosaic.