warbleR: an r package to streamline analysis of animal acoustic signals

Widespread cultural change in declining populations of Amazon parrots

Species worldwide are experiencing anthropogenic environmental change, and the long-term impacts on animal cultural traditions such as vocal dialects are often unknown. Our prior studies of the yellow-naped amazon (Amazona auropalliata) revealed stable vocal dialects over an 11-year period (1994-2005), with modest shifts in geographic boundaries and acoustic structure of contact calls. Here, we examined whether yellow-naped amazons maintained stable dialects over the subsequent 11-year time span from 2005 to 2016, culminating in 22 years of study. Over this same period, this species suffered a dramatic decrease in population size that prompted two successive uplists in IUCN status, from vulnerable to critically endangered. In this most recent 11-year time span, we found evidence of geographic shifts in call types, manifesting in more bilingual sites and introgression across the formerly distinct North-South acoustic boundary. We also found greater evidence of acoustic drift, in the form of new emerging call types and greater acoustic variation overall. These results suggest cultural traditions such as dialects may change in response to demographic and environmental conditions, with broad implications for threatened species.

Persistent vocal learning in an aging open-ended learner reflected in neural FoxP2 expression

BACKGROUND

Most vocal learning species exhibit an early critical period during which their vocal control neural circuitry facilitates the acquisition of new vocalizations. Some taxa, most notably humans and parrots, retain some degree of neurobehavioral plasticity throughout adulthood, but both the extent of this plasticity and the neurogenetic mechanisms underlying it remain unclear. Differential expression of the transcription factor FoxP2 in both songbird and parrot vocal control nuclei has been identified previously as a key pattern facilitating vocal learning. We hypothesize that the resilience of vocal learning to cognitive decline in open-ended learners will be reflected in an absence of age-related changes in neural FoxP2 expression. We tested this hypothesis in the budgerigar (Melopsittacus undulatus), a small gregarious parrot in which adults converge on shared call types in response to shifts in group membership. We formed novel flocks of 4 previously unfamiliar males belonging to the same age class, either "young adult" (6 mo - 1 year) or "older adult" (≥ 3 year), and then collected audio-recordings over a 20-day learning period to assess vocal learning ability. Following behavioral recording, immunohistochemistry was performed on collected neural tissue to measure FoxP2 protein expression in a parrot vocal learning center, the magnocellular nucleus of the medial striatum (MMSt), and its adjacent striatum.

RESULTS

Although older adults show lower vocal diversity (i.e. repertoire size) and higher absolute levels of FoxP2 in the MMSt than young adults, we find similarly persistent downregulation of FoxP2 and equivalent vocal plasticity and vocal convergence in the two age cohorts. No relationship between individual variation in vocal learning measures and FoxP2 expression was detected.

CONCLUSIONS

We find neural evidence to support persistent vocal learning in the budgerigar, suggesting resilience to aging in the open-ended learning program of this species. The lack of a significant relationship between FoxP2 expression and individual variability in vocal learning performance suggests that other neurogenetic mechanisms could also regulate this complex behavior.

Song and genetic divergence within a subspecies of white-crowned sparrow (Zonotrichia leucophrys nuttalli)

Animal culture evolves alongside genomes, and the two modes of inheritance-culture and genes-interact in myriad ways. For example, stable geographic variation in culture can act as a reproductive barrier, thereby facilitating genetic divergence between "cultural populations." White-crowned sparrows (Zonotrichia leucophrys) are a well-established model species for bird song learning and cultural evolution, as they have distinct, geographically discrete, and culturally transmitted song types (i.e., song dialects). In this study, we tested the hypothesis that divergence between culturally transmitted songs drives genetic divergence within Nuttall's white-crowned sparrows (Z. l. nuttalli). In accordance with sexual selection theory, we hypothesized that cultural divergence between mating signals both preceded and generated genetic divergence. We characterized the population structure and song variation in the subspecies and found two genetically differentiated populations whose boundary coincides with a major song boundary at Monterey Bay, California. We then conducted a song playback experiment that demonstrated males discriminate between songs based on their degree of divergence from their local dialect. These results support the idea that discrimination against non-local songs is driving genetic divergence between the northern and southern populations. Altogether, this study provides evidence that culturally transmitted bird songs can act as the foundation for speciation by sexual selection.

Vocal convergence and social proximity shape the calls of the most basal Passeriformes, New Zealand Wrens

Despite extensive research on avian vocal learning, we still lack a general understanding of how and when this ability evolved in birds. As the closest living relatives of the earliest Passeriformes, the New Zealand wrens (Acanthisitti) hold a key phylogenetic position for furthering our understanding of the evolution of vocal learning because they share a common ancestor with two vocal learners: oscines and parrots. However, the vocal learning abilities of New Zealand wrens remain unexplored. Here, we test for the presence of prerequisite behaviors for vocal learning in one of the two extant species of New Zealand wrens, the rifleman (Acanthisitta chloris). We detect the presence of unique individual vocal signatures and show how these signatures are shaped by social proximity, as demonstrated by group vocal signatures and strong acoustic similarities among distantly related individuals in close social proximity. Further, we reveal that rifleman calls share similar phenotypic variance ratios to those previously reported in the learned vocalizations of the zebra finch, Taeniopygia guttata. Together these findings provide strong evidence that riflemen vocally converge, and though the mechanism still remains to be determined, they may also suggest that this vocal convergence is the result of rudimentary vocal learning abilities.

Vocal complexity in the long calls of Bornean orangutans

Vocal complexity is central to many evolutionary hypotheses about animal communication. Yet, quantifying and comparing complexity remains a challenge, particularly when vocal types are highly graded. Male Bornean orangutans (Pongo pygmaeus wurmbii) produce complex and variable "long call" vocalizations comprising multiple sound types that vary within and among individuals. Previous studies described six distinct call (or pulse) types within these complex vocalizations, but none quantified their discreteness or the ability of human observers to reliably classify them. We studied the long calls of 13 individuals to: (1) evaluate and quantify the reliability of audio-visual classification by three well-trained observers, (2) distinguish among call types using supervised classification and unsupervised clustering, and (3) compare the performance of different feature sets. Using 46 acoustic features, we used machine learning (i.e., support vector machines, affinity propagation, and fuzzy c-means) to identify call types and assess their discreteness. We additionally used Uniform Manifold Approximation and Projection (UMAP) to visualize the separation of pulses using both extracted features and spectrogram representations. Supervised approaches showed low inter-observer reliability and poor classification accuracy, indicating that pulse types were not discrete. We propose an updated pulse classification approach that is highly reproducible across observers and exhibits strong classification accuracy using support vector machines. Although the low number of call types suggests long calls are fairly simple, the continuous gradation of sounds seems to greatly boost the complexity of this system. This work responds to calls for more quantitative research to define call types and quantify gradedness in animal vocal systems and highlights the need for a more comprehensive framework for studying vocal complexity vis-à-vis graded repertoires.

