Tropical mountains offer an opportunity to understand the importance of local and regional processes in shaping spatial diversity patterns as environmental variation along their sharp elevations enable to observe those processes partly separated. Compositions of avian assemblages frequently show high levels of turnover at mid-elevations, where two different environments, montane and lowland forest, meet in a cloudy contact zone. It implies the presence of a distinct border between the two environments with some of its inhabitants likely being members of different regional pools. Surprisingly, the role of mists in separating montane and lowland biotopes is still rarely investigated. We will utilize an established research scheme on Mt. Cameroon in order to unravel the environmental and physiological factors limiting bird spatial distributions. We will focus on avian communities inhabiting the cloud zone (900-1400 m asl) and explain abundances and year-round activity by field estimates of temperature, air humidity (mists), solar radiation and species specific eco-physiological traits.