A framework for the quantification of soundscape diversity using Hill numbers

1. Soundscape studies are increasingly common to capture landscape-scale ecological patterns. Yet, several aspects of soundscape diversity quantification remain unexplored. Although some processes influencing acoustic niche usage may operate in the 24h domain, most acoustic indices only capture the diversity of sounds co-occurring in sound files at a specific time of day. Moreover, many indices do not consider the relationship between the spectral and temporal traits of sounds simultaneously. To provide novel insights into landscape-scale patterns of acoustic niche usage at broader temporal scales, we present a workflow to quantify soundscape diversity through the lens of functional ecology. 2. Our workflow quantifies the functional diversity of sound in the 24-hour acoustic trait space. We put forward an entity, the Operational Sound Unit (OSU), which groups sounds by their shared functional properties. Using OSUs as our unit of diversity measurement, and building on the framework of Hill numbers, we propose three metrics that capture different aspects of acoustic trait space usage: (i) soundscape richness; (ii) soundscape diversity; (iii) soundscape evenness. We demonstrate the use of these metrics by (a) simulating soundscapes to assess if the indices possess a set of desirable behaviours; and (b) quantifying the soundscape richness and evenness along a gradient in species richness to illustrate how these metrics can be used to shed unique insights into patterns of acoustic niche usage. 3. We demonstrate that: (a) the indices outlined herein have desirable behaviours; and (b) the soundscape richness and evenness are positively correlated with the richness of soniferous species. This suggests that the acoustic niche space is more filled where taxonomic richness is higher. Moreover, species-poor acoustic communities have a higher proportion of rare sounds and use the acoustic space less effectively. As the correlation between the soundscape and taxonomic richness is strong (>0.8) and holds at low sampling intensities, soundscape richness could serve as a proxy for taxonomic richness. 4. Quantifying the soundscape diversity through the lens of functional ecology using the analytical framework of Hill numbers generates novel insights into acoustic niche usage at a landscape scale and provides a useful proxy for taxonomic richness measurement.

Vowel allophony in Ness Gaelic: Phonetic and phonological patterns of laxing and retraction

The vowel system of the dialect of Scottish Gaelic spoken in Ness, Lewis differs from that of other dialects in several important ways. In particular, several vowels display patterns of allophony that have not been investigated instrumentally and, in some cases, have not been reported before for Scottish Gaelic. This paper documents the Ness system in detail, focusing in particular on the tense–lax opposition in /i e/ and retraction of /a(ː)/ next to velarised consonants. The results of a traditional linguistic fieldwork study are presented first, followed by a detailed acoustic study of nine speakers. The acoustic reality of these allophonic patterns, reflected in F1 and F2 values, is verified statistically using LME modelling. Bimodality in the distribution of tokens in acoustic space, confirmed statistically with Hartigan’s Dip Test, is taken as evidence for the existence of discrete phonological categories (Bermúdez-Otero & Trousdale 2011). It is found that speakers vary as to whether these allophonic oppositions are restricted to the phonetic grammar, or have undergone stabilisation and advanced into the categorical phonology (Bermúdez-Otero 2007, 2015). It is observed that laxing of /i e/ in Ness Gaelic occurs in exactly those contexts where there is a direct transition between the vowel and a following supra-glottal consonant. It is therefore proposed that this tense–lax opposition is grounded in conflicting strategies of contrast enhancement, whereby laxing increases the perceptual distinctiveness of a following consonant by allowing for more distinctive formant transitions, at the expense of the distinctiveness of the vowel itself (Storme 2019).

The Beauty of the Fragment Reconstituted in the Great Wall

Max Hattler’s short abstract animations demonstrate an awareness of the form’s historic 1920’s European Abstract Animation precedents, is informed by the structurally focused minimalism of the 60’s and re-tools pre-cinema toys. Yet his work speaks to the contemporary technological environment he occupies and experiences directly. His move to Hong Kong and his recent Serial Parallels is also a predictive probe into future media environments. Hattler’s digital architectures are designed to make sense of the technological situation of speed and information overload which Vilem Flusser marks as amnesic and Marshall McLuhan identifies as an acoustic space readable through pattern recognition. His practice makes productive use of the flexible and modular qualities of contemporary digital image-making technologies for both production and publication purposes.