callsync: An R package for alignment and analysis of multi-microphone animal recordings

To better understand how vocalisations are used during interactions of multiple individuals, studies are increasingly deploying on-board devices with a microphone on each animal. The resulting recordings are extremely challenging to analyse, since microphone clocks drift non-linearly and record the vocalisations of non-focal individuals as well as noise. Here we address this issue with callsync, an R package designed to align recordings, detect and assign vocalisations to the caller, trace the fundamental frequency, filter out noise and perform basic analysis on the resulting clips. We present a case study where the pipeline is used on a dataset of six captive cockatiels (Nymphicus hollandicus) wearing backpack microphones. Recordings initially had a drift of ~2 min, but were aligned to within ~2 s with our package. Using callsync, we detected and assigned 2101 calls across three multi-hour recording sessions. Two had loud beep markers in the background designed to help the manual alignment process. One contained no obvious markers, in order to demonstrate that markers were not necessary to obtain optimal alignment. We then used a function that traces the fundamental frequency and applied spectrographic cross correlation to show a possible analytical pipeline where vocal similarity is visually assessed. The callsync package can be used to go from raw recordings to a clean dataset of features. The package is designed to be modular and allows users to replace functions as they wish. We also discuss the challenges that might be faced in each step and how the available literature can provide alternatives for each step.

Body size shapes song in honeyeaters

Birdsongs are among the most distinctive animal signals. Their evolution is thought to be shaped simultaneously by habitat structure and by the constraints of morphology. Habitat structure affects song transmission and detectability, thus influencing song (the acoustic adaptation hypothesis), while body size and beak size and shape necessarily constrain song characteristics (the morphological constraint hypothesis). Yet, support for the acoustic adaptation and morphological constraint hypotheses remains equivocal, and their simultaneous examination is infrequent. Using a phenotypically diverse Australasian bird clade, the honeyeaters (Aves: Meliphagidae), we compile a dataset consisting of song, environmental, and morphological variables for 163 species and jointly examine predictions of these two hypotheses. Overall, we find that body size constrains song frequency and pace in honeyeaters. Although habitat type and environmental temperature influence aspects of song, that influence is indirect, likely via effects of environmental variation on body size, with some evidence that elevation constrains the evolution of song peak frequency. Our results demonstrate that morphology has an overwhelming influence on birdsong, in support of the morphological constraint hypothesis, with the environment playing a secondary role generally via body size rather than habitat structure. These results suggest that changing body size (a consequence of both global effects such as climate change and local effects such as habitat transformation) will substantially influence the nature of birdsong.

Vocal fingerprinting reveals a substantially smaller global population of the Critically Endangered cao vit gibbon (Nomascus nasutus) than previously thought

The cao vit gibbon (Nomascus nasutus) is one of the rarest primates on Earth and now only survives in a single forest patch of less than 5000 ha on the Vietnam-China border. Accurate monitoring of the last remaining population is critical to inform ongoing conservation interventions and track conservation success over time. However, traditional methods for monitoring gibbons, involving triangulation of groups from their songs, are inherently subjective and likely subject to considerable measurement errors. To overcome this, we aimed to use 'vocal fingerprinting' to distinguish the different singing males in the population. During the 2021 population survey, we complemented the traditional observations made by survey teams with a concurrent passive acoustic monitoring array. Counts of gibbon group sizes were also assisted with a UAV-mounted thermal camera. After identifying eight family groups in the acoustic data and incorporating long-term data, we estimate that the population was comprised of 74 individuals in 11 family groups, which is 38% smaller than previously thought. We have no evidence that the population has declined-indeed it appears to be growing, with new groups having formed in recent years-and the difference is instead due to double-counting of groups in previous surveys employing the triangulation method. Indeed, using spatially explicit capture-recapture modelling, we uncovered substantial measurement error in the bearings and distances from field teams. We also applied semi- and fully-automatic approaches to clustering the male calls into groups, finding no evidence that we had missed any males with the manual approach. Given the very small size of the population, conservation actions are now even more urgent, in particular habitat restoration to allow the population to expand. Our new population estimate now serves as a more robust basis for informing management actions and tracking conservation success over time.

Culturally determined interspecies communication between humans and honeyguides

Species interactions that vary across environments can create geographical mosaics of genetic coevolution. However, traits mediating species interactions are sometimes culturally inherited. Here we show that traditions of interspecies communication between people and wild birds vary in a culturally determined geographical mosaic. Honey hunters in different parts of Africa use different calls to communicate with greater honeyguides (Indicator indicator) that lead them to bees' nests. We show experimentally that honeyguides in Tanzania and Mozambique discriminate among honey hunters' calls, responding more readily to local than to foreign calls. This was not explained by variation in sound transmission and instead suggests that honeyguides learn local human signals. We discuss the forces stabilizing and diversifying interspecies communication traditions, and the potential for cultural coevolution between species.

A limit to sustained performance constrains trill length in birdsong

In birds, song performance determines the outcome of contests over crucial resources. We hypothesized that 1) sustained performance is limited within song, resulting in a performance decline towards the end and 2) the impact of song length is compromised if performance declines. To test these hypotheses, we analyzed the songs of 597 bird species (26 families) and conducted a playback experiment on blue tits (Cyanistes caeruleus). Our multi-species analysis showed that song performance declines after sustained singing, supporting our hypothesis. If the performance decline is determined by individual attributes (i.e., physical condition), our results explain how trill length can honestly signal quality. Our experiment showed that longer trills of high performance elicited a stronger response during territorial interactions. However, long trills that declined in performance elicited a weaker response than short, high-performance trills. A trade-off between the duration and performance quality of a motor display can be an important aspect in communication across taxa.

