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1.
While the evasive responses of many flying acoustic insects to aerial‐hawking bats are duly recognized and studied, the responses of non‐aerial insects to gleaning bats are generally overlooked. It has been assumed that acoustic insects are deaf to these predators because gleaning bat echolocation calls are typically low in amplitude, brief (1–3 ms) and very high in frequency (>60 kHz). We tested this assumption in a series of playback experiments with a moth (Achroia grisella) that uses hearing in both predator evasion and mating. We report that ultrasound pulses ≥78 dB peSPL (peak equivalent sound pressure level) and ≥1 ms in duration inhibit stationary males from broadcasting their own ultrasonic advertisement calls, provided that the pulsed stimuli are delivered at a repetition rate ≤30/s. Further analyses suggest that inhibition by pulsed ultrasound comprises two processes performed serially. First, a startle response with a latency <50 ms is elicited by a single pulse ≥1 ms duration. Here, a male misses broadcasting several calls over a 50–100 ms interval. Secondly, the startle may be extended as a silence response lasting several to many seconds if subsequent pulses occur at a rate ≤30/s. Call inhibition cannot represent a simple response to acoustic power because of the inverse interaction between pulse duration and rate. On the other hand, the temporal and energy characteristics of inhibitory stimuli match those of gleaning bat echolocation calls, and we infer that inhibition is a specialized defensive behavior by which calling males may avoid detection by eavesdropping bats.  相似文献   

2.
Animals adopt different strategies to communicate by means of sound in noisy environments such that some species increase, while others decrease their vocal activity in the presence of interference. Anuran amphibians from diverse latitudes exhibit both kinds of responses. Recent studies have shown that males of Batrachyla taeniata and Batrachyla antartandica from the temperate austral forest do not call in response to the presentation of advertisement calls of sympatric congeneric species. In contrast, Batrachyla leptopus responds to these signals in a similar way as to conspecific calls. The responsiveness of B. taeniata to natural abiotic interference has also been tested and found that noises of such sources produce strong increases in vocal activity. To assess the diversity in responsiveness to acoustic intrusion in this group, we exposed males of B. leptopus and B. antartandica to prolonged pre‐recorded natural abiotic noises of wind, creek, rain, and to a band‐pass noise centered at 2,000 Hz, at 67 dB Sound Pressure Level (SPL). The subjects did not increase their vocal activity significantly when exposed to these sounds and to band‐pass noise at increasing intensities (55–79 dB SPL). These results contrast with the increase in vocal activity observed previously in B. taeniata to continuous abiotic noise and point to the existence of diverse strategies to confront acoustic intrusion among related species. The lack of vocal activation observed also contrasts with the responsiveness of B. leptopus to heterospecific signals, but parallels the lack of response to such sounds in B. antartandica. Furthermore, the results obtained contrast with the responsiveness of these species to synthetic prolonged sounds observed in previous studies, suggesting that the modes of responses to acoustic intrusion may depend on previous experience, rather than having a species‐specific nature.  相似文献   

3.
Angola free-tailed bats and little free-tailed bats occur in diverse habitats throughout most of Africa south of the Sahara. This study investigated the reproductive strategies and related biology of these species in Malawi where they were sympatric, and analysed data from elsewhere in Africa to show how the strategies varied along a gradient of habitats from approximately 12 degrees N to 25 degrees S. Both the Angola free-tailed bat and the little free-tailed bat were normally monotocous. Angola free-tailed bats invariably had 2 births/year, and the interval between consecutive births decreased with increasing latitude. When the interval was shortest (approximately 90 days) a post-partum oestrus occurred. Little free-tailed bats differed by having a shorter gestation (approximately 60 days), and the ability to have up to 5 births/year with a postpartum oestrus after each birth. The extent to which this potential is achieved varies with latitude and rainfall, mainly so that lactation can coincide with peaks in the abundance of food. The interaction between rainfall and reproductive characteristics results in the two species having patterns of reproduction which are sometimes similar, but more often different. Competition between the species is unlikely to be affected by differences in their reproduction.  相似文献   

