Rescuing Puerto Rico's Monkey Island

After a unique macaque colony off the island's coast was hit by Hurricane Maria, its caretakers are rushing to save it—and themselves.

A monkey grips a tree.
Laurie Santos

Off the eastern coast of Puerto Rico, barely a kilometer from the mainland, lies the tiny island of Cayo Santiago. Its 38 acres, shaped like a lowercase r, are home to some unexpected residents—a troop of around 1,000 rhesus macaque monkeys.

Rhesus macaques typically live half a world away in Southeast Asia. But after 406 of them were shipped over in 1938, they quickly took to Caribbean life, and thrived. So did the scientists who work with them. The island has become something of a destination for primatologists. It’s so small, and the monkeys so plentiful and habituated, that even though they are fully wild creatures, they are very easy to track and observe. The last time I spoke to someone on the island—James Higham from New York University—he was standing a few meters away from a female and a male, who were boisterously mating.

Cayo Santiago’s macaques are now among the best-studied primates anywhere on the planet. For 79 years and 9 generations, their births, deaths, and group dynamics have all been charted. Researchers have looked at their group dynamics, parenting styles, mental abilities, how their genes affect their social lives, how scratching helps them cope with conflict. “Many of our early discoveries about primate communication and behavior were discovered there,” says Laurie Santos from Yale University. “It’s an iconic place in primate behavior and science more generally.”

Scientists from at least nine universities still work on the island, which means commuting from the mainland town of Punta Santiago (often with bow-surfing dolphins in tow), and spending the day surrounded by turquoise, manatee-filled waters. The monkeys have it easy too. They have no natural predators. They have no permanent guests—no one stays on the island overnight. They have the run of the island—when researchers arrive, they eat lunch in cages while the monkeys roam freely. And they get regular supplies of monkey chow from the staff of the Caribbean Primate Research Center, to supplement what they can naturally forage.

But the monkeys were also among the first to feel the wrath of Hurricane Maria.

When the hurricane hit Puerto Rico on Wednesday, it pounded the island with winds of up to 175 kilometers per hour, destroying roads, homes, the island’s entire power grid, and most of its communications network. It was the worst hurricane to hit Puerto Rico in 85 years, and Cayo Santiago lay right in its path.

Satellite images confirmed the worst. Areas of lush green vegetation now look like an ugly brown bruise. “The island is completely devastated,” says Higham. “There’s a lot of damage to the vegetation and all the infrastructure is gone.” Buildings in which researchers worked are no more. The island’s isthmus—the horizontal stroke of that lowercase r—seems to be submerged. The feeding corrals, where monkeys would pick up their supplementary chow, have been demolished.

On Saturday, Higham chartered a helicopter to send Angelina Ruiz-Lambides, associate director of the Cayo Santiago Field Station, to the island so she could assess the damage. And amid the tragedy, she phoned in with some good news. All six of the monkey groups on the island have weathered the storm. “We have to do a proper census to really know,” says Santos. “They now seem more skittish than they were before. The psychologist in me wants to know: What were they thinking when it was happening?”

“You look at the island and think: Oh my goodness, how could anything have survived this?” says Higham. “But the monkeys huddle. They hide. They’re creative. They find places of shelter and they know the terrain and habitat really well.”

One of the pressing priorities is making sure that these survivors have enough to eat. Cayo Santiago is a small place, and researchers used to regularly provide the monkeys with chow to supplement whatever they foraged themselves. With so much vegetation leveled, this supplementary food is now all the more important. For now, researchers are loading the food directly onto boats in the mainland Punta Santiago, and rowing it across—fortunately, the dock at Cayo Santiago is one of few man-made structures that withstood Maria.

The monkey island was the brainchild of several scientists—notably Clarence Ray Carpenter, considered by many to be the grandfather of American primatology. From the 1930s onward, Carpenter traveled around the world studying howler monkeys in Panama and gibbons and rhesus macaques in Southeast Asia, and he was among the first to film these animals in the wild. Carpenter and his colleagues had a vision of establishing a free-ranging colony of these animals closer to home, where they could be studied more easily, and eventually be used for research.

And so, in 1938, Carpenter took some 500 rhesus macaques on a 51-day voyage from Calcutta to Puerto Rico, via Colombo, Boston, and New York. He single-handedly cared for the animals, which, as he later wrote, “covered the deck of a large freighter.” Most survived, and some were sold to a research institute to cover the exorbitant costs of the expedition. Some 406 were eventually released on Cayo Santiago. A year later, they were joined by 14 gibbons, but these apes, which typically swing through the canopies of Asian rainforests, didn’t take to the flat, small island. They also had a habit of attacking human observers, so they were later relocated to zoos.

The macaques took time to adjust too. A few plucky individuals swam across to Puerto Rico proper. Those who stayed quickly ate all the papayas and coconut palms, forcing researchers to provision them with food. No one had built facilities for collecting rain, so workers had to ferry over drums of fresh water. But they did survive, and they started breeding. “The suspense created by doubting Thomases ... was relieved after six or eight months by the birth of the first baby,” Carpenter later wrote. “You cannot imagine how welcome that baby was.”

There are now at least a thousand of them, and researchers have since meticulously documented their lives. They trap the macaques once a year to take blood samples and check on their health. Researchers have measured their hormone levels, and sequence their DNA. Whenever the animals die, their skeletons are preserved, and thousands of such skeletons now exist in storage. “Put that together, and you have a population with such a huge amount of information from birth to death and beyond,” says Higham. “There are other free-ranging, accessible primate populations but nowhere else with this breadth and depth of data.”

The monkeys have experienced hurricanes before, including Hugo in 1989 and Georges in 1998. But these earlier storms pale in comparison to those of this exceptional season. Hurricane Irma narrowly missed them, but Maria struck them head-on.

Punta Santiago, where the staff of the Caribbean Primate Research Center live, has been destroyed. One aerial snapshot revealed a plea for help—S.O.S. necesitamos agua/comida (we need food and water)—painted on the street.

Three employees are still unaccounted for, and it’s hard to know everyone’s whereabouts given the collapse of the island’s roads and communications network. One staff member, Omar, who runs the boats to the island, has lost his home, cars, and all his personal belongings to the flooding. “We were on the phone yesterday trying to find out his kids’ shoe size to send them a pair of shoes,” says Santos. Friends and alumni of the center, including a who’s who of primatologists, have also raised over $14,000 to support the beleaguered community.

And yet, a day after Maria hit, employees were already sailing to the island with monkey feed, wrote Ruiz-Lambides in a Facebook post. “Their commitment to our monkeys and courage is admirable.”

As far as the monkeys go, the immediate priority is rebuilding Cayo Santiago’s infrastructure. All the structures for collecting and purifying rainwater were destroyed, and the macaques are facing an incoming heat wave, on an island that’s been largely denuded of shade.

“It’s been a brutal week,” says Higham. “But it was a beautiful place and I’m sure it will be again. Most of the staff who work on the island and their families are all safe, and that's the most important thing. We can rebuild buildings and infrastructure as long as the population is okay, and thankfully we think it is.”