Introduction

The evolution and zoogeography of the montane forest avifaunas of Africa have long been a source of fascination to ornithologists (e.g. Chapin, 1923, 1932; Moreau, 1933, 1952, 1954, 1963, 1966; Dowsett, 1971, 1980a,b; Hamilton, 1976; Diamond & Hamilton, 1980; Stuart, 1981a, 1983, 1986; Jensen & Stuart, 1985). The montane forests are characterised by many altitudinally restricted species which usually have disjunct distributions reflecting the patchiness of the available habitat. Many lowland species occur in Africa's montane forests, but do not necessarily do so as isolated populations; these species are not considered here. For the purposes of this chapter we have defined montane forest species as those which do not normally occur below a certain altitude (in eastern Tanzania, few such species occur below 700–900 m a.s.l. during the breeding season), and which seem to be dependent upon forest for their survival (usually for nesting sites and food). Thus species restricted to forest at intermediate elevations (usually between 700 and 1500 m), such as the Banded Green Sunbird Anthreptes rubritorques, are considered here to be montane.

It is not always easy to decide what is a forest species and what is a montane species, since the distinctions are not necessarily hard and fast ones (see Stuart, 1983 for a fuller discussion of this problem). One complication is that many forest dependent species are able to survive in cleared areas within a few kilometres of forest (Stuart, 1983).