title: Rainforests as concert halls for birds: are reverberations improving sound transmission of long song elements?
abstract: In forests reverberations have probably detrimental and beneficial effects on avian communication. They constrain signal discrimination by masking fast repetitive sounds and they improve signal detection by elongating sounds. This ambivalence of reflections for animal signals in forests is similar to the influence of reverberations on speech or music in indoor sound transmission. Since comparisons of sound fields of forests and concert halls have demonstrated that reflections can contribute in both environments a considerable part to the energy of a received sound, it is here assumed that reverberations enforce also birdsong in forests. Song elements have to be long enough to be superimposed by reflections and therefore longer signals should be louder than shorter ones. An analysis of the influence of signal length on pure tones and on song elements of two sympatric rainforest thrush species demonstrates that longer sounds are less attenuated. The results indicate that higher sound pressure level is caused by superimposing reflections. It is suggested that this beneficial effect of reverberations explains interspecific birdsong differences in element length. Transmission paths with stronger reverberations in relation to direct sound should favor the use of longer signals for better propagation.
authors.affiliation: Konrad Lorenz Institute for Comparative Ethology, Austrian Academy of Sciences, Savoyenstrasse la, A-1160 Wien, Austria. e.nemeth@klivv.oeaw.ac.at
authors.forename: Erwin
authors.initials: E
authors.lastname: Nemeth
authors.forename: Torben
authors.initials: T
authors.lastname: Dabelsteen
authors.forename: Simon Boel
authors.initials: SB
authors.lastname: Pedersen
authors.forename: Hans
authors.initials: H
authors.lastname: Winkler
mesh_terms: D000162:Acoustics; D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal; D020308:Songbirds / Q000502:physiology*; D013016:Sound; D014197:Trees; D014329:Tropical Climate; D014828:Vocalization, Animal