On quiet nights across large swaths of the African bush, you may hear a series of whooping calls in the distance. This unique sound is the long-distance vocalisation used by spotted hyenas (Crocuta crocuta) to communicate with each other.

For hyenas, it’s advantageous to know who is calling before deciding to respond. They don’t treat every member of their group the same – and the caller could even be an intruder in their territory.

In animal societies, identity signals are common. They mediate interactions within groups, and allow individuals to discriminate group-mates from out-group competitors. However, individual recognition becomes increasingly challenging as group size increases and as signals must be transmitted over greater distances.

We hypothesised that for hyenas long-distance calls could be used to determine the individual identity and the group membership of the caller.

Our research sought to determine what information is in these calls, and how hyenas are able to determine whether they are hearing a group mate or an intruder.

We found these calls were individually distinct. Hyenas from the same clan did not sound similar enough to identify the caller’s group membership from voice alone. This means hyenas must be able to remember the voices of their group mates, an impressive feat of memorisation. It also has implications for how hyenas maintain contact with each other and coordinate their movements over long distances.

Our results suggest that individual identity of the caller is important enough and that a group signature is not enough information for a listening hyena to decide whether to respond or not. Furthermore, distinctive voices may more easily evolve and identifying the individual is enough for hyenas to remember what group the caller belongs to.

Hyena social groups

Spotted hyenas can be found in a range of habitats throughout sub-Saharan Africa. Their population is estimated to be between 20,000 and 50,000 individuals, with the highest known concentrations in Tanzania’s Serengeti ecosystem. They live in social groups, called clans, that range in size from only six in harsh semi-desert habitats in Namibia to over 125 individuals in Kenya’s Maasai Mara National Reserve.

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