Behaviour 2019
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When a stranger calls (who cares?): social variables shape spotted-hyena response to distant whoops
Andrew Gersick1, Frants Jensen2, Ariana Strandburg-Peshkin3, Kenna Lehmann4, Kay Holekamp4. 1Princeton University, Princeton, NJ, United States; 2Woods Hole Oceanographic Institution, Woods Hole, MA, United States; 3University of Konstanz, Konstanz, , Germany; 4Michigan State University, East Lansing, MI, United States

Spotted hyenas produce long-distance “recruitment whoop” vocalizations in response to direct threats - often in the context of territorial or food-related conflict. These calls can draw other hyenas from several kilometers away. We broadcast recruitment-type whoop bouts from three classes of callers - strangers, known individuals from a neighboring clan, and clan-mates - within our study clan’s territorial boundaries, and measured the responses of individual receivers. Although recruitment whoops from any of the three caller classes might indicate a highly salient resource conflict or territorial incursion, subjects were most likely to invest in energetically costly responses to long-distance calls from their clan-mates. Calls from familiar rivals and strangers were less likely to elicit the lengthy bouts of travel-and-search behavior that characterized the most intense responses. Our results implicate both the informational content of hyenas’ long-distance vocalizations, and the importance of shared group membership to hyenas’ decisions when opting into, or out of, collective behaviors that can be highly costly.