Voice-mediated interactions in a megaherbivore.

Planet Earth is becoming increasingly difficult for large animal species to inhabit. Yet, these species are of major importance for the functioning of the biosphere and their progressive disappearance is accompanied by profound negative alterations of ecosystems (Supplemental information). To implement effective conservation measures, it is essential to have a detailed knowledge of the biology of these species. Here, we show that the hippopotamus Hippopotamus amphibius, an iconic African megaherbivore for which little is known about social communication, uses vocal recognition to manage relationships between territorial groups. We conducted playback experiments on groups of hippos and observed their response to vocalizations from an individual of the same group (familiar), a group from the same lake (neighbor) and a distant group (stranger). We found that stranger vocalizations induced a stronger behavioral reaction than the other two stimuli. In addition to showing that hippos are able to identify categories of conspecifics based on vocal signatures, our study demonstrates that hippo groups are territorial entities that behave less aggressively toward their neighbors than toward strangers. These new behavioral data suggest that habituation playbacks prior to conservation translocation operations may help reduce the risk of conflict between individuals that have never seen each other.