Bat Calls Research Articles

Bat distribution and activity in Montréal Island green spaces: Responses to multi-scale habitat effects in a densely urbanized area

In Quebec, Canada, 5 out of the 8 species of bats are considered potentially threatened or vulnerable. Measuring the impact on bat species of environmental changes brought about by urban development is crucial for bat species conservation. At which spatial scale does a gradient of increasing urbanization have the most significant effect on the distribution and activity of bats? To address this question, 3 sampling points in each of 24 green spaces (of different sizes, degree of “naturalness”, and presence or not of water) across Montréal Island were sampled over 3 separate nights in June and July 2006. Echolocation calls of bats were recorded with Anabat detectors. Bat activity was determined by species or group of species for each green space. Various habitat factors associated with the urban gradient were acquired using GIS along a range of spatial scales, from local to landscape scales (areas of 0.1 km to 2 km radius around sampling points). Results show that patterns of distribution and bat activity differ according to species. Bats of the Myotis genus and Perimyotis subflavus were found mostly in areas with a high percentage of forest cover and near running water. Eptesicus fuscus and Lasiurus cinereus appeared to be less selective, as they were distributed much more uniformly across the study area. The more local spatial scales (from 0.1 km to 0.5 km radius) seem to have had a predominant influence on habitat requirements of bats, particularly for forest-dwelling species.

Virtual Bats and Real Insects: Effects of Echolocation on Pheromone-Tracking Behavior of Male Corn Earworm Moths, Helicoverpa zea

This study examines effects of simulated echolocation calls of bats in a field setting on the flight activity and pheromone-tracking behavior of the male corn earworm moth, Helicoverpa zea (Lepidoptera: Noctuidae), an insect that responds evasively to echolocation calls of bats. Simulated echolocation was broadcast over crop fields in an area where moths were abundant during summer. Field collections of free-flying moths and pheromone trapping of male moths were conducted in the presence and absence of simulated calls. Numbers of moths captured were not affected in either experiment by presence of simulated echolocation calls. Contrary to previous evidence, these data suggest that moths are not dissuaded from tracking pheromones under a perceived high risk of predation. Exhibiting a continual anti-predator response under a sustained risk of predation could have negative impacts on reproductive success, leading males to take higher risks compared to situations in which predators are sporadically present.

The relative influence of competition and prey defences on the trophic structure of animalivorous bat ensembles

Deterministic filters such as competition and prey defences should have a strong influence on the community structure of animals like animalivorous bats which have life histories characterized by low fecundity, low predation risk, long life expectancy and stable populations. We investigated the relative influence of these two deterministic filters on the trophic structure of animalivorous bat assemblages in South Africa. We used null models to test if patterns of dietary overlap were significantly different from patterns expected by chance and multivariate analyses to test the correlations between diet and phenotype (body size, wing morphology and echolocation). We found little evidence that competition structured the trophic niche of coexisting bats. Contrary to predictions from competition, dietary overlap between bats of ensembles and functional groups (open-air, clutter-edge, and clutter foragers) were significantly higher than expected by chance. Instead, we found support for the predictions of the allotonic frequency hypothesis: there were significant relationships between peak echolocation frequency and the proportion of moths in the diets of bats at local and regional scales, and peak echolocation frequency was the best predictor of diet even after we controlled for the influence of body size and phylogeny. These results suggest that echolocation frequency and prey hearing exert more influence on the trophic structure of sympatric animalivorous bats than competition. Nonetheless, differential habitat use and sensory bias may also be major determinants of trophic structure because these are also correlated with frequencies of bat calls.

