SummaryAn analysis is made of over a thousand precise bird breeding records for a forest area in West Cameroon. In the lowland forest there is no universal breeding season although most families have a preferred nesting season. On the other hand. in the montane forest breeding is seasonal and takes place in the drier months. These conclusions are supported by field observations and by the examination of over 5000 birds for gonad state, plumage wear and moult.The remarkable difference in seasonality between the lowland and montane avifaunas is discussed with reference to climate, particularly to the mist which envelops the montane forest in the rainy season.