Origins of vocal-entangled gesture

Humans move their upper limbs for communicative purposes during speaking. They gesture. Such movements interact on multiple levels with speaking. In connection to what is said, gestures meaningfully shape with varying means of representation. Yet, gestures also have non-representational aspects; they quasi-rhythmically pulse with prosodic structure in speech. In explaining how modern human gesturing practices emerge in phylogeny or ontogeny, it is undisputed that gestures proliferated because they provide particularly effective means to refer to absent or distal state of affairs. It suggested that displaced or deictic reference is gestures' most basic proper function. The upshot is that the non-representational pulsing quality of gesture is completely ignored as something a) that requires an explanation or b) something that can elucidate how gesture practices emerged from more basic beginnings shared with other animals. However, recent research provides evidence for direct biomechanical interaction between pulsing manual movements and respiratory-vocal activity. We argue that this physical link is enacted during infant vocal-motor babbling - way before infants learn to represent manually. Further, we argue that gesture-vocal biomechanics directly relates to the cross-species phenomenon of locomotor-respiratory(-vocal) coupling. Given that gesture-speech biomechanics has its roots in locomotor-respiratory coupling, it can be related to bipedalism and respiratory complexification, i.e., an adaptation for the faculty of speech. We conclude that the physical origins of vocal-entangled gesture run much deeper and unfolded more gradually than currently assumed. The entanglement of sound and movement arose out of natural physical coalitions between vocal, respiratory, and limb systems that are forced to interact. We thus invert current argumentation of how gesture and vocalization must have evolved and rethink what is foundational of human gesture. This perspective underlines that a more comprehensive investigation of the physical basis of bodily communication can yield new sources of semiotic significance in human and non-human animals.

Passive Acoustic Monitoring and Automatic Detection of Diel Patterns and Acoustic Structure of Howler Monkey Roars

Nighttime studies are underrepresented in ecological research. Even well-known behaviors, such as the loud call of howler monkeys, are rarely studied at night. Our goal was to help fill this knowledge gap by studying the 24 h vocal behavior of the Guianan red howler monkey (Alouatta macconnelli) and to compare the acoustic structures of howling bouts made during the day to those made at night. We used passive acoustic monitoring coupled with automatic acoustic detection to study three groups of howlers over three months in the Viruá National Park, Roraima, Brazil. The automatic classifier we built detected 171 howling bouts with a 42% recall rate and 100% precision. Though primarily diurnal, howlers vocalized mainly at night. Greater vocal activity before nautical twilight might be associated with territorial and resource defense behaviors, with howlers calling from roosting sites before starting their daily routines. We also found that during the day, howling bouts were longer and had lower harmonic-to-noise ratios, lower frequencies, and more symmetric energy distributions than bouts at night. Our study adds to growing evidence that passive acoustic monitoring and automatic acoustic detection can be used to study primates and improve our understanding of their vocal behavior.

Simultaneous acoustic monitoring uncovers evidence of biodiversity loss and overlooked temporal variation in a threatened Amazonian bird community

Birds are frequently used as indicator taxon in ecology, but traditional surveys are prone to error and largely inadequate in the dense, speciose tropical forests where they are most needed. Passive acoustic monitoring (PAM) has the potential to address many of these pitfalls, providing unique advantages for both long-term monitoring and rapid biodiversity assessment. Here, we evaluate the effectiveness of PAM for characterizing spatiotemporal variation in avian species richness, diversity, vocal activity, and community composition in the Amazon basin global biodiversity hotspot. We employed an array of ten autonomous recording units (ARUs) spanning edge, degraded, and interior forest at a reserve on the deforestation frontier of Madre de Dios, Peru, a region featuring some of the richest, most complex avian assemblages on Earth. Recordings from 21 dawn-hours across three days at seven sites were manually annotated by a single observer. ARUs and manual annotation performed well as an inventory method, especially for midstory and understory species. Sites in edge and degraded habitats featured significantly lower avian species richness, Shannon diversity, and vocal activity levels than in the forest interior, patterns that replicate the findings of prior high-effort avian censuses in the region. We observed significant temporal variation between days; at all featured sites, vocal activity was highest on January 20th and lowest on January 31st. We demonstrated that novel annotation-generated metrics can work as effective proxies for abundance data and per-capita song rate, correlating with diversity indices and efficiently characterizing habitats at a level of detail unobtainable with human observers. Generalist species were significantly overrepresented in the soundscapes of interior forest, relative to their contributed share of species richness, and interior specialists were underrepresented, suggesting that the entire 191ha site is degraded. The between-days temporal variation that we documented, almost certainly overlooked without simultaneous monitoring, may obfuscate or distort the results of traditional surveys. Synthesis & Applications. We propose that PAM should become a cornerstone of biodiversity research. The standardization advantages demonstrated in this study, permanent storage, multi-taxa applications, and potential of automated identification make bioacoustics an ideal methodological avenue for guiding management and policy under rapid global change.

