Identifying individual wild Eastern grey wolves (Canis lupus lycaon) using fundamental frequency and amplitude of howls

Individual recognition and long-term memory of inanimate interactive agents and humans in dogs

Investigation of individual recognition (IR) is difficult due to the lack of proper control of cues and previous experiences of subjects. Utilization of artificial agents (Unidentified Moving Objects: UMOs) may offer a better approach than using conspecifics or humans as partners. In Experiment 1, we investigated whether dogs are able to develop IR of UMOs (that is stable for at least 24 h) or that they only retain a more generalised memory about them. The UMO helped dogs to obtain an unreachable ball and played with them. One day, one week or one month later, we tested whether dogs display specific behaviour toward the familiar UMO over unfamiliar ones (four-way choice test). Dogs were also re-tested in the same helping context and playing interaction. Subjects did not approach the familiar UMO sooner than the others; however, they gazed at the familiar UMO earlier during re-testing of the problem solving task, irrespectively of the delay. In Experiment 2, we repeated the same procedure with human partners, applying a two-way choice test after a week delay, to study whether lack of IR was specific to the UMO. Dogs did not approach the familiar human sooner than the unfamiliar, but they gazed at the familiar partner earlier during re-testing. Thus, dogs do not seem to recognise an individual UMO or human after a short experience, but they remember the interaction with the novel partner in general, even after a long delay. We suggest that dogs need more experience with a specific social partner for the development of long-term memory.

Bioacoustic Detection of Wolves: Identifying Subspecies and Individuals by Howls

Simple Summary

This study evaluates the use of acoustic devices as a method to monitor wolves by analyzing different variables extracted from wolf howls. By analyzing the wolf howls, we focused on identifying individual wolves, subspecies. We analyzed 170 howls from 16 individuals from the three subspecies: Arctic wolves (Canis lupus arctos), Eurasian wolves (C.l. lupus), and Northwestern wolves (C.l. occidentalis). We assessed the potential for individual recognition and recognition of three subspecies: Arctic, Eurasian, and Northwestern wolves.

Abstract

Wolves (Canis lupus) are generally monitored by visual observations, camera traps, and DNA traces. In this study, we evaluated acoustic monitoring of wolf howls as a method for monitoring wolves, which may permit detection of wolves across longer distances than that permitted by camera traps. We analyzed acoustic data of wolves’ howls collected from both wild and captive ones. The analysis focused on individual and subspecies recognition. Furthermore, we aimed to determine the usefulness of acoustic monitoring in the field given the limited data for Eurasian wolves. We analyzed 170 howls from 16 individual wolves from 3 subspecies: Arctic (Canis lupus arctos), Eurasian (C. l. lupus), and Northwestern wolves (C. l. occidentalis). Variables from the fundamental frequency (f0) (lowest frequency band of a sound signal) were extracted and used in discriminant analysis, classification matrix, and pairwise post-hoc Hotelling test. The results indicated that Arctic and Eurasian wolves had subspecies identifiable calls, while Northwestern wolves did not, though this sample size was small. Identification on an individual level was successful for all subspecies. Individuals were correctly classified with 80%–100% accuracy, using discriminant function analysis. Our findings suggest acoustic monitoring could be a valuable and cost-effective tool that complements camera traps, by improving long-distance detection of wolves.

Bray-Call Sequences in the Mediterranean Common Bottlenose Dolphin (Tursiops truncatus) Acoustic Repertoire

Simple Summary

In the acoustic repertoire of common bottlenose dolphins (Tursiops truncatus), Gulps, Grunts, and Squeaks are part of a group of vocalizations called “bray-call” for which little has been previously studied. The name comes from the alternating structure characteristic of a donkey’s bray. Sounds can be of different types at low frequencies and audible to the human hear—of short duration, produced in sequence. The function of these sequences is not clarified yet, and it is not known if they are part of the vocal “catalog” of all the different populations of common bottlenose dolphin at global level. What is certain is that bray-calls are present in two geographical areas of the Mediterranean and that the “Capitoline” individuals (Rome, Tyrrhenian Sea, Italy) emit them with greater frequency and variety than the Sicilian ones (Mazara del Vallo, Sicilian Channel, Italy). A number of 13 different types of sequences have been identified, and only 2 of them are shared between the study areas. For the first time this study identifies variants of the main bray-call elements, highlights the structural complexity of these vocalizations, and suggests addressing future research on the context of emissions and the possible function(s) of such acoustic arrangements.

