With bone-crushing jaws and enlarged forebrains, spotted hyenas are some of the most formidable hunters on the planet. Even their cubs are born with a set of sharp teeth, ready to go. These carnivores are also known for their highly sophisticated social systems. According to new findings published in Ecology Letters this week, they instinctively form beneficial bonds with friends of their friends -- like us.
Spotted hyenas (Crocuta crocuta) have a life span of up to 22 years, and they live in large, stable clans that might contain more than 100 individuals. Females are the dominant sex in their society -- they get first dibs on any kill -- and the cubs of high-ranking females inherit their mothers’ standing. These sophisticated predators can even discriminate maternal and paternal kin from unrelated hyenas. Knowing how these animals form long-lasting relationships, or cohesive clusters, can help us understand cooperation and sociality across various species.
So, a trio led by University of Pennsylvania’s Amiyaal Ilany collected more than 55,000 observations of spotted hyena social interactions during a 20-year period in Kenya. They used a mathematical model to evaluate the effects of multiple factors on the dynamics of their social structure: genetics, the environment, and individual traits, for example.
Turns out they don’t form bonds with every hyena in the clan. When it comes to their social network, factors ranging from sex and rank to rainfall and prey availability do matter, but the ability of individuals to form and maintain bonds with friends of friends (or triads) had the strongest effect. This so-called “triadic closure” was the most consistent factor influencing the long-term dynamics of spotted hyena social structure.
“Cohesive clusters can facilitate efficient cooperation and hence maximize fitness, and so our study shows that hyenas exploit this advantage,” Ilany says in a news release. “Interestingly, clustering is something done in human societies, from hunter-gatherers to Facebook users.” Next time, maybe pay some attention to that “People You May Know” section.
This is one of the largest studies ever on social network dynamics in non-humans. And because it doesn't focus on a single static snapshot of the animals, the team have found that males follow rigid rules when forming bonds, while females change their preferences over time. She might care about social rank now, but she might let the weather influence her choice later, for instance. Since they’re the dominant sex, “they can be very flexible in their social preferences,” according to study co-author Kay Holekamp of Michigan State University. “Females also remain in the same clan all their lives, so they may know the social environment better. In contrast, males disperse to new clans after reaching puberty, and after they disperse they have virtually no social control because they are the lowest ranking individuals in the new clan, so we can speculate that perhaps this is why they are obliged to follow stricter social rules.”