Reception Of Acoustic Signals Research Articles

Anthropogenic disturbance affects calling and collective behaviour in corvid roosts.

Acoustic communication plays an important role in coordinating group dynamics and collective movements across a range of taxa. However, anthropogenic disturbance can inhibit the production or reception of acoustic signals. Here, we investigate the effects of noise and light pollution on the calling and collective behaviour of wild jackdaws (Corvus monedula), a highly social corvid species that uses vocalizations to coordinate collective movements at winter roosting sites. Using audio and video monitoring of roosts in areas with differing degrees of urbanization, we evaluate the influence of anthropogenic disturbance on vocalizations and collective movements. We found that when levels of background noise were higher, jackdaws took longer to settle following arrival at the roost in the evening and also called more during the night, suggesting that human disturbance may cause sleep disruption. High levels of overnight calling were, in turn, linked to disruption of vocal consensus decision-making and less cohesive group departures in the morning. These results raise the possibility that, by affecting cognitive and perceptual processes, human activities may interfere with animals' ability to coordinate collective behaviour. Understanding links between anthropogenic disturbance, communication, cognition and collective behaviour must be an important research priority in our increasingly urbanized world. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

Consistency in responses to conspecific advertisement calls with various signal-to-noise ratios in both sexes of the Anhui tree frog.

Environmental noise has a significant negative impact on acoustic communication in most situations, as it influences the production, transmission, and reception of acoustic signals. However, how animals respond to conspecific sounds when there is interference from environmental noise, and whether males and females display convergent behavioral responses in the face of noise masking remain poorly understood. In this study, we investigated the effects of conspecific male advertisement calls with different signal-to-noise ratios on male-male competition and female choice in the Anhui tree frog Rhacophorus zhoukaiyae using playback and phonotaxis experiments, respectively. The results showed that (1) female Anhui tree frogs preferentially selected the conspecific calls with higher SNR compared to calls with lower SNR; (2) males preferentially responded vocally to the conspecific calls with higher SNR compared to calls with lower SNR; and (3) males' competitive strategies were flexible in the face of noise interference. These results suggest that preferences of both sexes converge in outcome, and that male competitive strategies may depend on predictable female preferences. This study will provide an important basis for further research on decision-making in animals.

Vocal production learning in the pale spear-nosed bat, Phyllostomus discolor.

Vocal production learning (VPL), or the ability to modify vocalizations through the imitation of sounds, is a rare trait in the animal kingdom. While humans are exceptional vocal learners, few other mammalian species share this trait. Owing to their singular ecology and lifestyle, bats are highly specialized for the precise emission and reception of acoustic signals. This specialization makes them ideal candidates for the study of vocal learning, and several bat species have previously shown evidence supportive of vocal learning. Here we use a sophisticated automated set-up and a contingency training paradigm to explore the vocal learning capacity of pale spear-nosed bats. We show that these bats are capable of directional change of the fundamental frequency of their calls according to an auditory target. With this study, we further highlight the importance of bats for the study of vocal learning and provide evidence for the VPL capacity of the pale spear-nosed bat.

Background noise disrupts host-parasitoid interactions.

The soundscape serves as a backdrop for acoustic signals dispatched within and among species, spanning mate attraction to parasite host detection. Elevated background sound levels from human-made and natural sources may interfere with the reception of acoustic signals and alter species interactions and whole ecological communities. We investigated whether background noise influences the ability of the obligate parasitoid Ormia ochracea to locate its host, the variable field cricket (Gryllus lineaticeps). As O. ochracea use auditory cues to locate their hosts, we hypothesized that higher background noise levels would mask or distract flies from cricket calls and result in a decreased ability to detect and navigate to hosts. We used a field manipulation where fly traps baited with playback of male cricket advertisement calls were exposed to a gradient of experimental traffic and ocean surf noise. We found that increases in noise amplitude caused a significant decline in O. ochracea caught, suggesting that background noise can influence parasitoid–host interactions and potentially benefit hosts. As human-caused sensory pollution increases globally, soundscapes may influence the evolution of tightly co-evolved host–parasitoid relationships. Future work should investigate whether female cricket phonotaxis towards males is similarly affected by noise levels.