4.
Divergence of acoustic signals in a geographic scale results from diverse evolutionary forces acting in parallel and affecting directly inter-male vocal interactions among disjunct populations. Pleurodema thaul is a frog having an extensive latitudinal distribution in Chile along which males'' advertisement calls exhibit an important variation. Using the playback paradigm we studied the evoked vocal responses of males of three populations of P. thaul in Chile, from northern, central and southern distribution. In each population, males were stimulated with standard synthetic calls having the acoustic structure of local and foreign populations. Males of both northern and central populations displayed strong vocal responses when were confronted with the synthetic call of their own populations, giving weaker responses to the call of the southern population. The southern population gave stronger responses to calls of the northern population than to the local call. Furthermore, males in all populations were stimulated with synthetic calls for which the dominant frequency, pulse rate and modulation depth were varied parametrically. Individuals from the northern and central populations gave lower responses to a synthetic call devoid of amplitude modulation relative to stimuli containing modulation depths between 30–100%, whereas the southern population responded similarly to all stimuli in this series. Geographic variation in the evoked vocal responses of males of P. thaul underlines the importance of inter-male interactions in driving the divergence of the acoustic traits and contributes evidence for a role of intra-sexual selection in the evolution of the sound communication system of this anuran.  相似文献   

5.
Anthropogenic noise is prevalent across the globe and can exclude birds from otherwise suitable habitat and negatively influence fitness; however, the mechanisms responsible for species' responses to noise are not always clear. One effect of noise is a reduction in effective acoustic communication through acoustic masking, yet some urban songbirds may compensate for masking by noise through altering their songs. Whether this vocal flexibility accounts for species persistence in noisy areas is unknown. Here, we investigated the influence of noise on habitat use and vocal frequency in two suboscine flycatchers using a natural experiment that isolated effects of noise from confounding stimuli common to urban habitats. With increased noise exposure, grey flycatcher (Empidonax wrightii) occupancy declined, but vocal frequency did not change. By contrast, ash-throated flycatcher (Myiarchus cinerascens) occupancy was uninfluenced by noise, but individuals in areas with greater noise amplitudes vocalized at a higher frequency, although the increase (≈200 kHz) may only marginally improve communication and may represent a secondary effect from increased vocal amplitude. Even so, the different flycatcher behavioural responses suggest that signal change may help some species persist in noisy areas and prompt important questions regarding which species will cope with an increasingly noisy world.  相似文献   

6.
During the reproductive season, male Hyla versicolor produce advertisement calls to attract females. Females exhibit phonotaxis and approach the individual callers, resulting in amplexus. For frogs that call from dense choruses, the extent to which and the range from which a male’s advertisement call within a chorus can be heard by a receptive female leading to phonotaxis is unclear. We investigated females’ responses to natural choruses in the field and found that they were attracted and showed directed orientation to breeding choruses at distances up to 100 m. To assess the role of acoustic cues in the directed orientation, we conducted acoustic playback experiments in the laboratory using conspecific call and noise as stimuli, as well as chorus sounds (that contained calls from a focal male) recorded at various distances, all played at naturalistic intensities. Using two response metrics (females’ normalized response times and their phonotaxis trajectories) we found that, unlike the field experiments, females oriented and were attracted to chorus sounds from 1 to 32 m only, but not from >32 m, or to band-limited noise. Possible reasons for the observed difference in phonotaxis behavior in the two experimental conditions were discussed.  相似文献   

7.
Fast movement in complex environments requires the controlled evasion of obstacles. Sonar-based obstacle evasion involves analysing the acoustic features of object-echoes (e.g., echo amplitude) that correlate with this object's physical features (e.g., object size). Here, we investigated sonar-based obstacle evasion in bats emerging in groups from their day roost. Using video-recordings, we first show that the bats evaded a small real object (ultrasonic loudspeaker) despite the familiar flight situation. Secondly, we studied the sonar coding of object size by adding a larger virtual object. The virtual object echo was generated by real-time convolution of the bats’ calls with the acoustic impulse response of a large spherical disc and played from the loudspeaker. Contrary to the real object, the virtual object did not elicit evasive flight, despite the spectro-temporal similarity of real and virtual object echoes. Yet, their spatial echo features differ: virtual object echoes lack the spread of angles of incidence from which the echoes of large objects arrive at a bat's ears (sonar aperture). We hypothesise that this mismatch of spectro-temporal and spatial echo features caused the lack of virtual object evasion and suggest that the sonar aperture of object echoscapes contributes to the sonar coding of object size.  相似文献   

