Pattern amplitude is related to pattern imitation during the song development of nightingales

Song intensity has been neglected in studies on the song development of oscine birds. We analysed this ontogenetic trajectory in the singing of hand-reared nightingales, Luscinia megarhynchos, from their earliest song vocalizations (subsong) through plastic singing, to their adult full song. Embedded in an age-dependent increase in overall sound level, nightingales showed systematic amplitude differences within their song performances. Episodes of song performance containing many imitations of acquired model songs (IPA phases) were produced with a higher amplitude than episodes with only few or no imitations (UPA phases). Further analysis of song patterns revealed that this difference was mainly due to the high number of imitations occurring during the IPA phases. However, unidentified patterns (UPA) that were vocalized during IPA phases had a significantly higher vocal amplitude than UPAs vocalized during UPA phases. This finding indicates that, besides pattern-related amplitude differences, performance phases as a whole also differed in amplitude. The consistent pattern- and phase-related differences in sound level indicate that the control of vocal amplitude should be viewed as an integrative part of the vocal learning process. (C) 2001 The Association for the Study of Animal Behaviour.