The vocal development of the pale spear-nosed bat is dependent on auditory feedback

Human vocal development and speech learning require acoustic feedback, and humans who are born deaf do not acquire a normal adult speech capacity. Most other mammals display a largely innate vocal repertoire. Like humans, bats are thought to be one of the few taxa capable of vocal learning as they can acquire new vocalizations by modifying vocalizations according to auditory experiences. We investigated the effect of acoustic deafening on the vocal development of the pale spear-nosed bat. Three juvenile pale spear-nosed bats were deafened, and their vocal development was studied in comparison with an age-matched, hearing control group. The results show that during development the deafened bats increased their vocal activity, and their vocalizations were substantially altered, being much shorter, higher in pitch, and more aperiodic than the vocalizations of the control animals. The pale spear-nosed bat relies on auditory feedback for vocal development and, in the absence of auditory input, species-atypical vocalizations are acquired. This work serves as a basis for further research using the pale spear-nosed bat as a mammalian model for vocal learning, and contributes to comparative studies on hearing impairment across species. This article is part of the theme issue ‘Vocal learning in animals and humans’.

Using Bioacoustics to Examine Vocal Phenology of Neotropical Migratory Birds on a Wild and Scenic River in Arizona

Passive acoustic recorders have been used successfully as automated survey tools to detect terrestrial wildlife. However, few studies have monitored Neotropical migratory bird use of riparian forest habitat using this technology. Within dryland ecosystems, the forests along rivers support high bird diversity. Many bird species of conservation concern require these floodplain forest habitats for foraging, migration stop-overs, and breeding. Few studies have explored the use of acoustic records in riverine systems designated for conservation for their natural resource value via the Wild and Scenic Rivers Act in the USA. Using acoustic recorders, we document vocal activity of four riparian-obligate species (Bell’s Vireo, Vireo bellii; Summer Tanager, Piranga rubra; Yellow Warbler, Setophaga petechial; and Yellow-billed Cuckoo, Coccyzus americanus) to determine species occurrence along a Wild and Scenic River. We established three study reaches along the perennial Lower Verde River, in the Sonoran Desert of central Arizona, USA. Nine acoustic recorders were used over the period of 80–120 days during the summer of 2018. We measured vegetation composition and structure in 100 m2 plots paired with acoustic recorders. Visualizing vocal activity showed that three species were calling and singing at each reach; whereas, one species, the cuckoo, had fewer recordings and occurred later in the summer. We demonstrate the utility of acoustic monitoring even when applied to rare birds in complex riparian habitats. This information is important for land management and conservation efforts concerning these species of interest and identifying important habitat features in Southwestern US riparian woodlands.

Seasonal Climate Impacts on Vocal Activity in Two Neotropical Nonpasserines

Climatic conditions represent one of the main constraints that influence avian calling behavior. Here, we monitored the daily calling activity of the Undulated Tinamou (Crypturellus undulatus) and the Chaco Chachalaca (Ortalis canicollis) during the dry and wet seasons in the Brazilian Pantanal. We aimed to assess the effects of climate predictors on the vocal activity of these focal species and evaluate whether these effects may vary among seasons. Air temperature was positively associated with the daily calling activity of both species during the dry season. However, the vocal activity of both species was unrelated to air temperature during the wet season, when higher temperatures occur. Daily rainfall was positively related to the daily calling activity of both species during the dry season, when rainfall events are scarce and seem to act as a trigger for breeding phenology of the focal species. Nonetheless, air temperature was negatively associated with the daily calling activity of the Undulated Tinamou during the wet season, when rainfall was abundant. This study improves our understanding of the vocal behavior of tropical birds and their relationships with climate, but further research is needed to elucidate the mechanisms behind the associations found in our study.

Replay of innate vocal patterns during night sleep in suboscines

Activation of forebrain circuitry during sleep has been variably characterized as ‘pre- or replay’ and has been linked to memory consolidation. The evolutionary origins of this mechanism, however, are unknown. Sleep activation of the sensorimotor pathways of learned birdsong is a particularly useful model system because the muscles controlling the vocal organ are activated, revealing syringeal activity patterns for direct comparison with those of daytime vocal activity. Here, we show that suboscine birds, which develop their species-typical songs innately without the elaborate forebrain–thalamic circuitry of the vocal learning taxa, also engage in replay during sleep. In two tyrannid species, the characteristic syringeal activation patterns of the song could also be identified during sleep. Similar to song-learning oscines, the burst structure was more variable during sleep than daytime song production. In kiskadees ( Pitangus sulphuratus ), a second vocalization, which is part of a multi-modal display, was also replayed during sleep along with one component of the visual display. These data show unambiguously that variable ‘replay’ of stereotyped vocal motor programmes is not restricted to programmes confined within forebrain circuitry. The proposed effects on vocal motor programme maintenance are, therefore, building on a pre-existing neural mechanism that predates the evolution of learned vocal motor behaviour.