Bat Calls Research Articles

Bat Activity in the Boreal Forest: Importance of Stand Type and Vertical Strata

We examined habitat use by bats in the boreal forest of central Saskatchewan during summer 1995 by monitoring echolocation calls across forest types and through the canopy of mature forest. We sampled bat activity in mature aspen ( Populus tremuloides )-white spruce ( Picea glauca ) mixedwood, aspen, and jack pine ( Pinus banksiana ) stands and recorded passes from little brown ( Myotis lucifugus ), northern long-eared ( M. septentrionalis ), big brown ( Eptesicus fuscus ) or silver-haired bats ( Lasionycteris noctivagans ), and hoary ( Lasiurus cinereus ) bats. There were significantly more bat passes per night in the aspen-white spruce mixedwood forest than in aspen or jack pine forest. There was no difference in the proportion of feeding buzzes recorded from aspen-white spruce mixedwood and aspen forest. In aspen forest, mean number of hoary bat calls per night was higher above than below the canopy, whereas number of Myotis calls was higher within and above the canopy than below the canopy. There was no difference in the number of feeding buzzes recorded among the three canopy heights. Bat activity peaked toward sunset below the canopy but was more uniform within and above the canopy. Our results highlight the importance of mature aspen-white spruce mixedwood and aspen forest as habitat for boreal forest-dwelling bats and demonstrate for the first time that insectivorous bats are active both within and above canopy levels of the boreal forest.

The relationships between echolocation calls, morphology and diet in insectivorous bats

AbstractIn this study we explored quantitatively the relationships between the size of bats, the frequencies in their echolocation calls, and the incidence of moths and beetles in their diets. We focused on the predictions of the allotonic frequency hypothesis which states that some insectivorous bats increase their access to moths that can hear echolocation calls by shifting to frequencies to which the ears of these insects are less sensitive. The hypothesis predicts that the frequencies dominating the echolocation calls of bats may be correlated with the incidence of moths in their diets. We collected data for 62 species of bats that take airborne prey, usually flying insects, 25 species of high duty cycle echolocating bats (Rhinolophidae and Hipposideridae) and 37 species that are low duty cycle echolocators (Vespertilionidae and Molossidae). For bats whose echolocation calls are dominated by frequencies < 100 kHz our regression analyses showed a parabolic dependency between moth consumption (% volume or % frequency) and echolocation call frequency (kHz), supporting the allotonic frequency hypothesis. The use of echolocation calls dominated by frequencies outside the range of best hearing by moths may indeed increase the availability of these insects to the bats. However, when the same analysis was performed with only the bat species using echolocation calls dominated by sounds > 100 kHz, the relationship was not statistically significant, suggesting that morphological characteristics rather than echolocation call frequency may limit the range of potential prey items. Our analyses also demonstrate the importance of jaw morphology as a predictor of the incidence of beetles or moths in the diets of bats, and reveal that generally bigger species (as defined by forearm length) use echolocation calls dominated by lower frequencies than smaller species. In both high duty and low duty cycle echolocating bats the relationship between body size and dominant call frequency was best described by a linear model. We also propose that perch hunting was central in the development of the high duty cycle approach to echolocation.

The relationships between echolocation calls, morphology and diet in insectivorous bats

In this study we explored quantitatively the relationships between the size of bats, the frequencies in their echolocation calls, and the incidence of moths and beetles in their diets. We focused on the predictions of the allotonic frequency hypothesis which states that some insectivorous bats increase their access to moths that can hear echolocation calls by shifting to frequencies to which the ears of these insects are less sensitive. The hypothesis predicts that the frequencies dominating the echolocation calls of bats may be correlated with the incidence of moths in their diets. We collected data for 62 species of bats that take airborne prey, usually flying insects, 25 species of high duty cycle echolocating bats (Rhinolophidae and Hipposideridae) and 37 species that are low duty cycle echolocators (Vespertilionidae and Molossidae). For bats whose echolocation calls are dominated by frequencies < 100 kHz our regression analyses showed a parabolic dependency between moth consumption (% volume or % frequency) and echolocation call frequency (kHz), supporting the allotonic frequency hypothesis. The use of echolocation calls dominated by frequencies outside the range of best hearing by moths may indeed increase the availability of these insects to the bats. However, when the same analysis was performed with only the bat species using echolocation calls dominated by sounds > 100 kHz, the relationship was not statistically significant, suggesting that morphological characteristics rather than echolocation call frequency may limit the range of potential prey items. Our analyses also demonstrate the importance of jaw morphology as a predictor of the incidence of beetles or moths in the diets of bats, and reveal that generally bigger species (as defined by forearm length) use echolocation calls dominated by lower frequencies than smaller species. In both high duty and low duty cycle echolocating bats the relationship between body size and dominant call frequency was best described by a linear model. We also propose that perch hunting was central in the development of the high duty cycle approach to echolocation.