8.
Bats have recently been implicated as reservoirs of important emerging diseases. However, few studies have examined immune responses in bats, and even fewer have evaluated these responses in an ecological context. We examined aspects of both innate and adaptive immune response in adult female Brazilian free-tailed bats (Tadarida brasiliensis) at four maternity roosts (two natural caves and two human-made bridges) in south-central Texas. Immune measurements included in vitro bactericidal ability of whole blood and in vivo T cell mediated response to mitogenic challenge. Bactericidal activity in T. brasiliensis varied with roosting ecology, but appears to be sensitive to colony-level effects. Blood from females living at one cave had significantly lower bactericidal ability than blood from females at three other sites. T cell mediated response in this species was associated with variation in roost ecology, with females from two caves having greater responses than females from two bridges. T cell mediated response and bactericidal activity were negatively correlated with one another within individuals that were tested for both. Variation in immunological response of T. brasiliensis is important for understanding the influence of the environment on the frequency and distribution of immunologically competent individuals and for understanding disease-host dynamics in this and other colonial species.  相似文献   

9.
Animals are communicating by sound face interference from biotic and abiotic sources. Contrasting strategies have been reported in different taxa in the presence of prolonged noises, but in particular, interactions among acoustically active species have been studied to a very limited extent. In addition, reactions of a single species to interferences having contrasting structural patterns have not been explored systematically. The vocal responses of 16 male frogs Batrachyla antartandica from the temperate austral forest in Chile were tested with conspecific calls and with the calls of two sympatric species: B. taeniata and B. leptopus, broadcast at amplitudes of 73, 79, 85, 91, and 97 dB peak sound pressure level (SPL). Also, the vocal activity of the subjects during exposure to a 3‐min continuous broadband noise presented at 67 dB root mean square (RMS) SPL was monitored. The subjects gave significantly higher responses to the conspecific relative to the heterospecific calls but increased their vocal output in the presence of continuous noise. The preference of vocal responses for the conspecific relative to heterospecific signals bears a general resemblance to those exhibited by B. taeniata in a previous study and potentially contributes to the typical segregation in conspecific choruses observed in areas where these frogs breed in sympatry. Such lack of vocal responses to heterospecific stimuli contrasts with the increase in vocal activity during exposure to continuous noise lacking a temporal fine structure and points to identify different strategies in confronting interferences of diverse origin.  相似文献   

10.
Vocal learning is well known among passerine and psittacine birds, but most data on mammals are equivocal. Specific benefits of vocal learning are poorly understood for most species. One case where vocal learning should be favoured by selection is where calls indicate group membership and group mates are unrelated. Female greater spear-nosed bats, Phyllostomus hastatus, live in stable groups of unrelated bats and use loud, broadband calls to coordinate foraging movements of social group mates. Bats benefit from group foraging. Calls differ between female social groups and cave colonies, and playback experiments demonstrate that bats perceive these acoustic differences. Here I show that the group distinctive structure of calls arises through vocal learning. Females change call structure when group composition changes, resulting in increased similarity among new social group mates. Comparisons of transfers with age-matched half-sibs indicate that call changes are not simply due to maturation, the physical environment or heredity. These results suggest that studies testing vocal learning in mammals could profit by focusing on vocalizations that signify group membership.  相似文献   

