Identification of sympatric bat species by the echolocation calls

One hundred and thirty-eight echolocation calls of 63 free-flying individuals of five bat species (Rhinolophus ferrumequinum, Myotis formosus, Myotis ikonnikovi, Myotis daubentoni and Murina leucogaster) were recorded (by ultrasonic bat detector (D980)) in Zhi’an village of Jilin Province, China. According to the frequency-time spectra, these calls were categorized into two types: FM/CF (constant frequency) / FM (R. ferrumequinum) and FM (frequency modulated) (M. formosus, M. ikonnikovi, M. daubentoni and M. leucogaster). Sonograms of the calls of R. ferrumequinum could easily be distinguished from those of the other four species. For the calls of the remaining four species, six echolocation call parameters, including starting frequency, ending frequency, peak frequency duration, longest inter-pulse interval and shortest inter-pulse interval, were examined by stepwise discriminant analysis. The results show that 84.1% of calls were correctly classified, which indicates that these parameters of echolocation calls play an important role in identifying bat species. These parameters can be used to test the accuracy of general predictions based on bats’ morphology in the same forest and can provide essential information for assessing patterns of bat habitat use. __________ Translated from Journal of Northeast Normal University (Natural Science Edition), 2006, 38 (3): 109–114 [译自: 东北师范大学学报(自然科学版)]     

Acoustic identification of eight species of bat (mammalia: chiroptera) inhabiting forests of southern hokkaido, Japan: potential for conservation monitoring

Assessing the impact of forest management on bat communities requires a reliable method for measuring patterns of habitat use by individual species. A measure of activity can be obtained by monitoring echolocation calls, but identification of species is not always straightforward. We assess the feasibility of using analysis of time-expanded echolocation calls to identify free-flying bats in the Tomakomai Experimental Forest of Hokkaido University, Hokkaido, northern Japan. Echolocation calls of eight bat species were recorded in one or more of three conditions: from hand-released individuals, from bats flying in a confined space and from bats emerging from their roost. Sonograms of 171 calls from 8 bat species were analyzed. These calls could be categorized into 3 types according to their structure: FM/CF/FM type (Rhinolophus ferrumequinum), FM types (Murina leucogaster, Murina ussuriensis, Myotis macrodactylus and Myotis ikonnikovi) and FM/QCF types (Eptesicus nilssonii, Vespertilio superans and Nyctalus aviator). Sonograms of the calls of R. ferrumequinum could easily be distinguished from those of all other species by eye. For the remaining calls, seven parameters (measures of frequency, duration and inter-call interval) were examined using discriminant function analysis, and 92% of calls were correctly classified to species. For each species, at least 80% of calls were correctly classified. We conclude that analysis of echolocation calls is a viable method for distinguishing between species of bats in the Tomakomai Experimental Forest, and that this approach could be applied to examine species differences in patterns of habitat-use within the forest.     

Flight performance, foraging tactics and echolocation in the trawling insectivorous bat Myotis adversus (Chiroptera: Vespertilionidae)

The bat Myotis adversus hunts for prey by aerial hawking and by taking prey from the water surface with its feet (trawling). The flight performance and echolocation of this species were studied in Queensland, Australia, and comparisons were made with Myotis daubentoni , a bat filling a similar ecological niche in the Palaearctic Region. The bats foraged in very similar ways, using the same foraging tactics and feeding in similar habitats, yet they were not geometrically similar in shape. The slightly larger Myotis adversus had relatively larger wings than M. daubentoni , conferring a slightly lower wing-loading. Nevertheless, M. adversus flew faster than M. daubentoni during the searching phase of foraging. Myotis daubentoni turned in tighter circles than M. adversus . Both species used short frequency-modulated (FM) echolocation calls of a characteristic sigmoidal structure, and nulls typically observed in the calls were an observational artefact. Myotis adversus also adopted an unusual 'long'FM call while foraging. The relations between echolocation frequencies and body size were explored in male M. adversus . Specialized morphological and acoustic adaptations for prey capture by trawling in insectivorous bats are discussed.     

