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PubMed1997

The combination of echolocation emission and ear reception enhances directional spectral cues of the big brown bat, Eptesicus fuscus.

The acoustic information used by bats is produced by a combination of the properties of the sound emission and the reception at the eardrum. The potential localization cues used by bats can only be fully revealed when the magnitude spectra of the emission and the external ear are convolved to produce the echolocation combination magnitude spectra. The spatially dependent changes in the magnitude spectra of the echolocation combination of Eptesicus fuscus are described. The emission and external ear magnitude spectra act together to enhance the potential localization cues. In the echolocation combination, the spectral peaks are sharpened and there is greater contrast in intensity between peaks and notches when compared to the spectra of the ear alone. The spectral localization cues in the echolocation combination appear to be restricted to a cone of space of approximately +/-30 degrees.

Animals↗
PubMed1997

Echolocation signals of the greater horseshoe bat (Rhinolophus ferrumequinum) in transfer flight and during landing.

Echolocation signals of horseshoe bats (Rhinolophidae) consist of a relatively long component of constant frequency (CF) which is preceded by an initial frequency-modulated (iFM) component and followed by a terminal frequency-modulated (tFM) component. To examine the role of these components in echolocation, four bats were trained to fly from a perch to a landing bar. A dual camera system allowed reconstruction of the flight paths in three dimensions. Echolocation signals were recorded, analyzed, and correlated with the flight behavior of the bats. It was confirmed that during flight the bats compensate the Doppler shifts which are produced by their own flight movement. In free flight they emit per wing beat one single signal of long duration, with little variation in the three signal components. In approach flight the bats reduce pulse duration and interval with decreasing target range. The iFM is not varied with respect to target range, suggesting that this component plays little role in the processing of echolocating a target of interest. The bandwidth of the tFM component is increased while its duration is shortened in proportion to decreasing target range, so that the signal-echo overlap of the FM component is avoided down to a target distance of 15 cm. These concurrent changes suggest that the tFM component is used for ranging. During the last 60 cm of the approach the bats compensated for the increase of echo SPL by lowering the emission level of the CF component by 6-9 dB and that of the tFM component by 9-11 dB per halving of range. The specific signal structure of horseshoe bats is discussed as an adaptation for the hunting of fluttering insects in highly cluttered environments.

Animals↗
PubMed1998

Phantom echo generation: a new technique for investigating dolphin echolocation.

In behavioral experiments where real targets are used to investigate dolphin echolocation, it is often very difficult to extract the relevant echo parameters that the animals use to discriminate or classify. The complex relationship between the physical dimensions and the reflection characteristic of real targets prevents separate control of various echo parameters of the stimuli presented in an echolocation experiment. A new echo simulation method presented in this paper avoids this problem. Dolphin echolocation sounds are transformed with the target impulse response into artificial echoes, which are played back to the animal. The phantom echo system is implemented on a digital signal processing board and gives an experimenter fully programmable control over the echo generating process and the echo structure itself. Echoes of several underwater targets were simulated to evaluate the quality of the method. A comparison of simulated echoes with the original echoes demonstrated very good agreement independent of the incident signal (cross-correlation coefficient > 0.95). The method has tremendous potential for investigating animal echolocation and understanding biosonar signal processing.

Acoustic Stimulation↗
PubMed1999

Target detection by an echolocating harbor porpoise (Phocoena phocoena).

Two echolocation experiments are described. They were conducted on the same harbor porpoise housed in a sea pen, one year apart at Neeltje Jans, The Netherlands. The aims were to determine the target detection ability of an echolocating harbor porpoise, with the ultimate goal to predict the distance at which harbor porpoises can detect fishing nets. In experiment 1, the maximum distance at which the 3-year-old porpoise could detect a 7.62-cm diameter water-filled stainless-steel sphere by echolocation was determined psychophysically. The 50%-current detection threshold was reached when the sphere was at a distance of 26 m from the porpoise's rostrum. In experiment 2, conducted a year later, the maximum detection distance for a 5.08-cm water-filled stainless-steel sphere was 15.9 m. The target strengths of both targets were measured using simulated harbor porpoise echolocation signals and the results, coupled with transmission-loss calculations, indicated that the echo levels received by the porpoise with the targets at the threshold ranges in the two experiments were only 1.3 dB apart. Together with information on the target strengths of various fishing nets, the results of the present study can be used to predict the distance at which the nets can be detected by harbor porpoises.

