Causes and consequences of song amplitude adjustment in a territorial bird: a case study in nightingales
Institute of Biology, Department of Behavioural Biology, Free University of Berlin, Haderslebener Str. 9, 12163 Berlin, Germany
Vocal amplitude, one of the crucial factors for the exchange of acoustic signals, has been neglected in studies of animal communication, but recent studies on song variation in Common Nightingales Luscinia megarhynchos have revealed new insights into its importance in the singing behavior of territorial birds. In nightingales song amplitude is not maximized per se, but is individually regulated according to the level of masking background noise. Also, birds adjust their vocal intensity according to social variables, as in male-male interactions. Moreover, during such interactions, males exploited the directionality of their songs to broadcast them in the direction of the intended receivers ensuring the most effective signal transmission. Studies of the development of this typical long-range signaling suggest that sound level is highly interrelated with overall developmental progression and learning, and thus should be viewed as an integral part of song ontogeny. I conclude that song amplitude is a dynamic feature of the avian signal system, which is individually regulated according to the ecological demands of signal transmission and the social context of communication.
Key words: acoustic communication, birdsong, Lombard effect, background noise, song development, vocal amplitude.
An. Acad. Bras. Ciênc. vol.76 no.2 Rio de Janeiro June 2004. Open Access Article.