Riparian bird diversity of the Ndumo Game Reserve, South Africa
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Riparian areas are the ecotones between aquatic and terrestrial landscapes. They are critical areas for biodiversity conservation as they are rich in species diversity. Riparian habitats have more complex vegetation structures, resulting in more heterogeneous habitats. This provides a larger variety of microhabitats, a greater range of microclimates, better hiding places from predators, and generally increased resources, leading to increased bird diversity and intricate community compositions. Riparian ecosystems create corridors for migrating bird species and serve as corridors to pass through from one habitat to another. They supply nesting habitats during breeding season with abundant food resources. Riparian ecosystems are popular overwintering habitats for birds from adjacent non-riparian areas and have been found to be more species rich than non-riparian habitats. Vegetation structure plays a role in habitat selection as it affects aspects such as foraging, resting, perching, finding a mate, selecting a nesting site, and successfully breeding and raising offspring. The complex vegetation structures in riparian habitats create favourable conditions and abundant resources for the survival of bird species. Anthropogenic disturbances affect the integrity of riparian ecosystems and could lead to habitat destruction if not managed. Ndumo Game Reserve is a protected area and because of the different habitat types within riparian areas many species could use these sites as refuge sites during winter. Change in seasons may affect food availability, influx of competition when migrating species arrive, access to water, as well as the change in vegetation structure as seasons change. Bird species richness and abundance would therefore differ among diverse habitats and over time, and create intricate community structures. This was the subject of this study. The Phongolo River flowing through Ndumo Game Reserve was chosen as the study area, with five sites comprising of four sub-plots each chosen within the reserve. Four were riverine sites and one was located next to a pan where the river flows into the pan. Riparian forest was the dominant vegetation type with differences between each site in the composition of plant species as well as vegetation structure. One site had visible anthropogenic disturbances, including burnt-down trees and crops growing across the river from the site. Five surveys were undertaken over a period of 10 months, resulting in 100 sub-plot samples. Sampling was done using the point-count method within a radius of 50 m. Multivariate analyses consisted of indicator analysis, Shannon diversity index and NMS ordinations, as well as PCAs. NMS bi-plots were used to define avian community structures responding to vegetation structure and seasonal changes. The results showed that species richness, abundance, and diversity differed between the sites. There were more bird species and individual birds at the pan site, but the site that was structurally most diverse also had the highest bird species richness. Feeding and nesting behaviours also affected habitat selection. One of the sites showed anthropogenic disturbances, but it seems the use of larger birds as indicators of disturbance was not sucsessful as there were no clear differences in pattern to distinguish it from the other sites. Birds smaller than one kilogram per individual also did not show any effects of disturbance. It could be that the approach that was followed was not applicable, or ordinations might not be applicable to investigate the effect of disturbances. It can be deduced that environmental factors such as vegetation structures and seasonality had an effect on the distribution of birds along the riparian corridors of Ndumo Game Reserve, and disturbances do not yet show any effects.