Birds as indicators for the environmental impact of anthropogenic activities on Onguma, Namibia

Abstract

Protected areas must be managed to maintain biodiversity. Management strategies can be optimized by assessing the impact of implemented management tools and land uses.

This study assesses the environmental impact of the major anthropogenic forms of disturbance that occur or have occurred on Onguma Nature Reserve, including the presence or absence of game, cattle farming, manual plant removal, chemical plant control, and veld fires.

Birds were employed as indicator taxon for the state of the environment. Using generalized linear models, bird species richness, diversity, and abundance were predicted by the variables of interest as well as soil and vegetation gradients to account for the underlying environmental variability. Additionally, the species composition of the different sub-communities was examined with a NMDS ordination.

Manual plant removal increases, chemical plant removal decreases bird species richness and diversity. Veld fires act diversifying on the avifauna. Removing game significantly lowers the species richness and diversity of birds, indicating that the overall game numbers on Onguma are healthy. The species composition differs among land uses, with grassland specialists less present where cattle farming occurred, suggesting that habitat-selective degradation has taken place.

These results must be contextualized to the study site because the environmental effect of a land use depends on the intensity at which it is implemented, and the consequences of a management tool depend on the need and method of the intervention. Furthermore, the environment dictates the choice of treatment and reacts to the latter, ultimately impacting the bird fauna. Thus, the state of the underlying environment mediates the effect of the treatment on the indicator taxon.