. Bulletin of the British Ornithologists' Club. [Bull. 1976: 96(4)] 118 duets of other pairs of C. discolour which I recorded on the mountain together with those recorded by Chappuis (1974) showed that whereas the phrases of the first component were different for each pair, none coinciding with those in Fig. 2, the second component of the duet and its oscillatory nature varied little between duetting pairs. The male Evergreen-forest Warbler Bradypterus barratti was also very vocal during my stay on the mountain, usually singing from within dense thicket, creeping slowly through it betwe
. Bulletin of the British Ornithologists' Club. [Bull. 1976: 96(4)] 118 duets of other pairs of C. discolour which I recorded on the mountain together with those recorded by Chappuis (1974) showed that whereas the phrases of the first component were different for each pair, none coinciding with those in Fig. 2, the second component of the duet and its oscillatory nature varied little between duetting pairs. The male Evergreen-forest Warbler Bradypterus barratti was also very vocal during my stay on the mountain, usually singing from within dense thicket, creeping slowly through it between bouts of song. Males in song were invariably singing in response to neighbouring conspecifics and the function of the song appears, therefore, to be mainly territorial. A playback of a song always brought the singing bird nearer the tape-recorder, and resulted in further song. Serle (1965: 91) describes the song as "loud, explosive in quality, unvaried in pitch and rhythm" consisting of a number of repetitions of one phrase "o-chip, o-chip, o-chip", etc. On several oc- casions I noted aurally that one warbler was singing the same song as a neighbour, only to be proved wrong by the sonograms. These (Fig. 4) show that a male has a large number of song types which are quite different from those used by neighbours singing in competition. Other Evergreen- forest Warblers recorded at various heights on the mountain all showed this variability which suggests that a complex system of dialects exist. It is while the male sings his loud song that the female may join in a duet, adding in contrast a series of weak whistling notes (Fig. 5), only audible within a few. Figure 5. Diagrammatic sound spectograms of the duet structures of Bradypterus barratti recorded near the forest-grassland boundary at 2100 m on Mount Cameroun. Male dark, female open symbols. metres of the singing bird. As the pair are close together when they duet and visible to each other it is difficu
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