These monkeys formed an unlikely friendship after Hurricane Maria wrecked their home

After Hurricane Maria swept through Puerto Rico in 2017 and caused immense damage, researchers found rhesus macaques, a species of monkey living on Cayo Santiago became more sociable with each other, according to a study published in the journal Current Biology.

The monkeys live in a highly competitive society and can become aggressively protective over resources like food and water, said study author Camille Testard, doctoral candidate in neuroscience at the University of Pennsylvania' Perelman School of Medicine.

That's why researchers predicted that after the hurricane, the monkeys would stick with their closest friends in order to survive, Testard said. Instead, the island's residents became more tolerant of each other and greatly expanded their friend group.

To measure the monkeys' socialization and friendship-building, researchers tracked who they groomed, which is one of the ways monkeys bond with one another, Testard said.

"It serves a similar function for us to getting coffee or a beer with friends," she added.

After the hurricane, the "grooming networks" became denser, Testard said, meaning there were more connections being formed compared to the monkeys' behavior before the storm.

The social network

The scientists found the animals made friends with friends of their friends, which she said is a common "easy" route to making friends that's mirrored in human social circles.

The researchers didn't know why the monkeys decided to make more friends, but Testard hypothesized it could be "a strategy to gain tolerance and support from the greatest number of individuals and thereby access to limited resources like shade."

The monkeys could be forming additional bonds to "buffer" them from future hardship from the natural disaster, said Brenda McCowan, professor of population health and reproduction at the School of Veterinary Medicine at the University of California, Davis, who was not involved in the study.

She said the findings also provide insight into how humans might cope to the increasing threat of climate crisis. Rhesus macaques are "close evolutionary relatives to humans and share many features of their biology and behavior with us," Testard said.

The study results give important insight into human social connections, McCowan noted, and how they can buffer our physical and emotional health from ecological and societal challenges.

Going forward, Testard is interested in investigating the long-term impacts of the monkeys expanding their social circles -- or not -- after a natural disaster. Some potential factors that she hypothesized could be impacted are the monkeys' life spans and number of babies they have.

"Our best friends can give us many things," Testard said. "But sometimes, what we need is a social network where everyone is just friendly enough."