Wind energy has experienced a notable development during the last decades, driving new challenges for animal communities. Although bird collisions with wind turbines and spatial displacement due to disturbance have been widely described in the literature, other potential impacts remain unclear. In this study, we addressed the effect of turbine noise on the vocal behaviour of a threatened shrub-steppe passerine highly dependent on acoustic communication, the Dupont's lark Chersophilus duponti. Based on directional recordings of 49 calling and singing males exposed to a gradient of turbine noise level (from 15 up to 51 dBA), we tested for differences in signal diversity, redundancy, and complexity, as well as temporal and spectral characteristics of their vocalizations (particularly the characteristic whistle). Our results unveiled that Dupont's lark males varied the vocal structure when subject to turbine noise, by increasing the probability of emitting more complex whistles (with increased number of notes) and shifting the dominant note (emphasizing the longest and higher-pitched note). In addition, males increased duration and minimum frequency of specific notes of the whistle, while repertoire size and signal redundancy remain constant. To our knowledge, this is the first study reporting multiple and complex responses on the vocal repertoire of animals exposed to turbine noise and unveiling a shift of the dominant note in response to anthropogenic noise in general. These findings suggest that the Dupont's lark exhibits some level of phenotypic plasticity, which might enable the species to cope with noisy environments, although the vocal adjustments observed might have associated costs or alter the functionality of the signal. Future wind energy projects must include fine-scale noise assessments to quantify the consequences of chronic noise exposure.

In 2020, the COVID-19 pandemic led to government-enforced limits on activities worldwide, causing a marked reduction of human presence in outdoors environments, including in coastal areas that normally support substantial levels of boat traffic. These restrictions provided a unique opportunity to quantify the degree to which anthropogenic noise contributes to and impacts underwater soundscapes. In Guadeloupe, French West Indies, a significantly lower number of motor boats were recorded in the vicinity of the major urban marina during the peak of the first COVID-19 lockdown (April–May 2020), compared with the number recorded post-lockdown. The resumption of human activities at the end of May was correlated with a maximum increase of 6 decibels in the ambient noise level underwater. The change in noise level did not impact daily sound production patterns of vocal fishes, with increased activity at dusk seen both during and after the lockdown period. However, during the lockdown vocal activity was comprised of a reduced number of sounds, suggesting that anthropogenic noise has the potential to interfere with vocalization behaviours in fishes.

The structure and organization of acoustic signals arise through evolutionary processes and adaptive pressures on each species. During learning, natural or anthropogenic factors, such as high noise levels in urban areas, pose challenges to acoustic communication in birds. Many species adjust their acoustic signals to higher noise levels by increasing the frequency of vocalizations. The objectives of this study were to compare the dominant frequency of songs among birds dwelling in forest fragments distant from and near to urban areas, establish correlations between the dominant frequency of song and noise levels in these environments and verified the difference of response between oscines, suboscines and non-passerines. We recorded vocalizations of birds between July/2013 and November/2014 in four forest fragments, two of them near and two distant from urban areas. We used Audacity software to measure the dominant frequency. We measured the ambient noise by a calibrated sound pressure level meter in decibels (dBA) in each of the forest fragments. We analyzed 3740 vocalizations of nine tropical bird species. Forest fragments near to urban areas have higher noise levels than more distant forest fragments. Eight of nine studied species presented higher dominant frequencies of songs in forest fragments near to urban areas. Only one species, Myiothlypis flaveola, did not change the dominant frequency of song between the four analyzed forest fragments. The difference in dominant frequency between the forest fragments distant and closer to the urban areas did not vary between oscines, suboscines and non-passerines. Eight tropical birds exhibited higher dominant frequencies of song in forest fragments near urban areas with high level of ambient noise. Oscine, suboscine and non-passerine showed song variations. Bird species that have differences in the vocalization dominant frequency can be used in environmental monitoring and in ethological studies, as they are sensitive to high noise levels.Noise pollution caused by the vehicular traffic and urbanization are correlates with changes in the vocalization of tropical birds in forest fragments.

Ambient noise has increased in extent, duration and intensity with significant implications for species’ lives. Birds especially, because they heavily rely on vocal communication, are highly sensitive towards noise pollution. Noise can impair the quality of a territory or hamper the transmission of vocal signals such as song. The latter has significant fitness consequences as it may erode partner preferences in the context of mate choice. Additional fitness costs may arise if noise masks communication between soliciting offspring and providing parents during the period of parental care. Here, we experimentally manipulated the acoustic environment of blue tit (Cyanistes caeruleus) families within their nest boxes with playbacks of previously recorded highway noise and investigated the consequences on parent-offspring communication. We hypothesized that noise interferes with the acoustic cues of parental arrival and vocal components of offspring begging. As such we expected an increase in the frequency of missed detections, when nestlings fail to respond to the returning parent, and a decrease in parental provisioning rates. Parents significantly reduced their rate of provisioning in noisy conditions compared to a control treatment. This reduction is likely to be the consequence of a parental misinterpretation of the offspring hunger level, as we found that nestlings fail to respond to the returning parent more frequently in the presence of noise. Noise also potentially masks vocal begging components, again contributing to parental underestimation of offspring requirements. Either way, it appears that noise impaired parent-offspring communication is likely to reduce reproductive success.

