BIOACOUSTIC PUBLICATIONS, 1989

ABSTRACT

Coruros Spalacopus cyanus, social fossorial rodents from Chile, use a complex acoustic repertoire with eleven different true vocalisations and one mechanical sound in various behavioural contexts. The complex of contact calls is particularly well differentiated. Juvenile coruros produced six true vocalisations of which four were structurally identical to adult calls. One vocalisation had components of two adult sounds and one occurred only in juvenile animals. Certain calls from the adult repertoire were lacking. The frequencies of sounds of juveniles were considerably higher than those of adults, with many sounds reaching the ultrasonic range. Nevertheless, pure ultrasonic sounds were not recorded.

The frequencies of the analysed sounds of coruros extended from 0.17 to 20.33 kHz with dominant frequency components between 0.17 and 10 kHz. The acoustic properties of calls are suitable for transmission above and below ground, thus providing further indirect evidence that coruros are not strictly confined to an underground way of life. Indeed, the great variability of frequency ranges, with lower frequencies always being included, reflects a specialisation for communication in variable acoustic environments.

The most distinctive and unique vocalisation of coruros is the long duration musical trilling (lasting up to two minutes), which is a long-distance call emitted in alarm and arousal contexts. Recordings of this call from natural burrows in the field in Chile showed similar structural features to vocalisations from captive colonies in the laboratory.

Our findings provide a further example of matching physical properties of vocalisations to the acoustic conditions of the habitat. However, vocalisations in subterranean rodents consist almost exclusively of short-distance calls, the trilling of coruros being the notable exception. Since the selective pressure of the acoustic environment upon the evolution of short-distance vocalisations is probably minimal, we suggest that during their evolution, subterranean mammals have matched their vocalisations primarily to their hearing range and not directly to the acoustics underground. Hearing probably has been the primary target of natural selection, serving not only for communication but also for detection of predators (and, in carnivores, of prey).     

You talkin’ to me? Interactive playback is a powerful yet underused tool in animal communication research

Over the years, playback experiments have helped further our understanding of the wonderful world of animal communication. They have provided fundamental insights into animal behaviour and the function of communicative signals in numerous taxa. As important as these experiments are, however, there is strong evidence to suggest that the information conveyed in a signal may only have value when presented interactively. By their very nature, signalling exchanges are interactive and therefore, an interactive playback design is a powerful tool for examining the function of such exchanges. While researchers working on frog and songbird vocal interactions have long championed interactive playback, it remains surprisingly underused across other taxa. The interactive playback approach is not limited to studies of acoustic signalling, but can be applied to other sensory modalities, including visual, chemical and electrical communication. Here, I discuss interactive playback as a potent yet underused technique in the field of animal behaviour. I present a concise review of studies that have used interactive playback thus far, describe how it can be applied, and discuss its limitations and challenges. My hope is that this review will result in more scientists applying this innovative technique to their own study subjects, as a means of furthering our understanding of the function of signalling interactions in animal communication systems.     

Subharmonics increase the auditory impact of female koala rejection calls

Although non‐linear phenomena are common in human and non‐human animal vocalisations, their functional relevance remains poorly understood. One theory posits that non‐linear phenomena generate unpredictability in vocalisations, which increases the auditory impact of vocal signals, and makes animals less likely to habituate to call repetition. Female koalas (Phascolarctos cinereus) produce vocal signals when they reject male copulation attempts that contain relatively high levels of non‐linear phenomena, and thus may function as attention grabbing vocal signals during the breeding season. To test this hypothesis, we used playback experiments: firstly, to determine whether female rejection calls induce heightened behavioural responses in free‐ranging male koalas during the breeding season, and secondly, to examine how the relative amount of non‐linear phenomena in rejection calls influences male behavioural response. The results show that male koalas look for longer towards speakers broadcasting playback sequences of male bellows followed by a series of female rejection calls than those broadcasting only male bellows. In addition, female rejection call sequences with more subharmonics, higher harmonics‐to‐noise ratios, and less biphonation produced the greatest male looking responses. Our findings support the hypothesis that female koala rejection calls function to grab male attention during the breeding season, and indicate that subharmonics are the main acoustic feature that increases the auditory impact of these vocal signals.     

