Echolocation Sounds Research Articles

Following a Foraging Fish-Finder: Diel Habitat Use of Blainville's Beaked Whales Revealed by Echolocation

Simultaneous high resolution sampling of predator behavior and habitat characteristics is often difficult to achieve despite its importance in understanding the foraging decisions and habitat use of predators. Here we tap into the biosonar system of Blainville's beaked whales, Mesoplodon densirostris, using sound and orientation recording tags to uncover prey-finding cues available to echolocating predators in the deep-sea. Echolocation sounds indicate where whales search and encounter prey, as well as the altitude of whales above the sea-floor and the density of organisms around them, providing a link between foraging activity and the bio-physical environment. Tagged whales (n = 9) hunted exclusively at depth, investing most of their search time either in the lower part of the deep scattering layer (DSL) or near the sea-floor with little diel change. At least 43% (420/974) of recorded prey-capture attempts were performed within the benthic boundary layer despite a wide range of dive depths, and many dives included both meso- and bentho-pelagic foraging. Blainville's beaked whales only initiate searching when already deep in the descent and encounter prey suitable for capture within 2 min of the start of echolocation, suggesting that these whales are accessing prey in reliable vertical strata. Moreover, these prey resources are sufficiently dense to feed the animals in what is effectively four hours of hunting per day enabling a strategy in which long dives to exploit numerous deep-prey with low nutritional value require protracted recovery periods (average 1.5 h) between dives. This apparent searching efficiency maybe aided by inhabiting steep undersea slopes with access to both the DSL and the sea-floor over small spatial scales. Aggregations of prey in these biotopes are located using biosonar-derived landmarks and represent stable and abundant resources for Blainville's beaked whales in the otherwise food-limited deep-ocean.

Bat recording under controlled conditions: A replicable chamber for comparable results

In ecology, bats have become a major subject of study. Some pollinate and disperse the seeds of many tropical plants; some help to control insect populations; a few affect livestock by sucking blood, but in all cases bats are indispensable links in ecosystems. Bats use of sound waves make echolocation calls monitoring a powerful tool for distribution, census, and present studies. This technique depends on having a reliable database of sounds for species identification purposes. Although there are several databases of echolocation sounds; the signal emitted by a bat depends on environmental conditions (vegetation, weather conditions), biotic factors (prey size, movement, defensive measures), and the specific task (seek, flee, pursue, evade, wandering, obstacle avoiding). This variability makes comparisons among databases difficult. A portable chamber made of common materials for in situ recording under controlled conditions is presented. The use of the chamber is proposed as a tool which might help to generate databases that could be reliable compared. Nine species of desert bats from the northwest region of Mexico were recorder using the chamber under controlled conditions and compared with field recordings. The performance of the chamber and the utility of the database generated for filed identification are presented.

Passive acoustic tracking of marine mammals and anthropogenic sound sources with autonomous three-dimensional small-aperture arrays

Marine mammals produce a wide range of frequency-modulated sounds at low and high frequencies as well as directional broadband echolocation sounds in a refractive ocean environment. This creates several challenges for passive acoustic long-term tracking of the various marine mammal species. To overcome these, three-dimensional small-aperture hydrophone arrays coupled to seafloor multi-channel recording packages were deployed in a large aperture array in the Southern California Bight. Taking advantage of the experimental setup in the oceanic waveguide, time and frequency-domain tracking methods will be presented and tracks of marine mammals as well as anthropogenic sources will be shown. This provides a tool to study over long timescales behavioral responses of tracked marine mammals to tracked anthropogenic sources.

Foraging and Public Information use in Common Pipistrelle Bats (Pipistrellus pipistrellus): A Field Experiment

Decision making by animals is likely to be influenced strongly by the behaviour of conspecifics. In this study we tested whether public information affected the foraging behaviour of common pipistrelles (Pipistrellus pipistrellus) by manipulating public information about the quality of foraging patches. Capture attempts during foraging are revealed by terminal buzzes, which are a potential source of public information about prey abundance for other foraging bats. We tested whether the estimation of food patch quality was affected by the number of terminal buzzes emitted by conspecifics. We conducted an experiment at 12 different locations in an urban habitat in the Netherlands. At each location we played back recordings of echolocation sounds of hunting bats with different terminal buzz rates and scored the bat activity. No significant differences between treatments were found. Our results do not support the hypothesis that bat activity increases in response to an increase in simulated terminal buzzes, suggesting that public information does not influence the choice of foraging patches in P. pipistrellus. We propose that P. pipistrellus does not use this kind of information because of either the high reliability of personal information or of the low collection costs associated with personal information.

