Acoustic Communication

Babbling behavior in the sac-winged bat (Saccopteryx bilineata).

by Mirjam Knörnschild

Knörnschild M, Behr O, von Helversen O (2006) Babbling behavior in the sac-winged bat (Saccopteryx bilineata). Naturwissenschaften, 93(9): 451-455.

Infant babbling in humans and a few other primates plays an important role in allowing the young to practice the adult... more Infant babbling in humans and a few other primates plays an important role in allowing the young to practice the adult vocal repertoire during early behavioral development. Vocalizations uttered during babbling resemble, to some degree, the acoustic structure of adult vocalizations and are often produced in long bouts independent of any social context. Similar behavior, termed subsong or plastic song, is known from a variety of songbirds. Here, we show that pups of the sac-winged bat (Saccopteryx bilineata), a species with an unusually large vocal repertoire, produce renditions of all known adult vocalization
types during bouts of vocalizations, which appear to be independent of a distinct social context. Babbling occurs in pups of both sexes, even though only adult males, not females, utter all different vocalization types produced in infancy. To our knowledge, this is the first evidence of babbling in a nonprimate mammal and suggests that infant babbling may be necessary for the ontogeny of complex vocal repertoires.

Twin siblings sound alike – isolation call variation in the Noctule bat, Nyctalus noctula.

by Mirjam Knörnschild

Knörnschild M, von Helversen O, Mayer F (2007) Twin siblings sound alike – isolation call variation in the Noctule bat, Nyctalus noctula. Animal Behaviour, 74(4): 1055-1063.

We studied the individual variation in bat pups’ isolation calls in the noctule bat, one of the few bat species in... more We studied the individual variation in bat pups’ isolation calls in the noctule bat, one of the few bat species in which twin births are common. Based on discriminant function analyses we showed that pups’ isolation calls were individually distinct and therefore likely to bear vocal signatures suitable for acoustically mediated mother-offspring recognition. The comparison of individual variation of isolation calls in intra-twin and inter-twin pairs revealed that isolation calls of twin siblings were more similar to the calls of each other than to the isolation calls of unrelated pups of the same age. Therefore, isolation calls may not only encode individual identity but also affiliation to a certain social group (e.g. twin pairs). The distinctiveness of isolation calls increased with the age of the pups and calls of twin siblings remained similar to each other as the pups got older, whereas the calls of unrelated pups diverged, suggesting that vocal signatures become more distinct during ontogeny and that the similarity of twin siblings’ isolation calls is persistent over time.

Territorial counter-singing in male sac-winged bats (Saccopteryx bilineata): low frequency songs trigger a stronger response.

by Mirjam Knörnschild

Behr O, Knörnschild M, von Helversen O (2009) Territorial counter-singing in male sac-winged bats (Saccopteryx bilineata): low frequency songs trigger a stronger response. Behavioral Ecology and Sociobiology 63: 433-442.

In many animal species, individuals compete for resources but avoid escalated conflicts by threat displays, i.e. a... more In many animal species, individuals compete for resources but avoid escalated conflicts by threat displays, i.e. a mutual signalling behaviour that enables the opponents to predict the outcome of the conflict without the necessity of actual fighting. For example, territory holders may use acoustic signals to communicate not only their own identity and the borders of their territory but also their competitive quality, fighting ability and motivation. Here, we show that male sac-winged bats, Saccopteryx bilineata, adjust their vocal territorial displays according to the fundamental frequency of territorial songs of their opponents. In playback experiments with territorial males, low-frequency stimuli elicited a higher territorial song rate and length than high-frequency stimuli. Male S. bilineata that sing more often and with lower fundamental frequencies have been shown to sire more offspring than their competitors. Fundamental frequency of territorial songs, hence, may reveal male quality and, consequently, the resulting threat posed to competing males. We argue that this is reflected in the increased response of competitors to low-frequency territorial songs shown here. Such competitive signalling behaviour has been shown in a few mammal species like red deer and baboons but, thus far, not in bats.