Animals↗
PubMed1999

Classification of dolphin echolocation clicks by energy and frequency distributions.

Dolphins demonstrate an adaptive control over echolocation click production, but little is known of the manner or degree with which control is exercised. Echolocation clicks (N approximately 30,000) were collected from an Atlantic bottlenose dolphin (Tursiops truncatus) performing object discrimination tasks in order to investigate differential click production. Seven categories of clicks were identified using the spectral conformation and relative position of -3 and -10 dB peaks. A counterpropagation network utilizing 16 inputs, 50 hidden units, and 8 output units was trained to classify clicks using the same spectral variables. The network classified novel clicks with 92% success. Additional echolocation clicks (N > 24,000) from two other dolphins were submitted to the network for classification. Classified echolocation clicks were analyzed for animal specific differences, changes in predominant click type within click trains, and task-related specificity. Differences in animal and task performance may influence click type and click train length.

Animals↗
PubMed2000

Why pinnipeds don't echolocate.

Odontocete cetaceans have evolved a highly advanced system of active biosonar. It has been hypothesized that other groups of marine animals, such as the pinnipeds, possess analogous sound production, reception, and processing mechanisms that allow for underwater orientation using active echolocation. Despite sporadic investigation over the past 30 years, the accumulated evidence in favor of the pinniped echolocation hypothesis is unconvincing. We argue that an advanced echolocation system is unlikely to have evolved in pinnipeds primarily because of constraints imposed by the obligate amphibious functioning of the pinniped auditory system. As a result of these constraints, pinnipeds have not developed highly acute, aquatic, high frequency sound production or reception systems required for underwater echolocation. Instead, it appears that pinnipeds have evolved enhanced visual, tactile, and passive listening skills. The evolutionary refinement of alternative sensory systems allows pinnipeds to effectively forage, navigate, and avoid predators under water despite the lack of active biosonar capabilities.

Animals↗
PubMed2000

Vocal control of acoustic information for sonar discriminations by the echolocating bat, Eptesicus fuscus.

This study aimed to determine whether bats using frequency modulated (FM) echolocation signals adapt the features of their vocalizations to the perceptual demands of a particular sonar task. Quantitative measures were obtained from the vocal signals produced by echolocating bats (Eptesicus fuscus) that were trained to perform in two distinct perceptual tasks, echo delay and Doppler-shift discriminations. In both perceptual tasks, the bats learned to discriminate electronically manipulated playback signals of their own echolocation sounds, which simulated echoes from sonar targets. Both tasks utilized a single-channel electronic target simulator and tested the bat's in a two-alternative forced choice procedure. The results of this study demonstrate changes in the features of the FM bats' sonar sounds with echolocation task demands, lending support to the notion that this animal actively controls the echo information that guides its behavior.

Animals↗
PubMed1999

Single cortical neurons serve both echolocation and passive sound localization.

The pallid bat uses passive listening at low frequencies to detect and locate terrestrial prey and reserves its high-frequency echolocation for general orientation. While hunting, this bat must attend to both streams of information. These streams are processed through two parallel, functionally specialized pathways that are segregated at the level of the inferior colliculus. This report describes functionally bimodal neurons in auditory cortex that receive converging input from these two pathways. Each brain stem pathway imposes its own suite of response properties on these cortical neurons. Consequently, the neurons are bimodally tuned to low and high frequencies, and respond selectively to both noise transients used in prey detection, and downward frequency modulation (FM) sweeps used in echolocation. A novel finding is that the monaural and binaural response properties of these neurons can change as a function of the sound presented. The majority of neurons appeared binaurally inhibited when presented with noise but monaural or binaurally facilitated when presented with the echolocation pulse. Consequently, their spatial sensitivity will change, depending on whether the bat is engaged in echolocation or passive listening. These results demonstrate that the response properties of single cortical neurons can change with behavioral context and suggest that they are capable of supporting more than one behavior.

Animals↗
PubMed2004

Echolocation signal structure in the Megachiropteran bat Rousettus aegyptiacus Geoffroy 1810.