Paradoxical reference frequency shifts during paired flights in Japanese horseshoe bats evaluated with a Telemike.

In order to examine vocal behaviors for the echolocating bats to improve extraction of jammed echolocation signals, group flight experiments were conducted where two Japanese horseshoe bats were flown simultaneously in a flight chamber. Horseshoe bats are known to conduct Doppler-shift compensation, keeping their echo CF2 frequency constant to which their auditory system is sharply tuned. It was hypothesized that bats shifted their reference frequencies apart to avoid overlapping the reference frequencies. Echolocation sounds during sequential flights were recorded with an onboard wireless microphone, Telemike. Reference frequencies were investigated by measuring Doppler-shift compensated CF2 frequencies of the bats’ own echoes. Recorded data show that the bats kept their echo CF2 frequency constant with a standard deviation (SD) of 50–80 Hz, indicating that they exhibited Doppler-shift compensation with the same accuracy as that used for flying alone (SD = 83.2 Hz). However, the bats did not shift their reference frequency toward increasing the frequency difference even when the initial difference in the reference frequencies between individuals was less than 100 Hz. Rather, the bats tended to make their reference frequencies closer during group flight compared to those for single flights. These findings suggest that multiple bats may squeeze their echo CF2 frequencies into a narrow frequency range. In addition, horseshoe bats may adapt to acoustic interference without expanding the frequency difference between individuals. [Work supported by ONR grant.]

Echolocation behavior of pairs of flying Eptesicus fuscus recorded with a Telemike microphone.

Four big brown bats (Eptesicus fuscus) were flown singly and in pairs in a room containing a sparse array of vertically hanging plastic chains as obstacles. Each bat carried a lightweight radio telemetry microphone (Telemike) that recorded their emitted echolocation sounds without artifacts from Doppler shifts, directional effects, and atmospheric attenuation. The broadcasts of both bats were also recorded with two stationary ultrasonic microphones located at the far end of the flight room. The echolocation broadcasts of bats flying singly were compared to those emitted when the bats were flown together. The principal change was shifting of harmonic frequencies very slightly (<5 kHz) away from each other and from frequencies used when flying alone. In contrast, the duration of emissions was more stable between single and double bat flights. Changes in ending frequency have been associated with a jamming avoidance response in big brown bats and could indicate attempts to avoid interference while flying with conspecifics in an enclosed space. [Work supported by ONR and NSF.]

A bony connection signals laryngeal echolocation in bats

Echolocation is an active form of orientation in which animals emit sounds and then listen to reflected echoes of those sounds to form images of their surroundings in their brains. Although echolocation is usually associated with bats, it is not characteristic of all bats. Most echolocating bats produce signals in the larynx, but within one family of mainly non-echolocating species (Pteropodidae), a few species use echolocation sounds produced by tongue clicks. Here we demonstrate, using data obtained from micro-computed tomography scans of 26 species (n = 35 fluid-preserved bats), that proximal articulation of the stylohyal bone (part of the mammalian hyoid apparatus) with the tympanic bone always distinguishes laryngeally echolocating bats from all other bats (that is, non-echolocating pteropodids and those that echolocate with tongue clicks). In laryngeally echolocating bats, the proximal end of the stylohyal bone directly articulates with the tympanic bone and is often fused with it. Previous research on the morphology of the stylohyal bone in the oldest known fossil bat (Onychonycteris finneyi) suggested that it did not echolocate, but our findings suggest that O. finneyi may have used laryngeal echolocation because its stylohyal bones may have articulated with its tympanic bones. The present findings reopen basic questions about the timing and the origin of flight and echolocation in the early evolution of bats. Our data also provide an independent anatomical character by which to distinguish laryngeally echolocating bats from other bats.

