Frequency alternation and an offbeat rhythm indicate foraging behavior in the echolocating bat, <Emphasis Type="Italic">Saccopteryx bilineata</Emphasis>

The greater sac-winged bat, Saccopteryx bilineata (Emballonuridae), uses two distinct echolocation call sequences: a ‘monotonous’ sequence, where bats emit ~48 kHz calls at a relatively stable rate, and a frequency-alternating sequence, where bats emit calls at ~45 kHz (low-note call) and ~48 kHz (high-note call). The frequencies of these low–high-note pairs remain stable within sequences. In Panama, we recorded echolocation calls from S. bilineata with a multi-microphone array at two sites: one a known roosting site, the other a known foraging site. Our results indicate that this species (1) only produces monotonous sequences in non-foraging contexts and, at times, directly after emitting a feeding buzz and (2) produces frequency-alternating sequences when actively foraging. These latter sequences are also characterized by an unusual, offbeat emission rhythm. We found significant positive relationships between (1) call intensity and call duration and (2) call intensity and distance from clutter. However, these relationships were weaker than those reported for bats from other families. We speculate on how call frequency alternation and an offbeat emission rhythm might reflect a novel strategy for prey detection at the edge of complex habitat in this ancient family of bats.     

Spatial unmasking in the echolocating Big Brown Bat, <Emphasis Type="Italic">Eptesicus fuscus</Emphasis>

Masking affects the ability of echolocating bats to detect a target in the presence of clutter targets. It can be reduced by spatially separating the targets. Spatial unmasking was measured in a two-alternative-forced-choice detection experiment with four Big Brown Bats detecting a wire at 1 m distance. Depth dependent spatial unmasking was investigated by the bats detecting a wire with a diameter of 1.2 mm in front of a masker with a threshold distance of 11 cm behind the wire. For angle dependent spatial unmasking the masker was turned laterally, starting from its threshold position at 11 cm. With increasing masker angles the bats could detect thinner wires with diameters decreasing from 1.2 mm (target strength −36.8 dB) at 0° to 0.2 mm (target strength −63.0 dB) at 22°. Without masker, the bats detected wire diameters of 0.16 mm (target strength −66.2 dB), reached with masker positions beyond 23° (complete masking release). Analysis of the sonar signals indicated strategies in the echolocation behavior. The bats enhanced the second harmonics of their signals. This may improve the spatial separation between wire and masker due to frequency-dependent directionality increase of sound emission and echo reception.     

Spectral and temporal gating mechanisms enhance the clutter rejection in the echolocating bat,Rhinolophus rouxi

Summary Doppler shift compensation behaviour in horseshoe bats, Rhinolophus rouxi, was used to test the interference of pure tones and narrow band noise with compensation performance. The distortions in Doppler shift compensation to sinusoidally frequency shifted echoes (modulation frequency: 0.1 Hz, maximum frequency shift: 3 kHz) consisted of a reduced compensation amplitude and/or a shift of the emitted frequency to lower frequencies (Fig. 1).Pure tones at frequencies between 200 and 900 Hz above the bat's resting frequency (RF) disturbed the Doppler shift compensation, with a maximum of intererence between 400 and 550 Hz (Fig. 2). Minimum duration of pure tones for interference was 20 ms and durations above 40 ms were most effective (Fig. 3). Interfering pure tones arriving later than about 10 ms after the onset of the echolocation call showed markedly reduced interference (Fig. 4). Doppler shift compensation was affected by pure tones at the optimum interfering frequency with sound pressure levels down to –48 dB rel the intensity level of the emitted call (Figs. 5, 6).Narrow bandwidth noise (bandwidth from ± 100 Hz to ± 800 Hz) disturbed Doppler shift compensation at carrier frequencies between –250 Hz below and 800 Hz above RF with a maximum of interference between 250 and 500 Hz above resting frequency (Fig. 7). The duration and delay of the noise had similar influences on interference with Doppler shift compensation as did pure tones (Figs. 8, 9). Intensity dependence for noise interference was more variable than for pure tones (-32 dB to -45 dB rel emitted sound pressure level, Fig. 10).The temporal and spectral gating in Doppler shift compensation behaviour is discussed as an effective mechanism for clutter rejection by improving the processing of frequency and amplitude transients in the echoes of horseshoe bats.Abbreviations CF constant frequency - FM frequency modulation - RF resting frequency - SPL sound pressure level     