Rousettus aegyptiacus Geoffroy 1810 is a member of the only genus of Megachiropteran bats to use vocal echolocation, but the structure of its brief, click-like signal is poorly described. Although thought to have a simple echolocation system compared to that of Microchiroptera, R. aegyptiacus is capable of good obstacle avoidance using its impulse sonar. The energy content of the signal was at least an order of magnitude smaller than in Microchiropteran bats and dolphins (approximately 4 x 10(-8) J m(-2)). Measurement of the duration, amplitude and peak frequency demonstrate that the signals of this animal are broadly similar in structure and duration to those of dolphins. Gabor functions were used to model signals and to estimate signal parameters, and the quality of the Gabor function fit to the early part of the signal demonstrates that the echolocation signals of R. aegyptiacus match the minimum spectral spread for their duration and amplitude and are thus well matched to its best hearing sensitivity. However, the low energy content of the signals and short duration should make returning echoes difficult to detect. The performance of R. aegyptiacus in obstacle avoidance experiments using echolocation therefore remains something of a conundrum.

Animals↗
PubMed2005

Spatial orientation in echolocating harbour porpoises (Phocoena phocoena).

Studies concerning the echolocation behaviour of odontocetes focus mainly on target detection and discrimination, either in stationary animals or in animals approaching a specific target. We present the first data on the use of echolocation for spatial orientation or navigation. Synchronised video and high-frequency recordings were made of two harbour porpoises trained to swim from one position to another across an outdoor pool in order to correlate swimming and echolocation behaviour. Both porpoises showed a clear range-locking behaviour on specific positions near the end of the pool, as indicated by a decrease in click interval with decreasing distance. The decrease in click interval followed the two-way-transit time, which is the time interval between the outgoing click and the received echo from the focal object. This suggests that the porpoises used focal objects as landmarks. The lag time, defined as the time between the arrival of an echo from a landmark and the emission of the next click, was task specific. The lag time was longer for difficult tasks (26-36 ms) and shorter for simpler tasks (14-19 ms), with some individual differences between the two animals. Our results suggest that echolocation by odontocetes is used not only for target detection, localisation and classification but also for spatial orientation.

Animals↗
PubMed1994

Jamming bat echolocation: the dogbane tiger moth Cycnia tenera times its clicks to the terminal attack calls of the big brown bat Eptesicus fuscus.

Certain tiger moths emit high-frequency clicks to an attacking bat, causing it to break off its pursuit. The sounds may either orient the bat by providing it with information that it uses to make an attack decision (aposematism) or they may disorient the bat by interrupting the normal flow of echo information required to complete a successful capture (startle, jamming). At what point during a bat's attack does an arctiid emit its clicks? If the sounds are aposematic, the moth should emit them early in the attack echolocation sequence in order to allow the bat time to understand their meaning. If, however, the sounds disrupt the bat's echo-processing behaviour, one would expect them to be emitted later in the attack to maximize their confusion effects. To test this, we exposed dogbane tiger moths (Cycnia tenera) to a recording of the echolocation sequence emitted by a big brown bat (Eptesicus fuscus) as it attacked a stationary target. Our results demonstrate that, at normal echolocation intensities, C. tenera does not respond to approach calls but waits until the terminal phase of the attack before emitting its clicks. This timing is evident whether the moth is stationary or flying and is largely independent of the intensity of the echolocation calls. These results support the hypothesis of a jamming effect (e.g. 'phantom echoes') and suggest that, to determine experimentally the effects of arctiid clicks on bats, it is important that the bats be tested under conditions that simulate the natural context in which this defence operates.

Acoustics↗
PubMed2002

[Echolocation sound waves, morphological features and foraging strategies in Hipposideros pratti].

