Acoustic Overlap Research Articles

Passive acoustic monitoring of cave-dwelling bats with a sonotype classifier

ABSTRACT The aim of this study in the Republic of Congo was to test a new method to conduct a quantitative study of cave-dwelling bat communities using acoustics. This area is characterised by limited knowledge of the acoustic repertoire of bats. Over a period of 19 months for a total of 398 nights, we carried out 11 individual capture sessions to build a species inventory, record reference sounds and set up a passive acoustic monitoring protocol (PAM) at the exit of two caves. We used the Tadarida automatic sonotype classifier to classify acoustic vocalisations of bats in caves. For this, we enhanced the Tadarida classifier library with reference recordings of bats captured in both caves. Due to the acoustic overlap of several species, we grouped them into five distinct acoustic units using a posteriori classification based on four distinct parameters: call shape, acoustic frequency, a harmonics index and the identification probability. A random manual control stratified by sonotype showed an accuracy ranging from 82% to 98% depending on the group. This study is the first local application of a bat sonotype classifier designed and developed to function globally. It confirms the possibility of undertaking quantitative assessments of bat communities with relatively minimal effort, even in areas with limited knowledge of their acoustic repertoires.

Chirping across continents: variation in urban house sparrow (Passer domesticus) vocalizations across North America and Europe

The house sparrow (Passer domesticus) is one of the most widespread invasive bird species, with numerous and dense populations established across urban-agricultural landscapes of North America. Although this species has been widely studied to identify the traits that explain its global ubiquity, descriptions of house sparrow acoustic features across its native and introduced range are limited in the literature. We recorded male house sparrow vocalizations from 13 cities across Europe and North America to quantify the structural features of its common “chirrup” vocalization. Although the basic structure and duration were consistent across the two geographic regions, the vocalizations differed in their minimum frequencies and bandwidth. In a post hoc analysis of 140 museum specimens, we found that European house sparrows had larger bills and bodies than those in North America. Thus, we propose that these frequency shifts could be a result of synergistic interactions between morphological differences, potential differences in ambient noise, acoustic overlap with other species within the soundscape, or other acoustic features of European and North American cities. House sparrows seem to be a good model for future bioacoustics studies, given their worldwide distribution and acoustic plasticity, to test hypotheses related to urbanization traits and invasion potential.

Exploring acoustic overlaps in Djibouti Somali

Abstract Somali is well known to exhibit vowel harmony (Armstrong 1934), but linguists know remarkably little about how the system is implemented. Most presume that harmonic oppositions involve the tongue root and analyze the system relative to the feature [ATR], though the phonetic implementation of the contrast is complicated by a “quirky” (Krämer 2008) vocalic system. Reports also indicate that harmonic alternations vary between speakers and dialects, including in the bounds of the harmonic domain, but again, little systematic comparison has been pursued. To better understand the bearing that vowel quality and vocalic contrasts have on Somali vowel harmony, this paper reports the results of a study aimed at establishing details of the Djibouti Somali vocalic system. Our findings reveal that while a harmony system seems intact for all speakers studied, three consistent trends of acoustic (i.e., vowel space) overlap emerge from the data which may portend eventual mergers. These trends align in notable ways, but not entirely, with reports of harmonic decay elsewhere in the literature. They suggest that loss of harmonic distinctions in high vowels may be underway, but in different ways, in front vs. back vowels and that harmonic contrasts in long vowels are particularly susceptible to weakening. Our interpretation of these results, viewed alongside the typological literature on ATR harmony systems, is that Somali vowel harmony may be threatened or in decline as a result of these acoustic overlaps.