THE COMMUNICATIVE SIGNIFICANCE OF TONALITY IN BIRDSONG: RESPONSES TO SONGS PRODUCED IN HELIUM

ABSTRACT

“Pure tones” are a distinctive acoustic feature of many birdsongs. Recent research on songbird vocal physiology suggests that such tonal sounds result from a coordinated interaction between the syrinx and a vocal filter, as demonstrated by the emergence of harmonic overtones when a bird sings in helium. To investigate the communicative significance of vocal tract filtration in the production of birdsong, we used field playback experiments to compare the responses of male swamp sparrows Melospiza georgiana to normal songs and those same songs recorded in helium. We also measured responses to pure tone songs that had been shifted upward in frequency to match the average spectra of those songs with added harmonics. Male sparrows were significantly more responsive to the playback of normal songs than to either helium songs with added harmonics or frequency- shifted pure tone songs. Songs with harmonics retained a high degree of salience, however. We conclude that explanations for the occurrence of tonal sounds in birdsongs must consider perceptual attributes of songs as communicative signals, as well as problems of song production and transmission.     

ACOUSTIC COMMUNICATION AND MATING BEHAVIOUR IN WATER BUGS OF THE GENUS MICRONECTA

ABSTRACT

The role of male sounds in attracting females and in mating was investigated in the three most common species of Micronecta found in ponds 60 km NE of Melbourne, Australia: M. concordia, M. tasmanica and M. robusta. In playback experiments using recorded male signals, females were attracted to signals of conspecific males, in preference to signals of heterospecific sympatric males. Studies of mating behaviour, using video recording, showed that signals were obligatory for mating. These findings strongly suggest that acoustic signalling is important in reproductive isolation in Micronecta. Comparisons between matings and rejected matings showed that, within each species, copulation only occurred following a certain minimum number of acoustic signals with more pulse-trains than the mean for the species. Low amplitude sounds (after signals) were also important in courtship, immediately preceding mating. No sounds occurred during copulation.     

BIOACOUSTIC PUBLICATIONS, 1988

ABSTRACT

We examined vocalisations of a solitary subterranean rodent, the Silvery Mole-rat Heliophobius argenteocinereus (Bathyergidae). Seven true vocalisations and one mechanical vocalisation were identified. The main frequencies of the analysed sounds (0.34–13.17 kHz) match to a great extent the frequency range suitable for transmission in underground burrows. Due to the narrow frequency range of vocalisations, motivation is predominantly expressed by the rate of tonality rather than by frequency changes. The vocal repertoire of the Silvery Mole-rat perfectly matches to Morton's MS rules, i.e. that low-frequency and harsh vocalisations indicate hostility whereas high tonal calls signalise appeasement or fear. In comparison with social species, this solitary bathyergid produces fewer calls. It lacks contact and alarm calls, but has a rich repertoire of mating calls (mating ends with duet vocalization of male and female). Acoustic signals seem to play a major role in lowering natural aggressiveness during the mating period.     

Acoustic location of conspecifics in a nocturnal bird: the corncrake Crex crex

Although the use of sounds in spatial orientation is widespread among animals, only a few groups advanced such specific adaptations as echolocation. In contrast, practically all animals and night-active species in particular, must occasionally orient themselves relative to invisible but audible objects such as a hidden rival or predator. In this study, I would like to determine the impact of locating which involves the use of acoustic parameters of sender’s vocalisations by receivers and changes of positions and triangulation of sender’s vocalisations by receivers in estimating the distance to the sender during night-time territorial interactions of the corncrake (Crex crex). Males were subjected to two kinds of stimuli: approaching one, imitating the change of the distance of the calling intruder toward the focal male while keeping the direction constant, or stationary stimuli, involving acoustic stimulation with no motion. Although males subjected to approaching stimulation moved longer distances, in both stimuli groups, males moved predominantly toward or out of the playback speaker, and only occasionally made sideway movements. However, the results gave no evidence of corncrakes moving specifically in order to locate the source of the sound; they suggest that males moved toward or away from the already located sound. The fact that males moved longer distances in response to approaching than stationary stimuli indicates that they were able to perceive the change of the distance to the playback speaker based only on structural parameters or amplitude of the calls played.     