Active listening for spatial orientation in a complex auditory scene

To successfully negotiate a complex environment, an animal must control the timing of motor behaviors in coordination with dynamic sensory information. Here, we report on adaptive temporal control of vocal–motor behavior in an echolocating bat, Eptesicus fuscus, as it captured tethered insects close to background vegetation. Recordings of the bat's sonar vocalizations were synchronized with high-speed video images that were used to reconstruct the bat's three-dimensional flight path and the positions of target and vegetation. When the bat encountered the difficult task of taking insects as close as 10–20 cm from the vegetation, its behavior changed significantly from that under open room conditions. Its success rate decreased by about 50%, its time to initiate interception increased by a factor of ten, and its high repetition rate “terminal buzz” decreased in duration by a factor of three. Under all conditions, the bat produced prominent sonar “strobe groups,” clusters of echolocation pulses with stable intervals. In the final stages of insect capture, the bat produced strobe groups at a higher incidence when the insect was positioned near clutter. Strobe groups occurred at all phases of the wingbeat (and inferred respiration) cycle, challenging the hypothesis of strict synchronization between respiration and sound production in echolocating bats. The results of this study provide a clear demonstration of temporal vocal–motor control that directly impacts the signals used for perception.     

Sound-evoked oscillation and paradoxical latency shift in the inferior colliculus neurons of the big fruit-eating bat, <Emphasis Type="Italic">Artibeus jamaicensis</Emphasis>

Frequency tuning, temporal response pattern and latency properties of inferior colliculus neurons were investigated in the big fruit-eating bat, Artibeus jamaicensis. Neurons having best frequencies between 48–72 kHz and between 24–32 kHz are overrepresented. The inferior colliculus neurons had either phasic (consisting in only one response cycle at all stimulus intensities) or long-lasting oscillatory responses (consisting of multiple response cycles). Seventeen percent of neurons displayed paradoxical latency shift, i.e. their response latency increased with increasing sound level. Three types of paradoxical latency shift were found: (1) stable, that does not depend on sound duration, (2) duration-dependent, that grows with increasing sound duration, and (3) progressive, whose magnitude increases with increasing sound level. The temporal properties of paradoxical latency shift neurons compare well with those of neurons having long-lasting oscillatory responses, i.e. median inter-spike intervals and paradoxical latency shift below 6 ms are overrepresented. In addition, oscillatory and paradoxical latency shift neurons behave similarly when tested with tones of different durations. Temporal properties of oscillation and PLS found in the IC of fruit-eating bats are similar to those found in the IC of insectivorous bats using downward frequency-modulated echolocation calls.     

Prey pursuit strategy of Japanese horseshoe bats during an in-flight target-selection task

The prey pursuit behavior of Japanese horseshoe bats (Rhinolophus ferrumequinum nippon) was investigated by tasking bats during flight with choosing between two tethered fluttering moths. Echolocation pulses were recorded using a telemetry microphone mounted on the bat combined with a 17-channel horizontal microphone array to measure pulse directions. Flight paths of the bat and moths were monitored using two high-speed video cameras. Acoustical measurements of returning echoes from fluttering moths were first collected using an ultrasonic loudspeaker, turning the head direction of the moth relative to the loudspeaker from 0° (front) to 180° (back) in the horizontal plane. The amount of acoustical glints caused by moth fluttering varied with the sound direction, reaching a maximum at 70°–100° in the horizontal plane. In the flight experiment, moths chosen by the bat fluttered within or moved across these angles relative to the bat’s pulse direction, which would cause maximum dynamic changes in the frequency and amplitude of acoustical glints during flight. These results suggest that echoes with acoustical glints containing the strongest frequency and amplitude modulations appear to attract bats for prey selection.     

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 (FM₁ ~ 55–25 kHz, FM₂ ~ 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 FM₁ and FM₂ 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 FM₁ delayed 3.16 ms and FM₂ delayed 3.46 ms (300 μs delay split). Negative stimuli contained FM₁ and FM₂ 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 FM₁ and FM₂, but performance was overlaid by a broad pedestal of poor performance that extended for 800 μs. Splitting the harmonics by 300 μs appears to defocus the bat’s representation of delay, revealing the existence of a process for recognizing the normally simultaneous occurrence of the harmonics.     

