Long-distance communication facilitates cooperation among wild spotted hyaenas, Crocuta crocuta

Abstract

Calls that catalyse group defence, as in the mobbing of predators, appear to facilitate cooperation by recruiting receivers to act collectively. However, even when such signals reliably precede cooperative behaviour, the extent to which the calls function as recruitment signals is unclear. Calls might simply arouse listeners’ attention, setting off a cascade of independent responses to the threat. By contrast, they might convey information, for example, about signaller identity and the nature of a threat that affects receivers’ decisions to participate. We explored this distinction by investigating a possible long-distance recruitment call used by spotted hyaenas. These social carnivores live in fission–fusion clans and individuals disperse widely within their territories. Putative recruitment calls must therefore attract receivers that are distant from the inciting threat and free to opt out of risky collective aggression. Hyaenas compete with lions over food, and neighbouring clans sometimes engage in violent border clashes. These high-stakes contests are decided based on numerical asymmetries, so hyaenas can only protect critical resources if the dispersed clan can converge quickly at conflict sites. We recorded and analysed whoop bouts produced in multiple contexts and found that bouts produced in response to signs of lion–hyaena conflict had shorter inter-whoop intervals than spontaneous ‘display’ bouts. In subsequent field playback experiments, resting hyaenas were significantly more likely to move in response to ‘recruitment’ bouts with shortened intervals than to otherwise identical ‘display’ bouts. Whereas only stimulus type predicted movement, lower-ranked subjects responded most quickly, perhaps because their feeding opportunities depend on arriving early at any kill site. Results demonstrate that hyaenas possess a signal that can reliably recruit allies across long distances, despite moderating effects of individual circumstances on the strength of receivers’ responses.

The evolution of intelligence in mammalian carnivores

“…Like monkeys, spotted hyaenas can recognize individual group mates using cues from multiple sensory modalities [84]. For example, they can identify individual conspecifics based on their long distance 'whoop' vocalization [85][86][87][88][89][90], and they use olfactory cues to discriminate sex, reproductive state, clan membership and familiarity of conspecifics [91][92][93][94]. As in monkeys, nepotism is common among spotted hyaenas, social bonds are stronger among kin than non-kin [95][96][97], and individuals direct affiliative behaviour most frequently towards kin [97][98][99].…”

Brains, brawn and sociality: a hyaena's tale

“…For example, they can identify individual conspecifics, and distinguish kin from nonkin, on the basis of their long-distance ‘whoop’ vocalizations, and whoops also convey information about the caller’s age, sex and motivational state (Benson-Amram, Heinen, Dryer, & Holekamp, 2011; East & Hofer, 1991a, 1991b; Gersick et al, 2015; Holekamp et al, 1999; Theis, Greene, Benson-Amram, & Holekamp, 2007). Hyaenas also have a keen olfactory sense; each clan has a unique scent signature, mediated in part by volatile products of metabolism in the symbiotic microbes inhabiting the hyaenas’ scent glands (Hofer, East, Sammang, & Dehnhard, 2001; Theis, Schmidt, & Holekamp, 2012, Theis et al, 2013), and hyaenas can distinguish scents of their clan-mates from those of hyaenas from other clans (Theis, 2007).…”

Acoustic variation of spider monkeys’ contact calls (whinnies) is related to distance between vocalizing individuals and immediate caller behavior

“…Due to several factors such as habitat characteristics (e.g., vegetation density) and social dynamics (e.g., fission‐fusion), group living animals lose visual contact with individuals of their own group. Studies suggest that through the use of vocalizations denominated “contact calls” animals can maintain social relationships and achieve group flexibility in space with out‐of‐sight individuals (Gersick, Cheney, Schneider, Seyfarth, & Holekamp, ; Kondo & Watanabe, ; Soltis, Leong, & Savage, ). To achieve these functions contact calls should have an acoustic structure related to caller identity and suitable to propagate from callers to receivers.…”