To maximize their reproductive success, male birds have to acquire females, ensure their paternity, and increase the survival of their offspring. Males therefore allot their reproductive efforts to several activities during the nesting cycle, because there are trade-offs among the reproductive behaviours. In the Great Reed Warbler, Acrocephalus arundinaceus, there is a negative correlation between singing frequency and intensity of mate guarding, and between singing frequency and male feeding rate. Furthermore, male Great Reed Warblers adjust the time of singing by estimating the risk of paternity loss and abundance of potential secondary mates. In the Bush Warbler, Cettia diphone, males vigorously sing throughout the breeding season, which may be due to frequent female remating due to nest predation, resulting in a continuous source of potential mates for males. Thus, the timing of male singing is influenced by the costs and benefits of singing, which are related to other reproductive activities. Therefore, to understand singing activity, the social and ecological circumstances of the species should be considered, especially the occurrence of extra-pair fertilization, the pattern of parental care, the pattern of female arrival at the breeding area, and successiveness of pairbonds.