马铁菊头蝠(Rhinolophus ferrumequinum)回声定位声波与生境类型和环境因子的关系

2007年在吉林省罗通山自然保护区,利用超声波探测仪（Avisoft-SASLAB PRO）录制并分析不同生境中马铁菊头蝠的回声定位声波。结果显示马铁菊头蝠在不同类型生境中活动;各生境中回声定位声波参数存在显著差异（one-way ANOVA,P〈0.05）。从环境因子中通过主成分分析筛选出与其回声定位声波相关的植被、气候和地形因子,探讨回声定位声波与这些因子的相关性。结果显示FM1和FM2带宽与乔木高（r=-0.948,-0.825;P〈0.05）、FM1起始频率和FM2终止频率与林冠面积（r=-0.967,-0.958;P〈0.05）、FM1起始频率、FM2终止频率和峰频与湿度（r=-0.776、-0.875和-0.794,P〈0.05）、脉冲持续时间和脉冲间隔与平均灌木高均呈显著负相关（r=-0.911,-0.990;P〈0.05）,峰频与植被株数（r=0.756,P〈0.05）、脉冲持续时间与冠下高呈显著正相关（r=0.870,P〈0.05）。表明各种环境因子（植被因子、气候因子和地形因子）都在一定程度上影响回声定位声波,回声定位声波具有表型可塑性和生境适应性,这些特性决定了马铁菊头蝠生境利用的程度和可利用的资源。     

Echolocation calls of Rhinolophus ferrumequinum in relation to habitat type and environmental factors

The present experiment was carried out in Luotong Mountain Natural Reserve in Jilin Province of China in 2007. We recorded and analyzed the echolocation calls of Rhinolophus ferrumequinum in different habitats by using Avisoft Bioacoustics USG 116 and Avisoft-SASLAB PRO (Avisoft Bioacoustics, Berlin, Germany). Our results showed that R. ferrumequinum foraged in diverse habitats in the study area, and their echolocation calls were significantly variable in different habitats (One-Way ANOVA, P < 0.05). Vegetative, climatic and topographical factors were selected by using the principal component analysis and the correlations between the parameters of echolocation calls and these environmental factors were analyzed. The results indicated that although R. ferrumequinum always emitted FM/CF/FM echolocation calls in different habitats, the parameters of echolocation calls varied with variable environmental factors. Significant negative correlation existed between FM1 bandwidth and arbor height (r = ?0.948, P < 0.05), FM₂ bandwidth and arbor height (r = ?0.825; P < 0.05), FM1 starting frequency and canopy area (r = ?0.967, P < 0.05), FM₂ ending frequency and canopy area (r = ?0.958, P < 0.05), FM1 starting frequency and air relative humidity (r = ?0.776, P < 0.05), FM₂ ending frequency and air relative humidity (r = ?0.875, P < 0.05), peak frequency and air relative humidity (r = ?0.794, P < 0.05), pulse duration and average shrub height (r = ?0.911, P < 0.05), and inter-pulse interval and average shrub height (r = ?0.990, P < 0.05). Significant positive correlation existed between peak frequency and number of plants (r = 0.756, P < 0.05), and pulse duration and height below the canopy (r = 0.870, P < 0.05). Our results suggested that many kinds of ecological factors (such as vegetation factor, climatic factor and topographical factor) affected the structure of echolocation calls and made them diverse in different habitats, i.e., echolocation calls of bats had phenotypic flexibility and eco-adaptability. These characteristics determined the degree of available habitats and natural resources for R. ferrumequinum.     

三种共栖蝙蝠的回声定位信号特征及其夏季食性的比较

2005年6至9月,对桂林市郊区两个山洞中高颅鼠耳蝠(Myotissiligorensis)、菲菊头蝠(Rhinolo-phuspusillus)和黑髯墓蝠(Taphozousmelanopogon)的回声定位叫声特征和食性进行分析,并结合其形态特征与野外观察,推断其捕食生境和捕食策略。研究结果发现:黑髯墓蝠体型最大,声音特征属短调频型多谐波,一般为4个谐波,能量主要集中在第二谐波上,主频率为(32·84±1·17)kHz,选择鞘翅目和双翅目昆虫为主要食物;高颅鼠耳蝠(长调频型)和菲菊头蝠(长恒频-调频型),体型都较小,主频率分别是(84·44±8·13)kHz和(110·78±1·65)kHz,以双翅目昆虫为主要食物;而菲菊头蝠则以鞘翅目和双翅目昆虫为主要食物。上述结果证明,高颅鼠耳蝠、菲菊头蝠和黑髯墓蝠在声音和食物组成等方面出现了明显分化。     

