The dawn chorus is a period of peak singing activity of many songbirds. Numerous studies have sought to understand this widespread phenomenon, and many hypotheses have been proposed to explain the dawn chorus. The social dynamics hypothesis proposes that dawn singing plays an important role in the announcement of territorial occupancy and the regulation of social relationships between males; it predicts that the dawn chorus vocal behavior varies with changes in social relationships. In this study, we tested the influence of territorial insertions and the number of neighbors, on the intensity of the brownish-flanked bush warbler (Cettia fortipes)'s dawn singing. We found that simulated territorial insertions (playback) caused the males to increase their dawn singing significantly the next day, and males that had many neighbors exhibited more intense dawn singing than did males with few neighbors. Our study provides evidence that dawn singing plays an important role in the announcement of territorial occupancy and the regulation of the social relationships between the males.