Mapping the Soundscape in Communicative Forms for Cultural Heritage: Between Realism and Symbolism

The dimension of sound plays a central role as a form of cultural representation. Sound is a means of knowledge and experiential involvement, as it is inextricably linked to place and space, mind and body, cultural context and emotion. This contribution aims to explore how sound design follows different paradigms and methods in the various media. Virtual reality, videogame, cinema and documentary have differently codified rules to provide acoustic verisimilitude to the simulated space, to orient or stimulate the user, to suggest contents or evoke events and to emotionally involve the public. These rules follow artistic principles closer to psychoacoustics than to scientific reproduction of sound in the simulated space. Under what conditions, however, is the scientific simulation of an acoustic space preferable to the more common paradigms of psychoacoustics? How could this be created? Immersive and non-immersive virtual reality for cultural heritage is currently the field of experimentation most open to future developments. Some virtual reality and mixed reality applications will be presented, dedicated to archaeological or historical-artistic contexts, where a fundamental relationship between sound and multisensory interaction has been created.

Vocal Communication Within a Forest Bird Community

<p><b>This thesis takes a community approach to investigate the acoustics of forest birds in Zealandia sanctuary, Wellington. Initially, the annual changes in vocalisation output of 16 study species and their possible effect on bird conspicuousness were described. Environmental factors that may shape these avian vocalisations were addressed though invoking two key hypotheses, the acoustic adaptation hypothesis, and the acoustic niche hypothesis. In addition, the songs of selected species are investigated: the role of song harmonics in the native North Island saddleback, Philesturnus rufusater, and their role in ranging, change in song dialect through time and space in the introduced song thrush, Turdus philomelos, and temporal change in the song of the native grey warbler, Greygone igata. Vocal activity of the study species varied seasonally, affecting their detectability in bird counts. Some species were mostly first heard rather than seen and viceversa. The results lend support to the acoustic niche hypothesis in that vocalisations within the forest bird community appear to have evolved towards divergence, with native species’ vocalisations being more dispersed within the community acoustic space than those of the introduced species. However, all species concentrated their energy within relatively narrow frequency bands, supporting the predictions of the acoustic adaptation hypothesis. Adaptation to different transmission properties associated with different singing elevations or physiological parameters such as body weight may have an effect on shaping such bird vocalisations.</b></p> <p>Forests provide a complex acoustic space for sound transmission and a “sound window” may not be a constant property of a given forest. The study revealed that a prominent sound window persists in the lower frequency range that is less affected by habitat. Some high frequencies may have similar average attenuation values to those of low frequency, however, with greater fluctuation in attenuation. Ground effect is a further factor in determining how well different frequency ranges transmit and birds may use acoustic characteristics of their habitat to enhance their signal.</p> <p>Harmonics in North Island saddleback chatter song were found to play a potential role in ranging (estimating the distance of signaller), for playback songs with more relative energy within higher harmonics were evidently perceived as coming from a nearby individual.</p> <p>The repertoire size of the song thrush population studied in Zealandia has apparently evolved to become larger and more varied than the source population of song thrushes in the UK, with more syllables delivered with less repetition than the UK song recordings examined.</p> <p>Over a period of 7 years, syllables in grey warbler song have shifted to a higher frequency, but there was no difference in the temporal structure of the song. Habitat effect, competition on the acoustic signal from reintroduced birds and ambient noise level are considered as possible casual factors.</p>