Passive sound localization of prey by the pallid bat (Antrozous p. pallidus)

Summary The pallid bat (Antrozous p. pallidus) uses passive sound localization to capture terrestrial prey. This study of captive pallid bats examined the roles of echolocation and passive sound localization in prey capture, and focused on their spectral requirements for accurate passive sound localization.Crickets were used as prey throughout these studies. All tests were conducted in dim, red light in an effort to preclude the use of vision. Hunting performance did not differ significantly in red light and total darkness, nor did it differ when visual contrast between the terrestrial prey and the substrate was varied, demonstrating that the bats did not use vision to locate prey.Our bats apparently used echolocation for general orientation, but not to locate prey. They did not increase their pulse emission rate prior to prey capture, suggesting that they were not actively scanning prey. Instead, they required prey-generated sounds for localization. The bats attended to the sound of walking crickets for localization, and also attacked small, inanimate objects dragged across the floor. Stationary and/or anesthetized crickets were ignored, as were crickets walking on substrates that greatly attenuated walking sounds. Cricket communication sounds were not used in prey localization; the bats never captured stationary, calling crickets.The accuracy of their passive sound localization was tested with an open-loop passive sound localization task that required them to land upon an anesthetized cricket tossed on the floor. The impact of a cricket produced a single 10–20 ms duration sound, yet with this information, the bats were able to land within 7.6 cm of the cricket from a maximum distance of 4.9 m. This performance suggests a sound localization accuracy of approximately ±1° in the horizontal and vertical dimensions of auditory space. The lower frequency limit for accurate sound localization was between 3–8 kHz. A physiological survey of frequency representation in the pallid bat inferior colliculus suggests that this lower frequency limit is around 5 kHz.     

Adaptive mechanisms underlying the bat biosonar behavior

For survival, bats of the suborder Microchiropetra emit intense ultrasonic pulses and analyze the weak returning echoes to extract the direction, distance, velocity, size, and shape of the prey. Although these bats and other mammals share the common layout of the auditory pathway and sound coding mechanism, they have highly developed auditory systems to process biologically relevant pulses at the expense of a reduced visual system. During this active biosonar behavior, they progressively shorten the pulse duration, decrease the amplitude and pulse-echo gap as they search, approach and finally intercept the prey. Presumably, these changes in multiple pulse parameters throughout the entire course of hunting enable them to extract maximal information about localized prey from the returning echoes. To hunt successfully, the auditory system of these bats must be less sensitive to intense emitted pulses but highly sensitive to weak returning echoes. They also need to recognize and differentiate the echoes of their emitted pulses from echoes of pulses emitted by other conspecifics. Past studies have shown the following mechanical and neural adaptive mechanisms underlying the successful bat biosonar behavior: (1) Forward orienting and highly mobile pinnae for effective scanning, signal reception, sound pressure transformation and mobile auditory sensitivity; (2) Avoiding and detecting moving targets more successfully than stationary ones; (3) Coordinated activity of highly developed laryngeal and middle ear muscles during pulse emission and reception; (4) Mechanical and neural attenuation of intense emitted pulses to prepare for better reception of weak returning echoes; (5) Increasing pulse repetition rate to improve multiple-parametric selectivity to echoes; (6) Dynamic variation of duration selectivity and recovery cycle of auditory neurons with hunting phase for better echo analysis; (7) Maximal multiple-parametric selectivity to expected echoes returning within a time window after pulse emission; (8) Pulse-echo delaysensitive neurons in higher auditory centers for echo ranging; (9) Corticofugal modulation to improve on-going multiple-parametric signal processing and reorganize signal representation, and (10) A large area of the superior colliculus, pontine nuclei and cerebellum that is sensitive to sound for sensori-motor integration. All these adaptive mechanisms facilitate the bat to effectively extract prey features for successful hunting.     

