The Ecology of Avian Acoustical Signals
The acoustical communication of birds is reviewed with an emphasis on ecological aspects. Sound propagation in the environment has specific consequences for signal transmission. The intensively studied ground effect and other influences offer good predict
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Abstract The acoustical communication of birds is reviewed with an emphasis on ecological aspects. Sound propagation in the environment has specific consequences for signal transmission. The intensively studied ground effect and other influences offer good prediction for signal design in the frequency domain. The particular transmission properties observed in bird sounds are, in fact, at least as much governed by their temporal structure. Some principles of signal design are illustrated using woodpeckers as examples. They show how intimate and longdistance signals are structured, and how they relate to behavior and habitat use. The analysis of a set of species of antbirds of a rainforest community demonstrates that the temporal structure of the song is most important for explaining the transmission properties at singing post height. A review of the hypotheses proposed to explain the dawn chorus serves to point out the role of the receiver's demand for information played in the shaping of bird song. It is suggested that researchers should pay more attention to acoustical signals other than song, because these may offer better models for testing specific hypotheses about functional aspects. More and more evidence from different fields of research indicates that temporal characteristics of vocalizations need more attention. Finally, viewing acoustical communication more from the receiver's end may foster our understanding. Key words Acoustic communication, bird song, habitat, sound propagation
1 Introduction Birds rely extensively on sound as a means of communication. The diversity of sounds and vocal repertoires defies simple description. This chapter purports to review the ecological aspects of acoustical communication in birds. To that end I will concentrate on summarizing the current state of knowledge of basic aspects of sound transmission as far as they were not treated in the chapter by Romer, this Volume, ecological factors such as habitat and foraging, and sound reception. Some of the points made will be illustrated with examples from my own work. Recent reviews (e.g., Kroodsma and Miller 1996) show that our knowledge has F. G. Barth et al. (eds.), Ecology of Sensing © Springer-Verlag Berlin Heidelberg 2001
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Hans Winkler
progressed well in certain fields, but also that many gaps and open questions remain. Most of the examples given will deal with song and its analogues in nonsongbirds. However, various types of calls and instrumental signals will be discussed as well. With respect to ecology I will focus on sound transmission in natural habitats. However, other aspects of ecology, such as predation, will be treated as well. Particular attention will be paid to the receivers' role.
2 Sound Propagation in Terrestrial Habitats 2.1 Attenuation Sound attenuation by distance has several components, namely geometrical spreading, atmospheric absorption, effects of the ground, and miscellaneous environmental effects (noise, vegetation, see also Chapter II. 2). For a point source the spreading of sound is spher
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