Hans-Ulrich Schnitzler

From spatial orientation to food acquisition in echolocating bats

Field research on echolocation behavior in bats has emphasized studies of food acquisition, and the adaptive value of sonar signal design as been considered largely in the context of foraging. However, echolocation tasks related to spatial orientation also differ among bats and are relevant to understanding signal structure. Here, we argue that the evolution of echolocation in bats is characterized by two key innovations: first, the evolution of echolocation for spatial orientation and, second, a later transition for prey acquisition. This conceptual framework calls for a new view on field data from bats orienting and foraging in different types of habitats. According to the ecological constraints in which foraging bats operate, four distinct functional groups or guilds can be defined. Within each group, signal design and echolocation behavior are rather similar.

The acoustic startle response in rats—circuits mediating evocation, inhibition and potentiation

This review describes the neuronal mechanisms underlying the mediation and modulation of the acoustic startle response (ASR) in rats. The combination of anatomical, physiological and behavioral methods has identified pathways which mediate and modulate the ASR. The ASR is mediated by a relatively simple, oligosynaptic pathway located in the lower brainstem which activates spinal and cranial motor neurons. An important element of the pathway which mediates the ASR is the caudal nucleus of the pontine reticular formation (PnC). Interestingly, this nucleus is also the target of input from various brain nuclei which are involved in the modulation (e.g. fear-potentiation, sensitization, habituation, prepulse inhibition and pleasure-attenuation) of the ASR. Hence, the PnC can be described as a sensorimotor interface, where the transition of sensory input into the motor output can be directly influenced by excitatory or inhibitory afferents. On the basis of these facts we conclude that the ASR may be a valuable model for the study of general principles of sensorimotor-motivational information processing at the behavioral and neurophysiological level in mammals.

Plasticity in echolocation signals of European pipistrelle bats in search flight: implications for habitat use and prey detection

We studied the echolocation and hunting behavior of three aerial insectivorous species of bats (Vespertilionidae: Pipistrellus) in the field in order to characterize the signals used by the bats and to determine how call structure varies in relation to habitat structure (“uncluttered” versus “cluttered” space). We documented free-flying, naturally foraging wild pipistrelles in various habitats using multiflash stereophotography combined with simultaneous sound recordings. Then we reconstructed the bats flight position in three-dimensional space and correlated it with the corresponding echolocation sequences. In all three species of pipistrelles, signal structure varied substantially. In echolocation sequences of the search phase we found a consistent association of signal types with habitat types. In uncluttered habitats (obstacles more than 5 m from the bat) pipistrelles emitted almost exclusively narrowband signals with bandwidths less than 15 kHz. In cluttered habitats (obstacles less than 5 m from the bat) they switched to signals with bandwidths of more than 15 kHz. Wideband signals were also used when the bats were turning in cluttered and uncluttered spaces and for an instant after turning away from obstacles. Prey detection occured only when the outgoing signal did not overlap with the returning echo from potential prey. The bats also avoided overlap of echoes from potential prey and obstacles. Based on the results of this study, we propose an overlap-free “window” within which pipistrelles may detect potential prey and which allows predictions of minimum distances to prey and clutter-producing objects.

Die Ultraschall-Ortungslaute der Hufeisen-Fledermäuse (Chiroptera-Rhinolophidae) in verschiedenen Orientierungssituationen