Estimation of food intake and ingested energy in Daubenton’s bats (Myotis daubentonii) during pregnancy and spermatogenesis

We studied food intake of and estimated ingested energy in female and male Myotis daubentonii during the periods of pregnancy (period 1, 8 May–4 June) and of intense spermatogenetic activity (period 2, 24 July–22 August) over 8 years (1996–2003) in central Germany. We used radiotelemetry to determine the time spent foraging and marked animals with chemiluminescent light-sticks to determine prey attack rates. Body length, body mass, moisture content, and caloric content of chironomids, the main prey of Daubenton’s bats, were measured to estimate the nightly food intake and, in consequence, energy intake. Pregnant females spent significantly more time foraging than males during period 1 and females during the post-lactation period. In contrast, male foraged longer during the period of highest spermatogenetic activity than during late spring and also significantly longer than post-lactating females. Based on a mean number of 8.3 prey attacks per minute, the time spent foraging, and a capture success rate of either 50 or 92%, calculated intake values with a feeding rate of 7.6 insects per minute (=92% capture success) were more consistent with literature data for other insectivorous bats than that of values calculated on the basis of a capture success rate of 50%. In the high capture-success model, calculated insect intake of female bats was 8.0 g during pregnancy and 4.9 g per day during post-lactation, providing 5.0 and 3.0 kJ of ingested energy per gram body mass per day. Calculated intake of male bats was 3.6 g insects per day during late spring and 8.0 g during period of intensive spermatogenesis, providing 2.6 and 5.7 kJ of ingested energy per gram body mass.     

Variation in plant stem density and its effects on foraging success of juvenile bluegill sunfish

Synopsis Juvenile bluegill sunfish, Lepomis macrochirus, are known to use beds of aquatic vegetation as a refuge from predators. This study examines the effects of increasing plant stem density on juvenile bluegill foraging. Three stem densities (100, 250 and 500 stems m⁻²), varying in their refuge potential for bluegills from predators, were tested. Results demonstrate that stem densities chosen as a refuge from predation (i.e. 500 stems m⁻²) significantly reduced bluegill foraging success and increased time required to capture prey. Therefore, juvenile bluegills seeking safety in vegetation may be faced with a trade-off between foraging success and effective refuge from predation when choosing among plant stem densities.     

Horseshoe bats make adaptive prey-selection decisions, informed by echo cues

Foragers base their prey-selection decisions on the information acquired by the sensory systems. In bats that use echolocation to find prey in darkness, it is not clear whether the specialized diet, as sometimes found by faecal analysis, is a result of active decision-making or rather of biased sensory information. Here, we tested whether greater horseshoe bats decide economically when to attack a particular prey item and when not. This species is known to recognize different insects based on their wing-beat pattern imprinted in the echoes. We built a simulation of the natural foraging process in the laboratory, where the bats scanned for prey from a perch and, upon reaching the decision to attack, intercepted the prey in flight. To fully control echo information available to the bats and assure its unambiguity, we implemented computer-controlled propellers that produced echoes resembling those from natural insects of differing profitability. The bats monitored prey arrivals to sample the supply of prey categories in the environment and to inform foraging decisions. The bats adjusted selectivity for the more profitable prey to its inter-arrival intervals as predicted by foraging theory (an economic strategy known to benefit fitness). Moreover, unlike in previously studied vertebrates, foraging performance of horseshoe bats was not limited by costly rejections of the profitable prey. This calls for further research into the evolutionary selection pressures that sharpened the species's decision-making capacity.     

Echolocation constraints of Daubenton's Bat foraging over water

1. Daubenton's Bats ( Myotis daubentonii ) foraging over a stream concentrated their activity over calm surfaces, avoiding an adjacent area with small ripples (< 3 cm high). Aerial insects were most abundant over the ripples, so insect distribution could not explain why the bats avoided this area.
2. The bats flew low over water and always ( N = 22) directed the head forwards, presumably emitting the echolocation beam parallel to the surface, thus minimizing clutter. At an angle of incidence of 30° there was significantly more clutter from the rippled water.
3. The ripples produced ultrasonic noises in the form of transient pulses at an average rate of 6·2 per second. In the present case, such pulses were common enough potentially to interfere with target detection by the bats. Transient noises and echo clutter from moving ripples may be the principal reason why bats generally avoid foraging low over turbulent water.
4. The target strength of a potential insect prey at the water surface and the source levels of the bats' searching signals were measured to use in estimating the echo level at the bat when it detects the prey. The echo level at detection (+ 38 dB sound pressure level) was about the same as the clutter level extrapolated to the detection distance. This suggests that Daubenton's Bat operates at very low signal-to-noise ratios when foraging for insects near the water surface.     

