CLICK CHARACTERISTICS OF NORTHERN BOTTLENOSE WHALES (HYPEROODON AMPULLATUS)

Sounds produced by northern bottlenose whales ( Hyperoodon ampullatus ) recorded in the Gully, a submarine canyon off Nova Scotia, consisted predominately of clicks. In 428 min of recordings no whistles were heard which could unequivocally be attributed to bottlenose whales. There were two major types of click series, initially distinguished by large differences in received amplitude. Loud clicks (produced by nearby whales socializing at the surface) were rapid, with short and variable interclick intervals (mean 0.07 sec; CV 71%). The frequency spectra of these were variable and often multimodal, with peak frequencies ranging between 2 and 22 kHz (mean 11 kHz, CV 59%). Clicks received at low amplitude (produced by distant whales, presumably foraging at depth) had more consistent interclick intervals (mean 0.40 sec, CV 12.5%), generally unimodal frequency spectra with a mean peak frequency of 24 kHz (CV 7%) and 3 dB bandwidth of 4 kHz. Echolocation interclick intervals may reflect the approximate search distance of an animal, in this case 300 m, comparable to that found for sperm whales. The relationship between click frequency and the size of object being investigated, suggests that 24 kHz would be optimal for an object of approximately 6 cm or more, consistent with the size range of their squid prey.     

Highly Directional Sonar Beam of Narwhals (Monodon monoceros) Measured with a Vertical 16 Hydrophone Array

Recordings of narwhal (Monodon monoceros) echolocation signals were made using a linear 16 hydrophone array in the pack ice of Baffin Bay, West Greenland in 2013 at eleven sites. An average -3 dB beam width of 5.0° makes the narwhal click the most directional biosonar signal reported for any species to date. The beam shows a dorsal-ventral asymmetry with a narrower beam above the beam axis. This may be an evolutionary advantage for toothed whales to reduce echoes from the water surface or sea ice surface. Source level measurements show narwhal click intensities of up to 222 dB pp re 1 μPa, with a mean apparent source level of 215 dB pp re 1 μPa. During ascents and descents the narwhals perform scanning in the vertical plane with their sonar beam. This study provides valuable information for reference sonar parameters of narwhals and for the use of acoustic monitoring in the Arctic.     

CHANGES IN CLICK SOURCE LEVELS WITH DISTANCE TO TARGETS: STUDIES OF FREE-RANGING WHITE-BEAKED DOLPHINS LAGENORHYNCHUS ALBIROSTRIS AND CAPTIVE HARBOUR PORPOISES PHOCOENA PHOCOENA

ABSTRACT

Probably all odontocetes use echolocation for spatial orientation and detection of prey. We used a four hydrophone “Y” array to record the high frequency clicks from free-ranging White-beaked Dolphins Lagenorhynchus albirostris and captive Harbour Porpoises Phocoena phocoena. From the recordings we calculated distances to the animals and source levels of the clicks. The recordings from White-beaked Dolphins were made in Iceland and those from Harbour Porpoises at Fjord & Baelt, Kerteminde, Denmark during prey capture. We used stringent criteria to determine which clicks could be defined as being on the acoustic axis. Two dolphin and nine porpoise click series could be used to track individual animals, which presumably focused on the array hydrophones or a fish right in front of the array. The apparent source levels of clicks in the individual tracks increased with range. One individual White-beaked Dolphin and three Harbour Porpoises regulate their output signal level to nearly compensate for one-way transmission loss while approaching a target. The other dolphin regulated the output differently. For most of the recordings the sound level at the target remains nearly constant and the echo level at the animal increases as it closes on the target.     

Different modes of acoustic communication in deep‐diving short‐finned pilot whales (Globicephala macrorhynchus)

Toothed whales use a pneumatic sound generator to produce echolocation and communication sounds. Increasing hydrostatic pressure at depth influences the amplitude and duration of calls but not of echolocation clicks. Here we test the hypothesis that information transfer at depth might be facilitated by click‐based communication signals. Wild short‐finned pilot whales (27) instrumented with multisensor DTAGs produced four main types of communication signals: low‐ and medium‐frequency calls (median fundamental frequency: 1.7 and 2.9 kHz), two‐component calls (median frequency of the low and high frequency components: 2 and 9 kHz), and rasps (burst‐pulses with median interclick interval of 21 ms). Rasps can be confused with foraging buzzes, but rasps are shorter and slower, and are not associated with fast changes in body acceleration nor reduced acoustic output of buzzes, characteristic of prey capture attempts. Contrary to calls, the energy flux density of rasps was not significantly affected by depth. This, and a different information content, may explain the observed increase in the relative occurrence of rasps with respect to calls at depth, and supports the hypothesis that click‐based communication signals may facilitate communication under high hydrostatic pressure. However, calls are produced at depth also, indicating that they may carry additional information relevant for deep‐diving animals, including potential communication among whales diving at the same time in this highly social deep‐diving species.     

