The Faunistic Importance of the Scarp of Angola

Abstract

SUMMARY The geographical features, in particular the western escarpment, and the climate and vegetation of western Angola combine to divide the area into three avifaunal zones. An unusual relationship exists between some related forms of different zones. This is illustrated by two groups of examples in which the characters of the forms are summarised, their distribution is shown on maps, and an attempt is made to interpret in evolutionary terms the picture presented. Endemic or near‐endemic forms of the Escarpment Zone are listed with some notes on their affinities with other species. The botanical history of the area is discussed in relation to the conclusions reached on the evolution of the birds. The Escarpment Zone of Angola has been of considerable importance in the evolution of species in western Africa, south of the Equator.

Angola’s central scarp forests: patterns of bird diversity and conservation threats

“…This evidence may enable us to measure the period at which the endemic taxa diverged, which can be expected to coincide with periods of greatest aridity. In addition, climatic modelling and creation of forest-type climatic envelopes could be used to confirm predictions of habitat distribution in different climatic phases, and identify potential refugia for endemic taxa (Hall 1960).…”

“…Additional high summer rainfall from the east results in very mesic conditions, allowing forest and thickets to develop between the drier habitats of the coastal plain and woodland-covered inland plateau. These forests are an impoverished outlier of the Guinea-Congolian forests that extend southwards along the scarp and spill over to the coastal plain along some of the larger rivers, such as the Kwanza (Hall 1960;Huntley and Matos 1994).…”

“…Previously known to occur in the drier, higher-altitude forests above the main scarp near Assango, from where several specimens were collected in the 1950s (Rand 1957;Heinrich 1958;Hall 1960), and from a single specimen (Hall 1960) and two sight records between Chio and 40 miles south of Mumbondo at c. 300 m altitude (Dean 1974, P. vaz Pinto, pers. comm.).…”

“…Two key forest habitats form the core of the region: the tropical forests of the Angolan escarpment (hereafter 'scarp') and Afromontane forest of the Bailundu Highlands (Collar and Stuart 1988). The scarp itself is recognised as an important centre of bird speciation and endemism, as well as a biogeographic barrier driving bird speciation (Hall 1960), and is in critical need of conservation attention (Hawkins 1993;Stattersfield et al 1998). Besides the range-restricted species that occur in this EBA, several near-endemic species, endemic subspecies and species with isolated populations occur here (Hall 1960).…”

“…The scarp itself is recognised as an important centre of bird speciation and endemism, as well as a biogeographic barrier driving bird speciation (Hall 1960), and is in critical need of conservation attention (Hawkins 1993;Stattersfield et al 1998). Besides the range-restricted species that occur in this EBA, several near-endemic species, endemic subspecies and species with isolated populations occur here (Hall 1960). Near-endemic species are of interest because they may have evolved here despite their presently wider distribution.…”