Competition for acoustic space in a temperate-forest bird community

Animals that communicate by acoustic signaling share a common acoustic environment. Birds are particularly vocal examples, using a wide repertoire of broadcast signals for mate attraction and territorial defense. However, interference caused by sounds that overlap in frequency and time can disrupt signal detection and reduce reproductive success. Here, we investigated competition avoidance mechanisms used by the bird community inhabiting a primeval lowland temperate forest in Białowieża, Eastern Poland. We recorded the dawn chorus at 84 locations in early and late spring and calculated dissimilarity indices of the broadcast signals to examine how species with greater song similarities use spatial and temporal partitioning to avoid competition for acoustic space throughout the breeding season. The bird community changed its use of acoustic space throughout the day and season. Birds did not use spatial partitioning of signal space when we looked at recording locations over the whole study period, but they did in a seasonal context, with species more acoustically different than expected by chance recorded at the same point in the same part of the season. Our results also indicate that daily temporal niche partitioning may only occur at certain times before sunrise, with no evidence of large-scale temporal partitioning between species vocalizing during the same 1-min recordings in daytime. These results contribute toward our understanding of the evolution of bird communication and highlight the strategies employed by different species to improve their signal transmission.

Mine or my neighbours' offspring: an experimental study on parental discrimination of offspring in a colonial seabird, the little auk Alle alle

Individual recognition (IR) abilities may result from various ecological and naturally selected features of a species. Complex IR mechanisms should develop when the risk of misidentification of a chick is high. For colonial seabirds, the ability to identify their own brood is crucial to ensure parental fitness. Vocalizations seem to be a key component of most parent-offspring interactions, although few studies have assessed the interindividual differences in seabird chick calls and their potential usage in IR. The little auk (Alle alle), which breeds in dense colonies, constitutes a perfect model for testing IR. In this study, we (1) examined chick calls at different stages of the nesting period, and (2) cross-fostered chicks to examine the rate of acceptance/nonacceptance of chicks by parents. We found significant interindividual differences in chick begging and fledging calls. Surprisingly, all cross-fostered chicks in our experiments were accepted by their foster parents, and male parents were as equally likely to accept cross-fostered chicks as females, even though the sexes would be expected to differ in offspring recognition due to different postfledging interactions with the chick. The revealed individuality of chick calls suggests the potential for chick vocal recognition in the studied species, but parent birds may disregard the individual characteristics enabling chick discrimination. This may take place as long as the chick is found in the nest because of the high likelihood that the chick present there is the focal one. However, IR during and after fledging requires further study. Studying the complexity of IR mechanisms is important for better understanding various avian social relationships and interactions.

Hearing, seeing, and feeling speech: the neurophysiological correlates of trimodal speech perception

Introduction

To perceive speech, our brains process information from different sensory modalities. Previous electroencephalography (EEG) research has established that audio-visual information provides an advantage compared to auditory-only information during early auditory processing. In addition, behavioral research showed that auditory speech perception is not only enhanced by visual information but also by tactile information, transmitted by puffs of air arriving at the skin and aligned with speech. The current EEG study aimed to investigate whether the behavioral benefits of bimodal audio-aerotactile and trimodal audio-visual-aerotactile speech presentation are reflected in cortical auditory event-related neurophysiological responses.

Methods

To examine the influence of multimodal information on speech perception, 20 listeners conducted a two-alternative forced-choice syllable identification task at three different signal-to-noise levels.

Results

Behavioral results showed increased syllable identification accuracy when auditory information was complemented with visual information, but did not show the same effect for the addition of tactile information. Similarly, EEG results showed an amplitude suppression for the auditory N1 and P2 event-related potentials for the audio-visual and audio-visual-aerotactile modalities compared to auditory and audio-aerotactile presentations of the syllable/pa/. No statistically significant difference was present between audio-aerotactile and auditory-only modalities.

Discussion

Current findings are consistent with past EEG research showing a visually induced amplitude suppression during early auditory processing. In addition, the significant neurophysiological effect of audio-visual but not audio-aerotactile presentation is in line with the large benefit of visual information but comparatively much smaller effect of aerotactile information on auditory speech perception previously identified in behavioral research.

Taxonomy and bioacoustics of little-known Grylloidea crickets (Orthoptera, Ensifera) from Mindanao, Philippines

Orthopteran surveys were conducted recently on Mindanao Island of the Philippines. Four species new to science are described here: Mistshenkoana lunotan sp. nov., Mistshenkoana higaonon sp. nov. and Ectatoderus dubius sp. nov. from Misamis Oriental; and Phaloria (Phaloria) rotundata sp. nov. from Agusan del Sur. Based on new collected material, Madasumma fuscoirrorata Chopard, 1925, first described based on a single female from Mindanao, is transferred to Varitrella (Cantotrella) fuscoirrorata (Chopard, 1925) comb. nov. We also describe the male of this species for the first time. Madasumma zamboanga Otte, 2007, first described from Zamboanga del Norte (Mindanao), is also transferred to Mnesibulus (Amnesibulus) and redescribed: Mnesibulus (Amnesibulus) zamboanga (Otte, 2007) comb. nov. We also describe previously unknown calling songs of seven species: Falcerminthus parvus (Baroga-Barbecho & Robillard, 2020), Ajorama balatukanis Otte, 1988, Varitrella (Cantotrella) bakeri (Chopard, 1925), Varitrella (Cantotrella) fuscoirrorata (Chopard, 1925) comb. nov., Phaloria (Phaloria) rotundata sp. nov., Ornebius bioculatus Tan et al., 2019 and Ectatoderus dubius sp. nov.

Sex Differences in the Neural Song Circuit and Its Relationship to Song Acoustic Complexity in House Wrens (Troglodytes aedon)

The song circuit in passerine birds is an outstanding model system for understanding the relationship between brain morphology and behavior, in part due to varying degrees of sex differences in structure and function across species. House wrens (Troglodytes aedon) offer a unique opportunity to advance our understanding of this relationship. Intermediate sex differences in song rate and complexity exist in this species compared to other passerines, and, among individual females, song complexity varies dramatically. Acoustic complexity in wild house wrens was quantified using a new machine learning approach. Volume, cell number, cell density, and neuron soma size were then measured for three song circuit regions, Area X, HVC (used as a proper name), and the robust nucleus of the arcopallium (RA), and one control region, the nucleus rotundus (Rt). For each song control area, males had a larger volume with more cells, larger somas, and lower cell density. Male songs had greater acoustic complexity than female songs, but these distributions overlapped. In females, increased acoustic complexity was correlated with larger volumes of and more cells in Area X and RA, as well as larger soma size in RA. In males, song complexity was unrelated to morphology, although our methods may underestimate male song complexity. This is the first study to identify song control regions in house wrens and one of few examining individual variation in both sexes. Parallels between morphology and the striking variability in female song in this species provide a new model for understanding relationships between neural structure and function.