Potential social facilitation through song in bird communities

The main function of birdsong is to attract mates and defend territories among conspecifics, but little is known about the potential of this behavior in generating interactions among co-existing bird species that signal at the same time. Different hypotheses have been put forward to explain the mechanisms that govern signaling in crowded acoustic spaces, including competition for acoustic space, interspecific territoriality, environmental filters, and acoustic social facilitation. We tested these hypotheses in a forest bird community by studying the behavioral, acoustic, and ecological characteristics of 13 co-occurring species. We used passive recordings to assess the magnitude and the determinants of heterospecific song co-occurrence (i.e., when different species sing at the same time and place), and playback experiments to quantify the propensity of birds to sing if stimulated by heterospecific songs. Birds more frequently sang with species with dissimilar songs. In the breeding season, they also actively sang after the playback of other species, especially if these had dissimilar songs, and occasionally after non-avian unfamiliar playbacks. Heterospecific songs may trigger song utterance because they indicate a predator-free environment, or reduce predation risk through dilution effects, and these benefits may be maximized if there is little acoustic similarity. In line with ecological theory on community assembly mechanisms, these results are compatible with limiting similarity (species with similar songs sing at different times) and suggests social facilitation between phenotypically dissimilar species. These potential biotic interactions through songs may represent a mechanism that leads to bird species coexistence and are worth exploring at the community level.Significance statementIt is generally assumed that bird species avoid acoustic overlap with birds singing similar songs, but there is also evidence of active interspecific territoriality through song displays between pairs of species. Community-wide responses through songs have never been investigated in birds, and to fill this knowledge gap we performed both observations and experiments on multiple coexisting species. Birds tended to sing with species with more dissimilar songs and they were also actively stimulated to sing when the songs of species with dissimilar songs were played back. An interaction between species with dissimilar songs therefore emerged, potentially yielding anti-predatory benefits. Such active behavior, which would have gone unnoticed if observations only were performed, involves multiple species, and therefore may represent a community-wide mechanism of species coexistence.

Is [nuz] really the new [njuz]? Yod dropping in Toronto English

This article investigates yod dropping, i.e. the loss of the onglide after the coronals /t, d, n/, in Toronto English. Previous research has shown that this change is almost complete in Canadian English. However, most work has drawn on self-reported data rather than actual speech, and few studies have taken word frequency into consideration, although it has been shown to play a major role during earlier stages of the change. Combining auditory and acoustic analysis of production data from 20 speakers from the Greater Toronto Area, this study confirms that the change towards the yod-less pronunciation is largely complete. As in other varieties, there is considerable acoustic overlap between test words that historically had yod (new) and those that did not (too). This highlights the need to move away from predetermined cut-off points for determining yod presence, which are common in previous work, and find diagnostics that will allow us to distinguish between yod retention and /u/-fronting, another change that is currently underway in Canadian English (see also Roeder et al.2018). Possible solutions are discussed.

The ability to use contextual cues to achieve phonological constancy emerges by 14 months.

The ability to map similar sounding words to different meanings alone is far from enough for successful speech processing. To overcome variability in the speech signal, young learners must also recognize words across surface variations. Previous studies have shown that infants at 14 months are able to use variations in word-internal cues (i.e., acoustic cues within the target word) to form phonological categories and to learn words. The present study takes into consideration the fact that talker variability can easily lead to acoustic overlap between phonological categories, in which case reliance on word-external cues (i.e., acoustic cues in the context preceding and/or following the target word, also referred to as contextual cues) as a frame of reference is obligatory for successful talker adaptation. In a series of experiments, the present study examines when infants are able to use word-external cues to tune to different talkers for the benefit of word learning. Cantonese-learning 14-month-old, 18-month-old, and 24-month-old infants (N = 258) were tested on the associative learning of Cantonese Tone 1-Tone 3 contrast. Results showed that talker variability that yielded acoustic overlap between the two tonal categories compromised infants' ability to map the contrast onto word meanings. However, when given speaker-matched contextual cues, infants as young as 14 months of age demonstrated a certain degree of talker adaptation which may have subserved their use of phonetic details in novel word learning. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

A new method employing species‐specific thresholding identifies acoustically overlapping bats

