Barking pigs: differences in acoustic morphology predict juvenile responses to alarm calls

Alarm calls given by adults and juveniles sometimes elicit different responses in receivers, with the alarm calls of adults being more provocative than those of juveniles. We examined this possibility in the domestic pig, Sus scrofa domesticus. We hypothesized that alarm barks given by adults and juveniles would differ acoustically, and that weaned juvenile pigs would respond more strongly to the barks of adult sows than they would to the barks of peers. In support of our hypothesis, we found that the barks of adult sows were louder and had lower values for peak frequency parameters than those of juveniles. We conducted a playback experiment and found that juvenile pigs responded as if the barks of unfamiliar sows were more alarming than the barks of unfamiliar juvenile pigs or ambient noise (control sound), even after controlling for playback volume. We conclude that differences in acoustic morphology enable domestic pigs to discriminate between barks of adult sows and juveniles, with the former evoking a stronger response.