Bats are Not Birds--a Cautionary Note on Using Echolocation Calls to Identify Bats: a Comment

Monitoring and identifying echolocating bats in the field has been used extensively for many years, and O'Farrell et al. (1999) present an updated qualitative method for identifying species from their echolocation calls. However, they make the assumption that, like bird songs, echolocation calls of bats are species-specific. There is no reason to expect that natural selection favored incorporation of this information. Although identification of some species of bats by their calls is possible, variation at several levels makes other species indistinguishable. Monitoring echolocation in the field and identifying species can be useful in determining presence or absence of species and factors influencing activity of bats. However, limitations and degree of reliability of the technique must be recognized. Only by more explicitly defining how the method is used and quantifying characteristics that define calls of recognizable species will the method be scientifically sound and repeatable. I suggest a number of guidelines for use of the method in field studies.

Bat Activity in Thinned, Unthinned, and Old-Growth Forests in Western Oregon

Many aspects of the influences of forest management activities on bats (Chiroptera) in the Pacific Northwest are poorly known, We compared thinned and unthinned forest stands of the same age and old-growth forest stands to determine potential differences in structure and amount of use by bats. We hypothesized that activity levels of bats would differ in stands differing in structure as a result of management bistory and that activity of bats would be similar in stands of similar structure. We used automated ultrasonic detectors (Anabat II) to record calls of bats in 50-100-year-old thinned and unthinned stands, and in old-growth (200 yr old) stands in the Oregon Coast Range during the summers of 1994 and 1995. Our median index of bat activity was higher in old-growth than in unthinned stands and higher in thinned than in unthinned stands, We were not able to detect a significant difference between the index of median bat activity for old-growth and thinned stands. More than 90% of identifiable passes were identified as calls from Myotis species. The 3 stand types we examined differed in certain structural characteristics such as density and size of trees, and amount of overstory and understory cover. We concluded that the structural changes caused by thinning may benefit bats by creating habitat structure in young stands that bats are able to use more effectively.

Predation risk and mating behavior: the responses of moths to bat-like ultrasound

In the presence of predators, animal* may reduce or alter their mating activities. There has been little experimental study of whether mating behavior varies with the level of predation risk. Two species of moths, Pseudaletia unipuncta (Noctuidae) and Ostrinia nubilalis (Pyralidae), significantly reduced their mate-seeking behavior under high levels of simulated predation risk. Male moths aborted upwind flight in a pheromone phime, and females stopped releasing pheromone in response to sounds simulating the echolocation calls of bats. For 0. nubilalis, but not for P. unipuncta, the response varied significantly with the level of predation risk. Interspecific differences in behavioral responses likely reflect differences in physiological auditory sensitivity and/or behavioral thresholds. Female behavioral responses to sounds simulating the calls of bats that glean their prey from surfaces were significantly weaker than their responses to sounds resembling the calls of aerially hawking bats; these results support the neurophysiological data that the calls of gleaning bats are relatively inaudible to moths. This study indicates that some animals can modify their reproductive activities in response to auditory cues from predators. Key words: bats, mating behavior, moths, Ostrinia nubilalis, pheromone, predation risk, Pseudaletia unipuncta, ultrasound. [Behav Ecol 9:552-558 (1998)]

Effects of Interindividual Variation in Echolocation Calls on Identification of Big Brown and Silver-Haired Bats

