Role of cage material, working style and hearing sensitivity in perception of animal care noise

During daily care, laboratory animals are exposed to a variety of sounds which may have effects on welfare and also cause physiological and behavioural changes. So far, almost no attention has been paid to individual sounds or the sound level caused by animal care or the sound level inside the animal cage. In this study, sounds from selected rat care procedures were recorded: pulling cage out of the rack, placing it onto a table and replacing the cage back into the rack; with measurements made inside the rat cage and in the adjacent cage. Diet was poured into the food hopper and sounds were recorded inside the cage and also the adjacent cage. The work was repeated in a calm and also in a hurried style, using stainless steel and polycarbonate cages. Finally, the sounds produced by running tap water were recorded. Differences between rat and human hearing were compared using novel species-specific sound level weightings: R-weighting for rats dB(R) and H-weighting for human dB(H). Hurried work with steel caused sound exposure levels exceeding 90 dB(R) when the cages were placed into the rack and about 80 dB(R) when pulling them out of the rack or placing onto a table. With polycarbonate, the levels were 10-15 dB(R) lower. Unhurried calm working produced lower sound exposure levels than hurried working in many procedures. When the procedures were repeated with measurements in the adjacent cage, the sound exposure levels were lower, but the results were similar. Pouring food pellets into a hopper above the rat's head caused 15 dB(R) higher sound exposure levels than pouring food to an adjacent cage. In general, humans hear these sounds about 10-15 dB louder than rats. In conclusion, cage material, working style and hearing sensitivity all have an impact on the sound exposure level in the rodent cage. With correct working methods, high sound levels can be efficiently avoided in most cases.     

Sound production, hearing and possible interception under ambient noise conditions in the topmouth minnow Pseudorasbora parva

Sounds were produced by the topmouth minnow Pseudorasbora parva , a common Eurasian cyprinid, during feeding but not during intraspecific interactions. Feeding sounds were short broadband pulses with main energies between 100 and 800 Hz. They varied in their characteristics (number of single sounds per feeding sequence, sound duration and period, and sound pressure level) depending on the food type (chironomid larvae, Tubifex worms and flake food). The loudest sounds were emitted when food was taken up at the water surface, most probably reflecting 'suctorial' feeding. Auditory sensitivities were determined between 100 and 4000 Hz utilizing the auditory evoked potentials recording technique. Under laboratory conditions and in the presence of natural ambient noise recorded in Lake Neusiedl in eastern Austria, best hearing sensitivities were between 300 and 800 Hz (57 dB re 1 μPa v . 72 dB in the presence of ambient noise). Threshold-to-noise ratios were positively correlated to the sound frequency. The correlation between sound spectra and auditory thresholds revealed that P. parva can detect conspecific sounds up to 40 cm distance under ambient noise conditions. Thus, feeding sounds could serve as an auditory cue for the presence of food during foraging.     

Pacific herring hearing does not include ultrasound

Recent studies have shown that some clupeid fishes, including shad and menhaden, can detect ultrasound (sound with frequencies higher than 20 kHz) and actively avoid it. However, other clupeids, including sardines and anchovies, do not detect ultrasound. The hearing abilities of herring are of particular interest because of their commercial importance, our reliance on acoustics to monitor their populations and behavioural evidence of responses to high-frequency sound by some clupeid species. We measured the hearing sensitivity of Pacific herring (Clupea pallasii) using the auditory brainstem response and found that they were unable to detect ultrasonic signals at received levels up to 185 dB re 1 microPa. Herring had hearing thresholds at lower frequencies (100-5000 Hz) that were typical of other non-ultrasound-detecting clupeids. This lower-frequency hearing sensitivity could explain the results of several earlier studies showing responses to broadband sounds.     

