Animals can vary signal amplitude with receiver distance: evidence from zebra finch song
ABSTRACT Acoustic signals attenuate with the distance over which they travel, but a vocalizing animal might maintain signal transmission by increasing vocal amplitude when addressing a distant receiver. Such behaviour is well known in humans as speakers vary vocal amplitude with changing distance from an audience, a phenomenon that has been interpreted as resulting from our higher cognitive abilities. However, whether nonhuman animals are capable of this form of vocal adjustment appears to be unknown. We investigated whether birds are also able to regulate the amplitude of their vocal signals depending on receiver distance. Male zebra finches, Taeniopygia guttata, increased their song amplitude with increasing distance to addressed females, indicating that songbirds, like humans, respond to differences in communication distance and that they adjust vocal amplitude accordingly. Our findings show that animal communication is flexible in a previously unsuspected way, and that human speech and bird song share a basic mechanism for ensuring signal transmission. We suggest that this behaviour can be accounted for by simple proximate mechanisms rather than by the cognitive abilities that have been thought necessary in humans.
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ABSTRACT: The evolution of mating signals is closely linked to sexual selection. Acoustic ornaments are often used as secondary sexual traits that signal the quality of the signaller. Here we show that song performance reflects age and reproductive success in the rock sparrow (Petronia petronia). In an Alpine population in south-east France, we recorded the songs of males and assessed their genetic breeding success by microsatellite analysis. In addition to temporal and spectral song features, we also analysed for the first time whether the sound pressure level of bird song reflects reproductive success. Males with higher breeding success sang at a lower rate and with a higher maximum frequency. We found also that older males gained more extra-pair young and had a higher overall breeding success, although they also differed almost significantly by having a higher loss of paternity in their own nests. Older males could be distinguished from yearlings by singing at lower rate and higher amplitudes. Our findings suggest that song rate may be used as a signal of age and together with song pitch as a signal of reproductive success in this species. Alternatively, younger and less successful males might try to compensate their inferior status by increased song rates and lower pitch. Independent of age and quality, high-amplitude songs correlated with paternity loss in the own nest, suggesting that in this species song amplitude is not an indicator of male quality but high-intensity songs may be rather a response to unfaithful social mates.PLoS ONE 01/2012; 7(8):e43259. · 3.73 Impact Factor
Article: The Lombard effect.Current biology: CB 08/2011; 21(16):R614-5. · 10.99 Impact Factor
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ABSTRACT: Arboreal primates use loud vocalisations to transmit information in densely vegetated habitats. These vocalisations are likely to show adaptations to increase their propagation and to transmit information. Golden-backed uakaris, Cacajao melanocephalus, emit a loud vocalization termed the "tchó" call, which seems to function as a contact call and encodes information on the individual signaler and behavioural context. Because the call is often used for communication over relatively large distances, we were interested in its propagation in the wild. The aim of the present study was to investigate the degradation patterns of the tchó call in the flooded igapó forest. We examined via playback experiments how the acoustic parameters of this call changed with increasing distance from the playback speaker. We broadcast 12 tchó calls and rerecorded them along a transect at distances of 10, 20, 40, 80 and 160 m from the speaker in two igapó forest patches in Jaú National Park, Amazonas, Brazil. At 160 m from the speaker, the tchó call degraded in both patches and was barely recordable. Up to a distance of 80 m, the bandwidth and number of harmonics in the call decreased with increasing distance, while the lowest frequency increased. The highest frequency (HF) did not gradually decrease with increasing distance. However, when we compared the HF at distances of 10 and 80 m, we could see a clear decrease in this parameter. Call duration increased compared with the broadcast signal up to 40 m because of reverberation, but decreased at 80 m as the weaker echoes of the call attenuated. These changes may reveal information about the signaler's distance during signal transmission. The frequency of maximum energy (FME) of the tchó call decreased significantly when comparing recordings made at 10 and 80 m. Nevertheless, it did not show a consistent and gradual decrease with increasing rerecording distance (at least up to 80 m). FME remained relatively stable (±50 Hz on average, at least up to 80 m) when compared to the other call parameters, suggesting that the tchó call may be adapted to transmit information with some efficiency throughout the igapó forest.Primates 06/2012; 53(4):317-25. · 1.40 Impact Factor