11.
Experiments were conducted in anaesthetized and spinalized cats to measure the extent to which the non-linear response of Ia afferent fibers to sinusoidal muscle stretch as expressed by the peristimulus-time-histograms, PSTHs, can be transformed into a linear one by means of the superposition of random stretch ("mechanical noise"). The gastrocnemius muscles of one hind leg were stretched and the response to sinewave muscle stretch (amplitudes between 0.01 and 4.0 mm, frequencies between 0.1 and 20 Hz) were investigated while band-limited mechanical noise was superimposed on the sinewave stretch. The random stretch upper cut-off frequency was varied between 60 and 300 Hz; the displacements were normally distributed. The noise amplitude sigma, i.e. the standard deviation of the displacement distributions, was varied systematically between 0.002 and 0.4 mm. Mechanical noise was very effective in raising the mean discharge rate. Added to the sinusoidal stretch it prevented the cessation of firing during the release phase of the stretch cycle, or at least reduced the duration of discharge pauses, i.e., a linearization occurred. In general, the larger the noise amplitude, the more the amplitude of the fundamental harmonic component was attenuated and the phase lead reduced. Apart from this rule the particular combination of superimposing small noise (sigma less than 0.02 mm) on small sinewave stretch (A less than 0.02 mm) could enhance the depth of sinusoidal modulation of cycle histograms (compared with responses to pure sinusoids). Linearizing the sinewave response by additional noise allowed the estimation of frequency response characteristics in the otherwise non-linear range of amplitudes (sinewave amplitude 0.5-1.0 mm).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

12.
Francis CD  Ortega CP  Cruz A 《PloS one》2011,6(11):e27052

Background

Human-generated noise pollution now permeates natural habitats worldwide, presenting evolutionarily novel acoustic conditions unprecedented to most landscapes. These acoustics not only harm humans, but threaten wildlife, and especially birds, via changes to species densities, foraging behavior, reproductive success, and predator-prey interactions. Explanations for negative effects of noise on birds include disruption of acoustic communication through energetic masking, potentially forcing species that rely upon acoustic communication to abandon otherwise suitable areas. However, this hypothesis has not been adequately tested because confounding stimuli often co-vary with noise and are difficult to separate from noise exposure.

Methodology/Principal Findings

Using a natural experiment that controls for confounding stimuli, we evaluate whether species vocal features or urban-tolerance classifications explain their responses to noise measured through habitat use. Two data sets representing nesting and abundance responses reveal that noise filters bird communities nonrandomly. Signal duration and urban tolerance failed to explain species-specific responses, but birds with low-frequency signals that are more susceptible to masking from noise avoided noisy areas and birds with higher frequency vocalizations remained. Signal frequency was also negatively correlated with body mass, suggesting that larger birds may be more sensitive to noise due to the link between body size and vocal frequency.

Conclusions/Significance

Our findings suggest that acoustic masking by noise may be a strong selective force shaping the ecology of birds worldwide. Larger birds with lower frequency signals may be excluded from noisy areas, whereas smaller species persist via transmission of higher frequency signals. We discuss our findings as they relate to interspecific relationships among body size, vocal amplitude and frequency and suggest that they are immediately relevant to the global problem of increases in noise by providing critical insight as to which species traits influence tolerance of these novel acoustics.  相似文献   

13.
Bat echolocation calls: adaptation and convergent evolution   总被引:4,自引:0,他引:4  
Bat echolocation calls provide remarkable examples of 'good design' through evolution by natural selection. Theory developed from acoustics and sonar engineering permits a strong predictive basis for understanding echolocation performance. Call features, such as frequency, bandwidth, duration and pulse interval are all related to ecological niche. Recent technological breakthroughs have aided our understanding of adaptive aspects of call design in free-living bats. Stereo videogrammetry, laser scanning of habitat features and acoustic flight path tracking permit reconstruction of the flight paths of echolocating bats relative to obstacles and prey in nature. These methods show that echolocation calls are among the most intense airborne vocalizations produced by animals. Acoustic tracking has clarified how and why bats vary call structure in relation to flight speed. Bats using broadband echolocation calls adjust call design in a range-dependent manner so that nearby obstacles are localized accurately. Recent phylogenetic analyses based on gene sequences show that particular types of echolocation signals have evolved independently in several lineages of bats. Call design is often influenced more by perceptual challenges imposed by the environment than by phylogeny, and provides excellent examples of convergent evolution. Now that whole genome sequences of bats are imminent, understanding the functional genomics of echolocation will become a major challenge.  相似文献   