SummaryEcholocating Rhinolophus ferrum-equinum (RF) and Rhinolophus euryale (RE) produce ultrasonic pulses which always consist of three parts. In the initial part the frequency rises by 1–12 KHz reaching finally a frequency of about 83 KHz in RF and about 104 KHz in RE. These frequencies remain constant throughout the middle part which comprises at least 9/10 of the pulses. The terminal part is frequency-modulated. The frequency drops by 13–16 KHz. The animals emit either long pulses or groups of short pulses corresponding to the respiratory cycle.In situations, in which the bats are not echolocating a special object, e.g. while hanging, taking off or free flying, they emit long pulses with a repetition rate of 4–10 Hz and a duration of 50–65 msec in RF and 35–45 msec in RE. These pulses have their maximum intensity in the middle. When echolocating directly to an object, e.g. while echolocating a mealworm, passing an obstacle or landing, the pulses are emitted in groups and shortened down to a minimum duration of 10 msec in RF and 7 msec in RE, while the repetition rate rises to 702–80 Hz in RF and 100 Hz in RE. At the same time a second intensity maximum appears in the frequency-modulated terminal part. While landing, the pulses as well as the terminal parts are shortened in a linear relation to the distance from the landing bar.Flying animals lower the frequency of the middle part by such an amount that the Doppler shifts caused by the flight velocity are compensated. Therefore the frequency heard by the bats remains constant and is as high as the frequency emitted before the flight. One hanging RF even tried to compensate the Doppler shifts caused by a moving pendulum in order to keep the echo frequency constant.While passing obstacles animals of both species show a similar orientation performance. They are able to avoid wires down to a wire diameter of 0.08 mm. The minimum limit for detection lies between 0.08–0.05 mm in RF and about 0.05 mm in RE. The mean distance at which the bats react to an obstacle descreases from 140 cm at a wire diameter of 3 mm to 38 cm at 0.08 mm. Even at 0.05 mm RE changed its sound sequence in 3 of 8 flights at a distance of 18 cm from the obstacle, whereas RF did not react any more.ZusammenfassungRhinolophus ferrum-equinum (RF) und Rhinolophus euryale (RE) erzeugen in allen Orientierungssituationen dreiteilige Ortungslaute. Im nur wenig intensiven Anfangsteil steigt die Frequenz um 1–12 KHz bis zur Frequenz des folgenden Mittelteils an. Der Mittelteil nimmt mindestens 9/10 der Laute ein und hat eine konstante Frequenz von etwa 83 KHz bei RF und 104 KHz bei RE. Im Endteil fällt die Frequenz immer um 13–16 KHz ab. Entsprechend dem Atemrhythmus werden die Ortungslaute in Folgen von langen Einzellauten oder in Lautgruppen ausgesendet. Sie sind in der Vertikalen und der Horizontalen gleich stark gebündelt. 20,5° seitlich von der Vorausrichtung fällt die Intensität auf die Hälfte der Vorausintensität ab.In Situationen, in denen die Fledermäuse nicht unmittelbar ein Objekt anpeilen, wie beim ungestörten Hängen, beim Start und beim freien Flug, senden sie mit einer Wiederholfrequenz von 4–10 Hz lange Einzellaute aus, deren Dauer meist zwischen 50–65 msec bei RF und 35–45 msec bei RE liegt. Diese Laute haben ein ungefähr in der Lautmitte liegendes Intensitätsmaximum. Beim gezielten Anpeilen eines Objekts, wie beim Peilen nach einem vorgehaltenen Mehlwurm, beim Flug durch Hindernisse und bei der Landung, werden die Laute verkürzt bis zu minimal 10 msec bei RF und 7 msec bei RE und in Gruppen ausgesendet. Die Wiederholfrequenz steigt an bis zu maximal 70–80 Hz bei RF und 100 Hz bei RE und im frequenzmodulierten Endteil ergibt sich ein zweites Intensitätsmaximum. Bei der Landung wird die Dauer der Ortungslaute und ebenso die Dauer des frequenzmodulierten Endteiles in linearer Abhängigkeit von der Entfernung zur Landestange verkürzt.Fliegende Tiere senken die Frequenz des konstantfrequenten Mittelteils immer um den Betrag der durch die Fluggeschwindigkeit bedingten Dopplereffekte ab, so daß die von den Tieren gehörte Frequenz nahezu konstant in Höhe der vor dem Flug ausgesendeten Frequenz gehalten wird. Eine hängende und auf ein sich bewegendes Pendel peilende RF war ebenfalls bestrebt, die durch die Pendelbewegung entstehenden Dopplereffekte zu kompensieren und die Frequenz der gehörten Echos konstant zu halten.Beide Arten zeigen beim Flug durch Hindernisse ähnliche Ortungsleistungen. Sie sind bei horizontalen und vertikalen Drahthindernissen noch in der Lage Drähte von 0,08 mm Durchmesser zu vermeiden. Die untere Ortungsgrenze liegt bei RF zwischen 0,08-0,05 mm und bei RE etwa bei 0,05 mm. Der mittlere Abstand, bei dem Fledermäuse auf ein Hindernis reagieren, fällt von 140 cm bei 3 mm Drahtdurchmesser auf 38 cm bei 0,08 mm ab. Bei 0,05 mm reagierte RE in 3 von 8 Flügen noch auf das Hindernis, während RF keine Reaktion mehr zeigte.