UNDERWATER SOUND RECORDING OF ANIMALS

ABSTRACT

Underwater sound recording of animals uses specialized techniques to obtain faithful copies of sounds produced by animals during their normal activities underwater. Techniques have to be unobtrusive as well as nondisturbing to avoid changing the animal behaviors. The first scientific recording of underwater sounds from a marine mammal at sea was by William E. Schevill and Barbara Lawrence in 1948. Although the equipment has changed considerably since then, the techniques, approaches to animals and environmental impediments have remained essentially the same. However, the frequency and dynamic ranges of underwater sounds can easily exceed terrestrial sounds, so the selection of suitable equipment is critical. The elements of a useful system for bioacoustic recording of marine animals include the hydrophone, impedance transformer/preamplifier, cable, signal amplifier, recorder and sound monitor. The important criteria for each of these is discussed, along with directional listening systems, and the need for calibrations to verify the performance of the entire underwater recording system. For each situation, the ideal system is the one with the best compromise of interactive components to record that particular sound spectrum.     

Intraspecific acoustic communication and mechanical sensitivity of the tympanal ear of the gypsy moth Lymantria dispar

Tympanal ears of female gypsy moths Lymantria dispar dispar (L.) (Lepidoptera: Erebidae: Lymantriinae) are reportedly more sensitive than ears of conspecific males to sounds below 20 kHz. The hypothesis is tested that this differential sensitivity is a result of sex‐specific functional roles of sound during sexual communication, with males sending and females receiving acoustic signals. Analyses of sounds produced by flying males reveal a 33‐Hz wing beat frequency and 14‐kHz associated clicks, which remain unchanged in the presence of female sex pheromone. Females exposed to playback sounds of flying conspecific males respond with wing raising, fluttering and walking, generating distinctive visual signals that may be utilized by mate‐seeking males at close range. By contrast, females exposed to playback sounds of flying heterospecific males (Lymantria fumida Butler) do not exhibit the above behavioural responses. Laser Doppler vibrometry reveals that female tympana are particularly sensitive to frequencies in the range produced by flying conspecific males, including the 33‐Hz wing beat frequency, as well as the 7‐kHz fundamental frequency and 14‐kHz dominant frequency of associated clicks. These results support the hypothesis that the female L. dispar ear is tuned to sounds of flying conspecific males. Based on previous findings and the data of the present study, sexual communication in L. dispar appears to proceed as: (i) females emitting sex pheromone that attracts males; (ii) males flying toward calling females; and (iii) sound signals from flying males at close range inducing movement in females, which, in turn, provides visual signals that could orient males toward females.     

Flowers respond to pollinator sound within minutes by increasing nectar sugar concentration

Can plants sense natural airborne sounds and respond to them rapidly? We show that Oenothera drummondii flowers, exposed to playback sound of a flying bee or to synthetic sound signals at similar frequencies, produce sweeter nectar within 3 min, potentially increasing the chances of cross pollination. We found that the flowers vibrated mechanically in response to these sounds, suggesting a plausible mechanism where the flower serves as an auditory sensory organ. Both the vibration and the nectar response were frequency‐specific: the flowers responded and vibrated to pollinator sounds, but not to higher frequency sound. Our results document for the first time that plants can rapidly respond to pollinator sounds in an ecologically relevant way. Potential implications include plant resource allocation, the evolution of flower shape and the evolution of pollinators sound. Finally, our results suggest that plants may be affected by other sounds as well, including anthropogenic ones.     

Sounds Modulate Males’ Aggressiveness in a Cichlid Fish

Acoustic signals are produced in many fish species during agonistic or courtship interactions. A way to test the biological role of these sounds is the use of acoustic playback experiments. However, sounds are usually associated with visual displays and playback experiments performed in fish so far, often failed to match acoustic and visual stimuli. To avoid this mismatch issue, we experimentally separated or coupled visual and acoustic channels to test the role of sounds produced during male–male aggressive interactions in a cichlid fish, Metriaclima zebra. Results show that aggressive behaviour is based on visual stimuli and that acoustic signals alone never trigger aggression. Furthermore, the association between visual and acoustic channels lowers the level of aggressiveness found when fish can only interact visually. This suggests that acoustic signals used during a dispute may complement visual displays to modulate males’ behaviour by reducing their aggressiveness and the risk of escalated fights.     

Sounds Scary? Lack of Habituation following the Presentation of Novel Sounds

Background

Animals typically show less habituation to biologically meaningful sounds than to novel signals. We might therefore expect that acoustic deterrents should be based on natural sounds.

Methodology

We investigated responses by western grey kangaroos (Macropus fulignosus) towards playback of natural sounds (alarm foot stomps and Australian raven (Corvus coronoides) calls) and artificial sounds (faux snake hiss and bull whip crack). We then increased rate of presentation to examine whether animals would habituate. Finally, we varied frequency of playback to investigate optimal rates of delivery.

