Animals can vary signal amplitude with receiver distance: evidence from zebra finch song

Centre for Social Learning and Cognitive Evolution, School of Biology, University of St Andrews, U.K.
Animal Behaviour (Impact Factor: 3.14). 09/2006; 72(3):699-705. DOI: 10.1016/j.anbehav.2006.01.020


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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Available from: Henrik Brumm, Aug 12, 2015
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    • "Extending these results to other species, in particular canids known to carry individual identity information in their long-distance vocalizations such as coyotes (Mitchell et al. 2006) and African wild dogs (Lycaon pictus) (Hartwig 2005), could be possible. By improving the accuracy of individual identity, further insights into species' behavioural ecology may be made, similar to those reported for social learning in birds (Brumm and Slater 2006). "
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    • "Most knowledge on noise-dependent feedback mechanisms comes from studies on amplitude regulation, which is generally presumed to reflect an internal mechanism, known as the Lombard effect (Brumm & Slabbekoorn 2005). The Lombard effect specifically refers to an involuntarily control of amplitude in response to noise (Pick et al. 1989; Lombard 1911), but animals can also adjust signal amplitude outside the context of noise, as male birds have been shown to sing louder when their mates are further away (Brumm & Slater 2006). Males may have an internal mechanism that matches information on receiver-distance to song amplitude, but it seems more likely that males in the experiment of Brumm & Slater relied on an external feedback mechanism in the form of (a lack of) female response. "
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    • "Dunn and Zann, 1997; Elie et al., 2011). Secondly, our companion birds were at almost 1 m distance from the focal male, whereas directed singing mostly occurs at close distance to the female only (<20 cm, Zann, 1996; but see Brumm and Slater, 2006). Thirdly, even if males sung directed song towards females at this distance, it is important to keep in mind that for males in female company, directed song makes up only a fraction of their daily song output both in the wild and laboratory (Caryl, 1976; Dunn and Zann, 1996a,b). "
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    ABSTRACT: Zebra finches are a ubiquitous model system for the study of vocal learning in animal communication. Their song has been well described, but its possible function(s) in social communication are only partly understood. The so-called 'directed song' is a high-intensity, high-performance song given during courtship in close proximity to the female, which is known to mediate mate choice and mating. However, this singing mode constitutes only a fraction of zebra finch males' prolific song output. Potential communicative functions of their second, 'undirected' singing mode remain unresolved in the face of contradicting reports of both facilitating and inhibiting effects of social company on singing. We addressed this issue by experimentally manipulating social contexts in a within-subject design, comparing a solo versus male or female only company condition, each lasting for 24h. Males' total song output was significantly higher when a conspecific was in audible and visible distance than when they were alone. Male and female company had an equally facilitating effect on song output. Our findings thus indicate that singing motivation is facilitated rather than inhibited by social company, suggesting that singing in zebra finches might function both in inter- and intrasexual communication.
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