Echolocation sounds of hourglass dolphins (Lagenorhynchus cruciger) are similar to the narrow band high-frequency echolocation sounds of the dolphin genus Cephalorhynchus

Echolocation sounds of hourglass dolphins (Lagenorhynchus cruciger) are similar to the narrow band high-frequency echolocation sounds of the dolphin genus Cephalorhynchus

Role of broadcast harmonics in echo delay perception by big brown bats

Big brown bats (Eptesicus fuscus) emit frequency-modulated (FM) echolocation sounds containing two principal down-sweeping harmonics (FM(1) approximately 55-25 kHz, FM(2) approximately 105-50 kHz). To determine whether each harmonic contributes to perception of echo delay, bats were trained to discriminate between "split-harmonic" echoes that differed in delay. The bat's broadcasts were picked up with microphones, and FM(1) and FM(2) were separated with highpass and lowpass filters at about 55 kHz, where they overlap in frequency. Both harmonics then were delivered from loudspeakers as positive stimuli in a 2-choice delay discrimination procedure with FM(1) delayed 3.16 ms and FM(2) delayed 3.46 ms (300 mus delay split). Negative stimuli contained FM(1) and FM(2) with the same filtering but no delay separation. These were presented at different overall delays from 11 down to 3 ms to measure the bat's delay discrimination acuity for each harmonic in the split harmonic echoes. The bats determined the delays of both FM(1) and FM(2), but performance was overlaid by a broad pedestal of poor performance that extended for 800 micros. Splitting the harmonics by 300 micros appears to defocus the bat's representation of delay, revealing the existence of a process for recognizing the normally simultaneous occurrence of the harmonics.

Adaptive echolocation sounds of insectivorous bats, Pipistrellus abramus, during foraging flights in the field

Echolocation pulses emitted by wild Pipistrellus abramus were investigated while foraging for insects in the field. Similar to other European pipistrelles, the frequency structure during foraging varied. During the search phase, the bats emitted long shallow frequency-modulated pulses 9-11 ms in duration, whereas the maximum pulse duration of the bats approaching a large target wall in the laboratory was 3 ms. No significant difference was observed between decreases in the interpulse interval during these two approach flights. It is concluded that the bats use a long quasi-constant frequency pulse to find a weak echo from a small prey target.

Morphology of the melon and its tendinous connections to the facial muscles in bottlenose dolphins (Tursiops truncatus)

The melon is a lipid-rich structure located in the forehead of odontocetes that functions to propagate echolocation sounds into the surrounding aquatic environment. To date, the melon's ability to guide and impedance match biosonar sounds to seawater has been attributed to its unique fatty acid composition. However, the melon is also acted upon by complex facial muscles derived from the m. maxillonasolabialis. The goal of this study was to investigate the gross morphology of the melon in bottlenose dolphins (Tursiops truncatus) and to describe how it is tendinously connected to these facial muscles. Standard gross dissection (N = 8 specimens) and serial sectioning (N = 3 specimens) techniques were used to describe the melon and to identify its connections to the surrounding muscles and blubber in three orthogonal body planes. The dolphin forehead was also thin-sectioned in three body planes (N = 3 specimens), and polarized light was used to reveal the birefringent collagen fibers within and surrounding the melon. This study identified distinct regions of the melon that vary in shape and display locally specific muscle-tendon morphologies. These regions include the bilaterally symmetric main body and cone and the asymmetric right and left caudal melon. This study is the first to identify that each caudal melon terminates in a lipid cup that envelopes the echolocation sound generators. Facial muscles of the melon have highly organized tendon populations that traverse the melon and insert into either the surrounding blubber, the connective tissue matrix of the nasal plug, or the connective tissue sheath surrounding the sound generators. The facial muscles and tendons also lie within multiple orthogonal body planes, which suggest that the melon is capable of complex shape change. The results of this study suggest that these muscles could function to change the frequency, beam width, and directionality of the emitted sound beam in bottlenose dolphins. The echolocation sound propagation pathway within the dolphin forehead appears to be a tunable system.