Principal Findings

Nine behaviors clustered into five Principal Components. PC factors 1 and 2 (animals alert or looking, or hopping and moving out of area) accounted for 36% of variance. PC factor 3 (eating cessation, taking flight, movement out of area) accounted for 13% of variance. Factors 4 and 5 (relaxing, grooming and walking; 12 and 11% of variation, respectively) discontinued upon playback. The whip crack was most evocative; eating was reduced from 75% of time spent prior to playback to 6% following playback (post alarm stomp: 32%, raven call: 49%, hiss: 75%). Additionally, 24% of individuals took flight and moved out of area (50 m radius) in response to the whip crack (foot stomp: 0%, raven call: 8% and 4%, hiss: 6%). Increasing rate of presentation (12x/min ×2 min) caused 71% of animals to move out of the area.

Conclusions/Significance

The bull whip crack, an artificial sound, was as effective as the alarm stomp at eliciting aversive behaviors. Kangaroos did not fully habituate despite hearing the signal up to 20x/min. Highest rates of playback did not elicit the greatest responses, suggesting that ‘more is not always better’. Ultimately, by utilizing both artificial and biological sounds, predictability may be masked or offset, so that habituation is delayed and more effective deterrents may be produced.     

Female recognition of trills in the male calling song of the field cricket,<Emphasis Type="Italic"> Teleogryllus taiwanemma</Emphasis>

The calling song of the field cricket, Teleogryllus taiwanemma, is usually considered to consist of sequences of separate chirps. However, sometimes it comprises a phrase of several chirps in a row, with one long chirp (chirp) and a few short chirps (trills). In this study, I compared the phrase containing only chirps with that containing both chirps and trills by analyzing male songs and conducting playback experiments of male songs to females. The song analyses showed significant differences between chirps and trills for all song parameters except bandwidth. To test whether female preference differed with respect to the two phrases, I performed two-speaker playback experiments. When the same numbers of phrases were presented per unit time, females preferred the song with trills to that without trills. This result may reflect female preference for songs with greater sound density. In subsequent playback experiments, I equalized the total sound duration per unit time (duty cycle) in songs with and without trills. The numbers of females that preferred songs with and without trills did not differ significantly. This suggests that trills can attract females like chirps do, even though the two sounds have different components.     

The significance of sound interception to males of the bicolor damselfish,Pomacentrus partitus,during courtship

Synopsis Playback experiments conducted in the field and the laboratory demonstrated the use of sound interception in bicolor damselfish,Pomacentrus partitus. Two courtship sounds produced by male bicolors: the ‘chirp’ which occurs at the initiation of courting and the ‘grunt’ which occurs near the termination, just prior to spawning, were found to hold different meanings to intercepting male competitors. Males responded to grunt playback with directional swimming towards the sound source and increased courtship behavior. No directional response was observed during chirp playback. The grunt sound appears to indicate that a spawn-ready female is present near the sound source. Males therefore move towards it, likely to interfere with the imminent spawning or to gain a possible spawning partner. Such is not observed in response to chirps, as little advantage would be gained by moving to the source of a sound which is known to serve as an ‘advertisement’ or ‘territorial keep-out’ signal. Thus, upon intercepting a neighbor's chirps, males exhibit courting within their own territory, or directly court a nearby female.     

AUDIO COMPUTERS—THEORY OF OPERATION AND GUIDELINES FOR SELECTION OF SYSTEMS AND COMPONENTS

ABSTRACT

Computers are available that can store, synthesize and replay sounds using digital technology. I describe the major components of audio computers, the principles of digital sound acquisition and playback, and information and caveats for scientists interested in acquiring an audio computer system for their own use. A tutorial on analog filter application is also included as well as a diagnostic procedure and a buyer's check list.     