Long-term changes in abundance of bats as revealed by their frequency in tawny owls’ diet

Percentage of bats in tawny owls’ diet was compared in three periods: I — before 1976, II — 1976–1992, III — 1993–2009, by using the published and unpublished material from Poland (only samples over 100 vertebrate prey items). This species of owl showed an opportunistic predation on bats and took them more frequently in periods of higher abundance. Before the mass use of toxic pesticides in Poland, in the period I bats constituted more than 2% of vertebrates in four out of five diet samples (median 2.4%). The lowest bat abundance occurred in Poland in the 1980s and resulted in the lowest percentage of bats taken by owls in the period II (n = 11, median 0.2%). Due to the recovery of bat populations in the period III, the percentage of bats in tawny owls’ diet increased (n = 23, median 0.7%). In large samples (over 200 vertebrate items, n = 21) collected in central and north-eastern Poland the percentage of bats increased from 1980 to 2009 (the estimated average value at the end of that period slightly exceeded 1%). Samples collected at the same five sites in 1975–1992 and again in 2000–2009, confirmed the increasing trend in percentage of bats captured by tawny owls noted in last years.     

Bat defence in lekking ghost swifts (Hepialus humuli), a moth without ultrasonic hearing.

The Hepialidae represents an early branch of the Lepidoptera, whose members lack the ultrasonic hearing and other obvious predator defence systems present in other extant moths. I observed lekking male ghost swifts, Hepialus humuli, being exploited by northern bats, Eptesicus nilssonii, over a hayfield in southern Sweden. Because the moth''s display flight was restricted to a brief (30 min) period at dusk, they avoided most predators temporally but were exposed to early emerging aerial-hawking bats. Against these, they apparently employed ''acoustic crypsis'', achieved by flying close (< 0.5 m) to the vegetation, thereby hiding from the bats among clutter (echoes returning from the background). Nevertheless, the predation risk for the displaying moth males was very high (20% per night), mainly because they sometimes left the safety of the vegetation. The lack of ''advanced'' predator defence mechanisms in H. humuli requires alternative defence strategies, which, however, restrict the behavioural repertoire and still carry a high predation risk.     

Integration time for short broad band clicks in echolocating FM-bats (Eptesicus fuscus)

Vespertilionid FM-bats (four Eptesicus fuscus and one Vespertilio murinus) were trained in an electronic phantom target simulator to detect synthetic echoes consisting of either one or two clicks. The threshold sound pressure for single clicks was around 47 dB peSPL for all five bats corresponding to a threshold energy of -95 dB re 1 Pa² * s. By varying the interclick interval, T, for double clicks it was shown that the threshold intensity was around — 3 dB relative to the threshold for single clicks at T up to 2.4 ms, indicating perfect power summation of both clicks. A threshold shift of -13.5 dB for a 1 ms train of 20 clicks (0.05 ms interclick interval) confirmed that the bats integrated the power of the stimuli. At T longer than around 2.5 ms the threshold for double clicks was the same as for single clicks. Thus, the bats performed like perfect energy detectors with an integration time of approximately 2.4 ms. This integration time is an order of magnitude shorter than that reported for bats listening passively for pure tones. In our setup the bats emitted sonar signals with durations of 2–3 ms. Hence, the results may indicate that while echolocating the bats integration time is adapted to the duration of the sonar emissions.Abbreviations AGC automatic gain control - FM frequency modulated - peSPL peak equivalent sound pressure level - rms root mean square - SD standard deviation - SE standard error of mean - T interclick interval     

Temporal resolution of the Risso’s dolphin, Grampus griseus, auditory system

Toothed whales and dolphins (Odontocetes) are known to echolocate, producing short, broadband clicks and receiving the corresponding echoes, at extremely rapid rates. Auditory evoked potentials (AEP) and broadband click stimuli were used to determine the modulation rate transfer function (MRTF) of a neonate Risso’s dolphin, Grampus griseus, thus estimating the dolphin’s temporal resolution, and quantifying its physiological delay to sound stimuli. The Risso’s dolphin followed sound stimuli up to 1,000 Hz with a second peak response at 500 Hz. A weighted MRTF reflected that the animal followed a broad range of rates from 100 to 1,000 Hz, but beyond 1,250 Hz the animal’s hearing response was simply an onset/offset response. Similar to other mammals, the dolphin’s AEP response to a single stimulus was a series of waves. The delay of the first wave, PI, was 2.76 ms and the duration of the multi-peaked response was 4.13 ms. The MRTF was similar in shape to other marine mammals except that the response delay was among the fastest measured. Results predicted that the Risso’s dolphin should have the ability to follow clicks and echoes while foraging at close range.     