江西省翼手目新记录-绯鼠耳蝠

绯鼠耳蝠(Myotis formosus)采自江西吉安井冈山市梨坪村石燕洞(26°35′99″N,114°12′46″E)。该地区年平均气温14℃,年均降雨量1865mm,属中亚热带湿润性气候。当地日落时间19∶20。该地植被覆盖率高达70%以上,生物资源丰富,主要以毛竹(Phyllostachys hterocycla)、杉木(Cunninghamia lanceolata)和木荷(SchimaSuperba)为主,其中毛竹为优势种群。在江西发现绯鼠耳蝠的分布,丰富了该物种在中国的分布,为进一步的研究和保护提供基本依据。1研究方法1·1样本采集和鉴定傍晚19∶00左右,在石燕洞洞口张网捕捉蝙蝠,然后进行体形和头骨测量。…     

Moth hearing in response to bat echolocation calls manipulated independently in time and frequency

We measured the auditory responses of the noctuid moth Noctua pronuba to bat echolocation calls which were manipulated independently in time and frequency. Such manipulations are important in understanding how insect hearing influences the evolution of echolocation call characteristics. We manipulated the calls of three bat species (Rhinolophus hipposideros, Myotis nattereri and Pipistrellus pipistrellus) that use different echolocation call features by doubling their duration or reducing their frequency, and measured the auditory thresholds from the A1 cells of the moths. Knowing the auditory responses of the moth we tested three predictions. (i) The ranking of the audibility of unmanipulated calls to the moths should be predictable from their temporal and/or frequency structure. This was supported. (ii) Doubling the duration of the calls should increase their audibility by ca. 3 dB for all species. Their audibility did indeed increase by 2.1-3.5 dB. (iii) Reducing the frequency of the calls would increase their audibility for all species. Reducing the frequency had small effects for the two bat species which used short duration (2.7-3.6 ms) calls. However, the relatively long-duration (50 ms), largely constant-frequency calls of R. hipposideros increased in audibility by 21.6 dB when their frequency was halved. Time and frequency changes influence the audibility of calls to tympanate moths in different ways according to call design. Large changes in frequency and time had relatively small changes on the audibility of calls for short, largely broadband calls. Channelling energy into the second harmonic of the call substantially decreased the audibility of calls for bats which use long-duration, constant-frequency components in echolocation calls. We discuss our findings in the contexts of the evolution of both bat echolocation call design and the potential responses of insects which hear ultrasound.     

在不同状态和生境复杂度中大蹄蝠回声定位叫声的可塑性

蝙蝠回声定位声波的可塑性对其适应不同状态、生境以及捕食和社会交流具有重要的作用。为进一步研究大蹄蝠的回声定位声波在不同状态和生境下的可塑性,通过室内行为实验,对大蹄蝠在4 种不同状态(室内飞行、静息、布袋内和手持)和4 种不同生境复杂度(室外、室内0 棵树、室内1 棵树、室内5 棵树)条件下飞行的回声定位声波特征进行研究。结果表明:大蹄蝠的回声定位声波为CF - FM 型,通常连续发出2 - 4 个脉冲组成一个脉冲组。对比大蹄蝠在4 种不同状态下的回声定位叫声发现,主频按静息、布袋内、手持、飞行的顺序依次降低,后端FM 频宽则按手持、布袋内、飞行和静息的顺序依次变短;而脉冲间隔和脉冲时程则均按静 息、飞行、布袋内、手持的顺序依次增加。对比大蹄蝠在4 种不同生境复杂度中飞行的回声定位叫声发现,主频按室外、室内0 棵树、室内1 棵树、室内5 棵树依次提高,而脉冲时程及脉冲间隔则依次缩短;室外放飞条件下的后端FM 频宽比室内飞行的短。研究结果说明,大蹄蝠在不同状态、不同生境复杂度条件下的回声定位叫声具有明显的可塑性和生境适应性。     

