Comparison of avian assemblage structures in two upper montane forests of the Cameroon volcanic line: lessons for bird conservation

Abstract

The Cameroon volcanic line montane forests host specific avian assemblages with many endemic species. Such unique bird assemblages deserve adequate description for proper protection. For this purpose, we sampled birds in the upper montane forests of Mts Cameroon and Oku situated at ~2,250 m. We combined point counts and continuous observations to describe species composition and estimate densities of particular species. In total, we recorded 106 species; 45 only on Mt Oku, 21 only on Mt Cameroon, and 40 common to both mountains. The higher species richness on Mt Oku was due to non-forest species that invade the forest interior due to recent human disturbance. Endemic species of the Cameroon volcanic line and montane non-endemic species had higher abundances than widespread species in general. As a result, we did not find a positive abundance–range-size relationship for both locations. Our findings support a previously made observation that montane species of the Cameroon volcanic line have higher densities compared to widespread species. However, we also show that the structures of avian assemblages vary between sites as species spatial turnover was lower on Mt Cameroon than on Mt Oku and species common to both were more abundant on Mt Cameroon. This could be attributed to the more pristine forest on Mt Cameroon, with higher annual rainfall but also due to lower human impact and the existence of a continuous forest. Conservation action within the broader landscape context is thus necessary to secure diverse montane forests in West-Central Africa in the future.