Identifying bat species from their calls is a common technique in studies of habitat use. I tested the hypotheses that significant interindividual intraspecific variation exists in the echolocation calls of bats as detected by frequency-divide ultrasonic detectors, and that such variation could greatly affect the accuracy of species identification. I restricted analysis to 2 species that have similar hut reportedly distinguishable calls. There was significant intraspecific variation in 6 variables for each species, and frequency distributions of the 2 species overlapped greatly for all 6 variables; hence, univariate analysis was ineffective at differentiating between species. The best of experienced human observers correctly identified the species for only 70% of 47 call sequences compared to >95% correct classification by discriminant function analysis. Alterations in current methodology can improve accuracy of identification and thus the value of habitat studies and management decisions that rely on such identification.

Compromises: sound frequencies used in echolocation by aerial-feeding bats

Hunting aerial-feeding bats, species that take airborne prey (usually flying insects), use echolocation to detect, track,and assess targets. The echolocation calls of aerial-feeding bats at sites in Canada (British Columbia and Ontario), Mexico,Brazil, and Zimbabwe were significantly dominated by frequencies between 20 and 60 kHz, although at the more tropicallocations some aerial-feeding bats used echolocation calls with most energy &lt;20 or &gt;60 kHz. The impact of frequency-specificattenuation, perhaps combined with frequency-specific, hearing-based defenses of some insects, suggests that by usingecholocation calls &lt;20 kHz, bats could both extend the effective range of echolocation and make their calls less conspicuous toinsect ears. Bats using calls &gt;60 kHz would be less conspicuous to the insects. We found two patterns of echolocation-callbehaviour. Most adjacent echolocation calls, and all that were dominated by sounds &gt;20 kHz, showed large (80%) overlap inbandwidth. The other pattern involved much less overlap in bandwidth (0–30%) between adjacent calls and was evident in thecalls of the molossid Tadarida midas, which used echolocation calls dominated by sounds &lt;20 kHz. This behaviour wouldallow the echolocating bat to extend its effective range of perception by separating in frequency the echoes returning fromadjacent calls.

Towards standardized descriptions of the echolocation calls of microchiropteran bats: pulse design terminology for seventeen species from Queensland

The identification of Australian microchiropteran bats using acoustics is in its infancy, with the Anabat System (Corben 1989) predominantly being adopted as a tool to undertake such a task. Although species-significant call characteristics of free-flying bats have not been documented, identification of bats is generally achieved by comparison of recorded calls with calls accompanying the software and/or release calls of captured bats. This practice can be unreliable if a mechanism to describe the call characteristics is not in place for workers to describe their assessments. A much needed part of this mechanism is a common language of ultrasonic terms to facilitate the exchange of information among bat workers. By way of contributing to this need, a terminology to classify the structure of calls (shapes) and another of call parameters was developed. A selection of call parameters, based on international microchiropteran literature, was adapted for Anabat use. The proposed terminologies were used, with th...

Bat Predation on Eared Moths: A Test of the Allotonic Frequency Hypothesis

Many species of moths (Lepidoptera) possess ears which enable them to hear the echolocation calls of bats and avoid predation. The range of best hearing of eared moths is to frequencies usually between 20 and 50 kHz; therefore, bats with calls above or below these frequencies are predicted to capture eared moths more frequently than other bats. This prediction is the basis of the allotonic frequency hypothesis. We conducted a field test of the hypothesis using three species of flutter-detecting bats which capture flying insects. The species were diadem leafnosed bat Hipposideros diadema (call frequency 55-58 kHz), eastern horseshoe bat Rhinolophus megaphyllus (67-71 kHz) and dusky leafnosed bat H. ater (160-164 kHz). Eared moths represented only 7.2% of individuals among prey remains of H. diadema. Moths dominated the diet of both R. megaphyllus and H. ater, being present in almost all faeces and representing the vast majority of prey remains. However, R. megaphyllus captured predominantly non-eared moths (Anthelidae, Lasiocampidae, Hepialidae) or Gelechioid moths, a superfamily which has not been tested for hearing. By contrast, H. ater fed mostly on eared moths, predominantly members of the family Noctuidae. Eared moths made up 91.7% and 82.5% of all moths captured by H. ater at two sites. The data show that the incorporation of eared moths in the diet was much higher in the bat species, H. ater, with a call frequency well above the range of best hearing of moths. This result supports the allotonic frequency hypothesis. Our study indicates that flutter-detecting bats could have imposed selective pressures on moths during the evolution of moth hearing.