Abstract

Acoustic sequences are commonly observed in many animal taxa. The vast vocal repertoire of common bottlenose dolphins (Tursiops truncatus) also includes sequences of multi-unit rhythmic signals called bray-call which are still poorly documented, both functionally and geographically. This study aimed to (1) describe, classify, and characterize series of bray-call recorded in two sites of the Mediterranean basin (Rome—Tyrrhenian Sea and Mazara del Vallo—Strait of Sicily) and (2) investigate for the existence of possible geographic differences. The acoustic analysis identified 13 different sequence types, only two detected in both study areas. The Sørensen–Dice index revealed a low degree of similarity between the sequence repertoire of the two common bottlenose dolphin sub-populations, with the Tyrrhenian being more diversified and complex than the Sicilian one. The acoustic parameters also showed variability between the study area. Different variants of the main acoustic elements composing the bray-call sequences were detected in the Tyrrhenian Sea only. The Markov-chain model demonstrated that the transition probability between acoustic elements is not uniform, with specific combinations of elements having a higher probability of occurrence. These new findings on common bottlenose dolphin bray-call sequences highlight the structural complexity of these vocalizations and suggest addressing future research on the context of emissions and the possible function(s) of such acoustic arrangements.

The squeaking vocalization of grey wolves (Canis lupus): individuality in a close-range affiliative mammalian vocalisation

Wolves (Canis lupus) frequently use the close-range squeaking vocalization, a soft, multi-unit, high-pitched tonal vocalisation. We examined the social and movement contexts of the occurrence and acoustic characteristics of squeaking from videotapes of pack-reared, pack-living captive wolves living in semi-natural conditions at the Canadian Centre for Wolf Research over a three-year period. We only examined squeaking vocalisations for which the sender and potential receiver(s) could be determined. Wolves squeaked in many contexts, especially when approaching other wolves in prosocial and food contexts. Some wolves squeaked more than others. Acoustically, squeaking vocalisations were individually identifiable, primarily through frequency characteristics. Contextual use suggests that squeaking conveys the friendly motivation of an approaching wolf and in aggressive situations, a motivation to defuse or decrease aggression. This close-range vocalisation may play an important role in controlling and coordinating social interactions within the pack.

Conflicts with Wolves Can Originate from Their Parent Packs

Transmission of experience about prey and habitat supports the survival of next generation of wolves. Thus, the parent pack (PP) can affect whether young migrating wolves (loners) kill farm animals or choose to be in human environments, which generates human-wolf conflicts. Therefore, we researched whether the behavior of loners resembles PP behavior. After being extinct, 22 loners had entered the Netherlands between 2015 and 2019. Among them, 14 could be DNA-identified and linked with their PPs in Germany. Some loners were siblings. We assessed the behavior of each individual and PP through a structured Google search. PP behavior was determined for the loner's rearing period. Similarity between loner and PP behavior was significant (p = 0.022) and applied to 10 of 14 cases: like their PPs, three loners killed sheep and were near humans, five killed sheep and did not approach humans, while two loners were unproblematic, they did not kill sheep, nor were they near humans. Siblings behaved similarly. Thus, sheep killing and proximity to humans may develop during early-life experiences in the PP. However, by negative reinforcement that can be prevented. New methods are suggested to achieve that. As a result, new generations may not be problematic when leaving PPs.

