The density and stability of birds in shrubland and drainage line woodland in the southern Karoo, South Africa

Abstract

Comparative surveys of bird species richness and abundance showed that a total of 69 bird species was recorded on 1 km transects (n = 996) through shrubland, with a total estimated density of birds of 32.7 ± 32.8 (S.D.) birds/km2, of which resident birds made up 24.4 ± 21.0 birds/km2, nomads made up 1.9 ± 11.7 birds/km2 and local nomads made up 6.3 ± 20.1 birds/km2. There was no correlation in general between total bird numbers or total bird biomass and rain, but numbers and biomass of nomads showed the strongest correlations with rainfall two months previously. A total of 86 species was recorded on 276 surveys along a 1 km stretch of drainage line woodland. Species richness varied from an average of about nine species to 24 species each month, and only showed a marked change during the 'dry' period of 1990 to early 1991. Density of birds in this woodland was 59.2 ± 20.8 birds/km. Biomass of birds was relatively constant throughout the study period, with marked increases in certain months when large species were present.