Analysis of duet vocalizations in Myiothlypis leucoblephara (Aves, Parulidae)

Bird vocalizations might be used for specific recognition, territorial defense, and reproduction. Bioacoustic studies aim to understand the production, propagation and reception of acoustic signals, and they are an important component of research on animal behavior and evolution. In this study we analyzed the sound structure of duet vocalizations in pairs of Myiothlypis leucoblephara and evaluated whether the vocal variables differ among pairs and if there are differences in temporal characteristics and frequency of duets between pairs in forest edges vs. forest interior. Vocalizations were recorded from 17 bird pairs in three remnants of Atlantic Forest in southern Brazil. Six of the bird pairs were situated at the edge of the forest remnant, and 11 were in the interior of the remnant. The duets of different pairs between forest areas showed descriptive differences in the frequency, number of notes per call, and time between issuance of calls, with the main distinguishing feature being a change in frequency of a few notes in the second part of the musical phrase. The minimum frequency of vocalization was reduced at the private area than in the other two remnants (p <0.05). The duets of birds in the forest edge and forest interior did not significantly differ in minimum or maximum frequency of phrases (p> 0.05), phrase duration (p> 0.05) or number of notes per phrase (p> 0.05). Myiothlypis leucoblephara did not show a specific pattern with respect to issue of phrases in duets, but instead showed five different patterns, which were variable among pairs. There was a sharp decline or alternation in frequency between notes in the second part of the musical phrase for recognition among pairs. Variation in vocalization among M. leucoblephara duets may play a role in pair recognition.

Brain Activation Patterns in Response to Conspecific and Heterospecific Social Acoustic Signals in Female Plainfin Midshipman Fish, Porichthys notatus

While the peripheral auditory system of fish has been well studied, less is known about how the fish’s brain and central auditory system process complex social acoustic signals. The plainfin midshipman fish, Porichthys notatus, has become a good species for investigating the neural basis of acoustic communication because the production and reception of acoustic signals is paramount for this species’ reproductive success. Nesting males produce long-duration advertisement calls that females detect and localize among the noise in the intertidal zone to successfully find mates and spawn. How female midshipman are able to discriminate male advertisement calls from environmental noise and other acoustic stimuli is unknown. Using the immediate early gene product cFos as a marker for neural activity, we quantified neural activation of the ascending auditory pathway in female midshipman exposed to conspecific advertisement calls, heterospecific white seabass calls, or ambient environment noise. We hypothesized that auditory hindbrain nuclei would be activated by general acoustic stimuli (ambient noise and other biotic acoustic stimuli) whereas auditory neurons in the midbrain and forebrain would be selectively activated by conspecific advertisement calls. We show that neural activation in two regions of the auditory hindbrain, i.e., the rostral intermediate division of the descending octaval nucleus and the ventral division of the secondary octaval nucleus, did not differ via cFos immunoreactive (cFos-ir) activity when exposed to different acoustic stimuli. In contrast, female midshipman exposed to conspecific advertisement calls showed greater cFos-ir in the nucleus centralis of the midbrain torus semicircularis compared to fish exposed only to ambient noise. No difference in cFos-ir was observed in the torus semicircularis of animals exposed to conspecific versus heterospecific calls. However, cFos-ir was greater in two forebrain structures that receive auditory input, i.e., the central posterior nucleus of the thalamus and the anterior tuberal hypothalamus, when exposed to conspecific calls versus either ambient noise or heterospecific calls. Our results suggest that higher-order neurons in the female midshipman midbrain torus semicircularis, thalamic central posterior nucleus, and hypothalamic anterior tuberal nucleus may be necessary for the discrimination of complex social acoustic signals. Furthermore, neurons in the central posterior and anterior tuberal nuclei are differentially activated by exposure to conspecific versus other acoustic stimuli.