The effect of recording situation on the echolocation calls of the New Zealand lesser short‐tailed bat (Mystacina tuberculata Gray)

Using a broad‐band recording system (150 Hz‐100 kHz) the echolocation calls of the lesser short‐tailed bat (Mystacina tuberculata) were recorded under three very different situations: free‐flying, flying within a flight cage, and on release from the hand. Calls of bats landing and feeding on a platform in Wellington Zoo were also recorded. Both the lowest frequency and frequency of peak amplitude of calls were significantly affected by the situation under which calls were recorded. Although the calls of free‐flying bats are different from those produced by bats foraging on the ground, it is unlikely that M. tuberculata uses echolocation to locate prey on the ground. No significant differences could be found between the calls emitted by male and female bats, and no consistent relationships were obvious between temporal and spectral call characteristics. There was some evidence to suggest that individual bats could be identified by their echolocation calls.

Yearly Activity Patterns of Bats at Belair National Park, In Adelaide, South Australia.

Bat activity was surveyed at Belair National Park, Adelaide and an adjacent house in Glenalta, March 1996 to March 1997, using the Anabat system. 44 bats of 6 species (Chalinolobus gouldii, C. morio, Vespadelus darlingtoni, V. regulus, V. vulturnus, and Nyctophilus geoffroyi) were captured, providing positive identification of calls. Three additional species were recorded (Tadarida australis, Mormopterus planiceps and an unidentified species). At Playford Lake, Belair, 2522 bat calls were recorded in 35 h, with most calls from V. darlingtoni (76.3% of total). At Glenalta, 1521 calls were recorded in 238 h, with most calls from C. gouldii (69.2% of total). V. darlingtoni, V. regulus and M. planiceps showed significantly more activity at Playford Lake, Belair, a wooded site beside a lake, than at Glenalta, a suburban site with artificial lighting, while activity of C. gouldii and T. australis was similar at the two sites. Most bats showed significant lower activity in winter, apart from V darlingtoni, which was active all year round at Belair. Nocturnal temperatures during the study varied from 6-31°C. The activity of most bat species showed no significant correlation with temperature, apart from C. gouldii at Belair, which averaged 1.2 passes per hour below 13°C and 9.3 passes per hour above l3°C.

A METHOD FOR THE SYNCHRONISATION AND CONTROL OF ULTRASOUND RECORDING AND STEREOPHOTOGRAMMETRY IN THE RECONSTRUCTION OF ANIMAL FLIGHT

ABSTRACT We describe equipment that controls the operation of flash guns for use in stereophotogrammetry and enables recording or the playback of bat calls to be synchronised with the photographic data. This equipment can readily be built using standard components and is suitable for use in the field.

Observations on the distribution, ecology, and behaviour of bats on the Galapagos Islands

The distribution of bats on five Galapagos islands was assessed using ultrasonic detectors that can identify the feeding calls of different bat species. Red bats (Lasiurus brachyotis) were present on Santa Cruz and San Cristobal. Hoary bats (L. cinereus) were present on Santa Cruz, San Cristobal, Isabela, Floreana and Santiago. Species identifications were confirmed by recordings of bat calls, observations of flying bats, and the capture of 21 red bats and three hoary bats. There was no evidence of other species of bats on the Galapagos. Body size measurements were similar to those of South American red (L. borealis) and hoary (L. c. villosissimus) bats. Species status of L. brachyotis is not supported by morphological data. Both species were active in lowland and highland habitats, and foraging activity was high around street lights. Radio telemetry was used to locate day roosts and the nightly activity areas of four red bats in lowland areas of Santa Cruz. During the day, these bats roosted singly in the foliage of nine species of plant. Nightly activity areas were 10 to 20 ha in size. The activity areas of individuals overlapped, and included their known day roost sites. Both bat species were apparently more active in lowland habitats during the cool garua season, and less active in lowland habitats during the hot season. Female red bats were more abundant in lowland habitats during the cool season than were male red bats. Mesic, upland habitat may be critical to the survival of bats in the Galapagos.