Spatial and temporal variability of the acoustic repertoire of Antarctic minke whales (Balaenoptera bonaerensis) in the Weddell Sea

Since the attribution of the bio-duck call to Antarctic minke whales (AMW Balaenoptera bonaerensis), different studies have retrospectively identified several bio-duck call types at various sites throughout the Southern Hemisphere. The function of their vocal behavior however, remains largely unknown. Further insights into their repertoire usage may help to reveal the function of their calls. Here, we use passive acoustic monitoring (PAM) data collected across six locations throughout the Weddell Sea (WS) in 2013 and from PALAOA Station (Ekström Ice Shelf, eastern WS) in 2015, 2016 and 2017. In 2013, we detected 11 bio-duck call types throughout the WS between May and December, with additional acoustic activity in February on the western recorder AMW calls fell into four general call clusters. Seasonal patterns of calls showed variability between locations and years. Furthermore, this is the first study to show that similar to other baleen whale species, AMWs also produce songs.

Notes on the Eneopterinae (Orthoptera, Grylloidea, Gryllidae) from eastern Sabah

Based on material collected during recent fieldwork in eastern Sabah, the males of Nisitrus danum Robillard & Tan and Cardiodactylus variegatus Gorochov & Robillard are described for the first time, along with their calling songs. New locality records of N. danum, N. vittatus (Haan), Falcerminthus sandakan (Tan et al.), Cardiodactylus borneoe Robillard & Gorochov and C. variegatus are also presented. New material of Nisitrus species-N. danum and N. vittatus-allowed us to compare these syntopic species.

Individual identity information persists in learned calls of introduced parrot populations

Animals can actively encode different types of identity information in learned communication signals, such as group membership or individual identity. The social environments in which animals interact may favor different types of information, but whether identity information conveyed in learned signals is robust or responsive to social disruption over short evolutionary timescales is not well understood. We inferred the type of identity information that was most salient in vocal signals by combining computational tools, including supervised machine learning, with a conceptual framework of "hierarchical mapping", or patterns of relative acoustic convergence across social scales. We used populations of a vocal learning species as a natural experiment to test whether the type of identity information emphasized in learned vocalizations changed in populations that experienced the social disruption of introduction into new parts of the world. We compared the social scales with the most salient identity information among native and introduced range monk parakeet (Myiopsitta monachus) calls recorded in Uruguay and the United States, respectively. We also evaluated whether the identity information emphasized in introduced range calls changed over time. To place our findings in an evolutionary context, we compared our results with another parrot species that exhibits well-established and distinctive regional vocal dialects that are consistent with signaling group identity. We found that both native and introduced range monk parakeet calls displayed the strongest convergence at the individual scale and minimal convergence within sites. We did not identify changes in the strength of acoustic convergence within sites over time in the introduced range calls. These results indicate that the individual identity information in learned vocalizations did not change over short evolutionary timescales in populations that experienced the social disruption of introduction. Our findings point to exciting new research directions about the robustness or responsiveness of communication systems over different evolutionary timescales.

Directional speakers as a tool for animal vocal communication studies

Audio playbacks are a common experimental tool in vocal communication research. However, low directionality of sound makes it hard to control the audience exposed to the stimuli. Parametric speakers offer a solution for transmitting directional audible signals by using ultrasonic carrier waves. The targeted transmission of vocal signals offers exciting opportunities for testing the diffusion of information in animal groups and mechanisms for resolving informational ambiguities. We have field tested the quality and directionality of a commercial parametric speaker, Soundlazer SL-01. Additionally, we assessed its usability for performing playback experiments by comparing behavioural responses of free-ranging meerkats (Suricata suricatta) with calls transmitted from conventional and parametric speakers. Our results show that the tested parametric speaker is highly directional. However, the acoustic structure of meerkat calls was strongly affected and low frequencies were not reliably reproduced by the parametric speaker. The playback trials elicited weakened behavioural responses probably due to the partial distortion of the signal but also indicating the potential importance of social facilitation for initiating mobbing events in meerkats. We conclude that parametric speakers can be useful tools for directed transmission of animals calls but after a careful assessment of signal fidelity.

Machine learning and statistical classification of birdsong link vocal acoustic features with phylogeny

Birdsong is a longstanding model system for studying evolution and biodiversity. Here, we collected and analyzed high quality song recordings from seven species in the family Estrildidae. We measured the acoustic features of syllables and then used dimensionality reduction and machine learning classifiers to identify features that accurately assigned syllables to species. Species differences were captured by the first 3 principal components, corresponding to basic frequency, power distribution, and spectrotemporal features. We then identified the measured features underlying classification accuracy. We found that fundamental frequency, mean frequency, spectral flatness, and syllable duration were the most informative features for species identification. Next, we tested whether specific acoustic features of species' songs predicted phylogenetic distance. We found significant phylogenetic signal in syllable frequency features, but not in power distribution or spectrotemporal features. Results suggest that frequency features are more constrained by species' genetics than are other features, and are the best signal features for identifying species from song recordings. The absence of phylogenetic signal in power distribution and spectrotemporal features suggests that these song features are labile, reflecting learning processes and individual recognition.

The taxonomy and bioacoustics of the elusive crickets from the genus Pendleburyella Chopard, 1969 (Gryllidae: Pentacentrinae)

The taxonomy of poorly known crickets from the genus Pendleburyella Chopard, 1969 (Gryllidae, Pentacentrinae) is reviewed. The type specimens of described species were re-located and re-examined. Based on more recent collections, we describe two new species: Pendleburyella eirmosa sp. nov. and Pendleburyella pimela sp. nov., from Brunei Darussalam and Singapore respectively. The new material also allowed us to examine the male genitalia and describe the male calling song of the genus for the first time.

Acoustic communication: Deer mice join the chorus

A new study has identified two distinct pup vocalizations in deer mice, showing that discrete genetic loci explain the acoustic variation between these two call types and that the calls elicit different levels of maternal responsiveness.

Two pup vocalization types are genetically and functionally separable in deer mice

Vocalization is a widespread social behavior in vertebrates that can affect fitness in the wild. Although many vocal behaviors are highly conserved, heritable features of specific vocalization types can vary both within and between species, raising the questions of why and how some vocal behaviors evolve. Here, using new computational tools to automatically detect and cluster vocalizations into distinct acoustic categories, we compare pup isolation calls across neonatal development in eight taxa of deer mice (genus Peromyscus) and compare them with laboratory mice (C57BL6/J strain) and free-living, wild house mice (Mus musculus domesticus). Whereas both Peromyscus and Mus pups produce ultrasonic vocalizations (USVs), Peromyscus pups also produce a second call type with acoustic features, temporal rhythms, and developmental trajectories that are distinct from those of USVs. In deer mice, these lower frequency "cries" are predominantly emitted in postnatal days one through nine, whereas USVs are primarily made after day 9. Using playback assays, we show that cries result in a more rapid approach by Peromyscus mothers than USVs, suggesting a role for cries in eliciting parental care early in neonatal development. Using a genetic cross between two sister species of deer mice exhibiting large, innate differences in the acoustic structure of cries and USVs, we find that variation in vocalization rate, duration, and pitch displays different degrees of genetic dominance and that cry and USV features can be uncoupled in second-generation hybrids. Taken together, this work shows that vocal behavior can evolve quickly between closely related rodent species in which vocalization types, likely serving distinct functions in communication, are controlled by distinct genetic loci.

