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Echolocating animals that forage in social groups can potentially benefit from eavesdropping on other group members, cooperative foraging or social defence, but may also face problems of acoustic interference and intra-group competition for prey. Here, we investigate these potential trade-offs of sociality for extreme deep-diving Blainville′s and Cuvier's beaked whales. These species perform highly synchronous group dives as a presumed predator-avoidance behaviour, but the benefits and costs of this on foraging have not been investigated. We show that group members could hear their companions for a median of at least 91% of the vocal foraging phase of their dives. This enables whales to coordinate their mean travel direction despite differing individual headings as they pursue prey on a minute-by-minute basis. While beaked whales coordinate their echolocation-based foraging periods tightly, individual click and buzz rates are both independent of the number of whales in the group. Thus, their foraging performance is not affected by intra-group competition or interference from group members, and they do not seem to capitalize directly on eavesdropping on the echoes produced by the echolocation clicks of their companions. We conclude that the close diving and vocal synchronization of beaked whale groups that quantitatively reduces predation risk has little impact on foraging performance.

Active-sensing systems such as echolocation provide animals with distinct advantages in dark environments. For social animals, however, like many bat species, active sensing can present problems as well: when many individuals emit bio-sonar calls simultaneously, detecting and recognizing the faint echoes generated by one's own calls amid the general cacophony of the group becomes challenging. This problem is often termed ‘jamming’ and bats have been hypothesized to solve it by shifting the spectral content of their calls to decrease the overlap with the jamming signals. We tested bats’ response in situations of extreme interference, mimicking a high density of bats. We played-back bat echolocation calls from multiple speakers, to jam flying Pipistrellus kuhlii bats, simulating a naturally occurring situation of many bats flying in proximity. We examined behavioural and echolocation parameters during search phase and target approach. Under severe interference, bats emitted calls of higher intensity and longer duration, and called more often. Slight spectral shifts were observed but they did not decrease the spectral overlap with jamming signals. We also found that pre-existing inter-individual spectral differences could allow self-call recognition. Results suggest that the bats’ response aimed to increase the signal-to-noise ratio and not to avoid spectral overlap.

To reduce the impact of acoustic interference in a microelectromechanical system (MEMS) gyroscope and to improve the reliability of output data, a filtering algorithm based on orthogonal demodulation is proposed. According to the working principle and failure mechanism of a MEMS gyroscope, the sound and angular velocity frequencies are not identical, which lead to a different frequency signal output of the original single-channel demodulation scheme. Therefore, a Q channel demodulation filtering process was added to the origin single-channel demodulation scheme. For the Q channel demodulated signal, a Hilbert transform was used to compensate for the 90 degree phase shift. The IQ dual-channel difference can remove the acoustic interference signal. The simulation results indicate that the scheme can effectively suppress the acoustic interference signal and it can eliminate more than 95% of the impact of sound waves. We assembled the acoustic interference experimental platform, collected the driving and sensing data, and verified the denoising performance with our algorithm, which eliminated more than 70% of the noise signal. The simulation and experimental results demonstrate that the scheme can eliminate acoustic interference signal without destroying angular velocity signal.

This paper presents numerical and experimental investigations of acoustic agglomeration of solid particles in a chamber with three overlapping ultrasonic fields. The simultaneous generation of these fields produces an interference pattern with a greater number of pressure nodes, more evenly distributed across the chamber cross section. The chamber design is based on three piezoelectric transducers equipped with disc-shaped acoustic radiators and a cylindrical body. The transducers are evenly positioned around the cylinder’s horizontal axis of symmetry. Numerical simulations of their acoustic characteristics showed that, at a resonance frequency of 49.71 kHz and with a 125 Vp-p excitation, the system can generate up to 146 dB sound pressure level. The predicted interference field pattern indicated a high density of alternating pressure nodes across the chamber. Experimental results confirmed that, at a resonance frequency of 48.85 kHz and with the same excitation signal, the sound pressure in the chamber reached 144.8 dB. Particle agglomeration tests demonstrated effective performance: ultrafine particles in the 191–294 nm range decreased by 31.2%, while particles in the 0.75–1 µm range increased by up to 52.9%. These findings confirm the strong potential of interference acoustic fields for enhancing particle agglomeration and supporting air purification applications.

