When do males sing song?: Allocation of mate-attraction components
in total reproductive effort

Shoji HAMAO (Urawa-minami High School)

To maximize their reproductive success, male birds have to acquire females, insure their paternity, and increase the survival of their offspring. Males therefore share their reproductive effort to several activities during a breeding season: mate attraction, seeking extra-pair copulations (EPCs), mate guarding (close following of females), incubation, and feeding young. In these activities, song is used mainly for mate attraction.
Two main functions of song are obviously territorial defence and mate attraction. In some species, song has additional functions that is paternity guard, and to maximize their own EPC success. These functions of song are not mutually exclusive. The song of a certain species often has two or more functions. Male Great Reed Warblers sing to attract their mates, because they stop singing when they acquire mates. At the same time, their songs are evaluated by the potential EPC partners who prefer males with large repertoire size. For many species, at least one of the purpose of singing during breeding seasons must be to attract mates.
If a male tries only to acquire multiple females, he sing song throughout the breeding season irrespective of the breeding cycle of his mate(s). However, it may cause cuckoldry and starvation of his young, so that such a male can not enjoy high reproductive success. Thus, there are trade-offs among the reproductive behaviors of males. Each of the behaviors involves cost and benefit, and the cost and benefit of singing vary with the progress of a nesting cycle. Under the circumstances, when should males allocate their effort to mate attraction?
I review the seasonal pattern of singing by males in terms of effective mate attraction. On species whose singing frequency with the nesting cycle was investigated, the influence of ecological and social condition of the species to the seasonal singing pattern is discussed.