AbstractPassive acoustic detectors are increasingly used for monitoring biodiversity, particularly for echolocating bat species (Microchiroptera). However, identification of calls collected at large scales is hindered by substantial variation within and between species, and the considerable time investment needed to manually identify acoustic data. We use acoustic data from 14 species of echolocating bats, occurring in temperate forests and woodlands of southeastern Australia to build a supervised classification model that identifies species from large acoustic datasets. Acoustic data from hand‐release (39,567) and free‐flying (8851) bat calls were used to build a predictive model, which was then validated using field‐collected calls (149,097) from the same region. We maximized the model fit per species by validating the associated confidence scores against manually identified presence and absence values. This allowed us to model the identification success of each species as a function of the confidence score. From this relationship, we set specific thresholds for accepting species identification, enabling more accurate classification of calls and identification of multiple bat species within a single acoustic recording. Including calls from manually identified free‐flying bats improved overall identification accuracy, including a 60% improvement for bats that navigate in open spaces. Assigning species‐specific thresholds achieved substantial improvements in overall model confidence, with functionally meaningful changes in the identification of species exhibiting considerable acoustic overlap in time and frequency measures. Research into the ecological requirements of species is hampered by problems with identification. Our research illustrates that internal train–test validation overestimates model accuracy particularly for species that were in low abundance or for uncommon species, which are acoustically similar to more common ones. Recognizing this, we set specific thresholds per species below which identifications were not accepted. Our method is particularly relevant in locations with high overlap in species' call parameters, which can result in false negatives in preference for species that are easier to identify because of the common practice of assigning one species per acoustic recording. This research proposes a cautious method to substantially reduce the burden of manual identification of large acoustic datasets.

Acoustic competition within a tropical bird community: the case of the Resplendent QuetzalPharomachrus mocinnoin Guatemala

ABSTRACTThe 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 speciesPharomachrus mocinnoand 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 betweenP. mocinnoand 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 betweenP. mocinnoand 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.

Sample size matters when calculating Pillai scores

Pillai scores, an output statistic from a MANOVA model, are used to measure acoustic overlap between two merging, splitting, or shifting vowels (Hay et al., 2006; Nycz & Hall-Lew, 2013, inter alia). They range from 0 (complete overlap) to 1 (complete separation). In this paper, we demonstrate that sample size matters in two important ways when calculating Pillai. First, relatively small datasets (<60 per sample) tend to underreport mergers. In simulated data, we draw two samples (5–100 tokens in each) from the same normal distribution to represent two vowels known to be merged. We find that a sample size of at least 60 tokens is required for at least 95% of the iterations to return a Pillai score less than the commonly used threshold of 0.1. s, Pillai scores are sensitive to the difference in sample sizes across two samples, with large differences resulting in Pillai scores that overreport mergers for samples drawn from two distinct distributions. If Pillai scores are used to measure vowel overlap, we recommend (1) using the same number of tokens across both samples and (2) using p-values from the MANOVA model to accompany them to assess whether the difference between two distributions is significant.

A multi-method approach to correlate identification in acoustic data: The case of Media Lengua

This study of Media Lengua examines production differences between mid and high vowels in order to identify the major correlates that distinguish these vowel types. The Media Lengua vowel system is unusual in that it incorporates lexical items originating in Spanish’s five-vowel system into a three-vowel system inherited from Quichua, resulting in high degrees of overlap between the front versus back, mid and high vowel pairs /e, i/ and /o, u/ in F1xF2 space. As Media Lengua speakers utilize and differentiate between all five vowels despite the large degree of acoustic overlap between mid and high vowels, this raises the question of what other correlates beyond F1 and F2 might be involved. To address this, our study looks at a range of variables, both acoustic and qualitative, in a multi-method approach using both factor analysis for mixed data and linear mixed effects regression modelling. Each method provides a unique view on the correlates of vowel differentiation in Media Lengua. Taken together, our results indicate that Media Lengua speakers rely on both social and linguistic contextual cues to distinguish mid from high vowels, which overlap in acoustic space (F1 and F2).