Bat breath reveals metabolic substrate use in free-ranging vampires

We analysed the stable carbon isotope ratio in exhaled CO₂ (δ¹³C_breath) of free-ranging vampires to assess the type of metabolized substrate (endogenous or exogenous substrate) and its origin, i.e. whether the carbon atoms came from a C₄ food web (grass and cattle) or the C₃ food web in which they were captured (a rainforest remnant and its mammals). For an improved understanding of factors influencing the δ¹³C_breath of vampires, we conducted feeding experiments with captive animals. The mean δ¹³C_breath of starved bats was depleted in ¹³C in relation to the diet by 4.6‰ (n = 10). Once fed with blood, δ¹³C_breath levelled off within a short time approximately 2.2‰ above the stable carbon isotope signature of the diet. The median time required to exchange 50% of the carbon atoms in exhaled CO₂ with carbon atoms from the ingested blood was 18.6 min (mean 29.5 ± 19.0 min, n = 5). The average δ¹³C of wing membrane and fur in free-ranging vampire bats suggested that bats almost exclusively foraged for cattle blood during the past weeks. The δ¹³C_breath of the same bats averaged −19.1‰. Given that all free-ranging vampires were starving and that the δ¹³C of cattle was more in enriched in ¹³C by 5–6‰ than the δ¹³C_breath of vampires, we conclude that the vampire bats of our study metabolised fat that was predominantly built from carbon atoms originating from cattle blood. Since δ¹³C of wing membrane and fur integrates over weeks and months respectively and δ¹³C_breath over hours and days, we also conclude that vampire bats of the studied population consistently ignored rainforest mammals and chose cattle as their prey during and prior to our study.     

Molecular diet analysis finds an insectivorous desert bat community dominated by resource sharing despite diverse echolocation and foraging strategies

Interspecific differences in traits can alter the relative niche use of species within the same environment. Bats provide an excellent model to study niche use because they use a wide variety of behavioral, acoustic, and morphological traits that may lead to multi‐species, functional groups. Predatory bats have been classified by their foraging location (edge, clutter, open space), ability to use aerial hawking or substrate gleaning and echolocation call design and flexibility, all of which may dictate their prey use. For example, high frequency, broadband calls do not travel far but offer high object resolution while high intensity, low frequency calls travel further but provide lower resolution. Because these behaviors can be flexible, four behavioral categories have been proposed: (a) gleaning, (b) behaviorally flexible (gleaning and hawking), (c) clutter‐tolerant hawking, and (d) open space hawking. Many recent studies of diet in bats use molecular tools to identify prey but mainly focus on one or two species in isolation; few studies provide evidence for substantial differences in prey use despite the many behavioral, acoustic, and morphological differences. Here, we analyze the diet of 17 sympatric species in the Chihuahuan desert and test the hypothesis that peak echolocation frequency and behavioral categories are linked to differences in diet. We find no significant correlation between dietary richness and echolocation peak frequency though it spanned close to 100 kHz across species. Our data, however, suggest that bats which use both gleaning and hawking strategies have the broadest diets and are most differentiated from clutter‐tolerant aerial hawking species.     

Plasticity in echolocation calls of <Emphasis Type="Italic">Myotis macrodactylus</Emphasis> (Chiroptera: Vespertilionidae): implications for acoustic identification

Poor knowledge of the intraspecific variability in echolocation calls is recognized as an important limiting factor for the accurate acoustic identification of bats. We studied the echolocation behaviors of an ecologically poorly known bat species, Myotis macrodactylus, while they were commuting in three types of habitats differing significantly in the amount of background clutter, as well as searching for prey above the water surface in a river. Results showed that M. macrodactylus altered their echolocation call structure in the same way during commuting as foraging bats do in relation to the changing level of clutter. With increasing level of clutter, M. macrodactylus generally produced echolocation calls with higher start, end, and peak frequencies; wider bandwidth; and shorter pulse duration. Compared to commuting, bats emitted significantly lower frequency calls with narrower bandwidth while searching for prey. Discriminant function analysis indicated that 79.8% of the calls from the three commuting habitats were correctly grouped, and 87% of the calls were correctly classified to the commuting and foraging contexts. Our finding has implications for those who would identify species by their calls.