Support for the allotonic frequency hypothesis in an insectivorous bat community

The allotonic frequency hypothesis proposes that certain insectivorous bat species can prey upon moths that can hear bat echolocation calls by using echolocation frequencies outside the sensitivity range of moth ears. The hypothesis predicts that the peak frequencies of bat echolocation calls are correlated with the incidence of moths in the diets of these bats. The aim of this study was to test this prediction on a bat community dominated by bats using low duty cycle echolocation calls, i.e. aerial foraging, insectivorous species using frequency modulated calls. The community consisted of nine species, two molossids, Sauromys petrophillus and Tadarida aegyptiaca, five vespertilionids, Eptesicus capensis, Eptesicus hottentotus, Miniopteris schreibersii, Myotis tricolor, and Myotis lesueuri, one rhinolophid, Rhinolophus clivosus, and one nycterid, Nycteris thebaica. The insect fauna in the habitat used by the bat community was suited to the testing of the allotonic frequency hypothesis because more than 90% of the moths comprising the insect fauna were tympanate. These included Pyralidae (3.8%), Geometridae (44.9%), Notodontidae (3.8%), Arctiidae (4.6%), Lymantriidae (0.8%) and Noctuidae (32.4%). As predicted, peak echolocation frequency was correlated with the incidence of moths in the diets of these nine species (r=0.98, df=7, P<0.01). Furthermore, multivariate analysis revealed that echolocation frequency (t=9.91, n=129, P<0.001) was a better predictor of diet than forearm length (t=5.51, n=129, P<0.001) or wing area (t=-3.41, n=129, P<0.001). This suggests that the selection pressure exerted by moth hearing might have acted directly on call frequency and secondarily on body size and wing morphology, as part of the same adaptive complex. It is unlikely that dietary differences were due to temporal and spatial differences in the availability of prey because the pattern of differences in skull morphology of the nine species supported our dietary analyses. The skull morphology of a bat represents a historical record of the kind of diet it has become adapted to over its evolutionary history. These results suggest that prey defences may mediate other factors structuring bat communities, e.g. competition. Competition may be reduced for those species of bats that can circumvent prey defences.     

Acoustic characterization of bats from Malta: setting a baseline for monitoring and conservation of bat populations

Bioacoustic research has made several advancements in developing systems to record extensive acoustic data and classify bat echolocation calls to species level using automated classifiers. These systems are useful as echolocation calls give valuable information on bat behaviour and ecology and hence are widely used for research and conservation of bat populations. Despite the challenges associated with automated classifiers, due to the interspecific differences in call characteristics of bat species found in the Maltese Islands, the use of a quantitative and automated approach is investigated. The sound analysis pipeline involved the use of an algorithm to clean sound files from background noise and measure temporal and spectral parameters of bat echolocation calls. These parameters were then fed to a trained and validated artificial neural network using a bat call library built from reference bat calls from Malta. The automatic classifier achieved an overall correct classification rate of 98%. This high correct classification rate for reliable species identification may have benefitted from the absence of typically problematic species, such as species in the genus Myotis, in the analyses. This study’s results pave the way for efficient and reliable bat acoustic surveys in Malta in aid of necessary monitoring and conservation by providing an updated bat species list and their echolocation characteristics.     

高颅鼠耳蝠回声定位声波特征与分析

在自建的野外实验事内,录制雌雄成体高颅鼠耳蝠Myotis siligorensis不同行为状态(飞行、爬行、手持)回声定位声波,利用单因素方差分析(One-Way ANOVA)对不同状态及不同性别的回声定位声波参数进行均值多重比较和显著性差异分析.结果 表明,高颅鼠耳蝠回声定位声波为长的宽频带调频(FM)声波,有1~3个谐波,但能量主要集中在第一谐波.不同行为状态下,高颅鼠耳蝠声脉冲持续时间、声脉冲间隔和能率环均存在显著性差异(P<0.05),第一谐波起始频率和终止频率、主频率、带宽差异不显著;第一谐波终止频率、带宽、声脉冲持续时间和能率环的性别差异显著(P<0.05),具有性别二态性.高颅鼠耳蝠回声定位声波特征体现了其在捕食策略和捕食生境方面的生态适应.     

