After a frightening experience, some people like company 鈥� and that might go for monkeys too. When a hurricane devastated a small island, its resident rhesus macaques became more sociable, spending more time close to each other in the following months.
The uninhabited island of Cayo Santiago, off the coast of Puerto Rico, is home to about 1500 macaques, descendants of animals taken there 80 years ago for medical research. Ever since, they have been given food but otherwise left to live naturally. The site, called Monkey Island, has become a useful way to study primate behaviour and genetics.
Two years ago, hurricane Maria hit the Carribbean, killing听thousands of people on Puerto Rico听and leaving many without electricity and water. On Monkey Island, much of the vegetation was destroyed, with trees uprooted or stripped of their leaves.
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It must have been terrifying for the animals, says Sam Larson of the University of Pennsylvania. 鈥淚f I woke up and all those trees had gone I would feel like something was wrong. And the hurricane itself has got to be the scariest thing. I would be clinging on to trees for dear life.鈥�
A tenth of the monkeys died in the storm, their feeding stations and water sources were disrupted and their social lives changed too.
Before the hurricane, the monkeys were fairly stand-offish with unrelated individuals, and often attacked unfamiliar monkeys who got too close. The year after, they were more often seen alongside other animals, even unrelated ones, although they didn鈥檛 groom each other more.
In one group, monkeys were observed with another within a two-metre radius up to 10 times as often as before the hurricane.
Larson says one possibility is the company helped the animals feel less stressed by the radical changes to their environment.
But they also could have been forced to get closer because there was less shade from trees. 鈥淚t suggests that if the resources go, they have to become more tolerant of each other,鈥� says Larson. The team presented the findings at the recent American Association of Physical Anthropologists meeting in Cleveland.
After the hurricane, there may have been a combination of limited shade and a need for closer proximity with others, says Joanna Setchell of Durham University, UK, who wasn鈥檛 involved in the study. 鈥淎 couple of decades ago in primatology we were very much against the idea that you could anthropomorphise. But perhaps our first hypothesis should be that they are going to react to things the way we do.鈥�
Larson鈥檚 team also found that previously lower-ranking individuals became more accepted. 鈥淭his indicates how shared hardship brings everyone together, which is perhaps the opposite of what people would expect,鈥� says Frans de Waal of Emory University in Georgia. 鈥淲e always think that hardship will lead to more competition, but here it leads to more cohesion.鈥�
