Nicolas Mathevon

Audience drives male songbird response to partner's voice

According to the social intelligence hypothesis, social context represents an important force driving the selection of animal cognitive abilities such as the capacity to estimate the nature of the social relationships between other individuals. Despite this importance, the influence of this force has been assessed only in primates and never in other animals showing social interactions. In this way, avian communication generally takes place in a network of signallers and receivers, which represents an audience altering individual signalling behaviours. Indeed, vocal amplitude and repertoire are known to be socially regulated and the attitude towards the opposite sex may change depending on the audience. This ‘audience effect’ provides support for the reality of social awareness in some bird species. However no evidence has yet been found to suggest that birds are able to estimate the characteristics of the social relationships between group-mates. Here we show that the male of a gregarious songbird species—the zebra finch (Taeniopygia guttata)—pays attention to the mating status of conspecific pairs, and uses this information to control its behaviour towards its female partner.

Mother's voice recognition by seal pups.

Newborns need to learn their mothers call before she can take off on a fishing trip.

Mate recognition by female zebra finch: Analysis of individuality in male call and first investigations on female decoding process

Zebra finches are monogamous birds living in large assemblies, which represent a source of confusion for recognition between mates. Because the members of a pair use distance calls to remain in contact, call-based mate recognition is highly probable in this species. Whereas it had been previously demonstrated in males [Vignal, C., Mathevon, N., Mottin, S., 2004. Audience drives male songbird response to mates voice. Nature 430, 448-451], call-based mate recognition remained to be shown in females. By analysing the acoustic structure of male calls, we investigated the existence of an individual signature and identified the involved acoustic cues. We tested to see if females can identify their mates on the basis of their calls alone, and performed preliminary experiments using modified signals to investigate the acoustic basis of this recognition. Playback tests carried on six individuals showed that a female zebra finch is able to perform the call-based recognition of its mate. Our experiments suggested that the female uses both the energy spectrum and the frequency modulation of the male signal. More experiments are now needed to decipher precisely which acoustic cues are used by females for recognition.

Social context modulates behavioural and brain immediate early gene responses to sound in male songbird

Although it is well known that brain sensory information processing is a highly modulated phenomenon, how this brain function is shaped by experience and social context remains a question to explore. In this paper, we present the first attempt to investigate this problem using a songbird acoustic communication paradigm. Social context is well known to influence acoustic communicating behaviours in birds. The present paper investigates whether brain processing of auditory inputs can be modulated by this ‘audience effect’. Given that call‐based communication is known to be highly context‐dependent, we focused on the response of male zebra finches (Taeniopygia guttata) to female calls. We tested to see if the current social context surrounding the hearing bird can modify a sound‐induced immediate early gene (IEG) activation in the specific region of the caudomedial nidopallium (NCM), a songbird brain analogous to the superficial layers of the mammalian primary auditory cortex. Our results show that the expression of the sound‐induced immediate early gene ZENK in the NCM is considerably enhanced when the hearing bird is in the presence of conspecifics, compared to when he is alone. This context‐dependent increase of a sound‐induced immediate early gene expression can be correlated with the differential behavioural response of males to the playback of the same acoustic stimulus as a function of social context.

Why do songbirds sing intensively at dawn

Abstract. Among the ideas proposed to explain the existence of the dawn chorus in songbirds, the acoustic transmission hypothesis claims that birds sing most intensively at dawn because this is the time of the day when songs suffer least from environmentally induced degradation and hence propagate over the longest distances. In this article, we report on the first sound transmission experiment that directly tests this assumption using natural song from a typically forest-living dawn chorusing bird, the blackcap Sylvia atricapilla. Representative sound elements from the introductory twitter part and from the terminating motif part of the blackcap song were transmitted and re-recorded at three different times of the day: dawn, midmorning, and early afternoon. These recordings were then compared with respect to the following measures of sound degradation: signal-to-noise ratio (SNR), excess attenuation, blurring over song elements, and elongation of song elements by tails of echoes. As could be expected, both the background noise and the SNR varied considerably over the day. More surprisingly the excess attenuation decreased during the day, being lowest in the afternoon. There was no diurnal variation in blurring and elongation by echoes. The results may be explained by the diurnal variation in physical parameters such as temperature, relative humidity, and wind speed. The implications of this for different communication activities are discussed. Overall, the results show that dawn conditions in a temperate deciduous forest do not always constitute the best circumstances for long-range communication and therefore that the dawn chorus cannot be explained by the sound transmission hypothesis.