Intra- and Interspecific Responses to Rafinesque's Big-Eared Bat (Corynorhinus rafinesquii) Social Calls

Bats respond to the calls of conspecifics as well as to calls of other species; however, few studies have attempted to quantify these responses or understand the functions of these calls. We tested the response of Rafinesque's big-eared bats (Corynorhinus rafinesquii) to social calls as a possible method to increase capture success and to understand the function of social calls. We also tested if calls of bats within the range of the previously designated subspecies differed, if the responses of Rafinesque's big-eared bats varied with geographic origin of the calls, and if other species responded to the calls of C. rafinesquii. We recorded calls of Rafinesque's big-eared bats at two colony roost sites in South Carolina, USA. Calls were recorded while bats were in the roosts and as they exited. Playback sequences for each site were created by copying typical pulses into the playback file. Two mist nets were placed approximately 50–500 m from known roost sites; the net with the playback equipment served as the Experimental net and the one without the equipment served as the Control net. Call structures differed significantly between the Mountain and Coastal Plains populations with calls from the Mountains being of higher frequency and longer duration. Ten of 11 Rafinesque's big-eared bats were caught in the Control nets and, 13 of 19 bats of other species were captured at Experimental nets even though overall bat activity did not differ significantly between Control and Experimental nets. Our results suggest that Rafinesque's big-eared bats are not attracted to conspecifics' calls and that these calls may act as an intraspecific spacing mechanism during foraging.

Echolocation Call Analysis and Presence-Only Modelling as Conservation Monitoring Tools for Rhinolophoid Bats in Thailand

Bats are an important component of biodiversity in Southeast Asia, and are key indicators of habitat quality. Acoustic analysis of echolocation calls not only allows the identification of bat species that are difficult to capture, but also allows for rapid and standardised ways to survey and monitor bats over large areas. However keys based on call parameters must also account for geographic variation in call parameters, and consider any effects of morphology and sex on call frequency. Presence-only modelling can predict likely geographic locations of specific taxa, and can used to refine decision making so that species unlikely to occur in a specific region can be omitted from more localised acoustic libraries. Here we develop an acoustic library for the echolocation calls of rhinolophoid bats in Thailand, and use presence-only modelling (Maxent) to explore how species with similar calls in a library developed at the national level can sometimes be largely allopatric, and hence identifiable, once geographic range is predicted. Presence-only modelling can also be used to explore whether species with similar calls adjust call frequency in likely areas of sympatry. We analysed calls from fourteen species of rhinolophid and twelve hipposiderid species from Thailand. Calls from a further three rhinolophid and one hipposiderid species are also described but not analysed statistically because of small sample sizes. Even without considering geographic variation, 69% of rhinolophid (14 species with a minimum of five individuals/ species) and 91% of hipposiderid calls (12 species) could be classified successfully to species using two call parameters (frequency of most energy (FMAXE) and duration) in a discriminant function analysis. Most of the discrimination was achieved because species often utilised different frequency bands. Morphology can also affect call frequency both across and within species. In both rhinolophids and hipposiderid families there was a negative relationship between FMAXE and forearm length. Within species, FMAXE was negatively related to forearm length in Rhinolophus microglobosus, R. pusillus and R. thomasi, and positively related to forearm length in R. affinis and R. pearsonii. Male R. pusillus called at higher frequencies than females, although there was no sexual size dimorphism in forearm length. Call frequency was negatively related to relative humidity in R. pusillus, suggesting that bats called at lower frequencies in humid environments to counter increases in atmospheric attenuation. Presence-only modelling was used to show that some species with similar call frequencies (e.g., R. lepidus and R. microglobosus; R. yunanensis and R. trifoliatus are predicted to occur largely in allopatry, and so could be identified reliably in particular parts of the country. Presenceonly modeling can assist in predicting areas of overlap between species with similar call frequencies. Other species (e.g., R. malayanus, R. coelophyllus) overlap in frequency when data from all of Thailand are combined, but seem to avoid call overlap when syntopic. Hence acoustic identification can be improved by taking into account local distribution patterns and patterns of species coexistence. The creation of call libraries at a local scale would have extensive potential as a resource to monitor changes in species distributions through time.

Effects of Orientation and Weatherproofing on the Detection of Bat Echolocation Calls

Abstract Ultrasonic detectors are powerful tools for the study of bat ecology. Many options are available for deploying acoustic detectors including various weatherproofing designs and microphone orientations, but the impacts of these options on the quantity and quality of the bat calls that are recorded are unknown. We compared the impacts of three microphone orientations (horizontal, 45°, and vertical) and two weatherproofing designs (polyvinyl chloride tubes and the BatHat) on the number of calls detected, call quality, and species detected by the Anabat II bat detector system at 17 sites in central Kentucky in May and June 2008. Detectors with BatHat weatherproofing recorded significantly fewer call sequences, pulses per file, species per site, and lower quality calls. Detectors in the horizontal position also tended to record fewer files, fewer species, and lower quality calls. These results illustrate potential impacts of deployment method on quality and quantity of data obtained. Because weatherproofing and orientation impacted the quality and quantity of data recorded, comparison of results using different methodologies should be made with caution.