14.
Animal communication follows many coding schemes. Less is known about the coding strategy for signal length and rates of use in animal vocal communication. A generalized brevity (negative relation between signal length and frequency of use) is innovatively explored but remains controversial in animal vocal communication. We tested brevity for short-range social and distress sounds from four echolocating bats: adult black-bearded tomb bat Taphozous melanopogon, Mexican free-tailed bat Tadarida brasiliensis, adult greater horseshoe bat Rhinolophus ferrumequinum, and adult least horseshoe bat Rhinolophus pusillus. There was a negative association between duration and number of social but not distress calls emitted. The most frequently emitted social calls were brief, while most distress calls were long. Brevity or lengthiness was consistently selected in vocal communications for each species. Echolocating bats seem to have convergent coding strategy for communication calls. The results provide the evidence of efficient coding in bat social vocalizations, and lay the basis of future researches on the convergence for neural control on bats’ communication calls.  相似文献   

15.
Echolocating insectivorous bats consummate prey captures using a distinct vocal motor pattern commonly known as the terminal or feeding buzz, which is widely considered a fixed motor pattern executed independently of auditory feedback influences. The Mexican free-tailed bat, Tadarida brasiliensis, offers an opportunity to explore the role of sensory feedback in buzzing because they emit similar buzzes both in flight during foraging and while stationary as communication sounds. Here we compared the spectral and temporal patterns of foraging and communication buzzes to address whether or not auditory feedback may influence buzz patterns. We found that while foraging buzzes uttered in open space were composed of generic FM calls, communication buzzes were composed of an adapted CF–FM call similar to the call type used by T. brasiliensis when navigating in confined spaces. This provides the first evidence that some bats can make significant context-dependent changes in the spectral parameters of calls within their buzz. We also found that inter-pulse intervals, but not call durations, were different within the two buzz types. These observations indicate that though a common pattern generator hierarchically organizes all buzzes, T. brasiliensis retains a significant capacity to adapt the spectral and temporal patterns of elements within its buzzes.  相似文献   

16.
Animals that rely on vocal communication must broadcast sound so that a perceptible signal is transmitted over an appropriate distance. We found that male blue-throated hummingbirds modified the amplitude of their vocalizations in response to both naturally occurring and experimenter-controlled changes in ambient noise levels. This phenomenon is known as the Lombard effect and may increase the efficiency of acoustic signalling. This study demonstrates the effect under natural field conditions and documents the first hummingbird species (Apodiformes: Trochilidae) to show this behaviour. We measured sound pressure levels (SPLs) of Serial Chip territorial advertisement calls across a natural range of ambient noise, primarily due to creeks within male territories. We found a significant correlation between the amplitude of Serial Chips and the amplitude of background noise. To test this relationship, we broadcast recordings of creek noise at high and low amplitudes while target individuals were producing Serial Chip vocalizations. We measured vocal SPLs before and during the playback. Individuals responded to changes in playback creek noise by changing the amplitude of Serial Chip production. We also measured transmission properties of Serial Chip calls through natural habitat to calculate the approximate amplitude of vocalizations at the position of the calling bird. We suggest that amplitude regulation of vocalizations contibutes to signal transmission distance along with the established relationships between singing behaviour, acoustic structure and habitat. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.  相似文献   

17.
Active-sensing systems such as echolocation provide animals with distinct advantages in dark environments. For social animals, however, like many bat species, active sensing can present problems as well: when many individuals emit bio-sonar calls simultaneously, detecting and recognizing the faint echoes generated by one''s own calls amid the general cacophony of the group becomes challenging. This problem is often termed ‘jamming’ and bats have been hypothesized to solve it by shifting the spectral content of their calls to decrease the overlap with the jamming signals. We tested bats’ response in situations of extreme interference, mimicking a high density of bats. We played-back bat echolocation calls from multiple speakers, to jam flying Pipistrellus kuhlii bats, simulating a naturally occurring situation of many bats flying in proximity. We examined behavioural and echolocation parameters during search phase and target approach. Under severe interference, bats emitted calls of higher intensity and longer duration, and called more often. Slight spectral shifts were observed but they did not decrease the spectral overlap with jamming signals. We also found that pre-existing inter-individual spectral differences could allow self-call recognition. Results suggest that the bats’ response aimed to increase the signal-to-noise ratio and not to avoid spectral overlap.  相似文献   

18.
Signal plasticity is considered an important step in the evolution of animal communication. In acoustic communication, signal transmission is often constrained by background noise. One adaptation to evade acoustic signal masking is the Lombard effect, in which an animal increases its vocal amplitude in response to an increase in background noise. This form of signal plasticity has been found in mammals, including humans, and some birds, but not frogs. However, the evolution of the Lombard effect is still unclear. Here we demonstrate for the first time the Lombard effect in a phylogentically basal bird species, the tinamou Eudromia elegans. By doing so, we take a step towards reconstructing the evolutionary history of noise-dependent vocal plasticity in birds. Similar to humans, the tinamous also raised their vocal pitch in noise, irrespective of any release from signal masking. The occurrence of the Lombard effect in a basal bird group suggests that this form of vocal plasticity was present in the common ancestor of all living birds and thus evolved at least as early as 119 Ma.  相似文献   

19.
Bats rely heavily on acoustic signals in order to communicate with each other in a variety of social contexts. Among those, agonistic interactions and accompanying vocalizations have received comparatively little study. Here, we studied the communicational behaviour between male greater mouse-eared bats (Myotis myotis) during agonistic encounters. Two randomly paired adult males were placed in a box that allowed us to record video and sound synchronously. We describe their vocal repertoire and compare the acoustic structure of vocalizations between two aggression levels, which we quantified via the bats’ behaviour. By inspecting thirty, one-minute long encounters, we identified a rich variety of social calls that can be described as two basic call types: echolocation-like, low-frequency sweeps and long, broadband squawks. Squawks, the most common vocalization, were often noisy, i.e. exhibited a chaotic spectral structure. We further provide evidence for individual signatures and the presence of nonlinear phenomena in this species’ vocal repertoire. As the usage and acoustic structure of vocalizations is known to encode the internal state of the caller, we had predicted that the spectral structure of squawks would be affected by the caller’s aggression level. Confirming our hypothesis, we found that increased aggression positively correlated with an increase in call frequency and tonality. We hypothesize that the extreme spectral variability between and within squawks can be explained by small fluctuations in vocal control parameters (e.g. subglottal pressure) that are caused by the elevated arousal, which is in turn influenced by the aggression level.  相似文献   

20.
Bats feature prominently among organisms that occupy the aerosphereas they extensively use this environment for foraging, but alsofor dispersal, migration, and behavioral interactions. Differentialuse of the aerosphere is an important factor structuring batassemblages, with species exhibiting distinct morphological,physiological, and sensory adaptations to different habitattypes. This necessitates comprehensive sampling methodologiessuch as combined ground-level and canopy-level mist nettingas well as acoustic monitoring to assess the presence, diversity,and activity of different functional groups of species adequately.Recent technological advances in acoustic detection and in methodsof analysis, coupled with the expansion of libraries of echolocationcalls for species identification, now allow for the reliablequantification of species numbers and activity of the scarcelyknown group of aerial insectivorous bats, particularly in species-richtropical assemblages. We provide a brief, exemplary overviewof recent studies on bats conducted in Panamá to demonstratethe necessity of comprehensive sampling methods and applicationof new technologies in order to adequately depict assemblagecomposition and responses of bats to structural changes in habitatsinduced by fragmentation. In addition to acoustic methods, miniaturizationof radio transmitters has provided new insights into the patternsof spatial use of the aerosphere by bats and has identifiedspecies-specific differences in mobility as one of the importanttraits that determines bats’ reactions to anthropogenicalterations of the landscape. Following the goals of the symposiumon aeroecology, we propose new avenues of research for probingthe aerosphere. We discuss how integration of a diverse arrayof remote sensing tools with data on species distribution andspecies traits, such as mobility and edge-sensitivity, mightprovide novel opportunities for the development, and applicationof conservation-oriented monitoring systems.  相似文献   

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