Avian diversity in an urbanized South African grassland

Abstract

The most critical gaps for urban wildlife researchers are in rapidly urbanizing areas in South America, Africa and Asia. This article presents quantitative studies on birds carried out in South Africa, in the inner part of the city of Bloemfontein during the years 1993–2002. Three methods were employed to quantify the avian assemblages: atlas, mapping and line transects. Atlas studies were conducted in 1997. The whole study area was divided into 1 × 1 km grid squares (100 ha). A total of 67 squares were achieved with a total surface of 5100 ha. Densities as well as the dominance of resident breeding birds were estimated by means of a simplified version of the mapping method in four plots. For a few selected species, namely Crowned Lapwing, Blacksmith Lapwing, Spotted Thick-knee, Crested Barbet, Bokmakierie, Little Swift and African Hoopoe, the numbers of breeding pairs over the whole study area (5100 ha) were estimated by means of the mapping method in a simplified version. A total of 131 bird species were recorded in Bloemfontein, 78 (59.5%) of them were breeding, 7 (5.3%) probably breeding, 27 (20.6%) visitors and 19 (14.5%) vagrants. The most common bird species (more than 1000 pairs of each) were Speckled Pigeon, Cape Turtle-Dove, Laughing Dove, Little Swift, House Sparrow and Cape Sparrow. A group of very common species (201–1000 pairs) included Rock Dove, Red-faced Mousebird, Red-eyed Bulbul, Olive Thrush, Cape Robin-Chat, Common Fiscal, Cape White-eye and Southern Masked Weaver. Nine (6.9%) other breeding species were classified as common (51–200 pairs), 14 (10.7%) as fairly common (11–50 pairs), 31 (23.7%) as rare (1–10 pairs). Ten other species (7.7%) nested irregularly in Bloemfontein during the years 1993–2002. Granivores were the most dominant guild both in terms of the number of individuals and the biomass. However, in terms of the number of species, insectivores were by far the most numerous group. During the years 1993–2002, a total of 61 non-breeding and non-resident species were recorded in Bloemfontein, including 14 regular visitors, 18 irregular visitors and 29 vagrant species. Nearly 2/3 of all vagrant species were recorded only once during that period.