environmental acoustics

Little information exists about how noise exposure may modulate agonistic behaviour of some sonic fish in which perception of sounds produced by conspecifics is crucial in interpreting the message conveyed by the opponents. Recently, it has been demonstrated that temporary hearing impairment can be induced by exposing fish to certain periods of white noise. Experiments were designed to test the hypothesis that elevation of hearing thresholds my means of exposure to noise) of a sonic fish, the croaking gourami Trichopsis vittata, could alter the quality of sound produced because of the altered feedback route in sound perception and production loop. This experiment also tested the hypothesis that altered characteristics of the sound produced would subsequently modulate the outcome of the behavioural contest. Test subjects were exposed to 300 - 4000 Hz white noise (142 dB; re: 1 mPa) for 12 and 24 hours, respectively. The hearing threshold shifts were evaluated at the end of noise exposure as well as one day and five days after exposure with the use of the auditory brainstem response recording protocol. The frequency range tested (600 - 2500 Hz) corresponded to the fish best hearing range as well as to the range of the croaking sounds emitted by the fish. Hearing threshold was found significantly elevated after noise exposure. Recovery, however, appeared faster in 12-hr noise exposed fish than those from the 24-hr exposure group. The croaking sounds produced by noise-exposed fish were also recorded through staged contests. The results were used to compare with the sounds produced prior to the exposure. Details of differences in sound spectra as well as changes of agonistic behaviour are presented and discussed (supported by National Organization for Hearing Research, NIMH-58198, Institute of Museum and Library Service-LL90187).

Seismic signals occur in at least two distinct lineages of subterranean rodents (Bathyergidae and Spalacinae), indicating that this mode of communication cannot be explained solely in terms of phylogenetic history. Understanding the evolutionary context in which each signal type has developed remains a significant challenge to biologists studying communication in subterranean rodents. The importance of social behaviour for the type of vibrational signals used has been emphasised, implying that solitary taxa are more likely to exhibit seismic signals than social taxa because of their greater need for communication between burrows. Because seismic signals propagate better through the soil than vocal signals, the former should be favoured in solitary species in which communication occurs primarily between burrows. The majority of Ctenomys species are solitary and territorial, living in individual burrows that never approach other burrows nearer than 40 cm outside of the reproductive season, thus long distance inter-burrow communication is a candidate for the use of seismic signals. Nevertheless, no Ctenomys is known to produce seismic signals but almost all of them vocalise loud enough to be heard at a considerable distance outside the burrows. Data from six Ctenomys species show that these vocalisations are low frequency, repetitive, rhythmic signals which present structural similarities with the seismic signals emitted by other subterranean rodents. These facts suggest that the use of low-frequency rhythmic signals could be a result of the constraints imposed by the underground environment and that the propagation conditions may determine that rhythm is more reliable than frequency modulation. Then, solitary subterranean rodents may use low frequency, rhythmic, repetitive signals for long distance communication, either vocal or seismic, to overcome the environmental constraints. A possible explanation for the use of one of both channels by different species has been discussed elsewhere.

Some animals that use sound to communicate have evolved adaptations to counteract the masking effects of environmental background noise. In the short-term, one such adaptation is the Lombard effect, in which a signaller increases the amplitude of its vocalisations in response to an increase of the background noise amplitude. Such a capacity has been demonstrated for zebra finches (Cynx et al. 1998: Anim. Behav. 56, 107-113), a non-territorial songbird. Territorial songbirds, on the other hand, may benefit from singing as loud as possible to defend territories and attract females. Therefore, they may maximise the amplitude of their songs rather than regulating it according to the background noise level. I addressed this issue by experimentally manipulating the background noise and measuring the sound level of the vocalisations of a territorial songbird, the Common Nightingale Luscinia megarhynchos. This species is a good model to investigate the mechanisms of vocal amplitude regulation in detail, because males typically produce their territorial songs with specific amplitude differences between the diverse song sections (Hultsch, personal communication). Subjects (n = 4) increased the mean sound level of their songs in response to increased sound levels of white noise. Within songs, such regulation was found in both the loudest and the softest notes. One bird increased its call amplitude in response to increased levels of noise, showing that nightingales may also exhibit the Lombard effect in non-territorial signals. These findings show that nightingales do not maximise song amplitude but regulate vocal intensity dependent on the level of environmental noise. Possibly, such adjustment of vocal amplitude serves to maintain a specific signal-to-noise ratio that is favourable for signal production. Concurrently, amplitude regulation may ensure maintaining a given active space for communication. Thus, vocal amplitude in a territorial songbird is be a flexible trait, which is regulated according to ecological demands from signal transmission, as recently discussed by Brumm and Hultsch (2001, Anim. Behav., 61, 747-754).