Bat calls while preying: A method for reconstructing the signal emitted by a directional sound source.

Understanding and modeling bat biosonar behavior should take into account what the bat actually emitted while exploring the surrounding environment. Recording of the bat calls could be performed by means of a telemetry system small enough to sit on the bat head, though filtering due to bat directivity affects recordings and not all bat species are able to carry such a device. Instead, remote microphone recordings of the bat calls could be processed by means of a mathematical method that estimates bat head orientation as a first step before calculating the amplitudes of each call for each frequency. This approach considers bat position with respect to each microphone, directivity, and head orientation for compensating microphone recordings of bat calls. The method has been tested in a laboratory environment using data from a Polaroid transducer as sound source: results are presented and discussed. A further improvement of the method is necessary as its performance for call reconstruction strongly depends on correct choice of the sample at which the recorded call is thought to start in each microphone data set.

Reliable detection of predator cues in afferent spike trains of a katydid under high background noise levels

Katydid receivers face the problem of detecting behaviourally relevant predatory cues from echolocating bats in the same frequency domain as their own conspecific mating signals. We therefore tested the hypothesis that katydids are able to detect the presence of insectivorous bats in spike discharges at early stages of nervous processing in the auditory pathway by using the temporal details characteristic for responses to echolocation sequences. Spike activity was recorded from an identified nerve cell (omega neuron) under both laboratory and field conditions. In the laboratory, the preparation was stimulated with sequences of bat calls at different repetition rates typical for the guild of insectivorous bats, in the presence of background noise. The omega cell fired brief high-frequency bursts of action potentials in response to each bat sound pulse. Repetition rates of 18 and 24 Hz of these pulses resulted in a suppression of activity resulting from background noise, thus facilitating the detection of bat calls. The spike activity typical for responses to bat echolocation contrasts to responses to background noise, producing different distributions of inter-spike intervals. This allowed development of a 'neuronal bat detector' algorithm, optimized to detect responses to bats in afferent spike trains. The algorithm was applied to more than 24 hours of outdoor omega-recordings performed either at a rainforest clearing with high bat activity or in rainforest understory, where bat activity was low. In 95% of cases, the algorithm detected a bat reliably, even under high background noise, and correctly rejected responses when an electronic bat detector showed no response.

Communication calls of little brown bats display individual-specific characteristics

Bats' echolocation signals have been shown to be situation-, colony-, and individual-specific, but whether or not these findings apply to bats' communication signals is not fully understood. The primary goal of this study was to test the hypothesis that the communication calls of adult little brown bats (Myotis lucifugus) are individual specific. Bats were paired to form focal pairs from June 2007 to August 2008. Each bat's vocalizations were recorded on a PC-based digital recorder with a custom made ultrasonic microphone. The vocal signals were first classified using a previously established classification scheme. Three acoustic parameters (the minimum and maximum frequencies, and the call duration) of two of the dominant call-types, the steep-FM and broadband noise bursts, of individual bats were further analyzed. Discriminant function analysis, and multi- and univariate analyses of variance of these parameters revealed that these vocal signals were individually distinct and likely contain individual signatures to allow bats to identify individuals acoustically.

Similar is not the same: Social calls of conspecifics are more effective in attracting wild bats to day roosts than those of other bat species

