The impact of a massive wildfire event on avian species richness and abundance in an arid African savanna ecosystem

Abstract

Fire shapes ecological diversity, but its influence on bird communities is poorly understood. Fire is often considered crucial to management of savanna systems. Here, we assess effects of fire on bird species richness and density after a wildfire in September 2021, in an arid South African savanna where fire is infrequent. Point counts initially surveyed in 2004 now occurred in burnt and unburnt habitats, and were revisited five times across seasons from December 2021 to January 2023. This enabled identification of interaction effects of change over time and with fire from linear models using site and survey as predictor variables in a Before-After Control-Impact (BACI) framework. Patterns of bird species richness were explored using subsets of repeated points and those of summer to autumn surveys. To explore fire impacts on bird density, we used ‘Distance Sampling’ using additional surveys. Although total species richness during counts did not differ between survey periods and burnt and unburnt areas, densities of all birds were ca. 50% higher in unburnt veld relative to burnt, with this difference driven mostly by granivores. Three of 24 common species were significantly negatively influenced by fire. Fires may profoundly affect this arid zone bird community, a finding that would be overlooked if only species richness had been considered, and densities not accounted for. Fire, although potentially positive for biodiversity in mesic savannas, may negatively impact multiple taxa in arid savannas, which have a very different evolutionary and ecological history to that of more mesic savannas. These differences must be considered in management strategies.