Male territorial songbirds interact with each other via full song over long distances. The relative timing of strophes in these singing interactions conveys information about male dominance with overlapping as a dominant signal indicating willingness to escalate. Other birds may eavesdrop on such interactions to assess future opponents. This requires that individuals at a distance perceive the intended time pattern of the interaction despite attenuation and masking effects. Particularly during the dawn chorus, song of individual males is masked by vocalisations of other birds of the same and other species. We here report on a dual-speaker playback experiment in which we simulate alternating, overlapping and random patterns of singing interactions between male blue tits in a natural habitat. We record these 'interactions' and the vocalisations masking them with an array of four microphones (Acoustic Location System, ALS) representing eavesdroppers. The ALS allows the location of the masking birds. Masking in time and frequency range as well as signal-to-noise ratio between 'interactants' and masking birds are taken into consideration in the analysis. We expect the 'eavesdroppers' to perceive the temporal pattern of the interaction differently, depending on their location relative to the 'interactants' and the masking they experience. This study gives insight into how masking may constrain the perception of time patterns in singing interactions that vary considerably and therefore cannot be reconstructed from any internal representation.

The transmission of high frequency sound through the environment has been studied using continuous and pulsed sound. The bush cricket Leptophyes punctatissima is able to communicate very successfully at ultrasonic frequencies, hence it is a significant biological model to use. Measurements of attenuation were made using a signal broadcast over reflecting and absorbing surfaces and over a pre-calibrated series of glasspapers, artificial surfaces for which there are also S.E.M. images available. Measurements of sound radiation around a singing insect suggest that leaf angle influences the reflection of sound at 40 kHz. It may be possible to identify potential acoustical effects that have enabled Leptophyes punctatissima to communicate so effectively at this high frequency, though it may also be the case that the insect's own size and shape have also determined the use of this particular frequency.

Nature sounds are treasure boxes of information. They give us some clues as to the sound sources in terms of the identity, life cycle and interactions with other elements in the environment. They also tell us the type and nature of different events that take place close to or afar in the environment. The range and significance of nature sounds is the general foundation for the study of sound environments. Different habitats respectively hold the unique sound environment in terms of their acoustical characteristics and sound source species composition (SSSC). The acoustical indices such as taxonomic groups, locality bonds and trophic levels have made it possible to carry out environmental surveys without imposing a harmful effect on the local ecosystem as the conventional methods of collection and capture tend to do. SSSC monitored in a local area will be the main source for diagnosing and assessing the environment. In order to make use of such treasure boxes of nature sounds, however, we first need to learn properly how to listen to and hear nature sounds using our own ears. As part of the sound and environmental education, I would like to propose .a sound map method. The sound map is a handy way for both children and adults to describe and discover the sound environment. It is also an effective way to develop their hearing sensitivity and aural recognition of nature sounds in an enjoyable manner. Further, the sound map provides us with the means to share the image of sound environment with other people and is a good foundation for communicating and making decisions on it. To show the potentials of sound map method in monitoring and diagnosing environments, a pilot study made at a planned site of EXPO 2005 in Kaisho-no-mori Forest, Aichi, Japan is briefly introduced.

There is growing concern that aquatic vertebrates may be affected by the increasing noise of anthropogenic origin in their environment. Several studies have been conducted on the effects of noise on marine mammals, but only a few studies have dealt with fish. The aim of the present study is to measure and compare the immediate effects of intense noise exposure (160 dB re 1 µPa for 12 and 24 hours) on two otophysine fish species, the non-vocal cyprinid Carassius auratus and the catfish Pimelodus pictus, which produces low-frequency drumming and high-pitched stridulatory-sounds. The second aim of this study was to determine the effects of noise on the ability of P. pictus to communicate acoustically. Hearing sensitivity was determined utilising the auditory evoked potential (AEP) recording technique. Measurements were performed prior and directly after noise exposure as well as after several days of recovery. Threshold shifts immediately after noise exposure ranged from 13-22 dB in C. auratus and from 7-34 dB in P. pictus. In both species the greatest hearing loss occurred at their most sensitive frequencies (C. auratus: 500 - 1000 Hz; P. pictus: 500-4000 Hz). Sound energies in the pimeloid catfish were maximally 10 dB above hearing curves immediately after noise exposure. Differences in recovery were observed between species. Carassius auratus recovered completely after 3 days, whereas in Pimelodus pictus reduced auditory sensitivity of up to 15 dB was still observed after 3 days. Our results showed that these two hearing specialists are differently affected by noise exposure and that the threshold shifts are more persistent in P. pictus. The hearing loss in the vocalising pimelodid catfish indicates that sound communication is impaired in noisy environments. This research was supported by the Austrian Science Fund (FWF No 12411 to F.L.).

