After Hurricane Maria devastated Puerto Rico in 2017, the monkeys who lived there formed new bonds to share an suddenly scarce resource: shade.
Rhesus macaques (Macaca mulatta( ) who were willing to hang around with others Their chances of survival are increased in the storm’s aftermath, researchers report July 24 at bioRxiv.org. The newfound sociability of animals may have helped them escape the heat of the sun under any trees that were left standing and any other sources of shade.
Amid Hurricane Maria’s heavy rain and furious winds — coming just two weeks after Hurricane Irma dumped a heavy deluge of rain — trees and other plants across Puerto Rico toppled. Nearly a quarter of Puerto Rico’s total forest biomassDemolishedSN: 3/17/20). Cayo Santiago, a once lush key located off Puerto Rico’s coast, was left largely barren after it lost nearly two-thirds of its vegetation.
More than five years later, Cayo Santiago’s flora hasn’t recovered, says Camille Testard, a behavioral ecologist and neuroscientist at the University of Pennsylvania. In April 2023 the tiny island had less than 600 living plants.
But a colony of around 1,600 macaques, managed by the University of Puerto Rico’s Caribbean Primate Research Center, also calls Cayo Santiago home. Without much remaining tree cover, the destructive hurricane left many monkeys searching for shady relief from temperatures that regularly exceed 40° Celsius (104° Fahrenheit). Now, some of the shade comes in smaller packages: boulders. water basins. or even shadows cast by humans.
“If you’re collecting data on the island, you’re gonna have monkeys that are sitting in your shade and following you around,” Testard says.
Before Hurricane Maria the macaques fought over food, status, or mates. After the hurricane, macaques were still fighting over food and status. Expanding their social network and forming new relationshipsTestard and his colleagues reported 2021. While monkey fights still happen, they aren’t as common as before. The team hypothesized that these new friendships would give them more shade in tight spots. The team lacked data to support their hypothesis.
Researchers examined the interactions between monkey groups over a 10 year period, five before and five after the hurricane. The team studied monkey groups from 6:00 am to 2:30 pm in 10-minute intervals. One year, 2020 was excluded due to the COVID-19 Pandemic.
The team found that from 2018 through 2022 the animals spent a lot of time together during the hot afternoons compared to cooler mornings. The recorded interactions don’t specifically note whether the monkeys were sitting in shade or sun, says coauthor Lauren Brent, a behavioral ecologist at the University of Exeter in England. More social monkeys died less in the five-year period following the storm. This suggests that the afternoon gatherings in the shade helped the animals cool off.
The findings are a “wonderful” example showing how behavior can be an important factor for survival as environments change, says Richard Buchholz, a behavioral ecologist at the University of Mississippi in Oxford. Because researchers on Cayo Santiago ensure macaques have food and water, it’s unclear whether the same might happen in a group of wild monkeys, he says. But “it’s exciting that [the researchers have] shown this impact on mortality.”
It’s possible that the boost in sociality comes not from a benefit of being tolerant of their primate peers after a natural disaster, but because there’s a cost to being intolerant, Buchholz says. “We tend to get lethargic when things get superhot.” The animals may be calmly sitting together in the shade so as not to raise their metabolisms, “avoiding the metabolic cost of chasing after somebody and building up more heat that you’ll have to get rid of somehow.”
The gathering of monkeys could have other effects. Testard, Brent, and co-workers used computer simulations in a separate paper, published on July 19, to demonstrate that Socializing more may increase the risk of infectious diseasesSpreading will be a problem.
“So even if you’re really flexible, and you’re able … to adapt to this new environment, the way that you have to adapt actually makes you more vulnerable to other external shocks to the system,” Testard says. “I think that needs to be kept in mind when we think about the effects of natural disasters on wildlife health.”