Studies on the echolocation sound waves in different states (flying and hanging), morphological features and ecological processes (foraging strategies, foraging habitat and diet type) of Hipposideros pratti showed that H. pratti had CF (constant frequency)-FM (frequency modulated) echolocation sounds. There were some differences in dominant frequency (caused by Doppler compensating effect), pulse repetition rate, pulse duration and interpulse interval between the bats at flying and hanging. The dominant frequency, FM bandwidth, pulse duration and interpulse interval were lower, while the pulse repetition rate and duty cycle were higher at flying than at hanging. All the differences indicated that H. pratti could adopt specific echolocation sounds to adapt to specific environments and conditions to detect, approach and capture their preys successfully. On the basis of echolocation sound and field observation, it was concluded that H. pratti might search the preys at flying in the period of insect fastigium, and after the period, it might search the targets at hanging. The foraging habitat was near the tree crowns, and the preys consisted mainly of relatively large insects, such as beetles.

Animals↗
PubMed2002

The object behind the echo: dolphins (Tursiops truncatus) perceive object shape globally through echolocation.

Two experiments tested a bottlenosed dolphin's ability to match objects across echolocation and vision. Matching was tested from echolocation sample to visual alternatives (E-V) and from visual sample to echolocation alternatives (V-E). In Experiment 1, the dolphin chose a match from among three-alternative objects that differed in overall (global) shape, but shared several 'local' features with the sample. The dolphin conducted a right-to-left serial nonexhaustive search among the alternatives, stopping when a match was encountered. It matched correctly on 93% of V-E trials and on 99% of E-V trials with completely novel combinations of objects despite the presence of many overlapping features. In Experiment 2, a fourth alternative was added in the form of a paddle that the dolphin could press if it decided that none of the three-alternatives matched the sample. When a match was present, the dolphin selected it on 94% of V-E trials and 95% of E-V trials. When a match was absent, the dolphin pressed the paddle on 74% and 76%, respectively, of V-E and E-V trials. The approximate 25% error rate, which consisted of a choice of one of the three non-matching alternatives in lieu of the paddle press, increased from right to center to left alternative object, reflecting successively later times in the dolphin's search path. A weakening in memory for the sample seemed the most likely cause of this error pattern. Overall, the results gave strong support to the hypothesis that the echolocating dolphin represents an object by its global appearance rather than by local features.

Journal Article↗
PubMed2005

Neurobiological specializations in echolocating bats.

Although the bat's nervous system follows the general mammalian plan in both its structure and function, it has undergone a number of modifications associated with flight and echolocation. The most obvious neuroanatomical specializations are seen in the cochleas of certain species of bats and in the lower brainstem auditory pathways of all microchiroptera. This article is a review of peripheral and central auditory neuroanatomical specializations in echolocating bats. Findings show that although the structural features of the central nervous system of echolocating microchiropteran bats are basically the same as those of more generalized mammals, certain pathways, mainly those having to do with accurate processing of temporal information and auditory control of motor activity, are hypertrophied and/or organized somewhat differently from those same pathways in nonecholocating species. Through the resulting changes in strengths and timing of synaptic inputs to neurons in these pathways, bats have optimized the mechanisms for analysis of complex sound patterns to derive accurate information about objects in their environment and direct behavior toward those objects.

Animals↗
PubMed1994

Substrate-gleaning versus aerial-hawking: plasticity in the foraging and echolocation behaviour of the long-eared bat, Myotis evotis.

The foraging and echolocation behaviour of Myotis evotis was investigated during substrate-gleaning and aerial-hawking attacks. Bats gleaned moths from both the ground and a bark-covered trellis, however, they were equally adept at capturing flying moths. The calls emitted by M. evotis during substrate-gleaning sequences were short, broadband, and frequency-modulated (FM). Three behavioural phases were identified: search, hover, and attack. Gleaning search calls were significantly longer in duration, lower in highest frequency, and larger in bandwidth than hover/attack calls. Calls were detected in only 68% of gleaning sequences, and when they were emitted, bats ceased calling approximately 200 ms before attacking. Terminal feeding buzzes, the rapid increase in pulse repetition rate associated with an attempted prey capture, were never recorded during gleaning attacks. The echolocation calls uttered by M. evotis during aerial-hawking foraging sequences were also short duration, high frequency, FM calls. Two distinct acoustic phases were identified: approach and terminal. Approach calls were significantly different from terminal calls in all variables measured. Calls were detected in 100% of aerial-hawking attacks and terminal feeding buzzes were invariably produced. Gleaning hover/attack calls were spectrally similar to aerial approach calls, but were shorter in duration and emitted at a significantly lower (but constant) repetition rate than aerial signals. Although the foraging environment (flight cage contents) remained unchanged between tasks (substrate-gleaning vs. aerial-hawking), bats emitted significantly lower amplitude calls while gleaning. We conclude that M. evotis adjusts its echolocation behaviour to meet the perceptual demands (acoustical constraints) imposed by each foraging situation.