褐菖鲉的听觉阈值研究

利用听觉诱发电位记录技术研究了褐菖鲉(Sebasticus marmoratus)的听觉阈值。通过采用听觉生理系统记录和分析了8尾褐菖鲉对频率范围在100—1000 Hz的7种不同频率的声音刺激的诱发电位反应。结果表明, 褐菖鲉的听觉阈值在整体上随着频率增加而增加, 对100—300 Hz的低频声音信号敏感, 最敏感频率为150 Hz, 对应的听觉阈值为70 dB re 1 μPa。褐菖鲉的听觉敏感区间与其发声频率具有较高的匹配性, 表明其声讯交流的重要性。同时, 人为低频噪声可能对其声讯交流造成影响。     

Measuring noise

High levels of noise encountered both in leisure activities and at workplaces can be somewhat annoying, but they can also cause hearing damage. In order to lessen these risks, some physical characteristics of the sound phenomenon need to be understood. The level of a sound is given in dB, a logarithmic unit in which simple addition is not available : 100 dB + 100 dB = 103 dB. The highest level of noise which can be tolerated by the human ear is considered to be 120 dB. Another component of sound characteristics is the frequency, which describes the height of a sound. The frequency is given in Hz, the human hearing field is comprised in the range of 20 to 20,000 Hz. Regarding the sensitivity of the ear, depending on the frequency, acusticians use a weighed dB, called dB(A), which takes into account a lower risk to hearing below 500 Hz and above 6 kHz. They also integrate the energy measured during a period of time to take the fluctuation of usual noise levels into account. So that currently, the levels of noise are often given in LAeq (equivalent to the level of continuous noise given in dBA). For moderate levels of noise, another weighted filter is used in sound level meters : the C curve, because low frequencies, although they are less dangerous for the ear, are more disturbing. In every day life, we sometimes have noise levels reaching 100 dB, and even 120 dB (fire alarms). Amplified music can reach 110 dBA, but a French regulation limits the output of PCPs (Walkmans) to 100 dB and the levels in concerts and discotheques to 105 dBA. At the workplace, the maximum level of noise allowed by French Law is 90 dBA for an 8 hour exposure, and 140 dB for peaks. In order to improve the protection of all workers in the EC, a recent European Directive will decrease the maximum level to 87 dBA before March 2006.     

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).     

Correlations between hearing and sound production in piranhas

Summary In order to determine whether correlations exist between hearing and the known soundproduction abilities in piranhas (Serrasalmus nattereri), behavioral auditory thresholds were obtained with continuous tones and tone pulses. A new avoidance conditioning method was developed, where fin movements of caged animals were taken as response to a tone. The mean values of the far-field audiogram ranged from –26 dB re. 0.1 Pa at 80 Hz to a low point of about –43 dB between 220–350 Hz and rose to –14 dB at 1500 Hz. The frequency spectrum of typical drumming sounds (barks) covers the range of best hearing (100–600 Hz).Piranhas are able to integrate temporally acoustic signals: in threshold investigations with repeated tone pulses, the thresholds rose approximately exponentially with decreasing pulse duration and repetition rate; thresholds of single pulses were higher with shorter pulses. The temporal patterning of the calls and the temporal integration ability are well correlated in piranhas, optimizing intraspecific detectability and total length of sound production with respect to the fatigue characteristics of drumming muscles and habituation of the neural pacemaker.The lagenae of the piranhas were found to face laterofrontally; this is thought to be a morphological adaptation to sound production, saving the lagenae from excessive strain during activation of the drumming muscles.Abbreviations Cl acoustic condition 1, where a board with the air loudspeaker rested on the experimental tank upon a layer of felt - C2 acoustic condition 2, where the loudspeaker was freely mounted 20 cm above the water surface - d _p pulse duration - f _p pulse repetition rate - D duty cycle     

Hearing in honeybees: operant conditioning and spontaneous reactions to airborne sound

Summary Airborne sound signals emitted by dancing bees (Apis mellifera) play an essential role in the bees' dance communication. It has been shown earlier that bees can learn to respond to airborne sounds in an aversive conditioning paradigm. Here we present a new training paradigm. A Y-choice situation was used to determine the frequency range and amplitude thresholds of hearing in bees. In addition, spontaneous reactions of bees to airborne sound were observed and used to determine thresholds of hearing. Both methods revealed that bees are able to detect sound frequencies up to about 500 Hz. The hearing threshold is 100–300 mm/s peak-to-peak velocity and is roughly constant over the range of detectable frequencies. The amplitude of the signals emitted in the dance language is 5 to 10 times higher, so we can conclude that bees can easily detect the dance sounds.     