ESTIMATES OF SPERM WHALE ABUNDANCE IN THE NORTHEASTERN TEMPERATE PACIFIC FROM A COMBINED ACOUSTIC AND VISUAL SURVEY

We estimate the abundance of sperm whales in a 7.8 million km² study area in the eastern temperate North Pacific using data from a ship-based acoustic and visual line-transect survey in spring 1997. Sperm whales were detected acoustically using a hydrophone array towed at 15 km/h and 100 m depth. The hydrophone array was towed for 14,500 km, and locations were estimated acoustically for 45 distinct sperm whale groups. Whales producing slow clicks (>2-s period) were detected at greater distance (up to 37 km), and the estimation of effective strip widths was stratified based on initial click period. Visual survey effort (using 25° binoculars and naked eyes) covered 8,100 km in Beaufort sea states 0–5 and resulted in only eight sightings. The effective strip width for visual detections was estimated from previous surveys conducted using the same methods and similar vessels in the eastern Pacific. Estimated sperm whale abundance in the study area was not significantly different between acoustic (32,100, CV = 0.36) and visual (26,300, CV = 0.81) detection methods. Acoustic techniques substantially increased the number of sperm whales detected on this line-transect survey by increasing the range of detection and allowing nighttime surveys; however, visual observations were necessary for estimating group size.     

Vertical auditory acuity of the bottlenose dolphin

The accuracy in locating underwater sounds in the vertical median plane was determined for the Black Sea bottlenose dolphin Tursiops truncatus trained by operant conditioning with food reinforcement. The minimal perceived angles for 1-s tone signals were 2.5° at 5 or 20 kHz and 2.0° at 120 kHz; for 1-s trains of clicks centered at 120 kHz the acuity was still better, ～1.5°. Dolphins may locate different sounds using different yet equally efficient mechanisms, and they are the best in analyzing the acoustic space among marine mammals studied.     

KILLER WHALE (ORCINUS ORCA) AUDITORY EVOKED POTENTIALS TO RHYTHMIC CLICKS

Temporal auditory mechanisms were measured in killer whales ( Orcinus orca ) by recording auditory evoked potentials (AEPs) to clicks. Clicks were presented at rates from 10/sec to 1,600/sec. At low rates, clicks evoked an AEP similar to the auditory brainstem response (ABR) of other odontocetes; however, peak latencies of the main waves were 3–3.7 msec longer than in bottlenose dolphins. Fourier analysis of the ABR showed a prominent peak at 300–400 Hz and a smaller one at 800–1,200 Hz. High-rate click presentation (more than 100/sec) evoked a rate-following response (RFR). The RFR amplitude depended little on rate up to 400/sec, decreased at higher rates and became undetectable at 1,120/sec. Fourier analysis showed that RFR fundamental amplitude dependence on frequency closely resembled the ABR spectrum. The fundamental could follow clicks to around 1,000/sec, although higher harmonics of lower rates could arise at frequencies as high as 1,200 Hz. Both RFR fundamental phase dependence on frequency and the response lag after a click train indicated an RFR group delay of around 7.5 msec. This corresponds to the latency of ABR waves PIII-NIV, which indicates the RFR originates as a rhythmic, overlapping ABR sequence. The data suggest the killer whale auditory system can follow high click rates, an ability that may have been selected for as a function of high-frequency hearing and the use of rapid clicks in echolocation.     

'Megapclicks': acoustic click trains and buzzes produced during night-time foraging of humpback whales (Megaptera novaeangliae)

Humpback whales (Megaptera novaeangliae) exhibit a variety of foraging behaviours, but neither they nor any baleen whale are known to produce broadband clicks in association with feeding, as do many odontocetes. We recorded underwater behaviour of humpback whales in a northwest Atlantic feeding area using suction-cup attached, multi-sensor, acoustic tags (DTAGs). Here we describe the first recordings of click production associated with underwater lunges from baleen whales. Recordings of over 34000 'megapclicks' from two whales indicated relatively low received levels at the tag (between 143 and 154dB re 1 microPa pp), most energy below 2kHz, and interclick intervals often decreasing towards the end of click trains to form a buzz. All clicks were recorded during night-time hours. Sharp body rolls also occurred at the end of click bouts containing buzzes, suggesting feeding events. This acoustic behaviour seems to form part of a night-time feeding tactic for humpbacks and also expands the known acoustic repertoire of baleen whales in general.     