The vocal repertoire of two sympatric species of nectar-feeding bats (Glossophaga soricina, G. commissarisi).

by Mirjam Knörnschild

Knörnschild M, Glöckner V, von Helversen O (2010) The vocal repertoire of two sympatric species of nectar-feeding bats (Glossophaga soricina, G. commissarisi). Acta Chiropterologica 12: 205-215.

We recorded social vocalizations from two sympatric species of glossophagine bats, Glossophaga soricina and G.... more We recorded social vocalizations from two sympatric species of glossophagine bats, Glossophaga soricina and G. commissarisi, using habituated captive groups that were housed in separate flight cages. Whenever possible, the species-specific vocalization types were described in the light of the social context in which they were produced. Several vocalization types within each species’ repertoire had remarkable similarities to vocalization types in the other species’ repertoire. Out of these, four vocalization types with interspecific acoustic similarities (approach pulses, distress calls, aggressive trills, and alert calls) were used in similar behavioral contexts in both species. Approach pulses were produced whenever a bat was flying towards an already occupied roost. Distress calls were uttered whenever a bat was attacked by conspecifics or restrained by the observer, whereas aggressive trills were produced during aggressive encounters prior to physical contact. Alert calls were uttered when bats were disturbed or when several individuals were circling the same location. The interspecific similarity of both the social context and the acoustic structure of vocalization types suggest that the potential for interspecific communication is high in G. soricina and G. commissarisi.

Complex vocal imitation during ontogeny in a bat.

by Mirjam Knörnschild

Knörnschild M, Nagy M, Metz M, Mayer F, von Helversen O (2010) Complex vocal imitation during ontogeny in a bat. Biology Letters 6: 156-159.

Vocal imitation—the ability to learn a previously unknown acoustic signal from a tutor—is considered to be a key... more Vocal imitation—the ability to learn a previously unknown acoustic signal from a tutor—is considered to be a key innovation in the evolution of speech. This faculty is very rare and patchily distributed within the animal kingdom, suggesting multiple instances of convergent evolution. It has long been predicted that bats should be capable of vocal imitation and our results provide evidence for this phenomenon. We report that pups of the bat Saccopteryx bilineata learn a complex vocalization through vocal imitation. During ontogeny, pups of both sexes imitate territorial song from adult males, starting with simple precursor songs that develop into genuine renditions. The resemblance of pup renditions to their acoustic model is not caused by physical maturation effects, is independent of pups’ gender and relatedness towards adult males and becomes more pronounced during ontogeny, showing that auditory experience is essential for vocal development. Our findings indicate that the faculty of vocal imitation is more widespread than previously thought and emphasize the importance of research on audiovocal communication in bats for a better understanding of the evolutionary origin of vocal imitation.

Individual identity encoding and environmental constraints in vocal recognition of pups by Australian sea lion mothers

by Benjamin Pitcher

Spatial release from masking in a free-field source identification task by gray treefrogs

by Vivek Nityananda

Humans and other animals often communicate acoustically in noisy social groups, in which the background noise... more Humans and other animals often communicate acoustically in noisy social groups, in which the background noise generated by other individuals can mask signals of interest. When listening to speech in the presence of speech-like noise, humans experience a release from auditory masking when target and masker are spatially separated. We investigated spatial release from masking (SRM) in a free-field call recognition task in Cope’s gray treefrog (Hyla chrysoscelis). In this species, reproduction requires that females successfully detect, recognize, and localize a conspecific male in the noisy social environment of a breeding chorus. Using no-choice phonotaxis assays, we measured females’ signal recognition thresholds in response to a target signal (an advertisement call) in the presence and absence of chorus-shaped noise. Females experienced about 3 dB of masking release, compared with a co-localized condition, when the masker was displaced 90° in azimuth from the target. The magnitude of masking release was independent of the spectral composition of the target (carriers of 1.3 kHz, 2.6 kHz, or both). Our results indicate that frogs experience a modest degree of spatial unmasking when performing a call recognition task in the free-field, and suggest that variation in signal spectral content has small effects on both source identification and spatial unmasking. We discuss these results in the context of spatial unmasking in vertebrates and call recognition in frogs.

