Association between avian communities and vegetation structure in a low-lying woodland-savanna ecosystem in Swaziland

Abstract

The community structure and population density of birds was studied at 10 sites in three broad woodland types in the lowveld of Swaziland. Birds were surveyed on a monthly basis at 12 locations per site using a standard point count technique. Each site was surveyed over a 12-month period. Vegetation characteristics of each location were recorded. Both cluster analysis and non-metric multidimensional scaling using bird densities, grouped the sites into two main habitats: riparian and non-riparian. The non-riparian habitat was further divisible into Acacia savanna and broadleaved woodland. A similar classification was obtained using vegetation characteristics. Principal components analysis (PCA) of the vegetation characteristics was conducted. The first axis (accounting for 57.7% of the total variation) represented variation in tree cover below 3.5m and grass cover above 0.25m. The second axis (24.8%) represented variation in tree cover above 3.5m and grass cover below 0.25m. These two axes accounted for 82.5% of the total variation. In general, the Acacia sites had lower tree cover and high grass cover, the broadleaved woodland sites had higher tree cover below 3.5m, and the riparian sites had the highest tree cover. Acacia savanna recorded the highest species richness of birds (128 species) with lower numbers recorded in riparian (101) and broadleaved woodland (94). A total of 161 species of birds was recorded across all sites, of which 48 species were recorded on fewer than four occasions, and 51 species were recorded in all three habitats. Of the remaining species, 14 species were confined to Acacia savanna, 14 species to riparian, and two species to broadleaved, woodland. Broadleaved woodland supports adepauperate, but indistinct, avian community compared to that of Acacia savanna; riverine forest, in contrast, supports a different set of species.

Ostrich 2005, 76(1&2): 45–55