Vocal Communication Within a Forest Bird Community

<p><b>This thesis takes a community approach to investigate the acoustics of forest birds in Zealandia sanctuary, Wellington. Initially, the annual changes in vocalisation output of 16 study species and their possible effect on bird conspicuousness were described. Environmental factors that may shape these avian vocalisations were addressed though invoking two key hypotheses, the acoustic adaptation hypothesis, and the acoustic niche hypothesis. In addition, the songs of selected species are investigated: the role of song harmonics in the native North Island saddleback, Philesturnus rufusater, and their role in ranging, change in song dialect through time and space in the introduced song thrush, Turdus philomelos, and temporal change in the song of the native grey warbler, Greygone igata. Vocal activity of the study species varied seasonally, affecting their detectability in bird counts. Some species were mostly first heard rather than seen and viceversa. The results lend support to the acoustic niche hypothesis in that vocalisations within the forest bird community appear to have evolved towards divergence, with native species’ vocalisations being more dispersed within the community acoustic space than those of the introduced species. However, all species concentrated their energy within relatively narrow frequency bands, supporting the predictions of the acoustic adaptation hypothesis. Adaptation to different transmission properties associated with different singing elevations or physiological parameters such as body weight may have an effect on shaping such bird vocalisations.</b></p> <p>Forests provide a complex acoustic space for sound transmission and a “sound window” may not be a constant property of a given forest. The study revealed that a prominent sound window persists in the lower frequency range that is less affected by habitat. Some high frequencies may have similar average attenuation values to those of low frequency, however, with greater fluctuation in attenuation. Ground effect is a further factor in determining how well different frequency ranges transmit and birds may use acoustic characteristics of their habitat to enhance their signal.</p> <p>Harmonics in North Island saddleback chatter song were found to play a potential role in ranging (estimating the distance of signaller), for playback songs with more relative energy within higher harmonics were evidently perceived as coming from a nearby individual.</p> <p>The repertoire size of the song thrush population studied in Zealandia has apparently evolved to become larger and more varied than the source population of song thrushes in the UK, with more syllables delivered with less repetition than the UK song recordings examined.</p> <p>Over a period of 7 years, syllables in grey warbler song have shifted to a higher frequency, but there was no difference in the temporal structure of the song. Habitat effect, competition on the acoustic signal from reintroduced birds and ambient noise level are considered as possible casual factors.</p>

Timing Is Everything: Acoustic Niche Partitioning in Two Tropical Wet Forest Bird Communities

When acoustic signals sent from individuals overlap in frequency and time, acoustic interference and signal masking may occur. Under the acoustic niche hypothesis (ANH), signaling behavior has evolved to partition acoustic space and minimize overlap with other calling individuals through selection on signal structure and/or the sender’s ability to adjust the timing of signals. Alternately, under the acoustic clustering hypothesis, there is potential benefit to convergence and synchronization of the structural or temporal characteristics of signals in the avian community, and organisms produce signals that overlap more than would be expected by chance. Interactive communication networks may also occur, where species living together are more likely to have songs with convergent spectral and or temporal characteristics. In this study, we examine the fine-scale use of acoustic space in montane tropical wet forest bird communities in Costa Rica and Hawai‘i. At multiple recording stations in each community, we identified the species associated with each recorded signal, measured observed signal overlap, and used null models to generate random distributions of expected signal overlap. We then compared observed vs. expected signal overlap to test predictions of the acoustic niche and acoustic clustering hypotheses. We found a high degree of overlap in the signal characteristics (frequency range) of species in both Costa Rica and Hawai‘i, however, as predicted under ANH, species significantly reduced observed overlap relative to the random distribution through temporal partitioning. There was little support for acoustic clustering or the prediction of the network hypothesis that species segregate across the landscape based on the frequency range of their vocalizations. These findings constitute strong support that there is competition for acoustic space in these signaling communities, and this has resulted primarily in temporal partitioning of the soundscape.

Acoustic competition within a tropical bird community: the case of the Resplendent Quetzal Pharomachrus mocinno in Guatemala

ABSTRACT The structure of ecological communities is thought to be mainly driven by competition processes between species. One special case of resource shaping community dynamics is the acoustic space. However, the acoustic communities have been rarely described for tropical birds. Here, we aimed at estimating acoustic competition between the iconic species Pharomachrus mocinno and the other bird species occupying the same habitat. An acoustic survey was conducted in a cloud forest in Guatemala for 17 days in six simultaneous recording sites. All species occurring in the same frequency bandwidth were identified, and the acoustic overlapping between P. mocinno and these species was estimated. Eighteen species were identified as acoustic competitors. Ecological traits and phylogenetic distance were defined for all species. The rate of acoustic competition between P. mocinno and other species was related to different ecological traits and competition for resources. The acoustic overlap was high with species competing for similar food resources and phylogenetically close species and low with predator species and phylogenetically distant species. These unique observations provide new behavioural and ecological information that might be useful for the knowledge of this species and the cloud forest.