Bachelor and paired male rufous-and-white wrens use different singing strategies

by David Bradley

To attract a breeding partner, males may behave differently when they are bachelors compared to when they are paired.... more To attract a breeding partner, males may behave differently when they are bachelors compared to when they are paired. Comparisons between groups of paired males versus groups of unpaired males in temperate-breeding animals have revealed such differences in signalling behaviour. Few studies, however, have explored how individual males alter their signalling behaviour with changes in pairing status, and very few investigations have explored paired versus unpaired male behaviour in tropical animals. During a 5-year study in Costa Rica, we analysed changes in the singing behaviour of male rufous-and-white wrens (Thryothorus rufalbus) when they were paired and when they were bachelors. We compared three aspects of male vocal behaviour: gross differences in song output, variation in repertoire use and differences in song structure. Males as bachelors had significantly higher song output and switched song types less frequently. Contrary to our expectation, bachelors sang significantly fewer song types from their repertoire compared to when those same males had a breeding partner. Songs sung by bachelor males were higher in syllabic diversity and had broader-bandwidth terminal syllables than the songs those males sang only when paired. Within song types, the fine structure of songs remained consistent across pairing status. Our results demonstrate that males change their singing behaviour with pairing status, delivering songs at a higher rate but with less variety when they are bachelors. Rufous-and-white wrens are renowned for their vocal duets, and we discuss the pattern of repertoire use in light of their duetting behaviour. These results enhance our understanding of how male behaviour varies with pairing status and the importance of vocal signalling behaviour in socially monogamous tropical animals.

Ethical questions about working with soundscapes

by Andra McCartney

Keynote presentation at World Forum for Acoustic Ecology conference in Koli, Finland, June 2010. A shorter version of this paper has been published in the Soundscape Journal.

When soundscape composers, documentarians and artists work with soundscapes, they are expressing relationships to the... more When soundscape composers, documentarians and artists work with soundscapes, they are expressing relationships to the place of work and its inhabitants and visitors, to the sounds listened to, recorded from or projected into the place, and to the audience of the work. Each time a soundscape composer designs a soundwalk or a theatre piece, an installation or broadcast work, relationships with the world are expressed through how the maker treats the place, the sounds and the audience. Does the maker want to reveal particular sonic aspects of the place as it is, as it used to be, as it might be? Does the composer want to create an ideal place through sound and if so, what are the characteristics of this imaginary place and what ideas and values inform this utopic creation? How does the composer treat the sounds? How prominent are the composer’s treatments in relation to the sounds originally heard in that place, and what are the characteristics of this electroacoustic ecology? What are the dominant and masked sounds in the piece and how do they interact? What connections are there in the work between what is heard in the piece and the place of recording? Does the maker imagine the audience as deafened into numbness and needing to be awakened to true listening by the composer or soundwalk leader’s approach to the soundscape? Do we imagine the listener is ignorant and needing enlightenment? Do we think of the listener as possessed of original and unusual ways of listening, contributing to an expanded awareness of how to work with soundscapes? What are the ethics of this expression, and how are these ethics informed by underlying ideologies of sound, of sound production, and of sound ecology?