Echolocation signals reflect niche differentiation in five sympatric congeneric bat species

Echolocating bats can be divided into guilds according to their preferred habitat and foraging behaviour, which coincide with distinct adaptations in wing morphology and structure of echolocation signals. Although coarse structuring of niche space between different guilds is generally accepted, it is not clear how niches differ within guilds, or whether there is fine-grained niche differentiation reflected in echolocation signal structure. Using a standardized performance test, here we show clutter-dependent differences in prey-capture success for bats from five species of European Myotis. These species are morphologically similar, sympatric, and all belong to the guild labelled “edge space aerial/trawling foragers”. We further demonstrate a strong correlation between the prey-detection ability of the species and the respective search-call bandwidth. Our findings indicate that differences in echolocation signals contribute to within-guild niche differentiation. This is the first study relating sensory abilities of a set of potentially competing animal species to a direct measure of their respective foraging performance, suggesting an important role of sensory ecology in the structuring of animal communities.

The echolocation and hunting behavior of Daubenton's bat, Myotis daubentoni

SummaryThe echolocation and hunting behavior of Daubentons bat (Myotis daubentoni) were studied in the field under completely natural conditions using a multiflash photographic system synchronized with high-speed tape recordings. The hunting behavior of M. daubentoni is separated into four stages. In the search flight stage Daubentons bat flies with an average speed of 3.4±0.6 m/s SD usually within 30 cm over water surfaces searching for insects. After the detection of potential prey, the approach flight stage occurs, during which the bat approaches the target in a goal-directed flight. The stage tail down indicates that M. daubentoni is close to the potential prey (approximately 10–22 cm) and is preparing for the catch. The insects are caught with the interfemoral membrane, the feet, and sometimes with the additional aid of a wing. In the stage head down, the bat seizes the prey during flight. Immediately afterwards, Daubentons bat returns to search flight. M. daubentoni shows the typical echolocation behavior of a vespertilionid bat, emitting frequency-modulated (FM) echolocation signals. The three behavioral stages search, approach, and terminal phase (Griffin et al. 1960) are used to describe the pulse pattern of foraging M. daubentoni in the field. The terminal phase (or buzz) of Daubentons bat is separated into two parts: buzz I and buzz II. Buzz II is distinguished from buzz I by the following characteristics: a sharp drop in terminal frequency, a distinct reduction in the bandwidth of the first harmonic, a continuous high repetition rate throughout the phase in the range 155–210 Hz, very short pulses (0,25–0.3 ms) and interpulse intervals (4.5–5.0 ms) at the end of the phase, and a distinct decrease in duty cycle. A pause in echolocation separates the end of the terminal phase from the ongoing search phase. The reduction in sound duration after the detection of a target and during pursuits with successfull or attempted catches is discussed in relation to the actual distance of the bat to the target at each stage. It is likely that Daubentons bat reduces sound duration during approach and terminal phase in order to prevent an overlap of an outgoing pulse with the returning echo from the target. It is argued that the minimum detection distance can be estimated from the sound duration during search flight. Estimates of detection and reaction distances of M. daubentoni based upon synchronized photos and echolocation sequences are given to corroborate this hypothesis. An average detection distance of 128 cm and an average reaction distance of 112 cm were determined. Each behavioral stage of foraging M. daubentoni is characterized by a distinct pattern of echolocation signals and a distinct stage in hunting behavior. The approach flight in hunting behavior coincides with the approach phase and with buzz I in echolocation behavior. The stage tail down corresponds to buzz II. The stage head down is correlated with a pause in echolocation. Immediately afterwards, the bat returns into search flight and into the search phase, emitting search signals.