The relationship among oceanography, prey fields, and beaked whale foraging habitat in the Tongue of the Ocean

Beaked whales, specifically Blainville's (Mesoplodon densirostris) and Cuvier's (Ziphius cavirostris), are known to feed in the Tongue of the Ocean, Bahamas. These whales can be reliably detected and often localized within the Atlantic Undersea Test and Evaluation Center (AUTEC) acoustic sensor system. The AUTEC range is a regularly spaced bottom mounted hydrophone array covering >350 nm(2) providing a valuable network to record anthropogenic noise and marine mammal vocalizations. Assessments of the potential risks of noise exposure to beaked whales have historically occurred in the absence of information about the physical and biological environments in which these animals are distributed. In the fall of 2008, we used a downward looking 38 kHz SIMRAD EK60 echosounder to measure prey scattering layers concurrent with fine scale turbulence measurements from an autonomous turbulence profiler. Using an 8 km, 4-leaf clover sampling pattern, we completed a total of 7.5 repeat surveys with concurrently measured physical and biological oceanographic parameters, so as to examine the spatiotemporal scales and relationships among turbulence levels, biological scattering layers, and beaked whale foraging activity. We found a strong correlation among increased prey density and ocean vertical structure relative to increased click densities. Understanding the habitats of these whales and their utilization patterns will improve future models of beaked whale habitat as well as allowing more comprehensive assessments of exposure risk to anthropogenic sound.     

Size Distribution of Sperm Whales Acoustically Identified during Long Term Deep-Sea Monitoring in the Ionian Sea

The sperm whale (Physeter macrocephalus) emits a typical short acoustic signal, defined as a “click”, almost continuously while diving. It is produced in different time patterns to acoustically explore the environment and communicate with conspecifics. Each emitted click has a multi-pulse structure, resulting from the production of the sound within the sperm whale’s head. A Stable Inter Pulse Interval (Stable IPI) can be identified among the pulses that compose a single click. Applying specific algorithms, the measurement of this interval provides useful information to assess the total length of the animal recorded. In January 2005, a cabled hydrophone array was deployed at a depth of 2,100 m in the Central Mediterranean Sea, 25 km offshore Catania (Ionian Sea). The acoustic antenna, named OνDE (Ocean noise Detection Experiment), was in operation until November 2006. OνDE provided real time acoustic data used to perform Passive Acoustic Monitoring (PAM) of cetacean sound emissions. In this work, an innovative approach was applied to automatically measure the Stable IPI of the clicks, performing a cepstrum analysis to the energy (square amplitude) of the signals. About 2,100 five-minute recordings were processed to study the size distribution of the sperm whales detected during the OνDE long term deep-sea acoustic monitoring. Stable IPIs were measured in the range between 2.1 ms and 6.4 ms. The equations of Gordon (1991) and of Growcott (2011) were used to convert the IPIs into measures of size. The results revealed that the sperm whales recorded were distributed in length from about 7.5 m to 14 m. The size category most represented was from 9 m to 12 m (adult females or juvenile males) and specimens longer than 14 m (old males) seemed to be absent.     

Localization of a sum of acoustic signals in air by the northern fur seal]

The localization of a sum of acoustic signals by two northern fur seals in air depending on sound parameters was investigated using the method of instrumental conditioned reflexes with food reinforcement. It was found that sound perception of northern fur seal proceeds by the binaural mechanism. The time/intensity interchange coefficient was 570 microseconds/dB for series of clicks (with amplitude maximum at 1 kHz) and 250 microseconds/dB for tonal impulses with a frequency of 1 kHz. With click amplitudes being equal, the number of approaches of the animal to the source of the first signal reached a 75% level at a delay of the second signal 0.07 ms (the minimum delay); with a delay of 6 ms (the maximum delay) and more, the fur seal, probably hears two separate signals. The minimum delay depended little on the duration of tonal impulses (with a frequency of 1 kHz) and was 0.3-0.7 ms; the maximum delay was 9-11 ms for tonal impulses with a duration of 3 ms and 37-40 ms with impulse duration 20 ms. The precedence effect became apparent at a greater delay for smooth fronts of impulses than for rectangular fronts.     