Animals↗
PubMed1991

Discrimination of wingbeat motion by bats, correlated with echolocation sound pattern.

Bats of the species Rhinolophus rouxi, Hipposideros lankadiva and Eptesicus fuscus were trained to discriminate between two simultaneously presented artificial insect wingbeat targets moving at different wingbeat rates. During the discrimination trials, R. rouxi, H. lankadiva and E. fuscus emitted long-CF/FM, short-CF/FM and FM echolocation sounds respectively. R. rouxi, H. lankadiva and E. fuscus were able to discriminate a difference in wingbeat rate of 2.7 Hz, 9.2 Hz and 15.8 Hz, respectively, between two simultaneously presented targets at an absolute wingbeat rate of 60 Hz, using a criterion of 75% correct responses. The performance of the different bat species is correlated with the echolocation signal design used by each species, particularly with the presence and relative duration of a narrowband component preceding a broadband FM component. These results provide behavioral evidence supporting the hypothesis that bats that use CF/FM echolocation sounds have adaptations for the perception of insect wingbeat motion and that long-CF/FM species are more specialized for this task than short CF/FM species.

Animals↗
PubMed1989

A comparison of signal detection between an echolocating dolphin and an optimal receiver.

An electronic simulated target apparatus was used in a two-experiment study to compare the target detection performance of an echolocating bottlenose dolphin with an optimal receiver. Random Gaussian noise with a relatively flat spectrum from 20 to 160 kHz was used as a masking source. Experiment I was conducted to establish a technique for estimating the echo energy-to-noise ratio, Ee/N, at the dolphin's threshold of detection. Dolphins typically vary the amplitude of their emitted signal over a large range making it difficult to estimate Ee/N. In the first part of experiment I, the simulated echo was a double click, the pulses separated by 200 microseconds, with each pulse being a replica of the dolphin's transmitted signal. A staircase psychophysical procedure was used to obtain the detection threshold, and the echo energy-to-noise ratio based on the highest amplitude click emitted per trial, (Ee/N)max, was determined at each reversal point. The second echo type consisted of one of the animal's echolocation clicks, previously measured, digitized and stored in an erasable programmable read-only memory (EPROM). The electronic target simulator was modified so that every time the dolphin emitted an echolocation signal, the EPROM was triggered to produce two pulses separated by 200 microseconds. On any trial, the EPROM signal was played back at a fixed amplitude, regardless of the amplitude of the dolphin's emitted signal. The Ee/N obtained with the EPROM signal at threshold was found to be 2.9 dB lower than (Ee/N)max obtained with the normal phantom target. Therefore an estimate of Ee/N can be obtained by subtracting 2.9 dB from (Ee/N)max.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2003

Vision complements echolocation in an aerial-hawking bat.

The northern bat Eptesicus nilssonii normally hunts flying insects in the air using frequency-modulated echolocation calls. It is also known to detect and catch visually conspicuous prey (white moths) hovering low among grass stalks. To overcome the problem with acoustic clutter from the grass, which interferes with target echo detection, the bats make use of visual cues in addition to those of echolocation. We therefore investigated the minimum size of prey that the bats could distinguish by using vision, by presenting the bats with different sized dead and spread moths. We found that vision increased the chance of detection only when the moths had a wingspan of at least 5 cm. Smaller targets were detected using echolocation alone. The mean detection range was 3.5 m, suggesting that the bats need a visual acuity of 49' of arc to detect the prey. This is consistent with results of optomotor response tests and counts of retinal ganglion cells in closely related species. Our results suggest that the visual acuity of Eptesicus bats may not be adequate for prey detection under normal conditions, but that the bats can use vision when the prey is unusually large and conspicuous. The northern bats display a flexibility in prey detection techniques not previously recognised among aerial-hawking bats and they are able to use their full visual capacity in the field.

Animals↗