Structure of the breeding bird community along the urban gradient in a town on the Zambezi River, north-eastern Namibia

Abstract

A simplified mapping method was employed to quantify avian assemblages in three study plots in a modified riparian forest on the Zambezi River in the town of Katima Mulilo, NE Namibia. The plots were arranged along the urbanization gradient: plot A (34 ha; 0–1 km from centre of the town), plot B (27 ha; 1–2 km from the centre), and plot C (24 ha; 2–3 km from the centre; periphery). In total, 51 breeding bird species were recorded in all three plots. Five of them, Columba livia domestica, Passer diffusus, Pycnonotus tricolor, Streptopelia senegalensis, and Uraeginthus angolensis were classified as dominant species. The cumulative dominance was 69.9%. The overall population density of all breeding species increased with the urban gradient. In general, granivorous birds were by far the most numerous feeding guild comprising 68.7% of all breeding birds. Two other guilds, frugivorous and insectivorous birds, together comprised 28.9%. While the proportion of granivores decreased along the urban gradient from the town centre to its periphery, the proportion of insectivores increased. The proportion of birds nesting in/on buildings decreased, and the share of tree/shrub- and hole-nesting birds increased along the urban gradient. The diversity indices were relatively high in all plots. They decreased only slightly along the urban gradient (from the centre to the periphery). However, the Pielou’s Evenness Index was comparatively low, but on a slight increase along the urbanization gradient. The Sorensen Similarity Index was low, but the values of the three studied plots were very similar.