A workflow for the automated detection and classification of female gibbon calls from long-term acoustic recordings

Passive acoustic monitoring (PAM) allows for the study of vocal animals on temporal and spatial scales difficult to achieve using only human observers. Recent improvements in recording technology, data storage, and battery capacity have led to increased use of PAM. One of the main obstacles in implementing wide-scale PAM programs is the lack of open-source programs that efficiently process terabytes of sound recordings and do not require large amounts of training data. Here we describe a workflow for detecting, classifying, and visualizing female Northern grey gibbon calls in Sabah, Malaysia. Our approach detects sound events using band-limited energy summation and does binary classification of these events (gibbon female or not) using machine learning algorithms (support vector machine and random forest). We then applied an unsupervised approach (affinity propagation clustering) to see if we could further differentiate between true and false positives or the number of gibbon females in our dataset. We used this workflow to address three questions: (1) does this automated approach provide reliable estimates of temporal patterns of gibbon calling activity; (2) can unsupervised approaches be applied as a post-processing step to improve the performance of the system; and (3) can unsupervised approaches be used to estimate how many female individuals (or clusters) there are in our study area? We found that performance plateaued with >160 clips of training data for each of our two classes. Using optimized settings, our automated approach achieved a satisfactory performance (F1 score ~ 80%). The unsupervised approach did not effectively differentiate between true and false positives or return clusters that appear to correspond to the number of females in our study area. Our results indicate that more work needs to be done before unsupervised approaches can be reliably used to estimate the number of individual animals occupying an area from PAM data. Future work applying these methods across sites and different gibbon species and comparisons to deep learning approaches will be crucial for future gibbon conservation initiatives across Southeast Asia.

Using Acoustic Data Repositories to Study Vocal Responses to Playback in a Neotropical Songbird

Birds may alter song structure in response to territorial challenges to convey information about aggressive intent or fighting ability. Professional and amateur ornithologists upload daily many birdsong recordings into acoustic data repositories, usually scoring whether songs were recorded in response to a conspecific playback or produced spontaneously. We analyzed recordings from these repositories to evaluate if song traits of Rufous-browed Peppershrikes (Cyclarhis gujanensis) vary between playback-elicited songs and spontaneous songs. For each recording after playback, we chose one spatially closer spontaneous recording to avoid geographic bias. Birds recorded after playback produced slightly longer songs than birds that were singing spontaneously. This result was accounted for by increases in the amount of sound and silence within a song after the playback instead of changes in the mean number or duration of elements. Playback did not alter song frequency parameters (bandwidth, minimum, mean, and maximum frequencies) or song rate. These results indicate that song duration might mediate aggressive interactions in Rufous-browed Peppershrikes. Even considering limitations such as unknown playback stimulus identity and possible pseudoreplication, acoustic data repositories give a unique yet unexplored opportunity to gather insights into the evolution of song flexibility during aggressive encounters.

Animal linguistics: a primer

The evolution of language has been investigated by several research communities, including biologists and linguists, striving to highlight similar linguistic capacities across species. To date, however, no consensus exists on the linguistic capacities of non-human species. Major controversies remain on the use of linguistic terminology, analysis methods and behavioural data collection. The field of 'animal linguistics' has emerged to overcome these difficulties and attempt to reach uniform methods and terminology. This primer is a tutorial review of 'animal linguistics'. It describes the linguistic concepts of semantics, pragmatics and syntax, and proposes minimal criteria to be fulfilled to claim that a given species displays a particular linguistic capacity. Second, it reviews relevant methods successfully applied to the study of communication in animals and proposes a list of useful references to detect and overcome major pitfalls commonly observed in the collection of animal behaviour data. This primer represents a step towards mutual understanding and fruitful collaborations between linguists and biologists.

Testing drivers of acoustic divergence in cicadas (Cicadidae: Tettigettalna)

Divergence in acoustic signals may have a crucial role in the speciation process of animals that rely on sound for intra-specific recognition and mate attraction. The acoustic adaptation hypothesis (AAH) postulates that signals should diverge according to the physical properties of the signalling environment. To be efficient, signals should maximize transmission and decrease degradation. To test which drivers of divergence exert the most influence in a speciose group of insects, we used a phylogenetic approach to the evolution of acoustic signals in the cicada genus Tettigettalna, investigating the relationship between acoustic traits (and their mode of evolution) and body size, climate and micro-/macro-habitat usage. Different traits showed different evolutionary paths. While acoustic divergence was generally independent of phylogenetic history, some temporal variables' divergence was associated with genetic drift. We found support for ecological adaptation at the temporal but not the spectral level. Temporal patterns are correlated with micro- and macro-habitat usage and temperature stochasticity in ways that run against the AAH predictions, degrading signals more easily. These traits are likely to have evolved as an anti-predator strategy in conspicuous environments and low-density populations. Our results support a role of ecological selection, not excluding a likely role of sexual selection in the evolution of Tettigettalna calling songs, which should be further investigated in an integrative approach.

The evolution of sexually dimorphic traits in ecological gradients: an interplay between natural and sexual selection in hummingbirds

Traits that exhibit differences between the sexes have been of special interest in the study of phenotypic evolution. Classic hypotheses explain sexually dimorphic traits via intra-sexual competition and mate selection, yet natural selection may also act differentially on the sexes to produce dimorphism. Natural selection can act either through physiological and ecological constraints on one of the sexes, or by modulating the strength of sexual/social selection. This predicts an association between the degree of dimorphism and variation in ecological environments. Here, we characterize the variation in hummingbird dimorphism across ecological gradients using rich databases of morphology, colouration and song. We show that morphological dimorphism decreases with elevation in the understorey and increases with elevation in mixed habitats, that dichromatism increases at high altitudes in open and mixed habitats, and that song is less complex in mixed habitats. Our results are consistent with flight constraints, lower predation pressure at high elevations and with habitat effects on song transmission. We also show that dichromatism and song complexity are positively associated, while tail dimorphism and song complexity are negatively associated. Our results suggest that key ecological factors shape sexually dimorphic traits, and that different communication modalities do not always evolve in tandem.

