In elephant families, it’s the matriarchs who call the shots. They decide where a group goes, where it eats and when. They’re also the glue that holds elephant societies together. Elephants have a tiered social network of small “core groups” of close relatives, and larger, less cohesive “bond groups” and “clan groups” that include distant relatives and acquaintances. Older matriarchs with lots of social ties are the hubs that connect all these groups to each other.
These older female leaders are also frequent targets for ivory poachers because of their large tusks. When they’re killed, other elephants not only lose their mothers, sisters, and grandmothers, but also their links to the rest of their social networks.
In other animal societies, studies have shown that removing individuals who act as social hubs can collapse such networks. With demand for ivory leading to tens of thousands of elephant deaths a year, researchers feared that the same thing would happen to elephants. A new study published in the journal Current Biology shows, though, that elephant societies are more resilient than expected because younger females step into their mothers’ connective roles in the social network.
Biologists Shifra Goldenberg, Iain Douglas Hamilton, and George Wittemyer explored how elephant networks respond to the “selective knockouts” caused by poaching by looking at data they had collected while studying more than 100 elephants over the last 18 years in Kenya’s Samburu National Reserve. They knew many of the elephants by the shape of their ears, their scars and other body markings, and even their behavioral quirks. They also knew which elephants hung out together and how their different groups were connected.
The researchers went back to their observations and reconstructed the Samburu elephants’ social network at different points between 1998 and 2014, during which there were stretches of relatively little poaching and a recent period of intense poaching.
They found that over those 16 years, the average age of the Samburu elephants became much younger as older elephants were killed. There was a high turnover in the population’s adult females, and less than one-third of the elephants that the researchers encountered in 1998 were still alive last year.
Despite the death toll, the Samburu social network didn’t fall apart. It remained intact because daughter elephants stepped in to fill the roles that were left behind by their mothers. In some of these cases, the new matriarchs were barely fully grown, but their surviving relatives still rallied around them as the oldest females in the family.
These younger elephants not only took over the leadership of their core groups, but filled in the connective roles in the bigger network, often replicating the positions held by their mothers. Daughters maintained the social ties and relationships their mothers had built when they were alive, keeping their core group connected to the others in the bond group through matriarchs that their mothers had known, or their daughters if both moms had died. This helped them to keep the network intact with more or less the same structure that had existed before. When daughters couldn’t recreate their mothers’ networks exactly, they used the social opportunities that their mothers had provided them to strengthen relationships with elephants that were once only distant contacts of their moms, thus creating new bond groups.
The resilience of the elephants’ social structure is good news, but the researchers warn that there’s more work to be done before we know all the consequences of these families losing their oldest members. Even with the leadership roles filled and social ties maintained, elephants groups may run into problems with younger matriarchs in the lead. They lack the experience and knowledge that their mothers accrued over time, and other research has shown that older matriarchs are better than younger ones at distinguishing and responding to predators and other threats, and that families with older leaders have higher reproductive rates. The researchers plan to keep monitoring the Samburu elephants to see how these rebuilt families fare over time.