RANGE EXPANSION IN THE PIED BARBET AND THE SPREAD OF ALIEN TREE SPECIES IN SOUTHERN AFRICA

Abstract

Summary Macdonald, I. A. W. 1986. Range expansion in the Pied Barbet and the spread of alien tree species in southern Africa. Ostrich 57: 75–94 Apparent range expansions of the Pied Barbet Lybius leucomelas into fynbos, karoo, grassland and mesic savanna areas have occurred this century. The number of loci from which the barbet was recorded in each biome prior to 1903, from 1904 to 1963 and from 1964 to 1984 was analysed. Initially recorded from 1 to 2% of each biome's loci, the percentage increased most rapidly in the fynbos to reach 53% in the latest period. Savanna (31%), grassland (26%), karoo (16%) and forest (3%) had significantly lower reporting frequencies in this latest period. The expansion into the fynbos of the southwestern Cape is analysed in detail. Analyses of field-card records showed that the reporting frequency of L. leucomelas in the southwestern Cape increased from 9,7% to 27,5% between the period 1950–1979 and 1982–1984. The reporting frequency tended to be higher in those areas mapped as holding alien Acacia thickets in the early 1960s. Reporting frequencies in the different habitats found in the southwestern Cape showed the frequency from alien Acacia thicket not to be significantly higher than those for several indigenous fynbos vegetation types. However the reporting frequencies from “indigenous” vegetation types had increased markedly since the 1960s, and it is postulated that most of these types were significantly infested by alien trees. L. leucomelas was reported nesting in alien trees significantly more often from fynbos, karoo and grassland dominated areas than from savanna areas. The provision of alien nest substrates, alien fruits, artificial watering points and bush encroachment of previously open vegetation types are all proposed as factors favouring the observed range expansions. The relative contribution of each of these factors varies between different areas. In the fynbos biome the spread of alien tree species and their subsequent use as nesting sites is considered the most important factor.