Moderate evidence for a Lombard effect in a phylogenetically basal primate

Sex differences in the impact of social relationships on individual vocal signatures in grey mouse lemurs (Microcebus murinus)

Vocalizations coordinate social interactions between conspecifics by conveying information concerning the individual or group identity of the sender. Social accommodation is a form of vocal learning where social affinity is signalled by converging or diverging vocalizations with those of conspecifics. To investigate whether social accommodation is linked to the social lifestyle of the sender, we investigated sex-specific differences in social accommodation in a dispersed living primate, the grey mouse lemur (Microcebus murinus), where females form stable sleeping groups whereas males live solitarily. We used 482 trill calls of 36 individuals from our captive breeding colony to compare acoustic dissimilarity between individuals with genetic relatedness, social contact time and body weight. Our results showed that female trills become more similar the more time females spend with each other, independent of genetic relationship, suggesting vocal convergence. In contrast, male trills were affected more by genetic than social factors. However, focusing only on socialized males, increasing time as cage partners caused greater divergence in males' trills. Thus, grey mouse lemurs show the capacity for social accommodation, with females converging their trills to signal social closeness to sleeping group partners, whereas males do not adapt or diverge their trills to signal individual distinctiveness. This article is part of the theme issue 'The power of sound: unravelling how acoustic communication shapes group dynamics'.

Utilizing DeepSqueak for automatic detection and classification of mammalian vocalizations: a case study on primate vocalizations

Bioacoustic analyses of animal vocalizations are predominantly accomplished through manual scanning, a highly subjective and time-consuming process. Thus, validated automated analyses are needed that are usable for a variety of animal species and easy to handle by non-programing specialists. This study tested and validated whether DeepSqueak, a user-friendly software, developed for rodent ultrasonic vocalizations, can be generalized to automate the detection/segmentation, clustering and classification of high-frequency/ultrasonic vocalizations of a primate species. Our validation procedure showed that the trained detectors for vocalizations of the gray mouse lemur (Microcebus murinus) can deal with different call types, individual variation and different recording quality. Implementing additional filters drastically reduced noise signals (4225 events) and call fragments (637 events), resulting in 91% correct detections (N_total = 3040). Additionally, the detectors could be used to detect the vocalizations of an evolutionary closely related species, the Goodman’s mouse lemur (M. lehilahytsara). An integrated supervised classifier classified 93% of the 2683 calls correctly to the respective call type, and the unsupervised clustering model grouped the calls into clusters matching the published human-made categories. This study shows that DeepSqueak can be successfully utilized to detect, cluster and classify high-frequency/ultrasonic vocalizations of other taxa than rodents, and suggests a validation procedure usable to evaluate further bioacoustics software.

Signal-specific amplitude adjustment to noise in common bottlenose dolphins (Tursiops truncatus)

Anthropogenic underwater noise has increased over the past century, raising concern about the impact on cetaceans that rely on sound for communication, navigation, and locating prey and predators. Many terrestrial animals increase the amplitude of their acoustic signals to partially compensate for the masking effect of noise (the Lombard response), but it has been suggested that cetaceans almost fully compensate with amplitude adjustments for increasing noise levels. Here, we use sound-recording DTAGs on pairs of free-ranging common bottlenose dolphins (Tursiops truncatus) to test (i) if dolphins increase signal amplitude to compensate for increasing ambient noise and (ii) whether or not adjustments are identical for different signal types. We present evidence of a Lombard response in the range of 0.1-0.3 dB per 1 dB increase in ambient noise, which is similar to that of terrestrial animals, but much lower than the response reported for other cetaceans. We found that signature whistles tended to be louder and with a lower degree of amplitude adjustment to noise compared to non-signature whistles, suggesting that signature whistles may be selected for higher output levels and may have a smaller scope for amplitude adjustment to noise. The consequence of the limited degree of vocal amplitude compensation is a loss of active space during periods of increased noise, with potential consequences for group cohesion, conspecific encounter rates, and mate attraction.

Boat noise in an estuarine soundscape - A potential risk on the acoustic communication and reproduction of soniferous fish in the May River, South Carolina

The impact of boat related noise on marine life is a subject of concern, particularly for fish species that utilize acoustic communication for spawning purposes. The goal of this study was to quantify and examine the risk of boat noise on fish acoustic communication by performing acoustic monitoring of the May River, South Carolina (USA) from February to November 2013 using DSG-Ocean recorders. The number of boats detected increased from the source to the mouth with the highest detections near the Intracoastal Waterway (ICW). Boat noise frequency ranges overlapped with courtship sounds of silver perch (Bairdiella chrysoura), black drum (Pogonias cromis), oyster toadfish (Opsanus tau), spotted seatrout (Cynoscion nebulosus), and red drum (Sciaenops ocellatus). In the May River estuary, red drum may experience the greatest risk of auditory masking because of late afternoon choruses (21% time overlap with boat noise) and only one spawning location near the noisy ICW.