Narrow band high frequency clicks from Hourglass dolphins (Lagenorhynchus cruciger)

The source properties of toothed whale echolocation clicks are essential for evaluating the performance of biosonar systems. However, such data only exist for a small number of free ranging toothed whale species. Here we present a quantitative analysis of the first recordings of echolocation sounds from hour glass dolphins (Lagenorhynchus cruciger) made in the Drake Strait. Recordings were made with a vertical array of four broad‐band, calibrated hydrophones that allows for acoustic localization and source parameter derivation. Only apparent on‐axis clicks were used for analysis. Hour glass dolphins produce clicks with a mean peak and centroid frequency around 128kHz, a narrow, mean RMS bandwidth of 10kHz with no energy below 100kHz and a mean signal duration of 161μs. Echolocation clicks of hour glass dolphins are thus of the high frequency narrow band‐width type (NBHF type) found in porpoises, a few delphinids of the Cephalorhynchus genus and the pygmy sperm whale Kogia breviceps, but are strikingly different from other dolphins. Acoustic convergence from vastly different genera and ecotypes suggest that evolution of NBHF clicks are adaptations to special auditory processing or acoustic crypsis rather than to habitat.

Temporal patterns in the acoustic signals of beaked whales at Cross Seamount

Seamounts may influence the distribution of marine mammals through a combination of increased ocean mixing, enhanced local productivity and greater prey availability. To study the effects of seamounts on the presence and acoustic behaviour of cetaceans, we deployed a high-frequency acoustic recording package on the summit of Cross Seamount during April through October 2005. The most frequently detected cetacean vocalizations were echolocation sounds similar to those produced by ziphiid and mesoplodont beaked whales together with buzz-type signals consistent with prey-capture attempts. Beaked whale signals occurred almost entirely at night throughout the six-month deployment. Measurements of prey presence with a Simrad EK-60 fisheries acoustics echo sounder indicate that Cross Seamount may enhance local productivity in near-surface waters. Concentrations of micronekton were aggregated over the seamount in near-surface waters at night, and dense concentrations of nekton were detected across the surface of the summit. Our results suggest that seamounts may provide enhanced foraging opportunities for beaked whales during the night through a combination of increased productivity, vertical migrations by micronekton and local retention of prey. Furthermore, the summit of the seamount may act as a barrier against which whales concentrate prey.

1P10-2 Active ultrasonic SONAR system of bat : Relationship between 3-D flight path and acoustical characteristics of echolocation sounds during foraging(Poster Session)

1P10-2 Active ultrasonic SONAR system of bat : Relationship between 3-D flight path and acoustical characteristics of echolocation sounds during foraging(Poster Session)

Echo-intensity compensation in echolocating bats (Pipistrellus abramus) during flight measured by a telemetry microphone

An onboard microphone (Telemike) was developed to examine changes in the basic characteristics of echolocation sounds of small frequency-modulated echolocating bats, Pipistrellus abramus. Using a dual high-speed video camera system, spatiotemporal observations of echolocation characteristics were conducted on bats during a landing flight task in the laboratory. The Telemike allowed us to observe emitted pulses and returning echoes to which the flying bats listened during flight, and the acoustic parameters could be precisely measured without traditional problems such as the directional properties of the recording microphone and the emitted pulse, or traveling loss of the sound in the air. Pulse intensity in bats intending to land exhibited a marked decrease by 30 dB within 2 m of the target wall, and the reduction rate was approximately 6.5 dB per halving of distance. The intensity of echoes returning from the target wall indicated a nearly constant intensity (-42.6 +/- 5.5 dB weaker than the pulse emitted in search phase) within a target distance of 2 m. These findings provide direct evidence that bats adjust pulse intensity to compensate for changes in echo intensity to maintain a constant intensity of the echo returned from the approaching target at an optimal range.

