Encoding of Situations in the Vocal Repertoire of Piglets (Sus scrofa): A Comparison of Discrete and Graded Classifications

Abstract

Two important questions in bioacoustics are whether vocal repertoires of animals are graded or discrete and how the vocal expressions are linked to the context of emission. Here we address these questions in an ungulate species. The vocal repertoire of young domestic pigs, Sus scrofa, was quantitatively described based on 1513 calls recorded in 11 situations. We described the acoustic quality of calls with 8 acoustic parameters. Based on these parameters, the k-means clustering method showed a possibility to distinguish either two or five clusters although the call types are rather blurred than strictly discrete. The division of the vocal repertoire of piglets into two call types has previously been used in many experimental studies into pig acoustic communication and the five call types correspond well to previously published partial repertoires in specific situations. Clear links exist between the type of situation, its putative valence, and the vocal expression in that situation. These links can be described adequately both with a set of quantitative acoustic variables and through categorisation into call types. The information about the situation of emission of the calls is encoded through five call types almost as accurately as through the full quantitative description.

Deer Mothers Are Sensitive to Infant Distress Vocalizations of Diverse Mammalian Species

“…Recent studies have probed the evolutionary basis of emotional communication by identifying acoustic cues associated with arousal and valence (Briefer 2012;Tallet et al 2013;Zimmermann et al 2013), responses of humans to vocalizations of other primates and domestic animals (Belin et al 2008;McComb et al 2009;Tallet et al 2010;Andics et al 2014;Faragó et al 2014), and responses of domestic animals to human vocalizations (Custance and Mayer 2012;Andics et al 2014). We advance this body of work by conducting "cross-species playbacks" with undomesticated animals, using vocal stimuli from species that are taxonomically and ecologically distant from the subject species.…”

“…Humans are sensitive to distress vocalizations emitted by domestic animals, including cats (McComb et al 2009) and piglets (Tallet et al 2010(Tallet et al , 2013. Domestic dogs (Canis familiaris) may also be sensitive to the cries of adult humans (Custance and Mayer 2012).…”

Postnatal auditory preferences in piglets differ according to maternal emotional experience with the same sounds during gestation

“…Pigs express a large variety of sounds that depend on the situation. Negative states lead to the emission of high, long and tonal sounds that are frequency modulated (screams) or not (squeals) while positive states induce lower, shorter and more tonal calls (croaks)39. Thus vocal expression can be used to identify their emotional state quite accurately, and researchers typically distinguish high-pitched stress vocalizations from low-pitched neutral or positive vocalizations46.…”

“…so-called high pitched distress calls3839) emitted by piglets. This is a measure commonly used to assess the level of stress experienced by pigs40.…”

Piglets Learn to Use Combined Human-Given Visual and Auditory Signals to Find a Hidden Reward in an Object Choice Task

“…Hearing is well developed in pigs, with a large auditory spectrum ranging from 42 Hz to 40.5 kHz [36], into which human vocal productions fit (80 Hz to 1,4 kHz) [37]. Acoustic signals are various and of major importance in the social behaviour of pigs [38] and experienced handlers suggest that pigs respond to human voices and their variations [39]. The effects of human auditory signals were studied to assess the ability of piglets to discriminate between familiar handlers [34].…”