Many bat species regularly need to find new day roosts as they require numerous shelters each breeding season. It has been shown that bats exchange information about roosts among colony members, and use echolocation and social calls of conspecifics in order to find roosts. However, it is unclear if wild bats discriminate between social calls of conspecifics and other bat species while searching for roosts. Furthermore, the extent that bats are attracted to potential roosts by each of these two call types is unknown. We present a field experiment showing that social calls of conspecifics and other bat species both attract bats to roosts. During two summers, we played back social calls of Bechstein’s bats (Myotis bechsteinii) and Natterer’s bats (Myotis nattereri) from different bat boxes that can serve as roosts for these species. All experimental bat boxes were monitored with infrared video to identify the approaching bat species. Three species (M. bechsteinii, M. nattereri, and Plecotus auritus) approached the boxes significantly more often during nights when bat calls were played compared to nights without playbacks. Bechstein’s bats and Natterer’s bats were both more attracted to social calls of conspecifics than of the other species, whereas P. auritus did not discriminate between calls of either Myotis species. Only Bechstein’s bats entered experimental boxes and only at times when calls from conspecifics were played. Our findings show that wild bats discriminate between social calls of conspecifics and other bat species although they respond to both call types when searching for new roosts.

Behavioral Evidence for Community‐Wide Species Discrimination from Echolocation Calls in Bats

Recognizing species identity is crucial for many aspects of animal life and is often mediated by acoustic signals. Although most animals are able to distinguish acoustic signals of their own species from other sympatrically occurring species, it is yet unknown whether animals can distinguish among acoustic signals of different closely related sympatric species. In this context, echolocating bats are a particularly interesting model system: their echolocation system evolved primarily for spatial orientation and foraging, but recent studies indicate that echolocation also has an important communicative function. Yet, the role of echolocation calls for species discrimination and thus potentially for interspecific communication has not been investigated. Using a behavioral discrimination assay, we found that two species of wild horseshoe bats could discriminate calls of their own species from those of three sympatric congeneric species. We further show that the bats were able to discriminate between echolocation calls of different congeneric species from the local community. In both cases, discrimination ability was high despite strong overlap of species' call frequency bands. This study provides the first experimental evidence for species discrimination based on echolocation calls. On a more general level, it shows for the first time that animals can distinguish among acoustic signals of different closely related and ecologically similar species from their local community.

Reliable Automation of Bat Call Identification for Eastern New South Wales, Australia, Using Classification Trees and AnaScheme Software

Accurate and efficient identification of bat (Microchiroptera) echolocation calls has been hampered by poor knowledge of the intraspecific variability in calls (including regional variation), a lack of call parameters for use in separating species and the amount of time required to manually identify individual calls or call sequences. We constructed and tested automated bat call identification keys for three regions in New South Wales, Australia, using over 4,000 reference calls in ≈300 call sequences per region. We used the program AnaScheme to extract time, frequency and shape parameters from calls recorded with the Anabat system. Classification trees were built to separate species using these parameters and provided the decision rules for construction of the keys. An ‘Unknown’ category was included in the keys for sequences that could not be confidently identified to species. The reliability of the keys was tested automatically with AnaScheme, using independent sets of reference call sequences, and key...

Fear conditioned discrimination of frequency modulated sweeps within species-specific calls of mustached bats.

Social and echolocation vocalizations of bats contain different patterns of frequency modulations. An adult bat's ability to discriminate between various FM parameters, however, is not well established. Using changes in heart rate (HR) as a quantitative measure of associative learning, we demonstrate that mustached bats (Pteronotus parnellii) can be fear conditioned to linear frequency modulated (FM) sweeps typically centered at their acoustic fovea (∼60 kHz). We also show that HR is sensitive to a change in the direction of the conditional frequency modulation keeping all other parameters constant. In addition, a change in either depth or duration co-varied with FM rate is reflected in the change in HR. Finally, HR increases linearly with FM rate incremented by 0.1 kHz/ms from a pure tone to a target rate of 1.0 kHz/ms of the conditional stimulus. Learning is relatively rapid, occurring after a single training session. We also observed that fear conditioning enhances local field potential activity within the basolateral amygdala. Neural response enhancement coinciding with rapid learning and a fine scale cortical representation of FM sweeps shown earlier make FMs prime candidates for discriminating between different call types and possibly communicating socially relevant information within species-specific sounds.