Anthropogenic noise is rapidly becoming a universal environmental feature. While the impacts of such additional noise on avian sexual signals are well documented, our understanding of its effect in other terrestrial taxa, on other vocalisations, and on receivers is more limited. Little is known, for example, about the influence of anthropogenic noise on responses to vocalisations relating to predation risk, despite the potential fitness consequences. We use playback experiments to investigate the impact of traffic noise on the responses of foraging dwarf mongooses (Helogale parvula) to surveillance calls produced by sentinels, individuals scanning for danger from a raised position whose presence usually results in reduced vigilance by foragers. Foragers exhibited a lessened response to surveillance calls in traffic-noise compared to ambient-sound playback, increasing personal vigilance. A second playback experiment, using noise playbacks without surveillance calls, suggests that the increased vigilance could arise in part from the direct influence of additional noise as there was an increase in response to traffic-noise playback alone. Acoustic masking could also play a role. Foragers maintained the ability to distinguish between sentinels of different dominance class, increasing personal vigilance when presented with subordinate surveillance calls compared to calls of a dominant groupmate in both noise treatments, suggesting complete masking was not occurring. However, an acoustic-transmission experiment showed that while surveillance calls were potentially audible during approaching traffic noise, they were probably inaudible during peak traffic intensity noise. While recent work has demonstrated detrimental effects of anthropogenic noise on defensive responses to actual predatory attacks, which are relatively rare, our results provide evidence of a potentially more widespread influence since animals should constantly assess background risk to optimise the foraging–vigilance trade-off.

Anthropogenic noise is an evolutionarily novel and widespread pollutant in both terrestrial and aquatic habitats. Despite increasing evidence that the additional noise generated by human activities can affect vocal communication, the majority of research has focused on the use of conspecific acoustic information, especially sexual signals. Many animals are known to eavesdrop on the alarm calls produced by other species, enhancing their likelihood of avoiding predation, but how this use of heterospecific information is affected by anthropogenic noise has received little empirical attention. Here, we use two field-based playback experiments on a habituated wild population of dwarf mongooses (Helogale parvula) to determine how anthropogenic noise influences the response of foragers to heterospecific alarm calls. We begin by demonstrating that dwarf mongooses respond appropriately to the alarm calls of sympatric chacma baboons (Papio ursinus) and tree squirrels (Paraxerus cepapi); fleeing only to the latter. We then show that mongoose foragers are less likely to exhibit this flee response to tree squirrel alarm calls during road-noise playback compared to ambient-sound playback. One explanation for the change in response is that noise-induced distraction or stress result in maladaptive behaviour. However, further analysis revealed that road-noise playback results in increased vigilance and that mongooses showing the greatest vigilance increase are those that do not subsequently exhibit a flee response to the alarm call. These individuals may therefore be acting appropriately: if the greater gathering of personal information indicates the absence of an actual predator despite an alarm call, the need to undertake costly fleeing behaviour can be avoided. Either way, our study indicates the potential for anthropogenic noise to interfere with the use of acoustic information from other species, and suggests the importance of considering how heterospecific networks are affected by this global pollutant.

Soundscapes are vital to acoustically specialized animals. Using passive acoustic monitoring data, the temporal and spectral variations in the soundscape of a Chinese white dolphin hotspot were analyzed. By cluster analysis, the 1/3 octave band power spectrum can be grouped into three bands with median overall contribution rates of 35.24, 14.14 and 30.61%. Significant diel and tidal soundscape variations were observed with a generalized linear model. Temporal patterns and frequency ranges of middle frequency band sound matched well with those of fish vocalization, indicating that fish might serve as a signal source. Dolphin sounds were mainly detected in periods involving low levels of ambient sound and without fish vocalization, which could reflect noise avoidance and passive eavesdropping behaviors engaged in by the predator. Pre-construction data can be used to assess the effects of offshore windfarms on acoustic environments and aquatic animals by comparing them with the soundscape of postconstruction and/or postmitigation.

Cadmium (Cd) is a non-essential environmental endocrine-disrupting compound found in water and a potential threat to aquatic habitats. Cd has been shown to have various short-term effects on aquatic animals; however, evidence for long-term effects of Cd on vocal communications in amphibians is lacking. To better understand the long-term effects of low-dose Cd on acoustic communication in amphibians, male Xenopus laevis individuals were treated with low Cd concentrations (0.1, 1, and 10 μg/L) via aqueous exposure for 24 months. At the end of the exposure, the acoustic spectrum characteristics of male advertisement calls and male movement behaviors in response to female calls were recorded. The gene and protein expressions of the androgen receptor (AR) were determined using Western blot and RT-PCR. The results showed that long-term Cd treatment affected the spectrogram and formant of the advertisement call. Compared with the control group, 10 μg/L Cd significantly decreased the first and second formant frequency, and the fundamental and main frequency, and increased the third formant frequency. One and 10-μg/L Cd treatments significantly reduced the proportion of individuals responding to female calls and prolonged the time of first movement of the male. Long-term Cd treatment induced a downregulation in the AR protein. Treatments of 0.1, 1, and 10 μg/L Cd significantly decreased the expression of AR mRNA in the brain. These findings indicate that long-term exposure of Cd has negative effects on advertisement calls in male X. laevis.