Before the disaster the monkeys of Cayo Santiago had spent much of their time bickering and fighting.
So when a hurricane devastated their Caribbean island home, researchers assumed that the macaques would retreat into tight-knit cliques. The jungle had been stripped of most of its vegetation and the primates were expected to battle over scarce resources.
Instead, to the scientists’ surprise, the monkeys demonstrated something akin to a Blitz spirit: they started making friends with strangers.
A study that compared two groups of the primates before and after the hurricane, which struck in 2017, found an increase in friendly social connections after the disaster.
The research team found that macaques, which were brought to the Caribbean from India in the 1930s, worked on building new relationships rather than strengthening existing ones.
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They were more likely to share resources that had suddenly become limited in their tropical habitat, such as shade. “They extended their social networks to include more partners,” Camille Testard, of the University of Pennsylvania, who led the study, said.
The researchers analysed the monkeys’ social networks by watching how often the macaques sat close to each other and their grooming behaviour. The monkeys grew close to friends of friends. Primates that had once been on the periphery of the community were allowed in.
This friendliness was unexpected in part because the macaques are usually not very nice to each other. “It’s a notoriously nepotistic, despotic society,” Professor Lauren Brent, of the University of Exeter, a co-author of the study, said.
“They form close relationships on which their lives depend, but I think these emerge from the fact that it’s such a competitive society. They face these really strict dominance hierarchies.
“It’s almost like a caste system for the females: they’re born into a certain status that their mother had and they retain that status for life. If you have high status, you live longer, you have more babies who have greater access to food. It’s usually a pretty harsh place, socially.”
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She added: “The whole reason we did this study is that my research assistants said to me, ‘The monkeys are being weird. They’re not fighting as much; something is has changed.’ ”
The damage caused by Hurricane Maria on Cayo Santiago — the name means “Monkey Island” — was severe, with two thirds of the green vegetation destroyed. Across Puerto Rico more than 3,000 people lost their lives.
“We expected the monkeys would use their closest allies to cope with the ecological devastation of the hurricane and so would invest in their existing relationships,” Brent said.
“So we were surprised that, after the hurricane, they expanded their social networks and the number of individuals they tolerated.
“These were not always active interactions; tolerance might mean simply sharing a shady place to sit. Our closest friends can give us many things. But sometimes what we need is a social network where everyone is just friendly enough.”
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Even now, the island’s vegetation has not recovered fully and the macaques on Cayo Santiago seem to have maintained the connections formed after the hurricane.
“We haven’t been able to quantify it just yet, but those patterns that the research assistant said that they first noticed a few months after the hurricane — they think they are still there,” Brent added. “I think that when we go and look at it again, this is what we’re going to find.”
The findings were published yesterday in the journal Current Biology.