Better than fish on land? Hearing across metamorphosis in salamanders

Early tetrapods faced an auditory challenge from the impedance mismatch between air and tissue in the transition from aquatic to terrestrial lifestyles during the Early Carboniferous (350 Ma). Consequently, tetrapods may have been deaf to airborne sounds for up to 100 Myr until tympanic middle ears evolved during the Triassic. The middle ear morphology of recent urodeles is similar to that of early ‘lepospondyl’ microsaur tetrapods, and experimental studies on their hearing capabilities are therefore useful to understand the evolutionary and functional drivers behind the shift from aquatic to aerial hearing in early tetrapods. Here, we combine imaging techniques with neurophysiological measurements to resolve how the change from aquatic larvae to terrestrial adult affects the ear morphology and sensory capabilities of salamanders. We show that air-induced pressure detection enhances underwater hearing sensitivity of salamanders at frequencies above 120 Hz, and that both terrestrial adults and fully aquatic juvenile salamanders can detect airborne sound. Collectively, these findings suggest that early atympanic tetrapods may have been pre-equipped to aerial hearing and are able to hear airborne sound better than fish on land. When selected for, this rudimentary hearing could have led to the evolution of tympanic middle ears.     

Diversity in sound pressure levels and estimated active space of resident killer whale vocalizations

Signal source intensity and detection range, which integrates source intensity with propagation loss, background noise and receiver hearing abilities, are important characteristics of communication signals. Apparent source levels were calculated for 819 pulsed calls and 24 whistles produced by free-ranging resident killer whales by triangulating the angles-of-arrival of sounds on two beamforming arrays towed in series. Levels in the 1–20 kHz band ranged from 131 to 168 dB re 1 μPa at 1 m, with differences in the means of different sound classes (whistles: 140.2±4.1 dB; variable calls: 146.6±6.6 dB; stereotyped calls: 152.6±5.9 dB), and among stereotyped call types. Repertoire diversity carried through to estimates of active space, with “long-range” stereotyped calls all containing overlapping, independently-modulated high-frequency components (mean estimated active space of 10–16 km in sea state zero) and “short-range” sounds (5–9 km) included all stereotyped calls without a high-frequency component, whistles, and variable calls. Short-range sounds are reported to be more common during social and resting behaviors, while long-range stereotyped calls predominate in dispersed travel and foraging behaviors. These results suggest that variability in sound pressure levels may reflect diverse social and ecological functions of the acoustic repertoire of killer whales.     

Awareness reactions and avoidance responses to sound in juvenile Atlantic salmon, Salmo salar L.

The possibility of using intense sound as a deterrent for juvenile Atlantic salmon ( Sulmo salar L. ) was studied by recording both physiological awareness reactions in an acoustic tube and behavioural avoidance responses in a pool. The measured awareness reactions consisted of decreased heart rate and breathing movements. Three criteria for the awareness reaction were used to compare the effect of different frequencies between 5 and 150 Hz: (i) threshold for spontaneous awareness reactions relative to the hearing thresholds, (ii) magnitude of the change in heart rate, (iii) degree of habituation to sound. After these criteria the lowest frequencies (5–10 Hz) were most effective in eliciting an awareness reaction from the fish. The responses of freely swimming fish to 10 and 150 Hz sounds were studied in an artificial pool. Juvenile salmon showed avoidance responses to 10 Hz stimulation at intensities 10–15 dB above the threshold for spontaneous awareness reactions measured in the acoustic tube. The 150 Hz sound failed to evoke avoidance responses, even at a level 30 dB above the threshold for spontaneous awareness reactions.     