Neural responses of inferior colliculus to echolocation sounds in Japanese house bat ( Pipistrellus abramus)

Neural responses of inferior colliculus to echolocation sounds in Japanese house bat ( Pipistrellus abramus)

Depth/range localization of diving sperm whales using passive acoustics on a single hydrophone disregarding seafloor reflections

Depth and range of sound sources can be estimated using a single hydrophone. Such a passive acoustic technique requires the detection of direct path transmitted, sea surface, and seafloor reflected source signals, so as to measure their time of arrival differences (TOADs). Sperm whales almost continuously emit powerful, directional echolocation sounds (usual clicks) when diving. Sperm whales often dive in deep water, and click seafloor reflections are usually well detected only at the beginning of the dive. Surface echoes may be detected during the entire dive. If the measurement of the surface reflection TOAD of a single click is not enough for estimating the depth/range of the sperm whale at the time when this click was emitted, the joint consideration of delays emitted during the whole dive may provide this estimation. Such delays are indeed the measurements of a single phenomenon: the underwater movements of a single-clicking sperm whale. One can merge such data using a Bayesian technique, as well as use prior information (e.g., range when fluking-up). Such a method could make the single-hydrophone localization technique usable regardless of the properties of the sea bottom, e.g., in deep or high relief areas.

Doppler-shift compensation in the Taiwanese leaf-nosed bat (Hipposideros terasensis) recorded with a telemetry microphone system during flight

Biosonar behavior was examined in Taiwanese leaf-nosed bats (Hipposideros terasensis; CF-FM bats) during flight. Echolocation sounds were recorded using a telemetry microphone mounted on the bat's head. Flight speed and three-dimensional trajectory of the bat were reconstructed from images taken with a dual high-speed video camera system. Bats were observed to change the intensity and emission rate of pulses depending on the distance from the landing site. Frequencies of the dominant second harmonic constant frequency component (CF2) of calls estimated from the bats' flight speed agreed strongly with observed values. Taiwanese leaf-nosed bats changed CF2 frequencies depending on flight speed, which caused the CF2 frequencies of the Doppler-shifted echoes to remain constant. Pulse frequencies were also estimated using echoes returning directly ahead of the bat and from its sides for two different flight conditions: landing and U-turn. Bats in flight may periodically alter their attended angles from the front to the side when emitting echolocation pulses.

Male sperm whale acoustic behavior observed from multipaths at a single hydrophone

Sperm whales generate transient sounds (clicks) when foraging. These clicks have been described as echolocation sounds, a result of having measured the source level and the directionality of these signals and having extrapolated results from biosonar tests made on some small odontocetes. The authors propose a passive acoustic technique requiring only one hydrophone to investigate the acoustic behavior of free-ranging sperm whales. They estimate whale pitch angles from the multipath distribution of click energy. They emphasize the close bond between the sperm whale's physical and acoustic activity, leading to the hypothesis that sperm whales might, like some small odontocetes, control click level and rhythm. An echolocation model estimating the range of the sperm whale's targets from the interclick interval is computed and tested during different stages of the whale's dive. Such a hypothesis on the echolocation process would indicate that sperm whales echolocate their prey layer when initiating their dives and follow a methodic technique when foraging.

Prey detection by bottlenose dolphins, Tursiops truncatus: an experimental test of the passive listening hypothesis

Bottlenose dolphins possess a sophisticated echolocation system, but evidence suggests that they use this sensory modality sparingly in the wild. Several authors have noted that soniferous fish are prevalent in the diet of bottlenose dolphins, leading to the hypothesis that these predators detect their prey by passive listening. We tested this hypothesis by performing controlled acoustic playback experiments with free-ranging dolphins in Sarasota Bay, Florida. We used recorded calls of prey fish and sounds of snapping shrimp as experimental and control treatments, respectively, and measured the dolphins' direction of travel and rate of echolocation as response variables. Dolphins changed their direction of travel significantly, turning towards the sound source when fish sounds were played. In addition, dolphins significantly increased their rate of echolocation immediately following playbacks of fish sounds. The sounds of snapping shrimp elicited neither directional nor echolocation responses. The occurrence of echolocation sounds was low, except following playback of fish sounds. We conclude that bottlenose dolphins use passive listening extensively during the search phase of the foraging process. By listening passively, dolphins may obtain useful information on the identity, number, size and location of soniferous prey. Once dolphins discover prey by passive means, they then appear to use echolocation to track the prey during the pursuit and capture phases. Such judicious use of echolocation suggests that this sensory modality incurs significant energetic or ecological costs. These findings have implications for coevolution of dolphins and their prey with regard to sound production and detection.