Individual identity coding depends on call type in the South Polar skua Catharacta maccormicki

Abstract. In colonial birds, acoustic communication is essential for mate recognition. The South Polar skua (Catharacta maccormicki) lives in loose colonies and is highly territorial for feeding and breeding. We studied the potential of individual identity coding in the three main calls of the South Polar skua repertoire: the courtship, the contact and the alarm calls. We investigated parameters in both temporal and frequencial domains, i.e. amplitude modulation, frequency modulation and power spectrum density. For each parameter, the intra- and inter-individual variabilities were calculated. The ratio between these values represents the potential of individuality coding (PIC) of the considered feature. Low values of PICs for amplitude and frequency modulations show that both parameters may not be used for individual recognition. In contrast, high values of PIC for the power spectrum density indicate that the energy distribution among the frequency spectrum is likely to be an individual marker. PIC also varies according to the call type. Both courtship and contact calls have a higher potentiality of individual identity coding than the alarm call. The two former calls may allow individual recognition whereas the latter may not, and this last result can be extrapolated to many other species.

Crocodile egg sounds signal hatching time

Crocodilians are known to vocalize within the egg shortly before hatching [1,2]. Although a possible function of these calls - inducing hatching in siblings and stimulating the adult female to open the nest - has already been suggested, it has never been experimentally tested [1-5]. Here, we present the first experimental evidence that pre-hatching calls of Nile crocodile (Crocodylus niloticus) juveniles are informative acoustic signals which indeed target both siblings and mother.

Reaction to conspecific degraded song by the wren Troglodytes troglodytes: Territorial response and choice of song post

We investigated the response of the wren Troglodytes troglodytes to playback of a territorial song degraded by long-range propagation. It appears that the wren is sensitive to this degradation since the territorial reaction is less intense with the degraded song than with the undegraded one. However, the degraded song is still considered by the receiver as a specific territorial aggressive signal. This differential response suggests that the male wren can use the degradation characteristics of the signal to adapt its territorial reaction. Indeed, in response to this stimulus, the receiver wren chooses a higher song post. By so doing, the bird improves both the propagation distance of the emitted song and the receivers ability to hear the opponents song. This behavioural change may correspond to a communication strategy, counteracting the environmental constraints on sound propagation. Therefore, in response to sound degradation during long-range propagation, birds may have developed behavioural adaptations complementary to the various adaptations concerning song structure and coding-decoding processes.

Measuring brain hemodynamic changes in a songbird: responses to hypercapnia measured with functional MRI and near-infrared spectroscopy

Songbirds have been evolved into models of choice for the study of the cerebral underpinnings of vocal communication. Nevertheless, there is still a need for in vivo methods allowing the real-time monitoring of brain activity. Functional Magnetic Resonance Imaging (fMRI) has been applied in anesthetized intact songbirds. It relies on blood oxygen level-dependent (BOLD) contrast revealing hemodynamic changes. Non-invasive near-infrared spectroscopy (NIRS) is based on the weak absorption of near-infrared light by biological tissues. Time-resolved femtosecond white laser NIRS is a new probing method using real-time spectral measurements which give access to the local variation of absorbing chromophores such as hemoglobins. In this study, we test the efficiency of our time-resolved NIRS device in monitoring physiological hemodynamic brain responses in a songbird, the zebra finch (Taeniopygia guttata), using a hypercapnia event (7% inhaled CO(2)). The results are compared to those obtained using BOLD fMRI. The NIRS measurements clearly demonstrate that during hypercapnia the blood oxygen saturation level increases (increase in local concentration of oxyhemoglobin, decrease in deoxyhemoglobin concentration and total hemoglobin concentration). Our results provide the first correlation in songbirds of the variations in total hemoglobin and oxygen saturation level obtained from NIRS with local BOLD signal variations.

Propagation of bird acoustic signals : comparative study of starling and blackbird distress calls

Previous works have demonstrated that the information supported by a bird distress call is encoded both by the energy distribution among harmonics and the temporal evolution of the frequency modulation. In the present study, using these parameters, we compared long-range information transfer in a dense vegetation environment between the starling Sturnus vulgaris and the blackbird. Turdus merula distress calls. It appears that excess attenuation of high frequencies (higher than 4 kHz) after a long-range propagation is responsible for modifications in distress call spectra. The energy of propagated signals tends to be concentrated in a 1.5-4-kHz bandwidth whatever the initial spectrum. Owing to its broad spectrum (0.8-7 kHz), the starling distress call is greatly modified. On the contrary, owing to a narrower spectrum (2-5.5 kHz), the blackbird distress call is relatively preserved. The blackbird distress call appears to be well-adapted to long-range transmission in an environment with dense vegetation. In contrast, the starling distress call is far more easily degraded by propagation. Nevertheless, frequency modulation of the starling call is preserved and message decoding remains possible even if message reliability may diminish. This result is examined from an etho-ecological point of view, taking into account both habitat and social structure of both birds.