Acoustics of the mountain pine beetle (Dendroctonus ponderosae) (Curculionidae, Scolytinae): sonic, ultrasonic, and vibration characteristics

Acoustic signaling is widespread in bark beetles (Scolytinae), although little is known about the physical characteristics of signals, how they are transmitted, and how they differ among behavioural contexts. Signals were studied in the male mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902) during stress, male–female, and male–male interactions. Sounds are broadband with significant energy in the ultrasound (peaks between 15 and 26 kHz) and low amplitude (55 and 47 dB SPL at 2 and 4 cm, respectively), indicating that signaling functions at close range. Signal trains vary among contexts primarily in the proportions of chirp types. Chirps were categorized as being simple or interrupted, with the former having significantly lower tooth strike rates and shorter chirp durations. Stress chirps are predominantly simple with characteristics resembling other insect disturbance signals. Male–female interactions begin with the male producing predominantly interrupted chirps prior to gallery entrance, followed by simple chirps. Male–male (rivalry) chirps are predominantly simple, with evidence of antiphonal calling. Substrate-borne vibrations were detectable with a laser-doppler vibrometer at short distances (1–3 cm), suggesting that sensory organs could be tuned to either air or substrate-borne vibrations. These results have important implications for future research on the function and reception of acoustic signals in bark beetles.

Diversity reception of hydroacoustic signals from the results of experiments in the Black Sea

The results are presented of an experimental study of spatial and frequency correlation of amplitude fluctuations of hydroacoustic signals on two paths of the Black Sea under conditions of a thermal underwater sound channel and tonal-continuous emission at frequencies of 4 and 1.5 kHz. The emitters were located in the coastal wedge on the bottom slope at depths of 35 and 60 m; a receiver system was submerged to a depth of 50–60 m off the side of a ship drifting at various distances in the open sea. Data are presented on the spatial (horizontal and vertical) and frequency intervals of fluctuation correlation on the first path extending 100 km at an emission frequency of 4 kHz under conditions of dominant fast fluctuations, as well as on the second path extending 300 km at an omission frequency of 1.5 kHz under conditions of dominant slow fluctuations. The results of experiments are used to estimate the efficiency of space-diversity and frequency-diversity reception of acoustic signals in application to information transmission over a hydroacoustic channel.

Research of finite-amplitude acoustic pulse propagation in a thin capillary filled with a viscous-elastic fluid

Acoustic wave propagation in a thin capillary filled with a viscous fluid is accompanied by additional attenuation because of sound energy outflow to the capillary wall due to viscous forces. It is known that a whole class of fluids exists, which change their viscous properties (shift modulus) under the applied stress. It is the so-called Bingham fluids. The results of experimental research of wide frequency band sound pulse propagation in the capillary filled with a raw oil are presented. A pulse was generated by laser radiation. The amplitude of the pulse reached up to 1 MPa and its time duration was about 20 ns. Acoustic signal reception was provided by a PVDF gage and registered by a digital oscilloscope in the frequency range of 100 MHz. Experiment shows a kind of induced ‘‘transparency’’ for the high-amplitude sound pulse propagated along a capillary of 0.4-mm radius. This effect of acoustic-induced transparency of viscous fluid shows a rapid growth of high-frequency components of the sound signal passed through the capillary with respect to the growth of laser pulse energy. Meanwhile, for the small-amplitude sound signal propagation the linear relation between laser pulse energy and sound pulse amplitude is valid. [Work is partially supported by the Russian Foundation of Basic Research (project 97-02-17789).]

