Population density and habitat associations of restricted-range bird species at Ruhija, Bwindi Impenetrable Forest, Uganda

Abstract

Bwindi Impenetrable Forest, south-west Uganda, supports 24 of 37 restricted-range bird species of the Albertine Rift Mountains Endemic Bird Area (EBA). In common with other montane forest fragments in the EBA, Bwindi's structure and ecology have been substantially modified by human activities, the impact of which on its birds is difficult to gauge in the absence of quantitative information on their habitat use and abundance. During October 1999, habitat associations of nine restricted-range species and of 12 species with which they were commonly associated, were measured at Ruhija, Bwindi Impenetrable Forest. Logistic regression analysis was used to determine the relationship between habitat, topography, altitude and species occurrence. Population densities of 19 species were estimated using distance sampling, at survey points visited between dawn and midday. Although the detection rate declined during the morning, observations made towards midday helped to improve precision, without lowering density estimates. Eight habitat and topographical features significantly associated with restricted-range species are described. Few of the features measured were significantly associated with more than one species, underlining the importance of maintaining a diverse forest structure. Two restricted-range species were among the commonest birds in the study area, while a further four species were at least as abundant as their more widespread congeners.