Influence of meteorological conditions and topography on the active space of mountain birds assessed by a wave-based sound propagation model.

The active space is a central bioacoustic concept to understand communication networks and animal behavior. Propagation of biological acoustic signals has often been studied in homogeneous environments using an idealized circular active space representation, but few studies have assessed the variations of the active space due to environment heterogeneities and transmitter position. To study these variations for mountain birds like the rock ptarmigan, we developed a sound propagation model based on the parabolic equation method that accounts for the topography, the ground effects, and the meteorological conditions. The comparison of numerical simulations with measurements performed during an experimental campaign in the French Alps confirms the capacity of the model to accurately predict sound levels. We then use this model to show how mountain conditions affect surface and shape of active spaces, with topography being the most significant factor. Our data reveal that singing during display flights is a good strategy to adopt for a transmitter to expand its active space in such an environment. Overall, our study brings new perspectives to investigate the spatiotemporal dynamics of communication networks.

Using acoustics and artificial intelligence to monitor pollination by insects and tree use by woodpeckers.

The collection and interpretation of field data is a prerequisite for informed conservation in protected environments. Although several techniques, including camera trapping and passive acoustic monitoring, have been developed to estimate the presence of animal species, very few attempts have been made to monitor ecological functions. Pollination by insects and wood use, including tree related foraging and intraspecific communication, by woodpeckers are key functions that need to be assessed in order to better understand and preserve forest ecosystems within the context of climate change. Here, we developed and applied for the first time an acoustic survey to monitor pollination by insects and wood use by woodpeckers in a protected Alpine forest in France. We deployed four autonomous recorders over a year, resulting in 2285 h of recordings. We trained a convolutional neural network (CNN) on spectrographic images to automatically detect the sounds of flying insects' buzzing and woodpeckers' drumming as they forage and call. We used the output of the CNN to estimate the seasonality, diel pattern, climatic breadth and distribution of both functions and their relationships with weather parameters. Our method showed that insects were flying (therefore potentially pollinating flowers) in bright, warm and dry conditions, after dawn and before dusk during spring and summer. Woodpeckers were mainly drumming around March at the time of pair formation in cool and wet conditions. Having considered the role of weather parameters, climate change might have contrasting effects on insect buzzing and woodpecker drumming, with an increase in temperature being favorable to pollination by insects but not to wood use by woodpeckers, and a concomitant increase in relative humidity being favorable to wood use but not to pollination. This study reveals that a systemic facet of biodiversity can be tracked using sound, and that acoustics provide valuable information for the environment description.

Soundscape dynamics of a cold protected forest: dominance of aircraft noise.

CONTEXT: One mainstay of soundscape ecology is to understand acoustic pattern changes, in particular the relative balance between biophony (biotic sounds), geophony (abiotic sounds), and anthropophony (human-related sounds). However, little research has been pursued to automatically track these three components. OBJECTIVES: Here, we introduce a 15-year program that aims at estimating soundscape dynamics in relation to possible land use and climate change. We address the relative prevalence patterns of these components during the first year of recording. METHODS: Using four recorders, we monitored the soundscape of a large coniferous Alpine forest at the France-Switzerland border. We trained an artificial neural network (ANN) with mel frequency cepstral coefficients to systematically detect the occurrence of silence and sounds coming from birds, mammals, insects (biophony), rain (geophony), wind (geophony), and aircraft (anthropophony). RESULTS: The ANN satisfyingly classified each sound type. The soundscape was dominated by anthropophony (75% of all files), followed by geophony (57%), biophony (43%), and silence (14%). The classification revealed expected phenologies for biophony and geophony and a co-occurrence of biophony and anthropophony. Silence was rare and mostly limited to night time. CONCLUSIONS: It was possible to track the main soundscape components in order to empirically estimate their relative prevalence across seasons. This analysis reveals that anthropogenic noise is a major component of the soundscape of protected habitats, which can dramatically impact local animal behavior and ecology. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10980-021-01360-1.