Underwater noise pollution is becoming a pressing environmental issue that could affect aquatic wildlife, but very little research has been done on this topic. The effect can be even more dramatic for species actively using acoustic signals for communication and assessment of quality of opponents during agonistic encounters. We examined the effects of underwater noise on auditory sensitivity and aggressive behaviour in the vocalising skunk loach Botia morleti. Fish were exposed to white noise (142 do re: 1 µPa) for 12 hours and shifts of auditory threshold were measured with the auditory brainstem response protocol. Noise exposure resulted in elevated auditory thresholds throughout the entire auditory range. It was also found that significant recovery occurred in approximately 9 hours. The effects of noise-exposure on behaviour during aggressive contests were investigated by comparing contest dynamics between noise-exposed fish and a resident (non-exposed fish). The results showed that noise-exposure could influence behaviour in two ways: 1) contest durations with noise-exposed fish were significantly shorter; and 2) noise-exposed fish tended to engage in more re-escalation of contests than those with control fish. Two mechanisms (direct, indirect) were proposed to explain the findings. In the direct effect, noise exposure causes direct stress on the fish which results in decreased contest duration. In the indirect effect, the noise exposure cause a temporary hearing loss which results in a misperception of the acoustic signal emitted by the opponents. The sound perception and production feedback loop is compromised due to noise exposure (i.e., elevation of hearing threshold) and as a result, contests are repeatedly re-escalated because the information content of the signal can not be accurately perceived by the noise-exposed fish. The present study demonstrates that noise pollution could have dire physiological impacts as well as behavioural consequences (supported by National Organization for Hearing Research, N1MH-58198, Institute of Museum and Library Service-LL90187).

The underwater acoustic environment is inherently loud as a result of ambient sounds. In addition, there is an increasing amount of sound from anthropogenic sources, which produce noise within the hearing range of most fish (less than 1.0 kHz). For fish, the auditory system is one of the most important sensory systems because it provides information about ambient sounds, prey items, predators and potential mates. Since a fish's ability to accurately interpret its acoustic environment is essential for its survival, it is important to understand how noise affects sound perception ability of fish. This study examines the question: does noise exposure affect auditory sensitivity differently in hearing specialists (fish with coupling devices between the gasbladder or ancillary structures and inner ear, enhancing overall hearing with wider frequency range and lower threshold) and hearing generalists (fish without coupling devices, with narrow frequency range and higher threshold)? For this study, a hearing specialist species, the fathead minnow Pimephales promelas, and a hearing generalist species, the bluegill sunfish Lepomis macrochirus, were used to examine: (1) the immediate effects on auditory threshold of white noise exposure at various exposure durations (1-24 h at 0.3-4.0 kHz, 142 dB re: 1µPa); and (2) recovery time after noise exposure (1-14 days). Audiograms for noise-exposed fish were measured using the auditory brainstem response protocol, which records acoustically evoked brainwaves, and compared to control fish (no noise exposure). The results for specialists showed that their best hearing frequency range (0.8-2.0 kHz) was affected significantly more than other frequencies. In addition, recovery of hearing ability after noise exposure was found to be both frequency- and exposure-dependent. The results for hearing generalist fish will be presented and discussed (work supported by the Kentucky Academy of Science, National Organization for Hearing Research, NIMH-58198, Institute of Museum and Library Service-LL90187).

Acoustic researches were made in the Miramare Marine Reserve (Gulf of Trieste, Adriatic Sea, Italy) and just outside it in order to evaluate interferences between fish acoustic communication and man-made under- water noise due to the passage of outboard engine boats. Average sea ambient noise was recorded both inside and outside the protected area because in the reserve the passage of boats is intermittent, while outside the boat traffic is intense. Then observations in tanks and in the field were made on the territorial agonistic behaviour of the red mouth goby Gobius cruentatus, a benthic fish present in and out the protected area. Two different fish sounds were recorded: a train of distinct knocks and a drumming sound, a less regular spaced train. The frequency range is from 50 Hz up to 800 Hz with highest amplitude below 200 Hz. Meanwhile the boat noise was recorded from the smaller distance between engine source and fish inside (200 metres) and outside (10 metres) the preserved area. Finally all of these recordings were compared in a frequency - P.S.D. graph. The result of the comparison suggests that in the Reserve the acoustic communication in G. cruentatus is undisturbed and that this approach is a useful method to assess and prevent the impact of man-made noise in a protected area.