Field assistants are needed to study the contribution of anthropogenic environmental changes (especially climate change and land-use change) to the population decline of a medium sized passerine - Hair-crested Drongo (Dicrurus hottentottus) - in central China. We start this project from 2008 with around 70 colour-ringed pairs monitored in each year. The population of drongos in our study area has declined by half over the last 16 years presumably due to the reduction in survival rate. By identifying the critical environmental factors that contribute to population decline via demographic rates and projecting population size under the forecasted environmental change, this project is aiming to answer the central question of biodiversity loss which is why natural population declines,