Evolution of communication signals and information during species radiation.

Communicating species identity is a key component of many animal signals. However, whether selection for species recognition systematically increases signal diversity during clade radiation remains debated. Here we show that in woodpecker drumming, a rhythmic signal used during mating and territorial defense, the amount of species identity information encoded remained stable during woodpeckers' radiation. Acoustic analyses and evolutionary reconstructions show interchange among six main drumming types despite strong phylogenetic contingencies, suggesting evolutionary tinkering of drumming structure within a constrained acoustic space. Playback experiments and quantification of species discriminability demonstrate sufficient signal differentiation to support species recognition in local communities. Finally, we only find character displacement in the rare cases where sympatric species are also closely related. Overall, our results illustrate how historical contingencies and ecological interactions can promote conservatism in signals during a clade radiation without impairing the effectiveness of information transfer relevant to inter-specific discrimination.

Dawn-song onset coincides with increased HVC androgen receptor expression but is decoupled from high circulating testosterone in an equatorial songbird.

The song of songbirds is a testosterone-sensitive behavior that is controlled by brain regions expressing androgen receptors. At higher latitudes, seasonal singing is stimulated by increasing day-length and elevated circulating testosterone. However, a large number of songbird species inhabit equatorial regions under a nearly constant photoperiod, and the neuroendocrine mechanisms of seasonal song in these species have rarely been investigated. We studied males from an equatorial population of the silver-beaked tanager (Ramphocelus carbo), an Amazonian songbird. We found seasonality in dawn-song behavior, which was displayed continuously for more than half a year throughout an extended breeding territoriality stage. The seasonal activation of dawn-song was correlated with an increased area of androgen receptor expression in HVC, a major brain area of song control. However, testosterone levels remained low for several weeks after activation of dawn-song. Circulating levels of testosterone were elevated only later in the breeding season, coinciding with a higher dawn-song output and with the mating period. Our results suggest that the seasonal activation of dawn-song and territoriality involves an increase of androgen target cells in HVC. This mechanism could potentially function to circumvent adverse effects of high testosterone levels in a species with an extended breeding season.

Mother-young vocal communication and acoustic recognition promote preferential nursing in sheep.

In mammals with precocial neonates, exclusive maternal care and investment depend on mutual mother-young recognition. In sheep, this is ensured by rapid olfactory recognition of the neonate by its mother. However, recent studies suggest that other processes may participate in preferential maternal care. We investigated the possibility that acoustic communication promotes preferential nursing of the lamb. In the first of two studies, we examined the association between nursing and vocal activity in ewes and their lambs during the first 2 weeks of lactation. As early as 3 and 6 h postpartum, vocal activity was preferentially concentrated before nursing and by day 15 all vocal activity occurred within 2.5 min before nursing. In the second study, we tested the responses of ewes and lambs at 15 days postpartum to the playback of recorded bleats of their partner or from unrelated ewes and lambs. When playback was performed 30 min after a nursing episode, both ewes and lambs responded to bleats of their partner but not to bleats from alien subjects. When playback was performed 5 min after nursing, ewes did not respond to any lamb's bleats, while lambs continued responding to the bleats of their mothers, but significantly less than 30 min after nursing. Nursing therefore appears to play an important role in structuring very early vocal communication between the mother and her neonate. In turn, if the motivational state of the members of the mother-young dyad is adequate, this ensures the display of mutual acoustic recognition and prepares them for preferential nursing before maternal olfactory recognition of the lamb comes into play.

Singing in the rain forest: how a tropical bird song transfers information.

