Anthropogenic noise is an increasing threat to marine mammals that rely on sound for communication, navigation, detecting prey and predators, and finding mates. Auditory masking is one consequence of ...anthropogenic noise, the study of which is approached from multiple disciplines including field investigations of animal behavior, noise characterization from in-situ recordings, computational modeling of communication space, and hearing experiments conducted in the laboratory. This paper focuses on laboratory hearing experiments applying psychophysical methods, with an emphasis on the mechanisms that govern auditory masking. Topics include tone detection in simple, complex, and natural noise; mechanisms for comodulation masking release and other forms of release from masking; the role of temporal resolution in auditory masking; and energetic vs informational masking.
A psychophysical procedure was used to measure pure-tone detection thresholds for a killer whale (Orcinus orca) as a function of both signal frequency and signal duration. Frequencies ranged between ...1 and 100 kHz and signal durations ranged from 50 μs to 2 s, depending on the frequency. Detection thresholds decreased with an increase in signal duration up to a critical duration, which represents the auditory integration time. Integration times ranged from 4 ms at 100 kHz and increased up to 241 ms at 1 kHz. The killer whale data are similar to other odontocete species that have participated in similar experiments. The results have implications for noise impact predictions for signals with durations less than the auditory integration time.
The directional properties of bottlenose dolphin clicks, burst-pulse, and whistle signals were measured using a five element array, at horizontal angles of 0°, 45°, 90°, 135°, and 180° relative to a ...dolphin stationed on an underwater biteplate. Clicks and burst-pulse signals were highly directional with directivity indices of ~11 dB for both signal types. Higher frequencies and higher amplitudes dominated the forward, on-axis sound field. A similar result was found with whistles, where higher frequency harmonics had greater directivity indices than lower frequency harmonics. The results suggest the directional properties of these signals not only provide enhanced information to the sound producer (as in echolocation) but can provide valuable information to conspecific listeners during group coordination and socialization.
Why Has China Overinvested in Coal Power? Ren, Mengjia; Branstetter, Lee G.; Kovak, Brian K. ...
The Energy journal (Cambridge, Mass.),
03/2021, Letnik:
42, Številka:
2
Journal Article
Recenzirano
In spite of ambitious investments by the Chinese government in renewable energy sources, the country’s investment in coal power accelerated in recent years, raising concerns of massive overcapacity ...and undermining the central policy goal of promoting cleaner energy. In this paper, we ask why this happened, focusing on policies that incentivized excessive entry in the coal power sector and using a simple economic model to illustrate the policies’ effects. Using coal-power project approval records from 2013 to 2016, we find the approval rate of coal power was about 3 times higher after approval authority was decentralized, with larger effects in regions producing more coal. We estimate that local coal production accounts for an additional 54GW of approved coal power in 2015 (other things equal), which is about 1/4 of total approved capacity in that year.
In dolphins, natural selection has developed unihemispheric sleep where alternating hemispheres of their brain stay awake. This allows dolphins to maintain consciousness in response to respiratory ...demands of the ocean. Unihemispheric sleep may also allow dolphins to maintain vigilant states over long periods of time. Because of the relatively poor visibility in the ocean, dolphins use echolocation to interrogate their environment. During echolocation, dolphin produce clicks and listen to returning echoes to determine the location and identity of objects. The extent to which individual dolphins are able to maintain continuous vigilance through this active sense is unknown. Here we show that dolphins may continuously echolocate and accurately report the presence of targets for at least 15 days without interruption. During a total of three sessions, each lasting five days, two dolphins maintained echolocation behaviors while successfully detecting and reporting targets. Overall performance was between 75 to 86% correct for one dolphin and 97 to 99% correct for a second dolphin. Both animals demonstrated diel patterns in echolocation behavior. A 15-day testing session with one dolphin resulted in near perfect performance with no significant decrement over time. Our results demonstrate that dolphins can continuously monitor their environment and maintain long-term vigilant behavior through echolocation.
Bottlenose dolphins (Tursiops truncatus) use the frequency contour of whistles produced by conspecifics for individual recognition. Here we tested a bottlenose dolphin's (Tursiops truncatus) ability ...to recognize frequency modulated whistle-like sounds using a three alternative matching-to-sample paradigm. The dolphin was first trained to select a specific object (object A) in response to a specific sound (sound A) for a total of three object-sound associations. The sounds were then transformed by amplitude, duration, or frequency transposition while still preserving the frequency contour of each sound. For comparison purposes, 30 human participants completed an identical task with the same sounds, objects, and training procedure. The dolphin's ability to correctly match objects to sounds was robust to changes in amplitude with only a minor decrement in performance for short durations. The dolphin failed to recognize sounds that were frequency transposed by plus or minus ½ octaves. Human participants demonstrated robust recognition with all acoustic transformations. The results indicate that this dolphin's acoustic recognition of whistle-like sounds was constrained by absolute pitch. Unlike human speech, which varies considerably in average frequency, signature whistles are relatively stable in frequency, which may have selected for a whistle recognition system invariant to frequency transposition.
Bottlenose dolphins (Tursiops truncatus) depend on sounds at frequencies lower than 30 kHz for social communication, but little information on the directional dependence of hearing thresholds for ...these frequencies exists. This study measured underwater behavioral hearing thresholds for 2, 10, 20, and 30 kHz sounds projected from eight different positions around dolphins in both the horizontal and vertical planes. The results showed that the sound source direction relative to the dolphin affected hearing threshold, and that directional characteristics of the receiving beam pattern were frequency dependent. Hearing thresholds obtained from two adult dolphins demonstrated a positive relationship between directivity of hearing and stimulus frequency, with asymmetric receiving beam patterns in both the horizontal and vertical planes. Projecting sound from directly behind the dolphin resulted in frequency-dependent increases in hearing threshold up to 18.5 dB compared to when sound was projected in front. When the projector was situated above the dolphin thresholds were approximately 8 dB higher as compared to below. This study demonstrates that directional hearing exists for lower frequencies than previously expected.
Killer whale (Orcinus orca) behavioral audiograms Branstetter, Brian K; St Leger, Judy; Acton, Doug ...
The Journal of the Acoustical Society of America,
04/2017, Letnik:
141, Številka:
4
Journal Article
Recenzirano
Killer whales (Orcinus orca) are one of the most cosmopolitan marine mammal species with potential widespread exposure to anthropogenic noise impacts. Previous audiometric data on this species were ...from two adult females Szymanski, Bain, Kiehl, Pennington, Wong, and Henry (1999). J. Acoust. Soc. Am. 108, 1322-1326 and one sub-adult male Hall and Johnson (1972). J. Acoust. Soc. Am. 51, 515-517 with apparent high-frequency hearing loss. All three killer whales had best sensitivity between 15 and 20 kHz, with thresholds lower than any odontocete tested to date, suggesting this species might be particularly sensitive to acoustic disturbance. The current study reports the behavioral audiograms of eight killer whales at two different facilities. Hearing sensitivity was measured from 100 Hz to 160 kHz in killer whales ranging in age from 12 to 52 year. Previously measured low thresholds at 20 kHz were not replicated in any individual. Hearing in the killer whales was generally similar to other delphinids, with lowest threshold (49 dB re 1 μPa) at approximately 34 kHz, good hearing (i.e., within 20 dB of best sensitivity) from 5 to 81 kHz, and low- and high-frequency hearing cutoffs (>100 dB re μPa) of 600 Hz and 114 kHz, respectively.
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