Sources of variation in the long-distance vocalizations of spotted hyenas

Abstract

SummaryIt has long been recognized that vocal signals communicate information about the age, sex and affective state of callers. However, the mechanisms by which these types of information are communicated are less well understood. Here we investigated variation in the acoustic properties of the long-distance vocalizations, called 'whoops', emitted by free-living spotted hyenas, Crocuta crocuta. Specifically we investigated whether the fundamental frequency, length and rate of whoops provide information about the caller's age, sex and/or level of arousal. We determined the latter by contrasting whoops emitted spontaneously with whoops emitted during periods of social excitement, when callers typically also exhibited visual signals associated with heightened arousal. We found that the minimum fundamental frequency of a whoop provides reliable information about the caller's general age and, for adult callers, information about sex as well. The vast majority of adult male whoop bouts were emitted spontaneously, but juveniles and adult females produced many of their bouts during periods of social excitement. Although context did not significantly affect the whoop bouts of adult females, juvenile bouts emitted during social excitement had higher maximum fundamental frequencies, greater proportions of asymmetric whoop subtypes, and reduced inter-whoop intervals. By reducing the inter-whoop intervals of bouts, juvenile hyenas significantly increased the likelihood that conspecifics would respond to whoops by approaching the caller or its social companion. Peak fundamental frequency and the relative abundance of whoop subtypes did not appreciably affect response. We discuss the potential functions of whooping by juvenile and adult hyenas in light of these findings.

Dog growls express various contextual and affective content for human listeners

“…Our recent findings also support this, as in the case of playbacks of various dog vocalizations, the sounds containing shorter calls (along with shorter inter-call intervals) were rated to be more positive [22]. It was found in several other species that besides call length, inter-call intervals can be important indicators of arousal level, because the pauses between utterances shorten with a rise in arousal (mongoose: [38], hyena: [39], baboon: [40] pig: [14]). Nevertheless, studies showing the link between these temporal acoustic variables and emotional valence are scarce thus far.…”

What the hyena's laugh tells: Sex, age, dominance and individual signature in the giggling call of Crocuta crocuta

“…Status signalling is almost certainly not restricted to giggles. The whoop is used to transfer information to remote congeners and may allow individual identification of the sender as well as its current emotional state over distances up to 5 km [51,53,73,74]. Not only are whoop calls highly idiosyncratic making but it is also known that mothers will respond to the whoop from their own cub more frequently than to the whoop of a non-kin cub, demonstrating that the individual characteristics in the whoop sounds are recognized and utilized [73].…”

“…For instance, "whoops," with long inter-whoop intervals, are primarily used to signal separated individuals, supporting within- and between-clans acoustic interaction [51,52]; conversely, the "grunt" [39] ("soft growl" in [49]) is uttered during close meeting of clan mates and remains barely audible after a few meters of propagation. Previous studies have focused on the long-distance "whoop" call, showing that it supports information related to sex and individual identity and thus may allow discrimination between clan members and alien individuals [48,51,53]. Although they might play an important role in mediating the relationships within the clan, calls, other than the whoop, of adult hyenas have been neglected.…”

Numerical assessment in the wild: insights from social carnivores

“…Spotted hyenas can vary the duration of these inter-whoop intervals, resulting in faster or slower calls. Theis et al [115] found that the interwhoop interval encodes information about the current emotional state of the caller and that hyenas respond to this information. Whoop bouts emitted by juveniles during periods of social excitement have shorter inter-whoop intervals, and conspecifics are significantly more likely to respond to these whoop bouts by approaching the caller.…”