Auditory-based defence against gleaning bats in neotropical katydids (Orthoptera: Tettigoniidae)

Neotropical katydids (Orthoptera: Tettigoniidae) are preyed on by gleaning bats, which are known to use male calling songs to locate them. At least one katydid species has been reported to stop singing in response to bat echolocation calls. To investigate the relationship between this behavioural defence and ecological and sensory factors, we surveyed calling song characteristics, song cessation in response to the echolocation calls of a sympatric gleaning bat (Trachops cirrhosus), and T-cell responses (an auditory interneuron sensitive to ultrasound) in five katydid species from Panamá. The two katydid species that stopped singing in response to bat calls (Balboa tibialis and Ischnomela gracilis, Pseudophyllinae) also had the highest T-cell spike number and rate in response to these stimuli. The third pseudophylline species (Docidocercus gigliotosi) did not reliably cease singing and had low T-cell spiking activity. Neoconocephalus affinis (Copiphorinae) produced continuous calling song, possibly preventing males from hearing the bat during singing, and did not show a behavioural response despite high T-cell activity in response to bat calls. Steirodon rufolineatum (Phaneropterinae) did not cease singing and differed in T-cell activity compared to the other species. T-cell function might not be conserved in katydids, and evidence for this idea is discussed.

To females of a noctuid moth, male courtship songs are nothing more than bat echolocation calls

It has been proposed that intraspecific ultrasonic communication observed in some moths evolved, through sexual selection, subsequent to the development of ears sensitive to echolocation calls of insectivorous bats. Given this scenario, the receiver bias model of signal evolution argues that acoustic communication in moths should have evolved through the exploitation of receivers' sensory bias towards bat ultrasound. We tested this model using a noctuid moth Spodoptera litura, males of which were recently found to produce courtship ultrasound. We first investigated the mechanism of sound production in the male moth, and subsequently the role of the sound with reference to the female's ability to discriminate male courtship songs from bat calls. We found that males have sex-specific tymbals for ultrasound emission, and that the broadcast of either male songs or simulated bat calls equally increased the acceptance of muted males by the female. It was concluded that females of this moth do not distinguish between male songs and bat calls, supporting the idea that acoustic communication in this moth evolved through a sensory exploitation process.

Repertoire and possible functions of social calls in foraging big brown bats (Eptesicus fuscus).

While the echolocation calls of big brown bats (Eptesicus fuscus) have been studied extensively, this species’ communicative vocalizations have received little attention. Calls were recorded from pairs of bats flying in a laboratory flight room in a foraging context. Pairs consisted of naive bats flown with individuals that were either experienced about how to take a tethered insect or naive or of two experienced bats flying together. This situation elicited a variety of vocalizations with properties different from typical E. fuscus echolocation calls. Seven different call shapes that occurred only when two bats were present were identified and categorized. These included chirp-like calls, rising frequency calls, calls that were longer than 20 ms in duration, and series of ultrasonic, chirp-like calls (or “songs”) produced only by male bats and displaying individual variation. Some call types were only recorded when a juvenile was present or very rarely in adult-only pairs. Using high-speed video data collected in synchrony with the audio recordings, the contexts and possible functions of various calls are evaluated. The rate at which different call types were recorded with regard to bats’ knowledge of the foraging task and the age and sex of bats flown together is also considered.

Social calls used by a leaf-roosting bat to signal location.

Social calls in bats have many functions, including mate attraction and maintaining contact during flight. Research suggests that social calls may also be used to transfer information about roosts, but no studies have yet demonstrated that calls are used to actively attract conspecifics to roosting locations. We document the social calls used by Spix's disc-winged bat (Thyroptera tricolor) to actively recruit group members to roosts. In acoustic trials, we recorded two sets of calls; one from flying individuals termed 'inquiry calls', and another from roosting bats termed 'response calls'. Inquiry calls were emitted by flying bats immediately upon release, and quickly (i.e. 178 ms) elicited production of response calls from roosting individuals. Most flying bats entered the roost when roosting individuals responded, while few bats entered the roost in the absence of a response. We argue that information transfer concerning roost location may facilitate sociality in T. tricolor, given the ephemeral nature of roosting structures used by this species.