Reverberations and Amplitude Fluctuations in the Propagation of Sound in a Forest: Implications for Animal Communication

Effective communication requires that the receiver not only detect the presence of a signal but also discriminate significant variations in signals. Consequently, both attenuation and degradation of the structure of acoustic signals during transmission will limit the range of communication. In this study we document two primary sources of degradation of acoustic signals during propagation through natural environments, irregular amplitude fluctuations and reverberations. Amplitude fluctuations arise especially from atmospheric turbulence, while reverberations also result from scattering surfaces, such as vegetation. Both primarily mask information coded in amplitude modulation of the signal and repetitive frequency modulation, like the trills in the songs of many passerine birds. Irregular amplitude fluctuations primarily mask low frequencies of amplitude modulation in signals. Atmospheric turbulence from wind is the primary determinant of the intensity of irregular amplitude fluctuations, although amplitude fluctuations also increase with carrier frequency and range. In contrast, reverberations depend primarily on carrier frequency and range. Reverberations are least at intermediate frequencies (2-8 kHz). At lower frequencies reverberations in sound transmission near the ground often take the form of discrete echoes, probably from canopy foliage or from the change in acoustic impedance between air in the canopy and overlying air masses. At higher frequencies reverberations usually consist of a steady decay in acoustic energy. Consequently, in contrast to irregular amplitude fluctuations, reverberations primarily mask high rates of amplitude modulation and repetitive frequency modulation in acoustic signals. Intermediate frequencies (2-8 kHz) are most suitable for long-range acoustic communication, because irregular amplitude fluctuations, reverberations, and attenuation increase with carrier frequency, while reverberations and attenuation from ground interference increase at low frequencies. The great majority of animals that engage in long-range acoustic communication use this middle range of frequencies. Perhaps because of the increase in reverberations at low carrier frequencies, the songs of rufous-sided towhees show a correlation between trill rate and the minimum frequency in trills. To minimize the effects of amplitude fluctuations and reverberations on long-range acoustic communication, signals should encode information either in frequency modulation or in repetitive amplitude modulation that allow enough redundancy or signal averaging to permit recognition of signals by receivers. Because reverberations are more severe in environments with many scattering surfaces, long-range acoustic communication in forests, as opposed to open environments, should avoid rapid amplitude modulation or repetitive frequency modulation. Among North Carolina passerine birds, species that breed in forests tend to avoid rapid repetition rates at any given frequency in their long-distance songs. The directionality of both the broadcast and reception of acoustic signals will influence the effects of scattering on reverberations and attenuation of acoustic signals. In scattering environments, the optimal directionality of sound production and reception will require compromises.

Design and Calibration of Wide-Range Acoustic Transducers

Wide-range (5 cps-250 kcps) electrostatic transducers have been designed for the transmission and reception of acoustic signals through air. These transducers include both the solid dielectric-type transducer constructed from metalized plastic films, and conventional air dielectric condenser microphones of unusually high sensitivity. Techniques for designing an optimum transducer for various applications are discussed on the basis of signal-to-noise ratio. sensitivity, directivity, frequency response, and the complementing electronic equipment. Various methods for the calibration of these transducers over the frequency range from 5 cps to 250 kcps are discussed.

A Simple Electronic Correlator

Attention has been drawn in the literature to the possible utility of correlation techniques in the reception of acoustic signals. In applying such techniques, it is often necessary to find the average of the instantaneous product of two electrical signals; the black box which performs this function, which is that of a generalized detector, may be called a correlator. By use of the quarter-squares method of multiplication [AB = 14(A + B)2 − 14(A − B)2], correlators can be constructed using common triodes as the square-law devices. In practice, however, such multiplier-averagers depend strongly upon the vacuum tube characteristics which in turn require, for stability, regulated plate and heater supplies and frequent balance adjustments. If the square-law vacuum tubes in the circuit mentioned above are replaced by linear rectifiers, as many have suggested, it is shown that the resulting circuit is similar in action to a correlator. The output of this “linear rectifier correlator” is a somewhat distorted replica of the un-normalized cross-correlation function of the input signals, but the output signal-to-noise ratio for small input signal-to-noise ratios is not appreciably less than that for a multiplier-averager. The linear rectifier correlator has the practical advantage of being completely independent of power supplies, if contact rectifiers are used, and requires no balance adjustments if care is used in its construction.