Search-phase echolocation calls of the New Zealand lesser short-tailed bat (Mystacina tuberculata) and long-tailed bat (Chalinolobus tuberculatus)

This paper describes the search-phase echolocation calls of lesser short-tailed bats (Mystacina tuberculata) and long-tailed bats (Chalinolobus tuberculatus). Calls were recorded from all three subspecies of short-tailed bat and seven populations of long-tailed bat, three in Northland, two in the central North Island, and two in the lower South Island. The calls were recorded in the field and digitised, then three spectral components and one temporal component of the calls were measured. Calls of the lesser short-tailed bat could be loosely classified into subspecies by means of multivariate discriminant function analysis. Similarly, long-tailed bat calls showed regional variation, and discriminant function analysis was able to fit calls to regional groups with a high rate of success. The significance of the results presented is discussed in terms of the conservation of New Zealand bats and the unique ecology of the lesser short-tailed bat.

A New Examination of Echolocation Calls of Some Neotropical Bats (Emballonuridae and Mormoopidae)

In northwestern Belize, two emballonurids (Rhynchonycteris naso and Saccopteryx bili­ neata) and three monnoopids (Pteronotus pamellii. P. davyi, and P. personatus) were examined acoustically with the Anabat II bat detector and associated analysis system. R. naso used calls consisting of a short constant frequency (CF) at 47 kHz and concave downward frequency modulated (PM) sweep to ca. 40 kHz with two strong hannorucs. Echolocation sequences of S. bilineata revealed a paired cadence of calls. Both signals in a pair slowly increased in frequency, fonning a quasi-CF (QCF) component and tenninated with a short, downward PM sweep. The initial call of a pair ranged from 44.5 to 46.6 kHz and the second ranged from 46.6 to 48.7 kHz. P. parnellii used a long CF call at 63.5 kHz, with a tenninal downward PM sweep to ca. 54.5 kHz. P. davyi produced calls with an initial short CF at 68.1 kHz, a downward PM sweep, and a tenninal short CF at 58.0 kHz. P. personatus emitted calls similar in shape to P. davyi, with the initial CF at 83.0 kHz and the terminal CF at ca. 68.0 kHz. Previous descriptions of echolocation calls for these species compare favorably with those obtained in this study, but the Anabat equipment generally revealed more variation and detail than previously described. The echolocation calls described in this study provide precise vocal signatures for the accurate identification of free-flying individuals of the species studied. The recording and description of echo­ location calls of some Neotropical bats be­ gan with the pioneering work of Griffin (1953) and Griffin and Novick (1955). Al­ though data gathered were surprisingly good, technological limitations prevented recording under a variety of field condi­ tions. Thus, much of the early descriptions of vocalizations were generated from cap­ tive bats. Bats of the families Emballonur­ idae and Mormoopidae tended to produce high-intensity sounds that were easier to de­ tect and record than the low-intensity, high­ ly directional sounds produced by bats in the Phyllostomidae. Subsequent examina­ tion of some of these species. using im­ proved equipment, resulted in more defini­ tive descriptions of echolocation calls (Novick, 1963; Pye, 1973), although the

Echolocation Calls of the Long-Tailed Bat: A Quantitative Analysis of Types of Calls

The echolocation calls of long-tailed bats (Chalinolobus tuberculatus) were recorded in the Eglinton Valley, Fiordland, New Zealand, and digitized for analysis with signal-processing software. Univariate and multivariate analyses of measured features facilitated a quantitative classification of the calls. Cluster analysis was used to categorize calls into two groups equating to search and terminal-buzz calls described qualitatively for other species. When moving from search to terminal phases, the calls decrease in bandwidth, maximum and minimum frequency of call, and duration. Search calls begin with a steep-downward FM sweep followed by a short, less-modulated component. Buzz calls are FM sweeps. Although not found quantitatively, a broadband pre-buzz group of calls also was identified. Ambiguity analysis of calls from the three groups shows that search-phase calls are well suited to resolving the velocity of targets, and hence, identifying moving targets in stationary clutter. Pre-buzz and buzz calls are better suited to resolving range, a feature that may aid the bats in capture of evasive prey after it has been identified.