How information transmission processes between individuals are shaped by natural selection is a key question for the understanding of the evolution of acoustic communication systems. Environmental acoustics predict that signal structure will differ depending on general features of the habitat. Social features, like individual spacing and mating behavior, may also be important for the design of communication. Here we present the first experimental study investigating how a tropical rainforest bird, the white-browed warbler Basileuterus leucoblepharus, extracts various information from a received song: species-specific identity, individual identity and location of the sender. Species-specific information is encoded in a resistant acoustic feature and is thus a public signal helping males to reach a wide audience. Conversely, individual identity is supported by song features susceptible to propagation: this private signal is reserved for neighbors. Finally, the receivers can locate the singers by using propagation-induced song modifications. Thus, this communication system is well matched to the acoustic constraints of the rain forest and to the ecological requirements of the species. Our results emphasize that, in a constraining acoustic environment, the efficiency of a sound communication system results from a coding/decoding process particularly well tuned to the acoustic properties of this environment.

Establishment of vocal communication and discrimination between ewes and their lamb in the first two days after parturition.

In sheep, the mother-young relationship is characterized by an exclusive bond that relies on the rapid establishment of mutual recognition. However, the role of acoustic cues has been underestimated and neglected in this early discrimination. Therefore, the aim of the present study was (1) to characterize the vocal behavior of ewes and their lambs during the first 15 days postpartum and (2) to investigate the ability of newborn lambs and their mothers to discriminate each other from alien subjects within the first 48 hr postpartum on the basis of acoustic cues only. Ewes started to vocalize in the last 3 hr preceding parturition, emitting mainly high-pitched bleats. However, the bleating activity was highest during the first 3 hr following birth, consisting mainly of low-pitched bleats. Thereafter it decreased sharply until 24 hr postpartum, with most of the activity coming from the mother. In a two-choice test, ewes discriminated their own from an alien lamb on the basis of acoustic cues only at 24 hr postpartum, while lambs did so for their mother at 48 hr, which in both cases was much earlier than reported so far. We conclude that early vocal recognition between the ewe and her lamb may play an important role for the maintenance of mother-young contact.

How a simple and stereotyped acoustic signal transmits individual information: the song of the White-browed Warbler Basileuterus leucoblepharus.

The White-browed Warbler Basileuterus leucoblepharus, a common bird of the BrazilianAtlantic forest, emits only one distinct song type in the context of territorial defense. Individual or neighbor-stranger recognition may be more difficult when birds share similar songs. In fact, the analysis of songs of different individuals reveals slight differences in the temporal and the frequency domains. Effectively, a careful examination of the signals of different individuals (21) by 5 complementary methods of analysis reveals first, that one or two gaps in frequency occur between two successive notes at different moments of the song, and second, that their temporal and frequency positions are stereotyped for each individual. Playback experiments confirm these findings. By propagation experiments, we show that this individual information can be only transmitted at short range (< 100 m) in the forest. In regard to the size and the repartition of territories, this communication process appears efficient and adaptive.

How a simple and stereotyped acoustic signal transmits individual information: the song of the White-browed Warbler Basileuterus leucoblepharus

O Pula-pula-assobiador Basileuterus leucoblepharus, um pássaro comum da Mata Atlântica, emite um único e distintivo tipo de canto para defesa territorial. O reconhecimento individual ou entre vizinho e estranho pode ser mais difícil quando as aves compartilham cantos semelhantes. De fato, a análise dos cantos de diferentes indivíduos revelou ligeiras diferenças nos domínios temporal e das freqüências. Efetivamente, um exame cuidadoso dos sinais de 21 indivíduos diferentes por 5 métodos complementares de análise revelou que, primeiro, um ou dois espaços na série tonal ocorrem entre duas notas sucessivas em determinados momentos do canto e, segundo, ocupam posiçäes em tempo e freqüência estereotipadas para cada indivíduo. Experiências de "play-back" confirmam esses dados. Através de experiências de propagação, mostramos que esta informação individual pode ser transmitida somente a curta distância ( < 100 m) na mata. Considerando o tamanho e a repartição dos territórios, este processo de comunicação mostra-se eficiente e bem adaptado.