Monitoring the acoustic ecology of the shelf break of Georges Bank, Northwestern Atlantic Ocean: New approaches to visualizing complex acoustic data

Within a soundscape, anthropogenic sound often dominates frequency ranges used by various species, leading to signal overlap and potential communication masking. The acoustic niche hypothesis predicts species will avoid competition by vocalizing at unique bandwidths. To evaluate the extent of anthropogenic overlap, it’s helpful to understand acoustic niches across time. This study aims to assess the co-occurrence of cetaceans and anthropogenic activities, presenting simple and accessible visualizations of the temporal and spectral overlap. Continuous passive acoustic recordings from 10 Hz to 100 kHz were collected near three deep-water canyons (Heezen, Oceanographer, and Nantucket) along the continental shelf break of Georges Bank between April 2015 and March 2016. Daily presence was documented for five mysticete species (North Atlantic right, fin, blue, sei, humpback), five odontocete species and/or groups combined according to primary frequency ranges (delphinids, sperm whales, Kogia spp, Sowerby’s, and Cuviers’/True’s/Gervais’ beaked whales), and four anthropogenic activities (airgun noise, broadband ship noise, echosounders, and explosions). At each site, cetacean and anthropogenic sources were found to be significant contributors. Individual cetacean species/groups were present from 2% to 100% of days across sites, with delphinids, sperm whales, and fin whales detected most consistently. Airgun noise, the most frequently detected anthropogenic signal, ranged from 50% to 91% of days across all sites, followed by broadband ship noise (15–65% of days), echosounders (1–14% of days), and one explosion detected at Oceanographer Canyon. This approach allows for broad comparison of species and anthropogenic activity, providing understanding of variability in acoustic overlap and potential masking between sites.

Filling in the gaps: Acoustic gradation increases in the vocal ontogeny of chimpanzees (Pan troglodytes).

Human vocal ontogeny is considered to be a process whereby a large repertoire of discrete sounds seemingly emerges from a smaller number of acoustically graded vocalizations. While adult chimpanzee vocal behavior is highly graded, its developmental trajectory is poorly understood. In the present study, we therefore examined the size and structure of the chimpanzee vocal repertoire at different stages of ontogeny. Audio recordings were collected on infant (N = 13) and juvenile (N = 13) semi-wild chimpanzees at Chimfunshi Wildlife Orphanage, Zambia, using focal and ad libitum sampling. All observed call types were acoustically measured. These were predominantly grunts, whimpers, laughs, screams, hoos, and barks and squeaks. A range of spectral and temporal acoustic parameters were extracted, and fuzzy c-means clustering was used to quantify the size and structure of the repertoire. The infant and juvenile vocal repertoires were both best described with the same number of clusters. However, compared to infants, juvenile call clusters were less distinct from one another and could be extracted only when a low level of overlap between call clusters was permitted. Moreover, the acoustic overlap between call clusters was significantly higher for juveniles. Overall, this pattern shows greater acoustic overlap in juvenile vocalizations compared to infants, suggesting a trend toward increased acoustic gradation in chimpanzee vocal ontogeny. This may imply in contrast to humans, chimpanzees become increasingly proficient in using graded signals effectively rather than developing a larger repertoire of more discrete sounds in ontogeny.

Acoustic space partition by four Hylidae in an open habitat in Central Brazil

The use and partition of the acoustic space by anuran species is of special interest for evaluating inter-specific interactions in acoustic traits. Here we evaluate the acoustic space partitioning by four species of hylidae over the course of eleven months, at the Ecological Station of Águas Emendadas - DF, central Brazil. The acoustic niche overlap among species was smaller than expected by chance, indicating a competition in the use of this resource. If competition affects the use of acoustic resouces by species, low overlap on advertisement call traits are relevant in open habitats anuran assemblies.

Optimization of a Single Tube Practical Acoustic Thermometer.