Temporal Variation in Activity of Bats and the Design of Echolocation-Monitoring Studies

I used Anabat II bat detectors to monitor echolocation calls of bats over two streams in the Oregon Coast Range for a total of 195 detector-nights. Activity of bats was positively correlated with biomass of insects and minimum nightly temperature, and was negatively correlated with length of night; activity levels at the two streams were positively correlated. Activity of bats was not significantly correlated with either hours of moonlight or with phase of moon. Level of activity within a night generally peaked shortly after sunset with a second, smaller peak in activity shortly before sunrise, but patterns varied substantially among nights. Total nightly activity at a site also varied substantially among nights, sometimes varying several-fold on consecutive nights. To assess the implications of temporal variation in activity of bats on sampling, I randomly sampled subsets of the data using from 2- to 12-night sample periods and calculated mean levels of activity for each subset. For subsets with seven or more nights, >60% of the subsets had means that were within 20% of the mean of the entire dataset. Less than 50% of the subsets had means within 10% of the mean of the entire dataset for any number of nights subsampled. When comparing activity between sites, use of blocked or paired designs improved sampling efficiency by 20%. Failure to account for temporal variation in activity of bats when designing research projects and monitoring programs could result in biased estimates of activity of bats.

Science and the Conservation of Bats

The conservation implications of some recent advances in our knowledge about the ecology and behavior of bats are presented. A central question facing bat biologists is the relative importances of roosts and food as limiting factors in the population biology of bats. There is no reason to presume that the answer is the same for all species and the available data suggest intraspecific variation. This question is important for either conservation or behavior and ecology. Eavesdropping on the species-specific echolocation calls of bats has allowed documentation of distribution and habitat use by some bats although variability of calls complicates this picture. Radiotracking and surveys have produced data on use of space by bats. Although foraging areas and roosts are vital resources for bats, the associations between species of bats and habitats are not always clear. The mobility of bats and the low cost of flight together blur the link between bats and particular habitats. Radiotracking demonstrates how mobility gives bats access to mosaics of habitats, partly reflecting their size and flight characteristics, and the scale of habitat availability. For some species, access to mosaics of habitats for foraging is critical. Activities of humans influence the habitats available to bats and can generate feeding and roosting opportunities. The use that roosting bats make of buildings is an obvious example of bats benefitting from activities of humans. Another is bats feeding in the concentrations of insects at lights. In promoting the conservation of bats, it is important to consider people's perceptions of these animals, which are colored by the impact of bats on public health. Public interest in bats has vastly outstripped scientific research about them, presenting interesting challenges and opportunities for bat biologists.

The echolocation calls of the spotted bat Euderma maculatum are relatively inaudible to moths

Previous studies of the spotted bat Euderma maculatum have demonstrated that this bat emits echolocation calls that are lower in frequency, shorter in duration and fainter in intensity compared with those of most other insectivorous bats, acoustic characteristics which should render it less conspicuous to eared moths. We tested this prediction by monitoring electrophysiologically the ears of sympatric noctuoid (noctuid, arctiid and notodontid) moths in a site in western Canada. Auditory threshold curves demonstrate that most of the moths tested are less responsive to the calls of Eu. maculatum than to those of another sympatric bat, Eptesicus fuscus. Playbacks to moth ears of pre-recorded search- and approach-phase echolocation calls of Eu. maculatum and Ep. fuscus further demonstrate that the calls of Eu. maculatum are poorly detectable to moths and, in some cases, completely inaudible. We estimate that, in the wild, an average noctuoid moth would detect the calls of Eu. maculatum at distances of less than 1 m as opposed to the calls of Ep. fuscus which should be first heard at distances of 20&shy;25 m. Although most moths are unable to adequately hear Eu. maculatum, the observation that two individuals possessed ears sensitive to this bat's calls suggests the existence of auditory pre-adaptation to this type of echolocation.