In hyena societies, females are the leaders. Making a female your ally is a powerful social move and a high-ranking female will pass on this power to her offspring.

A research group, looking into female-led spotted hyena societies, captured their unique group behaviour in these photographs.

High rank is important because it gives females priority access to food and helps improve their reproductive success, says Jenn Smith of Mills College in Oakland, California.

She has found that hyenas often reunite with others by following a leader, usually an adult female. The analysis is published in the journal Animal Behaviour.

"Females are socially dominant to males and often call the shots in the group," says Smith.

"This common solution is not without costs," says Smith. "In fact, as group members reunite, this often causes tensions in the group."

Play helps to defuse these tensions.

Genital-to-genital greeting starts young. Here a youth greets an older female.

"Leadership roles are rarely occupied by young hyenas," says Smith. "Den cubs are parked at the den and don't yet travel around the territory. Sub-adults do lead on occasion but only adult females are consistent leaders."

High-ranking leaders are the ones that usually initiate fights, as well as greetings, on behalf of the group.

Many primate groups use social greetings to reduce agitation. Capuchin monkeys hug each other, and we see extreme forms of social bonding behaviour among bonobos, which use sex to bond.

These new insights reveal that hyenas also have similar mechanisms to manage tensions at reunions. It is the first time this has been shown in a non-primate species.

In addition to reducing conflict at reunions, adult females use greeting ceremonies to promote cooperation and to reinforce social bonds with kin and other close allies.

How and why genital greeting evolved is unclear.

"It's fascinating to watch one hyena take the lead and to see others one by one follow her towards a new location," says Smith.