The hearing abilities of the prawn Palaemon serratus

The mechanism of sound reception and the hearing abilities of the prawn (Palaemon serratus) have been studied using a combination of anatomical, electron microscopic and electrophysiological approaches, revealing that P. serratus is responsive to sounds ranging in frequency from 100 to 3000 Hz. It is the first time that the Auditory Brainstem Response (ABR) recording technique has been used on invertebrates, and the acquisition of hearing ability data from the present study adds valuable information to the inclusion of an entire sub-phylum of animals when assessing the potential impact of anthropogenic underwater sounds on marine organisms. Auditory evoked potentials were acquired from P. serratus, using two subcutaneous electrodes positioned in the carapace close to the supraesophageal ganglion and the statocyst (a small gravistatic organ located below the eyestalk on the peduncle of the bilateral antennules). The morphology of the statocyst receptors and the otic nerve pathways to the brain have also been studied, and reveal that P. serratus possesses an array of sensory hairs projecting from the floor of the statocyst into a mass of sand granules embedded in a gelatinous substance. It is the purpose of this work to show that the statocyst is responsive to sounds propagated through water from an air mounted transducer. The fundamental measure of the hearing ability of any organism possessing the appropriate receptor mechanism is its audiogram, which presents the lowest level of sound that the species can hear as a function of frequency. The statocyst of P. serratus is shown here to be sensitive to the motion of water particles displaced by low-frequency sounds ranging from 100 Hz up to 3000 Hz, with a hearing acuity similar to that of a generalist fish. Also, recorded neural waveforms were found to be similar in both amplitude and shape to those acquired from fish and higher vertebrates, when stimulated with low-frequency sound, and complete ablation of the electrophysiological response was achieved by removal of the statocyst.     

Avoidance responses to low frequency sound in downstream migrating Atlantic salmon smolt, Salmo salar

The possibility of using intense sound as an acoustic barrier for downstream migrating smolt of the Atlantic salmon ( Salmo salar ) was studied by observing, the reactions of smolt to 10 and 150 Hz sounds in a small river. At the observation site the river branched into a main course and a minor channel, the latter rejoining the main stream after 30 m. The sound sources were positioned at the lower end of the channel. The number of smolt re-entering the mam stream at the lower end of the channel was recorded during alternating periods with and without sound. Intense 150 Hz sound had no observable effects on the smolt, even at intensities 114 dB above the hearing threshold at this frequency. At intensities above 1.0. 10⁻²ms⁻² the 10 Hz sound was an effective deterrent for the smolt, which turned and left the channel at the upstream branching point.     

Hearing in reindeer (Rangifer tarandus)

The audiogram of two yearling male reindeer (Rangifer tarandus tarandus) were determined using a conditioned suppression/avoidance procedure. During testing, the animal was drinking from a metal bowl while pure tone signals were played at random intervals and followed by an electric shock in the bowl. By breaking contact with the bowl at sound signals, the animal avoided the shock. The animals detected sounds at intensities of 60 dB or less from 70 Hz to 38 kHz. The frequency range of best sensitivity was relatively flat from 1 kHz to 16 kHz, with a best sensitivity of 3 dB at 8 kHz. The hearing ability of reindeer is similar to the hearing ability of other ungulates.     

Factors Affecting the Transmission of Rodent Ultrasounds in Natural Environments

Recent evidence indicates that myomorph rodent species use ultrasoniccalls as communication signals. The range over which sound communicationsignals may travel and the ease with which they may be localizeddepends on their intensity and structure and the structure ismade. It is concluded that rodent calls are mainly within therange 20–100 kHz and not longer than 300 msec, exceptfor some rat calls which last up to 3 sec. Intensities may beas high as 103 dB SPL (at 10 cm) in pups and 86 dB SPL (at 5–30cm) in adults. Bandwidths between 1–104 kHz are found.High frequency sounds are attenuated with distance more thanlower frequency sounds, mainly by atmospheric attenuation, groundattenuation and scattering. These effects are not all linearso it is difficult to predict how far rodent sounds may travelwithout making measurements under the conditions in which soundsare known to be produced by rodents in the wild. It is shownthat there is little attenuation due to scattering from vegetationin a wood inhabited by woodmice. But in grass or wheat wherefield voles may live, sounds above 20 kHz are rapidly attenuated.Attenuation may be much less in rodent runs and burrows andthis is being studied by a new spark technique.     