Response to frequency shifted artificial echoes in the batRhinolophus ferrumequinum

SummaryIn 5 roosting bats the resting frequency, that is the mean frequency of the cf-portion of consecutive sounds, is kept constant with a standard deviation which varies between 30–120 Hz in different bats and at different days. In 15 bats the emitted sounds were electronically shifted in frequency and played back as artificial echoes. Upward frequency shifts were responded by a decrease of the emission frequency. This frequency compensation occurred at frequency shifts of up to 4400 Hz in all bats and up to 6000 Hz in a few bats. The frequency decrease in different bats over the whole compensation range was 50–300 Hz smaller than the frequency shifts in the echoes. The echoes, therefore, returned at a frequency, called the reference frequency, which was by this compensation offset higher than the resting frequency. The standard deviations of the emission frequency in compensating bats were only slightly larger than in roosting bats and the same in the whole compensation range. All bats started to compensate frequency shifts when they were slightly larger than the compensation offset. Downward frequency shifts were not responded by a change of the emission frequency, but the accuracy with which the emission frequency was kept decreased somewhat. From these results it is concluded that the Doppler shift compensation system of the Horseshoe bats compares the echo frequency with the reference frequency and compensates deviations of upward frequency shifts.

The echolocation and hunting behavior of the bat,Pipistrellus kuhli

SummaryThe echolocation and hunting behavior ofPipistrellus kuhli was studied in the field using multi-exposure photography synchronized with high-speed tape recordings. During the search phase, the bats used 8–12 ms signals with sweeps (sweep width 3–6 kHz) and pulse intervals near 100 ms or less often near 200 ms (Figs. 1 and 2). The bats seemed to have individual terminal frequencies that could lie between 35 and 40 kHz. The duty cycle of searching signals was about 8%. The flight speed of hunting bats was between 4.0 and 4.5 m/s. The bats reacted to insect prey at distances of about 70 to 120 cm. Given the flight speed, the detection distance was estimated to about 110 to 160 cm. Following detection the bat went into the approach phase where the FM sweep steepened (to about 60 kHz bandwidth) and the repetition rate increased (to about 30 Hz). The terminal phase or ‘buzz’, which indicates prey capture (or attempted capture), was composed of two sections. The first section contained signals similar to those in the approach phase except that the pulse duration decreased and the repetition rate increased. The second section was characterized by a sharp drop in the terminal frequency (to about 20 kHz) and by very short pulses (0.3 ms) at rates of up to 200 Hz (Figs. 1 and 3). Near the beginning of the buzz the bat prepared for capturing the prey by extending the wings and forming a tail pouch (Fig. 4). A pause of about 100 ms in sound emission after the buzz indicated a successful capture (Fig. 4). Pulse duration is discussed in relation to glint detection and detection distance. It is argued that the minimum detection distance can be estimated from the pulse duration as the distance where pulse-echo overlap is avoided.

Suppression of distortion product otoacoustic emissions (DPOAE) near 2f1−f2 removes DP-gram fine structure—Evidence for a secondary generator

Since the discovery of distortion product otoacoustic emissions (DPOAE) there has been a controversial discussion about their cochlear generation sites. Suppression experiments suggest that the place near f2 is the main generation site. On the other hand, the fact that DPOAE can be perceived subjectively indicates that there is also a cochlear excitation at the place of 2f1−f2 resulting in a stimulus frequency otoacoustic emission (SFOAE). The contribution of this SFOAE to the overall emission is still unknown. Different studies showed contradictory results. We demonstrate a secondary generator by successive suppression of the SFOAE with a sine wave close to the frequency 2f1−f2. Suppression growth functions (SGF) showed a three-step behavior. For low suppressor levels, the emission either decreased or increased when increasing the suppressor. For intermediate suppressor levels, DP amplitude was constant and independant of suppressor level. For high suppressor levels, the emission always decreased with fu...

Information in sonar echoes of fluttering insects available for echolocating bats

Insects were mounted in the acoustical beam of an ultrasonic loudspeaker transmitting either an 80‐kHz continuous constant frequency (CF) tone or a short frequency‐modulated (FM) signal (82–18 kHz). The returning CF or FM echoes were recorded and analyzed. Short amplitude peaks or amplitude glints, which occur in the echo in the rhythm of the wing beat, are produced each time some part of the wing surface moves into a plane perpendicular to the impinging sound waves. The amplitude glints are represented in spectrograms of echoes as transitory spectral broadenings or frequency glints. In CF echoes, the composition of positive and negative frequency shifts associated with glints encode the attitude of the flying insect relative to the sound source independent of the insect species. Further information in CF echoes allows a classification of insects as to wing beat frequency, wing structure, wing beat type, wing length, and insect size. Only the wing beat rate of a fluttering insect could be decoded from FM ...