湖南省蝙蝠新纪录——大足鼠耳蝠

于湖南省永州市铜岩洞采集到14只蝙蝠,经鉴定为大足鼠耳蝠(Myotis ricketti),为湖南省翼手目新纪录.本文报道了该物种体型和头骨特征,并与浙江和安徽样本进行比较.大足鼠耳蝠发出典型的下扫调频声波,其低峰频、短时程的声波特征以及强壮的后足和锋利的爪等形态特征与其在水面"拖网式(trawhng)"捕食鱼类的捕食...     

Morphology, echolocation and foraging behaviour in two sympatric sibling species of bat (Tylonycteris pachypus and Tylonycteris robustula) (Chiroptera: Vespertilionidae)

We studied the wing morphology, echolocation calls, foraging behaviour and flight speed of Tylonycteris pachypus and Tylonycteris robustula in Longzhou County, South China during the summer (June–August) of 2005. The wingspan, wing loading and aspect ratio of the two species were relatively low, and those of T. pachypus were lower compared with T. robustula . The echolocation calls of T. pachypus and T. robustula consist of a broadband frequency modulated (FM) sweep followed by a short narrowband FM sweep. The dominant frequency of calls of T. pachypus was 65.1 kHz, whereas that of T. robustula was 57.7 kHz. The call frequencies (including highest frequency of the call, lowest frequency of the call and frequency of the call that contained most energy) of T. pachypus were higher than those of T. robustula , and the pulse duration of the former was longer than that of the latter. The inter-pulse interval and bandwidth of the calls were not significantly different between the two species. Tylonycteris pachypus foraged in more complex environments than T. robustula , although the two species were both netted in edge habitats (around trees or houses), along pathways and in the tops of trees. Tylonycteris pachypus flew slower (straight level flight speed, 4.3 m s⁻¹) than T. robustula (straight level flight speed, 4.8 m s⁻¹). We discuss the relationship between wing morphology, echolocation calls, foraging behaviour and flight speed, and demonstrate resource partitioning between these two species in terms of morphological and behavioural factors.     

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.     

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

The foraging and echolocation behaviour of Myotis evotis was investigated during substrate-gleaning and aerial-hawking attacks. Bats gleaned moths from both the ground and a bark-covered trellis, however, they were equally adept at capturing flying moths. The calls emitted by M. evotis during substrate-gleaning sequences were short, broadband, and frequency-modulated (FM). Three behavioural phases were identified: search, hover, and attack. Gleaning search calls were significantly longer in duration, lower in highest frequency, and larger in bandwidth than hover/attack calls. Calls were detected in only 68% of gleaning sequences, and when they were emitted, bats ceased calling 200 ms before attacking. Terminal feeding buzzes, the rapid increase in pulse repetition rate associated with an attempted prey capture, were never recorded during gleaning attacks. The echolocation calls uttered by M. evotis during aerial-hawking foraging sequences were also short duration, high frequency, FM calls. Two distinct acoustic phases were identified: approach and terminal. Approach calls were significantly different from terminal calls in all variables measured. Calls were detected in 100% of aerial-hawking attacks and terminal feeding buzzes were invariably produced. Gleaning hover/attack calls were spectrally similar to aerial approach calls, but were shorter in duration and emitted at a significantly lower (but constant) repetition rate than aerial signals. Although the foraging environment (flight cage contents) remained unchanged between tasks (substrate-gleaning vs. aerial-hawking), bats emitted significantly lower amplitude calls while gleaning. We conclude that M. evotis adjusts its echolocation behaviour to meet the perceptual demands (acoustical constraints) imposed by each foraging situations.Abbreviations BW bandwidth - CF constant frequency - dB SPL decibels sound pressure level - FM frequency modulated - HF highest frequency - LF lowest frequency - PF peak frequency Presented at the meeting Acoustic Images in Bat Sonar, a conference on FM echolocation honoring Donald R. Griffin's contributions to experimental biology (June 14–16, Brown University, Providence RI).     