R-weighting provides better estimation for rat hearing sensitivity

Since sounds may induce physiological and behavioural changes in animals, it is necessary to assess and define the acoustic environment in laboratory animal facilities. Sound studies usually express sound levels as unweighted linear sound pressure levels. However, because a linear scale does not take account of hearing sensitivity-which may differ widely both between and within species at various frequencies-the results may be spurious. In this study a novel sound pressure level weighting for rats, R-weighting, was calculated according to a rat's hearing sensitivity. The sound level of a white noise signal was assessed using R-weighting, with H-weighting tailored for humans, A-weighting and linear sound pressure level combined with the response curves of two different loudspeakers. The sound signal resulted in different sound levels depending on the weighting and the type of loudspeaker. With a tweeter speaker reproducing sounds at high frequencies audible to a rat, R- and A-weightings gave similar results, but the H-weighted sound levels were lower. With a middle-range loudspeaker, unable to reproduce high frequencies, R-weighted sound showed the lowest sound levels. In conclusion, without a correct weighting system and proper equipment, the final sound level of an exposure stimulus can differ by several decibels from that intended. To achieve reliable and comparable results, standardization of sound experiments and assessment of the environment in animal facilities is a necessity. Hence, the use of appropriate species-specific sound pressure level weighting is essential. R-weighting for rats in sound studies is recommended.     

Female green treefrogs (Hyla cinerea) do not selectively respond to signals with a harmonic structure in noise

1. Females of the green treefrog, Hyla cinerea, communicate in noisy environments, with spectrally complicated signals. A previous study (Megela Simmons 1988), using the reflex modification technique, found that the masked threshold of green treefrogs to two-tone signals differed by about 10 dB depending on whether or not the two components were harmonically-related. The present study used the same two-component stimuli to test the prediction that gravid females would better detect harmonic sounds in noise than inharmonic ones. 2. We offered gravid treefrogs simultaneous choices between alternative two-component synthetic sounds: (1) an inharmonic sound of 831 + 3100 Hz, and a harmonic sound of 828 + 2760 Hz. We varied the sound pressure level (SPL in decibels [dB]) to which we equalized these alternatives at the female's release point (75 and 80 dB SPL), and we tested females in quiet conditions and in the presence of broadband background noise (52 dB/Hz at the female's release point). 3. At a signal playback level of 75 dB SPL, one-third of the females responded in the presence of background noise. Subtracting the spectrum level yields a critical ratio estimate of 23 dB, a value that is very similar to estimates for single pure tones in noise reported in other studies of this species (Ehret and Gerhardt 1980; Moss and Megela Simmons 1986). Females did not, however, choose the harmonic sound over the inharmonic sound in this condition, at the higher signal-to-noise ratio, or in either of the unmasked situations.(ABSTRACT TRUNCATED AT 250 WORDS)     

Contribution to the study of acoustic communication in two Belgian river bullheads (<Emphasis Type="Italic">Cottus rhenanus and C. perifretum</Emphasis>) with further insight into the sound-producing mechanism

Background

The freshwater sculpins (genus Cottus) are small, bottom-living fishes widely distributed in North America and Europe. The taxonomy of European species has remained unresolved for a long time due to the overlap of morphological characters. Sound production has already been documented in some cottid representatives, with sounds being involved in courtship and agonistic interactions. Although the movements associated with sound production have been observed, the underlying mechanism remains incomplete. Here, we focus on two closely related species from Belgium: C. rhenanus and C. perifretum. This study aims 1) to record and to compare acoustic communication in both species, 2) to give further insight into the sound-producing mechanism and 3) to look for new morphological traits allowing species differentiation.

Results

Both Cottus species produce multiple-pulsed agonistic sounds using a similar acoustic pattern: the first interpulse duration is always longer, making the first pulse unit distinct from the others. Recording sound production and hearing abilities showed a clear relationship between the sound spectra and auditory thresholds in both species: the peak frequencies of calls are around 150 Hz, which corresponds to their best hearing sensitivity. However, it appears that these fishes could not hear acoustic signals produced by conspecifics in their noisy habitat considering their hearing threshold expressed as sound pressure (~ 125 dB re 1 μPa). High-speed video recordings highlighted that each sound is produced during a complete back and forth movement of the pectoral girdle.

