Impacts of oil palm expansion on avian biodiversity in a Neotropical natural savanna

Abstract

The consequences of converting tropical rainforest to oil palm are well-documented, but the impacts of oil palm conversion on natural savanna landscapes remain little-known. Natural savannas in South America have been identified as fertile grounds for future oil palm expansion, partly due to perceived low biodiversity impacts relative to forest systems. We quantify the impacts of oil palm conversion for bird communities inhabiting natural savannas in the Colombian Llanos. Bird species richness and abundance were significantly reduced at sampling points in oil palm relative to adjacent natural savannas, with marked concomitant shifts in community composition. Aquatic, forest and grassland specialists all showed significantly lower abundances in oil palm habitat relative to savanna, as did migratory species and carnivorous/insectivorous dietary guilds. In both habitats, point-level species richness and total bird abundance increased with proximity to remnant forest patches. Within savanna, total bird abundance also decreased with proximity to adjacent oil palm, though species richness was not significantly affected. Within oil palm, point-level abundance increased with proximity to savanna, suggesting that communities in both habitats may be impacted by reciprocal edge or spill-over effects. Point-level abundance in oil palm also increased significantly with the presence of an invasive vine ‘kudzu’, a species introduced in some plantations as a soil protection measure, although species richness was not affected. Our work underlines the need for careful monitoring of further large-scale agro-industrial conversion in the Llanos. In particular, we suggest greater efforts to direct oil palm expansion towards already degraded lands (e.g. improved grassland areas currently used for intensive cattle grazing) to ensure remaining natural savannas are spared.