Howl variation across Himalayan, North African, Indian, and Holarctic wolf clades: tracing divergence in the world's oldest wolf lineages using acoustics

Vocal divergence within species often corresponds to morphological, environmental, and genetic differences between populations. Wolf howls are long-range signals that encode individual, group, and subspecies differences, yet the factors that may drive this variation are poorly understood. Furthermore, the taxonomic division within the Canis genus remains contended and additional data are required to clarify the position of the Himalayan, North African, and Indian wolves within Canis lupus. We recorded 451 howls from the 3 most basal wolf lineages-Himalayan C. lupus chanco-Himalayan haplotype, North African C. lupus lupaster, and Indian C. lupus pallipes wolves-and present a howl acoustic description within each clade. With an additional 619 howls from 7 Holarctic subspecies, we used a random forest classifier and principal component analysis on 9 acoustic parameters to assess whether Himalayan, North African, and Indian wolf howls exhibit acoustic differences compared to each other and Holarctic wolf howls. Generally, both the North African and Indian wolf howls exhibited high mean fundamental frequency (F0) and short duration compared to the Holarctic clade. In contrast, the Himalayan wolf howls typically had lower mean F0, unmodulated frequencies, and short howls compared to Holarctic wolf howls. The Himalayan and North African wolves had the most acoustically distinct howls and differed significantly from each other and to the Holarctic wolves. Along with the influence of body size and environmental differences, these results suggest that genetic divergence and/or geographic distance may play an important role in understanding howl variation across subspecies.

Automated detection of low-frequency rumbles of forest elephants: A critical tool for their conservation

African forest elephants (Loxodonta cyclotis) occupy large ranges in dense tropical forests and often use far-reaching vocal signals to coordinate social behavior. Elephant populations in Central Africa are in crisis, having declined by more than 60% in the last decade. Methods currently used to monitor these populations are expensive and time-intensive, though acoustic monitoring technology may offer an effective alternative if signals of interest can be efficiently extracted from the sound stream. This paper proposes an automated elephant call detection algorithm that was tested on nearly 4000 h of field recordings collected from five forest clearings in Central Africa, including sites both inside protected areas and in logging concessions. Recordings were obtained in different seasons, years, and under diverse weather conditions. The detector achieved an 83.2% true positive rate when the false positive rate is 5.5% (approximately 20 false positives per hour). These results suggest that this algorithm can enable analysis of long-term recording datasets or facilitate near-real-time monitoring of elephants in a wide range of settings and conditions.

Space use by gray wolves (Canis lupus) in response to simulated howling: a case study and a call for further investigation

Simulated wolf howling sessions are a popular ecotourism activity, but no exhaustive evaluation has been made on their potential impacts on wolf ecology. We evaluated the effects of simulated wolf howling sessions on the space use of gray wolves (Canis lupus L., 1758) in the Montmorency Forest (Quebec, Canada). Although we equipped 22 individuals with GPS collars from 2005 to 2008, only four wolves could potentially hear our 20 simulated howls (July to October 2008). We used power analyses to select two spatiotemporal scales of analysis with sufficient location data to investigate wolf reactions. We evaluated the distance and orientation of wolf movements relative to howling stations, their movement rates, and their mean distance to other collared pack members, which we used as an index of pack cohesion. We found that wolves approached howling stations (at both scales) and were closer to other pack members (at broad scale only) after simulated howls. The reactions of wolves were of relatively low magnitude, and we conclude that simulated howling sessions were unlikely to have strong negative impacts on the movement patterns of wolves. We encourage future studies to evaluate the effects of simulated howling on the activity levels and fine-scale space use by wolves.