Conclusions

Both Cottus species use an acoustic pattern that remained conserved during species diversification. Surprisingly, calls do not seem to have a communicative function. On the other hand, fish could detect substrate vibrations resulting from movements carried out during sound production. Similarities in temporal and spectral characteristics also suggest that both species share a common sound-producing mechanism, likely based on pectoral girdle vibrations. From a morphological point of view, only the shape of the spinelike scales covering the body allows species differentiation.

     

How Nemo finds home: the neuroecology of dispersal and of population connectivity in larvae of marine fishes

Nearly all demersal teleost marine fishes have pelagic larval stages lasting from several days to several weeks, during which time they are subject to dispersal. Fish larvae have considerable swimming abilities, and swim in an oriented manner in the sea. Thus, they can influence their dispersal and thereby, the connectivity of their populations. However, the sensory cues marine fish larvae use for orientation in the pelagic environment remain unclear. We review current understanding of these cues and how sensory abilities of larvae develop and are used to achieve orientation with particular emphasis on coral-reef fishes. The use of sound is best understood; it travels well underwater with little attenuation, and is current-independent but location-dependent, so species that primarily utilize sound for orientation will have location-dependent orientation. Larvae of many species and families can hear over a range of ~100-1000 Hz, and can distinguish among sounds. They can localize sources of sounds, but the means by which they do so is unclear. Larvae can hear during much of their pelagic larval phase, and ontogenetically, hearing sensitivity, and frequency range improve dramatically. Species differ in sensitivity to sound and in the rate of improvement in hearing during ontogeny. Due to large differences among-species within families, no significant differences in hearing sensitivity among families have been identified. Thus, distances over which larvae can detect a given sound vary among species and greatly increase ontogenetically. Olfactory cues are current-dependent and location-dependent, so species that primarily utilize olfactory cues will have location-dependent orientation, but must be able to swim upstream to locate sources of odor. Larvae can detect odors (e.g., predators, conspecifics), during most of their pelagic phase, and at least on small scales, can localize sources of odors in shallow water, although whether they can do this in pelagic environments is unknown. Little is known of the ontogeny of olfactory ability or the range over which larvae can localize sources of odors. Imprinting on an odor has been shown in one species of reef-fish. Celestial cues are current- and location-independent, so species that primarily utilize them will have location-independent orientation that can apply over broad scales. Use of sun compass or polarized light for orientation by fish larvae is implied by some behaviors, but has not been proven. Use of neither magnetic fields nor direction of waves for orientation has been shown in marine fish larvae. We highlight research priorities in this area.     

The ontogenetic development of auditory sensitivity, vocalization and acoustic communication in the labyrinth fish Trichopsis vittata

The anabantoid fish Trichopsis vittata starts vocalizing as 8-week-old juveniles. In order to determine whether juveniles are able to detect conspecific sounds, hearing sensitivities were measured in six size groups utilizing the auditory brainstem response-recording technique. Results were compared to sound pressure levels and spectra of sounds recorded during fighting. Auditory evoked potentials were present in all size groups and complete audiograms were obtained starting with 0.18 to 0.30 g juveniles. Auditory sensitivity during development primarily increased between 0.8 kHz and 3.0 kHz. The most sensitive frequency within this range shifted from 2.5 kHz to 1.5 kHz, whereas thresholds decreased by 14 dB. Sound production, on the other hand, started at 0.1 g and sound power spectra at dominant frequencies increased by 43 dB, while dominant frequencies shifted from 3 kHz to 1.5 kHz. Comparisons between audiograms and sound power spectra in similar-sized juveniles revealed no clear match between most sensitive frequencies and dominant frequencies of sounds. This also revealed that juveniles cannot detect conspecific sounds below the 0.31 to 0.65 g size class. These results indicate that auditory sensitivity develops prior to the ability to vocalize and that vocalization occurs prior to the ability to communicate acoustically.