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: Many bioacoustic studies have been able to identify individual mammals from variations in the fundamental frequency (F 0) of their vocalizations. Other characteristics of vocalization which encode individuality, such as amplitude, are less frequently used because of problems with background noise and recording fidelity over distance. In this paper, we investigate whether the inclusion of amplitude variables improves the accuracy of individual howl identification in captive Eastern grey wolves (Canis lupus lycaon). We also explore whether the use of a bespoke code to extract the howl features, combined with histogram-derived principal component analysis (PCA) values, can improve current individual wolf howl identification accuracies. From a total of 89 solo howls from six captive individuals, where distances between wolf and observer were short, we achieved 95.5% (+9.0% improvement) individual identification accuracy of captive wolves using discriminant function analysis (DFA) to classify simple scalar variables of F 0 and normalized amplitudes. Moreover, this accuracy was increased by 100% when using histogram-derived PCA values of F 0 and amplitudes of the first harmonic. We suggest that individual identification accuracy can be improved by including amplitude changes for species where F 0 has only been included so far. Using DFA on PCA values of both F 0 and amplitude could optimize vocal identification in a range of mammal bioacoustic studies.Bioacoustics 07/2014; DOI:10.1080/09524622.2013.817318 · 0.73 Impact Factor
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ABSTRACT: 1. Anthropogenic noise can affect intra-pair communication and therefore interfere with reproductive success. However, many animals have various signal strategies to cope with noise, although it is unclear whether they rely on direct auditory feedback from their own perception of noise or signal-to-noise level or on indirect social feedback from receivers. 2. We studied the role of social feedback on male great tit (Parus major) song adjustment by exclusively exposing females to artificial traffic noise inside their nest box. 3. We found a delay in female response latencies to male song in the noisy condition compared to the control condition on the first day of noise exposure. Males from the noise treatment group, not directly exposed to noise themselves, sang closer to the nest box within 3 days after the start of exposure. 4. The male's closer proximity to the nest box most likely led to the observed higher song amplitudes at the noisy nest boxes compared to quiet control nest boxes, and explains why the inside signal-to-noise ratios were restored to equal levels between treatment and control nest boxes after several days of exposure. 5. The initial difference between treatment groups in female response latencies at the start of exposure also disappeared accordingly. 6. Our results strongly suggest an active role for female birds in steering male song behaviour under noisy conditions. Males did not receive direct exposure during intra-pair communication, but adjusted their behaviour in the predicted direction. These data are important to understand the mechanisms related to communication in noise and reveal the critical role of ecology in shaping animal interactions.Functional Ecology 12/2012; 26(6-6):1339-1347. DOI:10.2307/23326828 · 4.86 Impact Factor
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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.Behavioural Processes 09/2012; 91(3):222-266. DOI:10.1016/j.beproc.2012.09.006 · 1.46 Impact Factor