Acoustically diverse vocalization repertoire in the Himalayan leaf-nosed bat, a widely distributed Hipposideros species

Insectivorous bats vocalize to both communicate with conspecifics and to echolocate. The communicative vocalizations or "calls" of bats either consist of or are constructed from discrete acoustic units, termed "syllables." This study examined syllable diversity in the Himalayan leaf-nosed bat, Hipposideros armiger, a species that is widely distributed across Southeast Asia. This social species' vocalizations were hypothesized to consist of a wide variety of syllables facilitating its social interactions. To test this hypothesis, multiple acoustic parameters were measured from recorded vocalizations to map the acoustic boundaries of syllables. Spectrographic signatures were used to classify all recorded sounds into 35 distinct syllable types-18 as simple syllables and 17 as composites. K-means clustering independently provided an optimal fit of simple syllables into 18 clusters with a good correspondence to 15 spectrographically assigned syllable types. Discriminant analysis further confirmed the spectrographic classification of constant frequency syllables (0% misclassification) and revealed a low (<15%) misclassification of spectrograms for all examples of frequency modulation syllables. Multidimensional scaling of mean values of multiple parameters provided a spectrographically constrained relational mapping of syllable types within two dimensions. These data suggest that H. armiger has a complex, well organized syllabic repertoire despite simple syllables being rarely emitted in isolation.

The bark, the howl and the bark-howl: Identity cues in dingoes' multicomponent calls

Dingoes (genus Canis) produce a stereotyped bark-howl vocalisation, which is a unimodal complex signal formed by the concatenation of two call types (a bark and a howl). Bark-howls may function as alarm signals, although there has been no empirical investigation of this vocalisation's structure or function. We quantified the content and efficacy of the bark and howl segments separately and when combined, using 140 calls from 10 individuals. We found that both segments are individually distinctive, although howl segments are more accurately classified, suggesting a higher level of individuality. Furthermore, howls convey signature characteristics that are conserved across different contexts of production, and thus may act as 'identity signals'. The individual distinctiveness of full bark-howls increases above that of isolated segments, which may be a result of selection on improved signal discriminability. Propagation tests revealed that bark-howls are best described as medium-range signals, with both segments potentially allowing for individual discrimination up to 200m regardless of environmental conditions. We discuss our findings regarding the fitness benefits of encoding identity cues in a potential alarm call and propose additional hypotheses for the function(s) of bark and howl segments.

Acoustic sequences in non-human animals: a tutorial review and prospectus

Animal acoustic communication often takes the form of complex sequences, made up of multiple distinct acoustic units. Apart from the well-known example of birdsong, other animals such as insects, amphibians, and mammals (including bats, rodents, primates, and cetaceans) also generate complex acoustic sequences. Occasionally, such as with birdsong, the adaptive role of these sequences seems clear (e.g. mate attraction and territorial defence). More often however, researchers have only begun to characterise - let alone understand - the significance and meaning of acoustic sequences. Hypotheses abound, but there is little agreement as to how sequences should be defined and analysed. Our review aims to outline suitable methods for testing these hypotheses, and to describe the major limitations to our current and near-future knowledge on questions of acoustic sequences. This review and prospectus is the result of a collaborative effort between 43 scientists from the fields of animal behaviour, ecology and evolution, signal processing, machine learning, quantitative linguistics, and information theory, who gathered for a 2013 workshop entitled, 'Analysing vocal sequences in animals'. Our goal is to present not just a review of the state of the art, but to propose a methodological framework that summarises what we suggest are the best practices for research in this field, across taxa and across disciplines. We also provide a tutorial-style introduction to some of the most promising algorithmic approaches for analysing sequences. We divide our review into three sections: identifying the distinct units of an acoustic sequence, describing the different ways that information can be contained within a sequence, and analysing the structure of that sequence. Each of these sections is further subdivided to address the key questions and approaches in that area. We propose a uniform, systematic, and comprehensive approach to studying sequences, with the goal of clarifying research terms used in different fields, and facilitating collaboration and comparative studies. Allowing greater interdisciplinary collaboration will facilitate the investigation of many important questions in the evolution of communication and sociality.