普通长翼蝠食性结构及其回声定位与体型特征

在普通长翼蝠(Miniopterus fuliginosus)的捕食区内用灯诱法和网捕法调查潜在食物(昆虫)种类; 用粪便分析法鉴定普通长翼蝠的食物组成,发现其主要捕食体型较大的鳞翅目和鞘翅目昆虫,体积百分比分别为55%和38%.普通长翼蝠具有相对狭长的翼,翼展比为6.94 ± 0.13;翼载为(9.85 ± 0.83)N/m2,相对较大.飞行状态下普通长翼蝠的回声定位叫声为调频下扫型,声脉冲时程为(1.45 ± 0.06)ms,脉冲间隔为(63.08 ± 21.55)ms,主频较低,为(44.50 ± 2.26)kHz.研究表明,普通长翼蝠的形态特征和回声定位特征与其捕食行为有着密切的联系.     

大卫鼠耳蝠回声定位声波、翼型特征及夏季食性分析

2005 ～2009年,野外采集大卫鼠耳蝠(Myotis davidii)的回声定位声波、翼型数据及粪便样本,分析了其回声定位声波、翼型特征和夏季食性.结果表明,大卫鼠耳蝠回声定位声波主频为(60.4±10.0)kHz (Mean±SD),带宽为(54.7±8.5)kHz,能率环为7.4％±3.5％;翼展比为6.2±0...     

皮氏菊头蝠回声定位声波与年龄的关系

皮氏菊头蝠 (Rhinolophuspearsoni)雌性成体 5只和幼体 2只采自贵州省贞丰县珉谷镇。采用超声波探测仪 (D980 ,ULTRASOUNDDETECTOR)接收皮氏菊头蝠的回声定位声波 ,转换到原频率的 1 / 1 0后导入计算机 ,然后用专业声谱分析软件 (Batsound 3 1 0 )进行分析。成蝠在飞行和悬挂状态下的声波结构相似 ,只是声波各项参数值略有不同 :它们发射FM CF FM型声波 ,具有 2～ 3个谐波 ,主频率在飞行时为 5 6 80± 0 6 2kHz ,悬挂时为 5 8 0 5± 0 2 4kHz ;声脉冲时间和间隔在飞行时分别为 3 4 6 2± 5 2 9ms和 86 5 0± 1 9 72ms ,悬挂时分别为 4 1 0 8± 5 87ms和 1 1 7 2 9± 6 6 4 4ms ;能率环飞行时为 ( 4 4 0 6± 1 2 5 8) % ,悬挂时为 ( 4 6 0 0±2 4 2 5 ) %。幼蝠声波为CF FM型 ,谐波数为 5～ 8个 ,主频率明显低于成体 ,FM带宽窄于成体 ,声脉冲时间和间隔短于成体 ,能率环低于成体。皮氏菊头蝠回声定位声波与年龄有关 ,这可能因成体的声波主要是探测食物和周围环境的详细信息 ,而幼体主要是与母蝠进行交流。     

Interspecific responses to distress calls in bats (Chiroptera: Vespertilionidae): a function for convergence in call design?

Distress calls were recorded from three sympatric species of pipistrelle bat (Pipistrellus nathusii, P. pipistrellus and P. pygmaeus) in England and Northern Ireland. At foraging sites, we conducted playback experiments, consisting of experimental distress call sequences from each species and control sequences of random noise and sound recorded with no bats present. We measured response by simultaneously recording ultrasound during playbacks and counting the echolocation pulses above a predetermined threshold which were then identified to species. All three species responded to each other's calls. The number of recorded echolocation pulses of all species increased eight-fold, on average, during the playback of distress call sequences compared with the playback of ultrasonic noise, and four-fold compared with the playback of silence. In a separate playback experiment, the number of echolocation pulses of P. pygmaeus increased 14-fold during the playback of distress calls of four endemic species of bat from Madagascar (Emballonura atrata, Myotis goudoti, Miniopterus majori and M. manavi) compared with the playback of silence. This increased response might have been caused by the high calling rates of the Malagasy species. Distress calls of P. nathusii, P. pipistrellus and P. pygmaeus were structurally convergent, consisting of a series of downward-sweeping, frequency-modulated elements of short duration and high intensity with a relatively strong harmonic content. Selection may favour convergence in the structure of distress calls among bat species, if attracting heterospecifics increases the chance of repelling predators by mobbing.