The impacts of fine-tuning, phylogenetic distance, and sample size on big-data bioacoustics

Vocalizations in animals, particularly birds, are critically important behaviors that influence their reproductive fitness. While recordings of bioacoustic data have been captured and stored in collections for decades, the automated extraction of data from these recordings has only recently been facilitated by artificial intelligence methods. These have yet to be evaluated with respect to accuracy of different automation strategies and features. Here, we use a recently published machine learning framework to extract syllables from ten bird species ranging in their phylogenetic relatedness from 1 to 85 million years, to compare how phylogenetic relatedness influences accuracy. We also evaluate the utility of applying trained models to novel species. Our results indicate that model performance is best on conspecifics, with accuracy progressively decreasing as phylogenetic distance increases between taxa. However, we also find that the application of models trained on multiple distantly related species can improve the overall accuracy to levels near that of training and analyzing a model on the same species. When planning big-data bioacoustics studies, care must be taken in sample design to maximize sample size and minimize human labor without sacrificing accuracy.

Behavioral responses to anthropogenic noise at highways vary across temporal scales

Anthropogenic noise is pervasive across the landscape and can be present at two temporal scales: acute (occurring sporadically and stochastically over the shortest time scales, e.g., milliseconds), and chronic (more persistent than instantaneous and occurring over longer timescales, e.g., minutes, days). Acute and chronic anthropogenic noise may induce a behavioral fear-mediated response in wildlife that is analogous to a prey response to predators. Understanding wildlife responses to anthropogenic noise is especially important in the case of wildlife crossing structures that provide wildlife with access to resources across busy roadways. Focusing on two species common at wildlife crossing structures, mule deer (Odocoileus hemionus) and coyotes (Canis latrans), we addressed the hypotheses that (1) acute traffic noise causes flight behavior; and (2) chronic traffic noise causes changes in a range of behaviors associated with the vigilance–foraging trade-off (vigilance, running, and foraging). We placed camera traps at entrances to ten crossing structures for a period of ∼ 2 months each throughout California, USA. Mule deer and coyotes demonstrated a flight response to acute traffic noise at entrances to crossing structures. Both species demonstrated shifts in behavioral response to chronic traffic noise within and among structures. Coyote behavior was indicative of fear, demonstrating increased vigilance at louder times within crossing structures, and switching from vigilance to running activity at louder crossings. Mule deer responded positively, increasing foraging at both spatial scales, and demonstrating decreased vigilance at louder structures, potentially using crossing structures as a Human Shield. Our results are the first to demonstrate that anthropogenic noise at crossing structures could alter wildlife passage, and that variations in fear response to anthropogenic noise exist across temporal, spatial, and amplitude scales. This dynamic response could alter natural predator-prey interactions and scale up to ecosystem-level consequences such as trophic cascades in areas with roads.

“Playing the beat”: Occurrence of Bio-duck calls in Santos Basin (Brazil) reveals a complex acoustic behaviour for the Antarctic minke whale (Balaenoptera bonaerensis)

The Antarctic minke whale (Balaenoptera bonaerensis) (AMW) is one of the smallest species among baleen whales, occurring in the southern hemisphere from Antarctica to near the equator, and performing seasonal migrations from polar to tropical waters. Information about (AMW) occurrence in the winter breeding grounds is scarce, mostly coming from old records from whaling stations before the 1960’s international moratorium, such as Costinha Station in Northeastern Brazil (6° S / 34° W) and some sightings from few dedicated visual surveys. Acoustic methods can provide important data on the occurrence and distribution of migratory species. This work describes the occurrence of the Antarctic minke whale through acoustic detections of their “Bioduck” vocalisations in the Santos Basin, South-Southeastern Brazil (22° and 28° S / 42° and 48° W). Data was recorded between November 12 and December 19, 2015. AMW calls were detected for 12 days. We detected and classified 9 different Bio-duck calls in Brazilian coastal waters, evidencing a highly diverse acoustic behavior for the minke whale breeding ground. This is the first attempt to describe the acoustic diversity of AMW vocalizations in lower latitudes, contributing important information for future conservation efforts and management of AMW populations and their habitat. Therefore, our study presents the foremost acoustic evidence of the Antarctic minke whale in Brazilian coastal waters.

Interactive and independent effects of light and noise pollution on sexual signaling in frogs

Urbanization drastically changes environmental conditions, including the introduction of sensory pollutants, such as artificial light at night (ALAN) and anthropogenic noise. To settle in urban habitats, animals need to cope with this new sensory environment. On a short timescale, animals might cope with sensory pollutants via behavioral adjustments, such as changes in sexual signaling, which can have important fitness consequences. While ALAN and anthropogenic noise generally co-occur in urban habitats and are known to be able to interact to modify behavioral responses, few studies have addressed their combined impact. Our aim was, therefore, to assess the effects of ALAN, anthropogenic noise, and their interaction on sexual signaling in túngara frogs (Engystomops pustulosus). We observed the calling behavior of frogs in urban and forest areas, and subsequently recorded these frogs in a laboratory set-up while independently manipulating light and noise levels. Frogs in urban areas called with a higher call rate and complexity, which was correlated with local sensory conditions. Furthermore, our lab experiment revealed that ALAN can directly alter sexual signaling independently as well as in combination with anthropogenic noise. Exposure to ALAN alone increased call amplitude, whereas a combination of ALAN and anthropogenic noise interacted to lead to a higher call complexity and amplitude. Overall, the response patterns consistently showed that exposure to ALAN and anthropogenic noise led to more conspicuous sexual signals than expected based on the additive effects of single pollutants. Our results support the notion that urban and forest population differences in sexual signaling can be partially explained by exposure to ALAN and anthropogenic noise. Furthermore, by demonstrating interactive effects between light and noise pollution, our study highlights the importance of examining the effects of multisensory pollution, instead of single pollutants, when trying to understand phenotypic divergence in urbanized vs. natural areas.

