The meaning of barks: Vocal communication of fearful and playful affective states in pigs

Winnie Y. Chan

If vocalizations reflect an individual's underlying affective state, they can be useful in animal welfare assessment. Domestic pigs, <italic> Sus scrofa domesticus<italic> , produce bark vocalizations that are characteristic of alarm. However, barks are also uttered in play, raising the possibility of different types of barks to which pigs respond differentially. The meaning of pig barks was examined through a series of experiments. An acoustic analysis of adult sow and juvenile pig barks was conducted, accompanied by a playback experiment, to address the hypothesis that age affects the acoustic structure of barks and that juvenile pigs exhibit differential responses to adult and juvenile barks. The findings demonstrated that juvenile pigs can discriminate between sow and juvenile barks produced in an alarm context based on differences in acoustic morphology, with the former evoking stronger fear responses. Juvenile barks given in alarm and play contexts were compared to assess whether the acoustic morphology of barks differs depending on affective context. Subtle, yet significant, differences were found in the acoustic structure of barks given in these different contexts, suggesting that bark morphology reflects affective states in pigs. Three playback experiments were conducted to assess the effects of acoustic structure, bark rate, and context on the behavioral responses of juvenile pigs to barks. In general, pigs responded more to playbacks of barks than silence or grunts. Responses to barks were further mediated by bark rate and contextual cues. Lastly, a novel barking device was developed for assessing the enrichment value of barks. A barking object was hypothesized to be more attractive to pigs than a non-barking object. Object use was similar between groups given the barking vs. non-barking object but there was a trend towards increased play in groups receiving the barking object, suggesting that enrichment objects incorporating barks could potentially induce positive affective states in pigs. Overall, acoustic variations in barks can provide pigs with information relating to an individual's underlying affective state. Responses to barks are mediated by an interaction between acoustic and contextual cues. Furthermore, effective enrichment devices incorporating barks could be developed for group-housed pigs.

The meaning of barks: Vocal communication of fearful and playful affective states in pigs

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