FORAGING OVERLAP AND MORPHOLOGICAL SIMILARITY AMONG SOME INSECTIVOROUS ARBOREAL BIRDS IN AN EASTERN TRANSVAAL FOREST

Summary Earle, R. A. 1983. Foraging overlap and morphological similarity among some arboreal insectivorous birds in an Eastern Transvaal forest. Ostrich 54:36-42. The foraging niches of eight common insectivorous bird species were studied in an evergreen forest for 16 months. Three species were much larger than the remaining five (by 200%) and were not considered to be in competition with the smaller ones. This excluded the Barthroated Apalis Apalis thoracica (< 12 g) and the Olive Bush Shake Telophorus olivaceus (30 g) as being competitors although both these species foraged mainly on the bark of twigs. The Yellowstreaked Bulbul Phyllastrephus flavostriatus and the Olive Woodpecker Mesopicos griseocephalus which mainly use the same foraging site and method are morphologically so dissimilar that they are probably not in competition. They were often seen together and even foraged in exactly the same spot. The Yellowthroated Warbler Seicercus ruficapillus and the Cape White-eye Zosterops pallidus- overlapped in both foraging site and method but Zosterops is partly frugivorous which probably reduces competition between these two morphologically similar species. All the species avoided foraging at about 3 m where there was a dense layer of vegetation. Species foraging on the bark of branches or twigs used the whole height of the forest while species foraging on leaves had more definite peak foraging heights.

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