Behaviour, Volume 141, Number 8 (August 2004)
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Blumenrath SH & T Dabelsteen (2004) Degradation of great tit (Parus major)
song before and after foliation: implications for vocal communication in a
deciduous forest. Behaviour 141: 935-958 .
Abstract: Songbirds living in temperate forests experience great seasonal
changes in habitat acoustics during the part of the breeding season when
singing activity is high. These changes, which are brought about by
accelerated vegetation growth and leaf burst in spring, affect sound
propagation and potentially render vocal communication more difficult as the
total number of scattering and absorbing obstacles increases. We
investigated this in a sound transmission experiment in which representative
great tit (Parus major) songs were broadcast in a typical forest habitat
before and after foliation. Speaker and microphone were placed at natural
separation distances and in typical sender and receiver positions. For each
song note we quantified several aspects of sound degradation and found that
they all increased considerably when leaves were present. Before foliation
the same amount of degradation would only be obtained by doubling the
transmission distance, i.e. foliage shortens the active space of great tit
song. This inevitably alters distance information, provided that
distance-dependent, structural changes of received songs are used as ranging
cues. Moreover, sender and receiver positions within the canopy become
unfavourable compared to heights just below the canopy when the aim is to
maximise song propagation distances. Altogether, the presence of foliage
greatly affects the potential for vocal information transfer in great tits
and requires behavioural and/or perceptual adjustment of the communicating
individuals to counteract or reduce the impact of foliage on signal
degradation.
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