The sound signals of hawkmoths (Lepidoptera,sphingidae)

Temporal and frequency characteristics of the acoustic signals emitted by the pharyngeal sound apparatus were investigated in the hawkmoths, Acherontia atropos (L.), A. lachesis (F.), and Langia zenzeroides Moore. The sound signals of A. atropos consist of sequences of low- and high-amplitude series of clicks with different frequency spectra. In the other two species, the signals are emitted as sequences of uniform series of clicks. The dominant frequencies in the spectra are 7–10 kHz (A. lachesis), 13–20 kHz (A. atropos), and 35–47 kHz (L. zenzeroides). The defensive function of the pharyngeal signals is hypothesized.     

Geographic distribution of the Cross Seamount beaked whale based on acoustic detections

Beaked whales produce frequency-modulated echolocation pulses that appear to be species-specific, allowing passive acoustic monitoring to play a role in understanding spatio-temporal patterns. The Cross Seamount beaked whale is known only from its unique echolocation signal (BWC) with no confirmed species identification. This beaked whale spans the Pacific Ocean from the Mariana Archipelago to Baja California, Mexico, south to the equator, but only as far north as latitude 29°N. Within these warm waters, 92% of BWC detections occurred at night, 6% during crepuscular periods, and only 2% during daylight hours. Detections of BWC signals on drifting recorders with a vertical hydrophone array at 150 m depth demonstrated that foraging often occurred shallow in the water column (<150 m). No other species of beaked whale to date has been documented foraging in waters this shallow. Given their nocturnal, shallow foraging dives, this species appears to prefer prey that may be available in the water column only during those hours. The foraging behavior of Cross Seamount beaked whales appears to be unique among all beaked whales, and these findings contribute additional ecological and acoustic information which can help guide future efforts to identify this cryptic whale.     

Auditory brain stem responses in characterization of dolphin hearing

Summary Auditory brain stem responses (ABR) were recorded from the head surface of non-anesthetized and non-relaxed bottle-nosed dolphins, Tursiops truncatus. The region of best ABR recording was shown to be located 6–9 cm caudal to the blowhole. The threshold values were about 1 mPa for noise bursts and –3 dB re 1 mPa for tone bursts of the optimal frequency (80 kHz). The maximum frequency at which ABR could be evoked was 140 kHz. The duration of temporal summation reached 0.5 ms at intensities near the threshold and decreased with an increase in intensity. When the stimuli were paired clicks of the same intensity, the time to complete recovery from the second response was about 5 ms, while that to its 50% recovery was 0.7 ms. When the conditioning click exceeded the testing one in intensity, prolongation of the recovery period was observed. A 40-dB intensity difference led to an approximately 10-fold prolongation of this period.Abbreviations ABR auditory brain stem response - EP evoked potential     

Harbor porpoise (Phocoena phocoena) reactions to pingers

The use of acoustic alarms (pingers) has been mandated in several gill net fisheries around the world. Even though pingers have shown to reduce the incidental catch there are still questions to be answered in relation to effective range, habituation and displacement. In the present studies, the vocalization behavior of porpoises was recorded in response to two different pingers, AQUAmark100 (20–160 kHz) and AQUAmark300 (10 kHz). The Scottish experiment included an AQUAmark100 pinger running in on/off cycles. The pinger was placed in an array of acoustic click detectors (C‐PODs) spaced at different distances from the pinger. In Denmark, three experiments were conducted. One had the same AQUAmark100 pinger placed in a C‐POD array. The second and third experiment used an AQUAmark300 pinger running in on/off cycles. Both trial results of the AQUAmark100 revealed significant pinger reduction effects at 0, 200, and 400 m distance; however, the vocalization behavior reveal no signs of habituation. The studies of the AQUAmark300 revealed a significant pinger effect at 0 m distance and either none or 17% reduction at 300 m distance. At one station, however, habituation effects were found indicated by an increase in clicks over time. These results are important in relation to pinger use and thus fisheries management.     