When designing a single tube practical acoustic thermometer (PAT), certain considerations should be addressed for optimal performance. This paper is concerned with the main issues involved in building a reliable PAT. It has to be emphasised that a PAT measures the ratio of the time delay between the single temperature calibration point (ice point) and any other temperature. Here, we present different models of the speed of sound in tubes, including the effects of real gases and an error analysis of the most accurate model with a Monte Carlo simulation. Additionally, we introduce the problem of acoustic signal overlap and some possible solutions, one of which is acoustic signal cancellation, which aims to eliminate the unwanted parts of an acoustic signal, and another is to optimize the tube length for the parameters of the gas used and specific temperature range.

Acoustic niche partitioning in an anuran community from the municipality of Floriano, Piauí, Brazil.

Vocalizations are an important trait for the identification of cryptic and/or closely related amphibian species. Different vocalizations also contribute to partitioning of the acoustic space by sympatric species. This study aimed to describe the advertisement calls of anurans in a pond of the municipality of Floriano, State of Piauí, Brazil, and infer the acoustic niche partitioning of amphibians. Euclidean distance was used in a cluster analysis approach to infer the acoustic similarities among species. Thirteen species were analysed: Boana raniceps, Dendropsophus nanus, D. rubicundulus , D. minutus, Leptodactylus fuscus, L. troglodytes, L. vastus, Pithecopus nordestinus , Physalaemus cuvieri, P. nattereri, Pleurodema diplolister, Proceratophrys cristiceps and Scinax ruber. From these, six showed more than 90% of acoustic overlap: P. nattereri , P. cuvieri, L. fuscus and L. vastus (Leptodactylidae); and, D. nanus and D. rubicundulus (Hylidae). Despite the acoustic similarities among these six species, the acoustic interference was reduced due to the small number of sympatric species and to distinct features on carrier frequency such as dominant frequency and the degree of modulation in the frequency. Environmental factors limit the periods and sites of reproduction respectively, which may maintain the low anuran diversity and consequently reduce acoustic overlap.

Hierarchical Encoding of Attended Auditory Objects in Multi-talker Speech Perception

Humans can easily focus on one speaker in a multi-talker acoustic environment, but how different areas of the human auditory cortex (AC) represent the acoustic components of mixed speech is unknown. We obtained invasive recordings from the primary and nonprimary AC in neurosurgical patients as they listened to multi-talker speech. We found that neural sites in the primary AC responded to individual speakers in the mixture and were relatively unchanged by attention. In contrast, neural sites in the nonprimary AC were less discerning of individual speakers but selectively represented the attended speaker. Moreover, the encoding of the attended speaker in the nonprimary AC was invariant to the degree of acoustic overlap with the unattended speaker. Finally, this emergent representation of attended speech in the nonprimary AC was linearly predictable from the primary AC responses. Our results reveal the neural computations underlying the hierarchical formation of auditory objects in human AC during multi-talker speech perception.

A natural orchestra: how are anuran choruses formed in artificial ponds in southeast Brazil?

Abstract Choruses are commonly observed phenomena in both terrestrial and aquatic environments and are the product of species vocalizing contemporaneously usually at dawn and dusk. This study analyzes the composition and temporal distribution of anuran choruses at a recently built artificial pond in Southeast Brazil. Data were collected using Passive Acoustic Monitoring devices set to record 24-hours per day, seven days a month, throughout an entire year (October 2016 to September 2017). A total of eight species participated in the studied choruses: Boana albopunctata, Boana faber, Boana lundii, Phyllomedusa burmeisteri, Physalaemus cuvieri, Rhinella ornata, Rhinella diptycha and Scinax aff. perereca. The number of species, call emission rate, temperature, and humidity were all higher before midnight and during the rainy season. The species differed significantly in mean call rate by hour at which they sang. Boana faber and B. albopunctata were the species with the greatest vocal activity in both seasons, and were predominantly responsible for initiating choruses in the rainy season, while R. diptycha and B. lundii initiated choruses in the dry season. Anuran choruses started around 18:30 h during the rainy season and varied according to the time of sunset, while they started later in the dry season and were not correlated with sunset time. There was a positive correlation between the number of species calling and the call emission rate per month in both seasons. The results show that the choruses were correlated with climatic factors and that the species distributed their vocalizations over time, thus reducing acoustic overlap.

