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Balsby, T.J.S., Dabelsteen, T. & Pedersen, S.B. 2003. Degradation of
whitethroat vocalisations: implications for song flight and communication
network activities. Behaviour 140: 695-719.
Abstract: Transmission of acoustic signals through the habitat modifies the
signals and may thus influence their use in communication. We investigated
the transmission of five different types of whitethroat (Sylvia communis)
vocalisations, three types of song and two calls. Typical examples were
broadcast and re-recorded in a whitethroat habitat with hedgerows and open
meadow. We used a complete factorial design with speaker and microphone
placed in different natural sender and receiver positions including high
perches and song flights. Sound degradation was quantified in terms of
signal-to-noise ratio, excess attenuation, tail-to-signal ratio and blur
ratio. The results suggest that sound degradation generally increased with
distance along a hedgerow, which means that birds here potentially may use
degradation in assessing the distance to a vocalising individual. This is
unlike the open meadow where the change in degradation with distance was
negligible. Surprisingly, song flight relative to perched singing seems not
to facilitate transmission of own vocalisations or perception of
vocalisations from other individuals, and song flight vocalisations do not
transmit differently from other types of vocalisations during song flights.
One purpose of song flights might therefore be visual location by potential
receivers and surveillance by the territory owner. Source level and
degradation differed between the five types of vocalisations in accordance
with their functions. Motif song and song flight songs used in attraction of
females and/or deterrence of males could transmit through neighbouring
territories, whereas the calls and the courtship diving song where a
specific individual within or near the territory is addressed had relatively
short communication ranges.
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