Vocal Mimicry of Alarm‐Associated Sounds by a Drongo Elicits Flee and Mobbing Responses from Other Species that Participate in Mixed‐Species Bird Flocks

A growing number of studies have shown that vocal mimicry appears to be adaptive for some bird species, although the exact function of this behaviour varies among species. Previous work has looked at the function of the vocal mimicry of non‐alarm sounds by the Greater Racket‐tailed Drongo (Dicurus paradiseus). But drongos also imitate sounds associated with danger, such as predators' vocalisations or the mobbing‐specific vocalisations of other prey species, raising the question of whether the function of mimicry can vary even within a species. In a playback experiment, we compared the effect on other species of different drongo vocalisations including: (1) predator mimicry, (2) mobbing mimicry, (3) drongo species‐specific alarms, (4) drongo species‐specific non‐alarms and (5) a control (barbet) sound. Both mobbing mimicry and drongo species‐specific alarms elicited flee responses from the most numerous species in the flocks, the Orange‐billed Babbler (Turdoides rufescens). Mobbing mimicry also elicited mobbing responses from the Orange‐billed Babbler and from another gregarious babbler, the Ashy‐headed Laughingthrush (Garrulax cinereifrons); when responses from both species were considered together, they were elicited at a significantly higher level by mobbing mimicry than by the barbet control, and a level that tended to be higher (0.07 < p < 0.10) than the response to drongo‐specific alarms. Predator mimicry elicited flee and mobbing responses at an intermediary level. Our results support the hypotheses that mobbing mimicry is a specific category of mimicry that helps attract the aid of heterospecifics during mobbing and that alarm mimicry can in some cases be beneficial to the caller.     

Courtship Sounds Advertise Species Identity and Male Quality in Sympatric Pomatoschistus spp. Gobies

Acoustic signals can encode crucial information about species identity and individual quality. We recorded and compared male courtship drum sounds of the sand goby Pomatoschistus minutus and the painted goby P. pictus and examined if they can function in species recognition within sympatric populations. We also examined which acoustic features are related to male quality and the factors that affect female courtship in the sand goby, to determine whether vocalisations potentially play a role in mate assessment. Drums produced by the painted goby showed significantly higher dominant frequencies, higher sound pulse repetition rates and longer intervals between sounds than those of the sand goby. In the sand goby, male quality was predicted by visual and acoustic courtship signals. Regression analyses showed that sound amplitude was a good predictor of male length, whereas the duration of nest behaviour and active calling rate (i.e. excluding silent periods) were good predictors of male condition factor and fat reserves respectively. In addition, the level of female courtship was predicted by male nest behaviour. The results suggest that the frequency and temporal patterns of sounds can encode species identity, whereas sound amplitude and calling activity reflects male size and fat reserves. Visual courtship duration (nest-related behaviour) also seems relevant to mate choice, since it reflects male condition and is related to female courtship. Our work suggests that acoustic communication can contribute to mate choice in the sand goby group, and invites further study.     

The Role of Agonistic Sounds in Male Nest Defence in the Painted Goby Pomatoschistus pictus

Animals often vocalize during territorial challenges as acoustic signals may indicate motivation and fighting ability and contribute to reduce aggressive escalation. Here, we tested the function of agonistic sounds in territorial defence in the painted goby. Pomatoschistus pictus, a small vocal marine fish that defends nests during the breeding season. We first measured the number of times a male approached, avoided, explored, entered and exited two unattended nests associated with either conspecific agonistic sounds or a control: silence or white noise. Acoustic stimuli were played back when the male approached a nest. In a second experimental set, we added visual stimuli, consisting of a conspecific male in a small confinement aquarium near each nest. Even though we found no effect of the visual stimuli, the sound playbacks induced similar effects in both experimental conditions. In the sound vs. silence treatment, we found that when males approached a nest, the playback of conspecific sounds usually triggered avoidance. However, this behaviour did not last as in longer periods males visited nests associated with agonistic sounds more often than silent ones. When the control was white noise, we found no significant effect of the playback treatment in male behaviour. Although we cannot exclude the possibility that other sounds may dissuade nest occupation, our results suggest that agonistic sounds act as territorial intrusion deterrents but are insufficient to prevent nest intrusion on their own. Further studies are needed to test the significance of sound production rate, spectral content and temporal patterns to deter territorial intrusion in fish.     

Hearing in honeybees: localization of the auditory sense organ

Airborne sound signals emitted by dancing honeybees (Apis mellifera) contain information about the locations of food sources. Honeybees can perceive these near field sounds and rely on them to decode the messages of the dance language. The dance sound is characterized by rhythmical air particle movement of high velocity amplitudes. The aim of the present study was to identify the sensory structures used to detect near field sound signals. In an operant conditioning experiment, bees were trained to respond to sound. Ablation experiments with these trained bees revealed that neither mechanosensory hairs on the antennae or head nor bristle fields at the joints of the antenna, but Johnston's organ, a chordotonal organ in the pedicel of the antenna, is used to detect near field sound in honeybees.