Microhabitat selection in an assemblage of crickets (Orthoptera: Ensifera) of a tropical evergreen forest in Southern India

by Manjari Jain

Insect Conservation and Diversity
Volume 4, Issue 2, pages 152–158, May 2011
DOI: 10.1111/j.1752-4598.2010.00118.x

Psychoacoustic sampling as a reliable, non-invasive method to monitor orthopteran species diversity in tropical forests

by Manjari Jain

Biodivers Conserv 2007

How to be fed but not eaten: nestling responses to parental food calls and the sound of a predator's footsteps

by Benjamin Pitcher

A mutual understanding? Interspecific responses by birds to each other's aerial alarm calls

by Benjamin Pitcher

The memory remains: long-term vocal recognition in Australian sea lions

by Benjamin Pitcher

Delayed onset of vocal recognition in Australian sea lion pups (Neophoca cinerea)

by Benjamin Pitcher

Vocal discrimination in mate guarding male Australian sea lions: familiarity breeds contempt

by Benjamin Pitcher

Comparison of anuran acoustic communities of two habitat types in the Danum Valley Conservation Area, Sabah, Malaysia

by Markus Böckle

A Diversity of Songs Among Morphologically Indistinguishable Katydids of the Genus Mecopoda (Orthoptera: Tettigoniidae) From Southern India

by Vivek Nityananda

Five distinct song types of the genus Mecopoda were found in Southern India. Four were morphologically... more Five distinct song types of the genus Mecopoda were found in Southern India. Four were morphologically indistinguishable. Some of them were both sympatric and had synchronous breeding seasons. The songs of these five song types ranged from simple short chirps to highly complex songs with multiple components. The temporal patterns of the songs of the five song types were very distinctive, whereas their spectral features were similar. Component elements of the different songs were distinct despite overall similarity. The song types possibly represent sibling species.

Synchrony During Acoustic Interactions In the Bushcricket Mecopoda 'Chirper'(Tettigoniidae: Orthoptera) is Generated by a Combination of Chirp-by-Chirp Resetting and …

by Vivek Nityananda

In several bushcricket species, individual males synchronise their chirps during acoustic interactions. Synchrony is... more In several bushcricket species, individual males synchronise their chirps during acoustic interactions. Synchrony is imperfect with the chirps of one male leading or lagging the other by a few milliseconds. Imperfect synchrony is believed to have evolved in response to female preferences for leading chirps. We investigated the mechanism underlying synchrony in the bushcricket species Mecopoda ‘Chirper’ from Southern India using playback experiments and simulations of pairwise interactions. We also investigated whether intrinsic chirp period is a good predictor of leading probability during interactions between males. The mechanism underlying synchrony in this species differs from previously reported mechanisms in that it involves both a change in the oscillator’s intrinsic rate and resetting on a chirp-by-chirp basis. The form of the phase response curve differs from those of previously reported firefly and bushcricket species including the closely related Malaysian species Mecopoda elongata. Simulations exploring oscillator properties showed that the outcome of pairwise interactions was independent of initial phase and alternation was not possible. Solo intrinsic chirp period was a relatively good predictor of leading probability. However, changing the intrinsic period during interactions could enable males with longer periods to lead during acoustic interactions.

Selective Attention In a Synchronising Bushcricket: Physiology, Behaviour and Ecology

by Vivek Nityananda

Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling neighbours. In... more Synchronising bushcricket males achieve synchrony by delaying their chirps in response to calling neighbours. In multi-male choruses, males that delay chirps in response to all their neighbours would remain silent most of the time and be unable to attract mates. This problem could be overcome if the afferent auditory system exhibited selective attention, and thus a male interacted only with a subset of neighbours. We investigated whether individuals of the bushcricket genus Mecopoda restricted their attention to louder chirps neurophysiologically, behaviourally and through spacing. We found that louder leading chirps were preferentially represented in the omega neuron but the representation of softer following chirps was not completely abolished. Following chirps that were 20 dB louder than leading chirps were better represented than leading chirps. During acoustic interactions, males synchronised with leading chirps even when the following chirps were 20 dB louder. Males did not restrict their attention to louder chirps during interactions but were affected by all chirps above a particular threshold. In the field, we found that males on average had only one or two neighbours whose calls were above this threshold. Selective attention is thus achieved in this bushcricket through spacing rather than neurophysiological filtering of softer signals.