Roadside habitats are important for a range of taxa including plants, insects, mammals, and birds, particularly in developed countries in which large expanses of native vegetation have been cleared for agriculture or urban development. Although roadside vegetation may provide suitable habitat for many species, resident animals can be exposed to high levels of traffic noise, visual disturbance from passing vehicles, and the risk of collision with cars and trucks. Traffic noise can reduce the distance over which acoustic signals such as song can be detected, an effect known as acoustic interference or masking. Studies from the northern hemisphere show that the singing behavior of birds changes in the presence of traffic noise. We investigated the impact of traffic noise and traffic volume on two species of birds, the Grey Shrike-thrush (Colluricincla harmonica) and the Grey Fantail (Rhipidura fuliginosa), at 58 roadside sites on the Mornington Peninsula, southeastern Australia. The lower singing Grey Shrike-thrush sang at a higher frequency in the presence of traffic noise, with a predicted increase in dominant frequency of 5.8 Hz/dB of traffic noise, and a total effect size of 209 Hz. In contrast, the higher singing Grey Fantail did not appear to change its song in traffic noise. The probability of detecting each species on a visit to a site declined substantially with increasing traffic noise and traffic volume, with several lines of evidence supporting a larger effect of traffic noise. Traffic noise could hamper detection of song by conspecifics, making it more difficult for birds to establish and maintain territories, attract mates and maintain pair bonds, and possibly leading to reduced breeding success in noisy roadside habitats. Closing key roads during the breeding season is a potential, but untested, management strategy to protect threatened bird species from traffic noise and collision with vehicles at the time of year when they are most vulnerable to their impacts. Other management options include reducing the speed and/or volume of traffic on such roads to an acceptably low level. Ours is the first study to investigate the effect of traffic noise on the singing behavior of birds in the southern hemisphere.

Male frogs call to attract females for mating and to defend territories from rival males. Female frogs of some species prefer lower-pitched calls, which indicate larger, more experienced males. Acoustic interference occurs when background noise reduces the active distance or the distance over which an acoustic signal can be detected. Birds are known to call at a higher pitch or frequency in urban noise, decreasing acoustic interference from low-frequency noise. Using Bayesian linear regression, we investigated the effect of traffic noise on the pitch of advertisement calls in two species of frogs, the southern brown tree frog (Litoria ewingii) and the common eastern froglet (Crinia signifera). We found evidence thatL. ewingiicalls at a higher pitch in traffic noise, with an average increase in dominant frequency of 4.1 Hz/dB of traffic noise, and a total effect size of 123 Hz. This frequency shift is smaller than that observed in birds, but is still large enough to be detected by conspecific frogs and confer a significant benefit to the caller. Mathematical modelling predicted a 24% increase in the active distance of aL. ewingiicall in traffic noise with a frequency shift of this size.Crinia signiferamay also call at a higher pitch in traffic noise, but more data are required to be confident of this effect. Because frog calls are innate rather than learned, the frequency shift demonstrated byL. ewingiimay represent an evolutionary adaptation to noisy conditions. The phenomenon of frogs calling at a higher pitch in traffic noise could therefore constitute an intriguing trade-off between audibility and attractiveness to potential mates.

Recent studies in the Northern Hemisphere have shown that songbirds living in noisy urban environments sing at higher frequencies than their rural counterparts. However, several aspects of this phenomenon remain poorly understood. These include the geographical scale over which such patterns occur (most studies have compared local populations), and whether they involve phenotypic plasticity or microevolutionary change. We conducted a field study of silvereye (Zosterops lateralis) vocalizations over more than 1 million km2 of urban and rural south-eastern Australia, and compared possible effects of urban noise on songs (which are learned) and contact calls (which are innate). Across 14 paired urban and rural populations, silvereyes consistently sang both songs and contact calls at higher frequencies in urban environments. Syllable rate (syllables per second) decreased in urban environments, consistent with the hypothesis that reflective structures degrade song and encourage longer intervals between syllables. This comprehensive study is, to our knowledge, the first to demonstrate varied adaptations of urban bird vocalizations over a vast geographical area, and to provide insight into the mechanism responsible for these changes.

