Encoding of Emotional Valence in Wild Boar (Sus scrofa) Calls

Abstract

Simple SummaryAnimal welfare today is assessed based on both the physical and mental health of animals. However, measuring animal mental health, which includes emotions (i.e., short-term positive or negative reactions to specific events), remains a challenge. Since animals are known to use vocalizations to communicate their emotions to their peers, knowledge about how the structure of vocalizations changes with emotions could be very useful in order to develop noninvasive indicators for assessing animal welfare under captive conditions. The aim of this study was thus to investigate if the type of calls (i.e., grunt, scream, or squeal) or the acoustic structure of the calls emitted by captive wild boars changed according to the emotions they were experiencing. We found that wild boars used different types of calls in positive and negative situations. We also found that their acoustic structure changed according to the emotions. Indeed, calls produced in positive situations were generally shorter and at lower frequencies than those produced in negative situations. It thus seems that wild boars express their emotional state through their vocalizations. Overall, our study gives us better knowledge about how the emotions of captive wild boars could be assessed, and how this compares to domestic pigs.AbstractMeasuring emotions in nonhuman mammals is challenging. As animals are not able to verbally report how they feel, we need to find reliable indicators to assess their emotional state. Emotions can be described using two key dimensions: valence (negative or positive) and arousal (bodily activation or excitation). In this study, we investigated vocal expression of emotional valence in wild boars (Sus scrofa). The animals were observed in three naturally occurring situations: anticipation of a food reward (positive), affiliative interactions (positive), and agonistic interactions (negative). Body movement was used as an indicator of emotional arousal to control for the effect of this dimension. We found that screams and squeals were mostly produced during negative situations, and grunts during positive situations. Additionally, the energy quartiles, duration, formants, and harmonicity indicated valence across call types and situations. The mean of the first and second formants also indicated valence, but varied according to the call type. Our results suggest that wild boars can vocally express their emotional states. Some of these indicators could allow us to identify the emotional valence that wild boars are experiencing during vocal production and thus inform us about their welfare.

Positive and negative contexts predict duration of pig vocalisations

“…Interestingly, we did not find significant differences in the other measured acoustic parameters between positive and negative contexts, which differs from recent studies 22,37,38 . There are several non-mutually exclusive explantions why the outcomes differ among studies: firstly, the emotional valence experienced by indiviudals may not have differed enough to be reflected in the measured acoustic parameters.…”

“…Secondly, the experimental design of previous studies differed from ours in several other aspects, including day of recording, number of individuals present during recording and the functional relevance of the context e.g. social isolation, startling and aggression as negative contexts and food anticipation and affiliative interactions as positive contexts 22,28,37,38 . Thirdly, it may be that the calls produced here were influenced more by unmeasured factors than the valence of the contexts.…”

Vocal individuality of Holstein-Friesian cattle is maintained across putatively positive and negative farming contexts

“…Secondly, this classification decline could relate to the within-heifer vocal variability which likely arose from cattle being exposed to different emotionally loaded contexts. Changes in emotional state have been shown to result in modulations of vocalisations 3,31,33,38 , with a growing body of literature on vocal indicators of emotion in pigs 39,40 , horses 38,41 and goats 31,42 . Thus, in addition to identity cues, vocal cues of emotion should be studied in cattle high-frequency calls.…”

Automated bioacoustics: methods in ecology and conservation and their potential for animal welfare monitoring

“…The analysis confirmed that vocalizations of wild boars could be broadly categorized into four classes listed above. Wild boar calls also contain information on emotional valence [137]. Animals were given three different treatments (anticipating a food award, affiliative interactions and antagonistic interactions) and had their calls recorded during these treatments.…”

“…Screams and squeals tended to be produced during negative interactions, and grunts were associated with positive situations. Maigrot et al [137] also used energy quartiles, duration, formants and harmonicity in order to infer emotional valence for the different call types and situations.…”