Avian Diversity Along An Altitudinal Gradient In Highveld/Drakensberg Grasslands

Abstract

Temperature and rainfall related to altitudinal gradients influence ecological and evolutionary responses of organisms to physical factors. In this study, the line transect method was used during the years 1996-2001 to compare resident (potentially breeding) bird communities in three altitudinal divisions in Highveld/Drakensberg grasslands in Lesotho: lowlands (< 1700 m a. s. l.), foothills (1700-2200 m a. s. l.) and highlands (> 2200 m a. s. l.). In total, 105 resident species were recorded. The total number of species recorded in lowlands was higher than that in highlands and foothills, but this difference was not statistically significant. The highland and foothill did not differ in numbers of species. A group of five species dominated at all three sites, and the proportion of dominant species in relation to the whole assemblage was very similar. The composition of the dominant group (species with more than 5 % of pairs) and the group of species most often encountered (in more than 80 % of transects) was, however, different. Only two species, Cape Canary [Serinuscanicollis] and Karoo Prinia [Priniamaculosa] were dominant in all three study areas, and just one species, the Cape Bunting [Emberizacapensis], was dominant in two plots. Similarly, only two species, the Cape Turtle-Dove [Streptopelia capicola] and Cape Canary had a high frequency of occurrence in all three study areas, and two otherspecies, theKaroo Prinia and Cape Bunting -- in two study areas. Simpson's Diversity Index was strikingly the same (S = 0.96) for all three avian assemblages (lowland, foothill and highland) investigated. However, proportions of breeding pairs of some congeneric species were found to change with the altitude. The granivores were more common (44-45 %) in the foothills and highlands than in lowlands (36%), while insectivores were more common in the highlands (50 %) than in foothills and lowlands (36-37 %). In general, avifauna is relatively diverse and unique in the Highveld/Drakensberg grasslands. Results presented here provide data for further investigation of the effect of the supposed climate warming on the diversity and structure of avian communities.