Songbirds, which rely heavily upon acoustic communication, employ a variety of strategies to reduce the degree to which their songs are masked by other sounds within the environment. One such strategy is to make active adjustments to song timing to avoid temporally overlapping other environmental sounds. While playback studies in many different songbird species have demonstrated that territorial males avoid overlapping conspecific songs in that context, there is comparatively little known about how such behavior varies across contexts. For example, there is relatively little information on avoidance of overlapping in naturalistic interactions (e.g., countersinging) among conspecific singers; likewise, few studies have assessed the degree to which males avoid overlapping heterospecific songs. Songbird researchers have also explored possible communicative functions of song overlapping, most notably the idea that overlapping conveys information related to aggression. The objectives of the present study were to compare song overlapping across contexts and to assess the relationship between song overlapping and physical responses to conspecific playback in the Hermit Thrush (Catharus guttatus). Degree of song overlapping in response to conspecific (n = 29) and heterospecific playback (n = 31), as well as during naturally occurring countersinging (n = 21 pairs), was compared to chance levels. Avoidance of overlapping occurred in all 3 contexts, although to a lesser degree in response to heterospecific playback. Comparison of physical responses to song overlapping during conspecific playback revealed no association, aligning with recent studies in other species indicating that song overlapping is not an aggressive signal. Instead, the avoidance of song overlapping appears to be an important tool for decreasing the risk of acoustic interference posed by both conspecific and heterospecific songs. Las aves canoras, que dependen fuertemente de la comunicación acústica, emplean una variedad de estrategias para reducir el grado en que sus canciones son enmascaradas por otros sonidos ambientales. Una de las estrategias que usan es hacer ajustes activos al ritmo de su canto para evitar traslape temporal con otros sonidos ambientales. Mientras estudios con cantos pregrabados en muchas especies de aves canoras han demostrado que machos territoriales evitan traslapes de cantos conespecíficos en ese contexto, se conoce comparativamente poco acerca de cómo ese comportamiento varía en diferentes contextos. Por ejemplo, existe relativamente poca información en cómo evitan el traslapes en interacciones en la naturaleza (por ejemplo contra-cantos) entre cantantes conespecíficos; igualmente, pocos estudios han evaluado el grado en que machos evitan cantos heteroespecíficos que se traslapan. Investigadores de aves canoras también han explorado posibles funciones comunicativas del traslape de cantos, notablemente la idea de que cantos que se traslapan brindan información relacionada a agresión. Los objetivos del presente estudio fueron comparar sobrelapamiento de cantos en diferentes contextos y evaluar la relación entre el sobrelapamiento del canto y las respuestas físicas a los cantos pregrabados de un conespecífico en zorzal Catharus guttatus. El grado de sobrelapamiento de canto en respuesta a los cantos pregrabados de un conespecífico (n=29), a los cantos pregrabados de un heteroespecífico (n=31) y contra-cantos que ocurrían naturalmente (n=21 pares), comparados con el azar. Evitar el traslape ocurrió en los tres contextos, aunque en menor grado en el caso de cantos pregrabados de heteroespecíficos. La comparación de respuestas físicas al traslape de cantos durante los cantos pregrabados de conespecíficos no mostraron asociación, lo que concuerda con estudios recientes en otras especies que indican que el traslape de canto no es una señal agresiva. En vez de eso, evitar el traslape de canto parece ser una herramienta importante para disminuir el riesgo de interferencia acústica que presentan tanto cantos conespecíficos como heteroespecíficos. Palabras clave: interferencia acústica, agresión, contra-cantos, heteroespecífico, reproducción de grabaciones.

Since acoustic agglomeration is an effective pre-treatment technique for removing fine particles, it can be considered as a potential technology for applications in aerosol pollution control, industrial dust and mist removal, and cloud and precipitation interference. In this study, the cloud-precipitation interference effect was evaluated in situ based on a multi-dimensional multi-scale monitoring system. The variations in the spatial and temporal distribution of rainfall near the surface and the characteristics of precipitation droplets in the air were investigated. The results indicate that strong low-frequency acoustic waves had a significant impact on the macro-characteristics of rainfall clouds, the microphysical structure of rain droplets and near-surface precipitation, and various microwave parameters. In terms of physical structure, the precipitation cloud’s base height decreased significantly upon opening the acoustic device, while agglomeration and de-agglomeration of raindrops were in a dynamic equilibrium. When the sound generator was on, the particle concentration at a sampling attitude of 500−1700 m and the proportion of particles with diameters of 1–1.5 mm decreased significantly (by 1–5 ln [1/m3·mm]). In contrast, the particle concentration increased by 1–3 ln [1/m3·mm] at a sampling attitude below 400 m. Moreover, during acoustic interference, the reflectivity factor surged by 2.71 dBZ within 1200 m of the operation centre. Overall, the spatial and temporal distributions of rainfall rates and cumulative precipitation within 5 km of acoustic operation were uneven and influenced by local terrain and background winds.

For a bottom-moored vertical line array in deep ocean, the underwater maneuvering source will produce interference patterns in both grazing angle–distance (vertical-time record, VTR) and frequency–grazing angle (wideband beamforming output) domains, respectively, and the interference period is modulated by the source depth. Based on these characteristics, an interference feature fusion (IFF) method is proposed in the space–time–frequency domain for source depth estimation, in which the principal interference mode of the VTR is extracted adaptively and the depth ambiguity function is constructed by fusing the ambiguity sequence, mapped by wideband beamforming intensity, and the principal interference mode, which can achieve the long-term depth estimation and recognition of underwater sources without requiring environmental information. Theoretical analysis and simulation results indicate that the IFF can suppress the false peaks generated by the generalized Fourier transform (GFT) method, and the depth estimation error of the IFF for a single source is reduced by at least 47% compared to GFT. In addition, the IFF is proven to be effective at separating the depth of multiple adjacent sources (with the average estimation error reduced by 28%) and exhibits a high degree of robustness within the fluctuating acoustic channel (with the average estimation error reduced by 12%).