Experimentally broadcast ocean surf and river noise alters birdsong

Anthropogenic noise and its effects on acoustic communication have received considerable attention in recent decades. Yet, the natural acoustic environment's influence on communication and its role in shaping acoustic signals remains unclear. We used large-scale playbacks of ocean surf in coastal areas and whitewater river noise in riparian areas to investigate how natural sounds influences song structure in six songbird species. We recorded individuals defending territories in a variety of acoustic conditions across 19 study sites in California and 18 sites in Idaho. Acoustic characteristics across the sites included naturally quiet 'control' sites, 'positive control' sites that were adjacent to the ocean or a whitewater river and thus were naturally noisy, 'phantom' playback sites that were exposed to continuous broadcast of low-frequency ocean surf or whitewater noise, and 'shifted' playback sites with continuous broadcast of ocean surf or whitewater noise shifted up in frequency. We predicted that spectral and temporal song structure would generally correlate with background sound amplitude and that signal features would differ across site types based on the spectral profile of the acoustic environment. We found that the ways in which song structure varied with background acoustics were quite variable from species to species. For instance, in Idaho both the frequency bandwidth and duration of lazuli bunting (Passerina amoena) and song sparrow (Melospiza melodia) songs decreased with elevated background noise, but these song features were unrelated to background noise in the warbling vireo (Vireo gilvus), which tended to increase both the minimum and maximum frequency of songs with background noise amplitude. In California, the bandwidth of the trill of white-crowned sparrow (Zonotrichia leucophrys) song decreased with background noise amplitude, matching results of previous studies involving both natural and anthropogenic noise. In contrast, wrentit (Chamaea fasciata) song bandwidth was positively related to the amplitude of background noise. Although responses were quite heterogeneous, song features of all six species varied with amplitude and/or frequency of background noise. Collectively, these results provide strong evidence that natural soundscapes have long influenced vocal behavior. More broadly, the evolved behavioral responses to the long-standing challenges presented by natural sources of noise likely explain the many responses observed for species communicating in difficult signal conditions presented by human-made noise.

A global analysis of aerial displays in passerines revealed an effect of habitat, mating system and migratory traits

Aerial displaying is a flamboyant part of the sexual behaviour of several volant animal groups, including birds. Nevertheless, little attention has been focused on identifying correlates of large-scale diversity in this trait. In this study, we scored the presence and absence of aerial displays in males of 1732 species of passerine birds (Passeriformes) and employed Bayesian phylogenetically informed mixed models to test for associations between aerial displays and a set of life-history and environmental predictors. Our multi-variate models revealed that species with males that perform aerial displays inhabited open rather than closed (forested) habitats. These species also exhibited higher levels of polygyny, had more elongated wings, migrated over longer distances and bred at higher latitudes. When we included species where the sexual function of displays has not been explicitly described but is likely to occur, we found that aerial displaying was also associated with smaller body size and increased male plumage coloration. Our results suggest that both sexual selection and natural selection have been important sources of selection on aerial displays in passerines.

A needle in a haystack: Integrative taxonomy reveals the existence of a new small species of fossorial frog (Anura, Microhylidae, Synapturanus) from the vast lower Putumayo basin, Peru

We describe a new species of microhylid frog of the genus Synapturanus from the lower Putumayo basin in Loreto, Perú. Specimens inhabited the soils of stunted pole forests growing on peat. The new species is distinguished from other species of Synapturanus through morphology, genetics, and acoustic characteristics. This species differs from most nominal congeners by having a head flat in lateral view (vs convex in the rest of species), a characteristic only shared by S. rabus and S. salseri. The new species can be distinguished from S. rabus and S. salseri by a combination of morphological characters and by having an advertisement call with a note length of 0.05–0.06 seconds (vs 0.03 seconds in S. rabus) and a dominant frequency ranging from 1.73 to 1.81 kHz (vs 1.10–1.47 kHz in S. salseri). Principal component analyses of 12 morphological characters and three acoustic variables further support differences between the new species and its described and undescribed congeners.

Body size and sexual selection shaped the evolution of parrot calls

Morphology, habitat and various selective pressures (e.g., social and sexual selection) can influence the evolution of acoustic signals, but the relative importance of their effects is not well understood. The order Psittaciformes (parrots, sensu lato) is a large clade of very vocal and often gregarious species for which large-scale comparative studies of vocalizations are lacking. We measured acoustic traits (duration, sound frequency, frequency bandwidth and sound entropy) of the predominant call type for >200 parrot species to test: (1) for associations with body size; (2) the acoustic adaptation hypothesis (predicting differences between forest and open-habitat species); (3) the social complexity hypothesis (predicting more complex calls in gregarious species); and (4) influences of sexual selection (predicting correlated evolution with colour ornamentation). Larger species had on average longer calls, lower sound frequency and wider frequency bandwidth. These associations with body size are all predicted by physical principles of sound production. We found no evidence for the acoustic adaptation and social complexity hypotheses, but perhaps social complexity is associated with vocal traits not studied here, such as call repertoire sizes. More sexually dichromatic species had on average simpler calls (shorter, with lower entropy and narrower frequency bandwidth) indicating an influence of sexual selection, namely an evolutionary negative correlation between colour ornamentation and elaborate acoustic signals, as predicted by the transference hypothesis. Our study is the first large-scale attempt at understanding acoustic diversity across the Psittaciformes, and indicates that body size and sexual selection influenced the evolution of species differences in vocal signals.

Application of Deep Learning to Community-Science-Based Mosquito Monitoring and Detection of Novel Species

Mosquito-borne diseases account for human morbidity and mortality worldwide, caused by the parasites (e.g., malaria) or viruses (e.g., dengue, Zika) transmitted through bites of infected female mosquitoes. Globally, billions of people are at risk of infection, imposing significant economic and public health burdens. As such, efficient methods to monitor mosquito populations and prevent the spread of these diseases are at a premium. One proposed technique is to apply acoustic monitoring to the challenge of identifying wingbeats of individual mosquitoes. Although researchers have successfully used wingbeats to survey mosquito populations, implementation of these techniques in areas most affected by mosquito-borne diseases remains challenging. Here, methods utilizing easily accessible equipment and encouraging community-scientist participation are more likely to provide sufficient monitoring. We present a practical, community-science-based method of monitoring mosquito populations using smartphones. We applied deep-learning algorithms (TensorFlow Inception v3) to spectrogram images generated from smartphone recordings associated with six mosquito species to develop a multiclass mosquito identification system, and flag potential invasive vectors not present in our sound reference library. Though TensorFlow did not flag potential invasive species with high accuracy, it was able to identify species present in the reference library at an 85% correct identification rate, an identification rate markedly higher than similar studies employing expensive recording devices. Given that we used smartphone recordings with limited sample sizes, these results are promising. With further optimization, we propose this novel technique as a way to accurately and efficiently monitor mosquito populations in areas where doing so is most critical.

