THE DISTRIBUTION OF AFRICAN EVERGREEN-FOREST BIRDS

Abstract

SUMMARY. 1 The montane-forest avifauna differs nearly, as much from the lowland-forest avifauna as it does from that of the ecologically very different savanna. Only about 12 per cent of the montane species occur regularly also in the lowland forest and a number of the montane genera are endemic. 2 Many of the montane species are widespread on island mountains throughout East Africa, and half those on the mountains of the Cameroons occur also in the east; but remarkably few species reach the Abyssinian highlands or south of the Zambesi. 3 Subspecific differentiation in montane species is often high, even on mountains within 20 miles of each other (example, Zosterops). 4 The present geography of the forest birds is discussed in relation to what is known of Tertiary and Pleistocene Africa. The problem of how and where the montane and lowland-forest avifaunas were differentiated is baffling. 5 The wide distribution of many montane species would have been facilitated by the Pleistocene pluvials and it is not inconceivable that the observed subspecific differentiation has taken place since the last of these. 6 The difference between the Guinean forest avifauna and the poorer East African (coastal) lowland avifauna, with its high specific endemism, is explicable by the increasing barrier of the East African highlands during the Pliocene and Pleistocene. The difference between the Lower Guinean and Upper Guinean avifaunas is explicable on a combination of factors.