Singers in the grass: call description of conehead katydids (family: Tettigoniidae) and observations on avoidance of acoustic overlap

ABSTRACTThe sub-family Conocephalinae constitutes one of the richest groups of katydids in terms of diversity and distribution. Tropical katydids especially in India have largely escaped academic attention. Here, we record and describe call patterns for six conehead katydids from India: Conocephalus melanus, Conocephalus sp X, Euconocephalus indicus, Euconocephalus mucro, and Euconocephalus sp Y from North-Eastern Himalayas and Euconocephalus pallidus from the Western Ghats. All the species showed broadband frequency spectra (10.5–42.4 kHz), and three of the six species showed high rates of calling (289–453 syllables/s). We observed that the co-occurring call types never called at the same time or from the same location. We hypothesized this partitioning between call types is due to similarity in their calls; we used non-metric multi-dimensional scaling (NMDS) to investigate patterns of temporal or habitat-partitioning that some of the co-occurring call types exhibited during the course of study. The co-occurring Euconocephalus sp Y and E. mucro with high degree of overlap and similarity in their calls exhibited partitioning on a spatial scale. Conocephalus sp. X and C. melanus with distinct calling activity peaks formed separate clusters based on temporal call structures. As females rely heavily on spectral qualities, we speculate partitioning on temporal scale to avoid heterospecific interference due to similar spectral properties between the two call types.

Acoustic masking of soniferous species of the St-Lawrence lowlands

How much of the acoustic resource shared by vocalizing animal species is masked by human-induced noise has become a central question in the emerging field of soundscape ecology. The goal of our study was to evaluate the joint probability that masking could occur for anuran, bird, or stridulating orthopteran species along the spectral, spatial and temporal dimensions of the acoustic space. We evaluated acoustic overlap in the dominant frequencies, absolute amplitudes (emitter-receiver distances), and time-series (temporal match-mismatch) of human- and animal-induced sounds in three landscape settings: urban, peri-urban and rural. Acoustic overlap was evaluated at the day scale during the active vocalizing period of each taxon. Our results suggest that acoustic masking is unlikely for a vast majority of species in the three taxonomic groups; ranging from 5–7% for anurans to 3–4% for birds and less than 1% for orthopterans. However, in urban contexts, acoustic masking could be a selective force when coupled to other factors that covary with the amount of noise produced by human activities, such as habitat loss and degradation.

Perspectives on invasive amphibians in Brazil.

Introduced species have the potential to become invasive and jeopardize entire ecosystems. The success of species establishing viable populations outside their original extent depends primarily on favorable climatic conditions in the invasive ranges. Species distribution modeling (SDM) can thus be used to estimate potential habitat suitability for populations of invasive species. Here we review the status of six amphibian species with invasive populations in Brazil (four domestic species and two imported species). We (i) modeled the current habitat suitability and future potential distribution of these six focal species, (ii) reported on the disease status of Eleutherodactylus johnstonei and Phyllodytes luteolus, and (iii) quantified the acoustic overlap of P. luteolus and Leptodactylus labyrinthicus with three co-occurring native species. Our models indicated that all six invasive species could potentially expand their ranges in Brazil within the next few decades. In addition, our SDMs predicted important expansions in available habitat for 2 out of 6 invasive species under future (2100) climatic conditions. We detected high acoustic niche overlap between invasive and native amphibian species, underscoring that acoustic interference might reduce mating success in local frogs. Despite the American bullfrog Lithobates catesbeianus being recognized as a potential reservoir for the frog-killing fungus Batrachochytrium dendrobatidis (Bd) in Brazil, we did not detect Bd in the recently introduced population of E. johnstonei and P. luteolus in the State of São Paulo. We emphasize that the number of invasive amphibian species in Brazil is increasing exponentially, highlighting the urgent need to monitor and control these populations and decrease potential impacts on the locally biodiverse wildlife.