Anti-bat tiger moth sounds: Form and function

Abstract The night sky is the venue of an ancient acoustic battle between echolocating bats and their insect prey. Many tiger moths (Lepidoptera: Arctiidae) answer the attack calls of bats with a barrage of high frequency clicks. Some moth species use these clicks for acoustic aposematism and mimicry, and others for sonar jamming, however, most of the work on these defensive functions has been done on individual moth species. We here analyze the diversity of structure in tiger moth sounds from 26 species collected at three locations in North and South America. A principal components analysis of the anti-bat tiger moth sounds reveals that they vary markedly along three axes: (1) frequency, (2) duty cycle (sound production per unit time) and frequency modulation, and (3) modulation cycle (clicks produced during flexion and relaxation of the sound producing tymbal) structure. Tiger moth species appear to cluster into two distinct groups: one with low duty cycle and few clicks per modulation cycle that supports an acoustic aposematism function, and a second with high duty cycle and many clicks per modulation cycle that is consistent with a sonar jamming function. This is the first evidence from a community-level analysis to support multiple functions for tiger moth sounds. We also provide evidence supporting an evolutionary history for the development of these strategies. Furthermore, cross-correlation and spectrogram correlation measurements failed to support a “phantom echo” mechanism underlying sonar jamming, and instead point towards echo interference.

Changing durations of southern resident killer whale (Orcinus orca) discrete calls between two periods spanning 28 years

Killer whales vocalize in order to navigate, forage, communicate, and engage in social behavior. The sounds made by killer whales are classified into three types of vocalizations: clicks, whistles, and discrete calls. Discrete calls are pulsed calls that have been categorized into stereotyped call types (Ford 1987). Discrete calls are easily differentiated by the human ear and also provide a unique spectrographic structure. Discrete call usage in killer whales of the eastern North Pacific represents one case in which long-term studies of underwater acoustic communication are available. There are several distinct populations of killer whales that use the inland waters of British Columbia and Washington. This study focuses on the fish-eating Southern Resident population that utilizes the waters off the southern end of Vancouver Island. The Southern Residents comprise three pods ( J-, K-, and L-Pods) that, as of July 2009, totaled 85 animals (Center for Whale Research 2009). The Southern Resident population is currently listed as endangered under the Endangered Species Act in the United States (as of 2005) and the Species at Risk Act in Canada (as of 2003). A standard catalogue of the 25 discrete call types used by Southern Residents has been developed (Ford 1987). Each call type has an alphanumeric designation made up of a letter that denotes the community of whales that produce that call and an arbitrary number that indicates the order in which the call was first identified. “S” is the prefix for the 25 call types and their associated subtypes made by Southern Residents (Ford 1987). In general, vocalizations can vary in multiple parameters, such as call rate, frequency, amplitude, or duration, and these parameters can change for many reasons. The factors influencing vocalization parameters vary between species and between vocalizations. For example, the calls of greater horseshoe bats (Rhinolophus ferrumequinum) are known to undergo maturational effects ( Jones and Ransome 1993), whereas the vocalizations of Weddell seals (Leptonychotes weddellii) vary with seasonality (Rouget et al. 2007). On a more rapid timescale, changing behavioral contexts are known to influence the parameters of vocalizations in species like bottlenose dolphins (Tursiops truncatus) ( Janik and Slater 1998). On a more prolonged timescale, factors in the social environment, such as group membership, will lead to changes in call

Ultrasonic courtship songs of male Asian corn borer moths assist copulation attempts by making the females motionless

Males of the Asian corn borer moth Ostrinia furnacalis (Guenee) produce an ultrasonic courtship song of extremely low-intensity during copulation attempts. The song has been shown to significantly increase the mating success of the male; however, the mode of action of the sound in courtship remains to be resolved. Behavioural experiments using pairs with deafened females or muted males show that, without the aid of the sound, 63% of males eventually succeed in mating after several copulation attempts, whereas the remainder (37%) make repeated attempts in vain until interrupted by the escape of the female. Because few (2%) males fail to copulate when females hear the courtship song, it is evident that the song has an effect on females, promoting the success of copulation attempts. In support of this view, males produce louder songs if the first copulation attempt fails, suggesting that the males increase their sound levels to achieve successful copulation. It is suggested that the ultrasonic songs of the male render the females motionless, which is the same response as that to ultrasonic bat calls. Because even slight movements by the female can interfere with the attempt of the male to copulate, it is likely that, by making her motionless, the success rate of a single copulation attempt is increased greatly.