A machine learning approach for classifying and quantifying acoustic diversity

1. Assessing diversity of discretely varying behavior is a classical ethological problem. In particular, the challenge of calculating an individuals' or species' vocal repertoire size is often an important step in ecological and behavioral studies, but a reproducible and broadly applicable method for accomplishing this task is not currently available. 2. We offer a generalizable method to automate the calculation and quantification of acoustic diversity using an unsupervised random forest framework. We tested our method using natural and synthetic datasets of known repertoire sizes that exhibit standardized variation in common acoustic features as well as in recording quality. We tested two approaches to estimate acoustic diversity using the output from unsupervised random forest analyses: (i) cluster analysis to estimate the number of discrete acoustic signals (e.g., repertoire size) and (ii) an estimation of acoustic area in acoustic feature space, as a proxy for repertoire size. 3. We find that our unsupervised analyses classify acoustic structure with high accuracy. Specifically, both approaches accurately estimate element diversity when repertoire size is small to intermediate (5-20 unique elements). However, for larger datasets (20-100 unique elements), we find that calculating the size of the area occupied in acoustic space is a more reliable proxy for estimating repertoire size. 4. We conclude that our implementation of unsupervised random forest analysis offers a generalizable tool that researchers can apply to classify acoustic structure of diverse datasets. Additionally, output from these analyses can be used to compare the distribution and diversity of signals in acoustic space, creating opportunities to quantify and compare the amount of acoustic variation among individuals, populations, or species in a standardized way. We provide R code and examples to aid researchers interested in using these techniques.

Thirteen new species of Chilecicada Sanborn, 2014 (Hemiptera: Auchenorrhyncha: Cicadidae: Tibicininae) expand the highly endemic cicada fauna of Chile

The genus Chilecicada Sanborn, 2014 is shown to be a complex of closely related species rather than a monospecific genus. Chilecicada citatatemporaria Sanborn & Cole n. sp., C. culenesensis Sanborn & Cole n. sp., C. curacaviensis Sanborn & Cole n. sp., C. impartemporaria Sanborn & Cole n. sp., C. magna Sanborn & Cole n. sp., C. mapuchensis Sanborn n. sp., C. oraria Sanborn & Cole n. sp., C. parrajaraorum Sanborn n. sp., C. partemporaria Sanborn & Cole n. sp., C. pehuenchesensis Sanborn & Cole n. sp., C. trifascia Sanborn n. sp., C. trifasciunca Sanborn & Cole n. sp., and C. viridicitata Sanborn & Cole n. sp. are described as new. Chilecicada occidentis Walker, 1850 is re-described to facilitate separation of the new species from the only previously known species. Song and cytochrome oxidase I analysis available for most species support the separation of the new taxa from the type species of the genus. Known species distributions and a key to the species of the genus are also provided. The new species increases the known cicada diversity 61.9% to 34 species, 91.2% of which are endemic to Chile.

Sex role similarity and sexual selection predict male and female song elaboration and dimorphism in fairy-wrens

Historically, bird song complexity was thought to evolve primarily through sexual selection on males; yet, in many species, both sexes sing and selection pressure on both sexes may be broader. Previous research suggests competition for mates and resources during short, synchronous breeding seasons leads to more elaborate male songs at high, temperate latitudes. Furthermore, we expect male-female song structure and elaboration to be more similar at lower, tropical latitudes, where longer breeding seasons and year-round territoriality yield similar social selection pressures in both sexes. However, studies seldom take both types of selective pressures and sexes into account. We examined song in both sexes in 15 populations of nine-fairy-wren species (Maluridae), a Southern Hemisphere clade with female song. We compared song elaboration (in both sexes) and sexual song dimorphism to latitude and life-history variables tied to sexual and social selection pressures and sex roles. Our results suggest that song elaboration evolved in part due to sexual competition in males: male songs were longer than female songs in populations with low male survival and less male provisioning. Also, female songs evolved independently of male songs: female songs were slower paced than male songs, although only in less synchronously breeding populations. We also found male and female songs were more similar when parental care was more equal and when male survival was high, which provides strong evidence that sex role similarity correlates with male-female song similarity. Contrary to Northern Hemisphere latitudinal patterns, male and female songs were more similar at higher, temperate latitudes. These results suggest that selection on song can be sex specific, with male song elaboration favored in contexts with stronger sexual selection. At the same time, selection pressures associated with sex role similarity appear to favor sex role similarity in song structure.

Correlated evolution of distinct signals associated with increased social selection in female white-shouldered fairywrens

Conspicuous female signals have recently received substantial scientific attention, but it remains unclear if their evolution is the result of selection acting on females independently of males or if mutual selection facilitates female change. Species that express female, but not male, phenotypic variation among populations represents a useful opportunity to address this knowledge gap. White-shouldered fairywrens (Malurus alboscapulatus) are tropical songbirds with a well-resolved phylogeny where female, but not male, coloration varies allopatrically across subspecies. We explored how four distinct signaling modalities, each putatively associated with increased social selection, are expressed in two populations that vary in competitive pressure on females. Females in a derived subspecies (M. a. moretoni) have evolved more ornamented plumage and have shorter tails (a signal of social dominance) relative to an ancestral subspecies (M. a. lorentzi) with drab females. In response to simulated territorial intrusions broadcasting female song, both sexes of M. a. moretoni are more aggressive and more coordinated with their mates in both movement and vocalizations. Finally, M. a. moretoni songs are more complex than M. a. lorentzi, but song complexity does not vary between sexes in either population. These results suggest that correlated phenotypic shifts in coloration and tail morphology in females as well as song complexity and aggression in both sexes may have occurred in response to changes in the intensity of social selection pressures. This highlights increased competitive pressures in both sexes can facilitate the evolution of complex multimodal signals.

Inter-individual differences of calling and exploratory behaviour in a lebinthine cricket species hint at different mate-finding strategies

Individual fitness can be boosted by behavioural strategies that maximise mate-finding probability while minimising predation risk. Animals that use acoustics to find mates may benefit from using both stationary calling and active exploration, but these also expose them to different types of predators. Studying calling and searching behaviours concurrently allows us to understand their evolutionary trade-offs between survival and reproduction. Unlike most other crickets, lebinthine males alternate between singing and exploration to find females, which offer a unique and excellent opportunity to test for inter-individual differences and behavioural syndrome between call properties and exploratory behaviours. Our data demonstrate that call properties and exploratory behaviour were repeatable. We did not, however, find that call properties correlate with exploration as some consistently exploratory individuals produce longer calls while others produce shorter calls. Our study suggests that lebinthine males use different combinations of calling and exploratory behaviours to cope with unpredictable risk–benefit scenarios.