Prey-Correlated Spectral Changes in Echolocation Sounds of the Indian False Vampire Megaderma lyra

False Vampires ( Megaderma lyra ) are gleaning bats which emit brief (1 ms) and faint echolocation signals consisting of four harmonics of a shallow frequency downward modulated fundamental (27–19 kHz). The complete signal spans a frequency range from 100 to 19 kHz. In sound recordings from three experimental animals we show that Megaderma lyra shifts the dominant frequency in the echolocation signals in relation to the type of prey offered and to flight style. During roaming flights the mean peak frequency was 63.2 ± 9 kHz (third harmonic). In prey catching flights, peak frequencies were shifted into the fourth harmonic. In flights towards a dish of crawling mealworms, mean peak frequency was raised to 91.2 ± 3.3 kHz. When the bats flew towards living mice the dominant frequency was further increased to 99.8 ± 5.2 kHz, and the second and third harmonic were at least 10 dB fainter or no longer recordable. The additional frequency shift when flying towards mice was not only a consequence of the dominance of the fourth harmonic but also of an additional rise of the fundamental harmonic by nearly 2 kHz. These prey-correlated frequency shifts in echolocation calls showed little variation between the three experimental animals and were reproducible over time. They occurred at or even before take-off of the bats. This is the first report of target-correlated transient adaptations in echolocation calls of any bat species.     

The relationship between the acoustic behaviour and surface activity of killer whales (<Emphasis Type="Italic">Orcinus orca</Emphasis>) that feed on herring (<Emphasis Type="Italic">Clupea harengus</Emphasis>)

We describe the acoustic behaviour of piscivorous killer whales in Norwegian and Icelandic waters. Whales were assigned to one of three activities (feeding, travelling or other), and sound recordings were made in their proximity with a single hydrophone and a digital audiotape (DAT) recorder. A quantitative analysis of the production of pulsed calls, whistles and echolocation clicks in the three activities revealed that there was a significant effect of activity on the production of these sound types. Both killer whales in Icelandic and Norwegian waters produced high rates of clicks and calls during feeding and low rates of click, calls and whistles during travelling. The differences can be used as acoustical markers and provides new possibilities for acoustic monitoring of killer whales in these areas. Based on the similarity between their prey choice, hunting strategies, phenotype and acoustic behaviour, we suggest that the killer whales in Icelandic and Norwegian waters belong to the same ecotype: Scandinavian herring-eating killer whales.     

Noise affects porpoise click detections – the magnitude of the effect depends on logger type and detection filter settings

Automatic click detectors and full-bandwidth sound recorders are widely used in passive acoustic monitoring of small cetaceans. Detection of these signals depends on a variety of factors, including signal to noise ratio. Passive acoustic monitoring is often used to study impact of underwater noise on small cetaceans, but as detection probability is affected by changes in signal to noise ratio, variable noise levels may affect conclusions drawn from these experiments. Therefore, we examine how different detectors and filters perform in varying ocean noise conditions. C-PODs and full-bandwidth recorders (Wildlife Acoustics, SM2M+) were deployed at two stations in an environment with fluctuating ambient noise for 42 days. Noise level and harbour porpoise (Phocoena phocoena) click trains simultaneously recorded on both loggers were compared. Overall, we found that porpoise click detections by the algorithm used to analyse full-band recorder data (Pamguard) paralleled detections by the C-POD. However, Pamguard detected significantly more clicks than the C-POD. A decrease in detections was seen for both loggers with increasing noise in the band 20 –160 kHz, in particular for levels above 100 dB re 1μPa rms. We also found that the Pamguard detection function changed the least over varying noise conditions when compared to the C-POD detectors. This study sheds light on the fact that inference of animal presence/absence or density that are based on echolocation cues (here, Porpoise Positive Minutes) shall account for the acoustic environments where probability of detecting signals may be affected by variability in ambient noise levels.     

Vibrational alarm communication in the damp-wood termite Zootermopsis nevadensis

Abstract. Vibrational alarm communication was studied in the New World, damp-wood termite Zootermopsis nevadensis (Isoptera: Termopsidae). Workers and soldiers react to disturbance such as sudden bright light or air currents by drumming their heads against the substratum. This drumming has been described as alarm signalling; its functional significance and perception by the nest mates, however, remained unclear. In the present study we analysed spectral and temporal properties and absolute amplitudes of the vibrational signals and used behavioural responses of the termites to determine the thresholds of the sense of vibration and to find out if and how the termites discriminate the conspecific alarm signals from the background noise.
The drumming signals are trains of pulses of vibrations of the substratum with a pulse repetition rate of about 20 Hz. The carrier frequency depends on the substratum; in the nests studied it was in the range 1–3 kHz. The highest vibrational amplitudes measured close to the signal emitters are usually about 10m/s² (acceleration, RMS). The threshold of the behavioural response is about 1m/s² over a wide range of frequencies (10 Hz to 5 kHz), indicating that the termites can detect these signals as vibrations of the substratum. The animals respond preferentially to temporal patterns similar those of the natural signals; temporal rather than spectral cues seem to be used for signal discrimination.