With extreme weather events increasingly occurring worldwide, such as the recent rare Category 5 hurricane in Mexico, we were intrigued by a study conducted on a remote, exclusive island where a group of scientists are examining the impact of these environmental crises on longevity and overall health. The subjects of this study are rhesus macaque monkeys, whose behavior has been observed on the island for over 80 years due to their genetic similarity of 94% to humans. These monkeys managed to thrive under relatively stable environmental conditions until six years ago when a devastating storm struck the island. After undergoing tests for tuberculosis, measles, and COVID-19, our team was granted permission to visit Cayo Santiago, also known as Monkey Island, located off the coast of Puerto Rico. This island is home to approximately 1,800 monkeys who live in isolation, creating a unique natural laboratory that lies between captivity and life in the wild. Leading this long-term research project are biologists James Higham from NYU and Noah Snyder-Mackler from Arizona State University.
Lesley Stahl: What is their typical lifespan?
Noah Snyder-Mackler: The median lifespan here on the island is around 18 years for females and about 15 years for males.
Lesley Stahl: Are there any predators?
James Higham: No, there are no predators on the island.
Unlike in the wild, the monkeys on Cayo Santiago receive their meals every morning. Researchers have identified a hierarchy among the monkeys, where those with higher rank get to eat first.
James Higham: I’ve even witnessed high-ranking individuals approaching low-ranking individuals who are eating and taking food directly from their mouths before closing them (laughs).
Lesley Stahl: What kind of food do they get?
Noah Snyder-Mackler: They are given Purina Monkey Chow (laughs).
Lesley Stahl: There’s actually Monkey Chow?
Noah Snyder-Mackler: Yes, it’s made by Purina.
Lesley Stahl: Oh my goodness!
Rhesus monkeys are frequently used in medical research due to their close genetic and physiological resemblance to humans.
James Higham: They have systems that are remarkably similar to ours, including eyes, lungs, and hearts.
These rhesus macaque monkeys are descendants of those brought to Cayo Santiago from India in 1938. American primatologist Clarence Carpenter embarked on a grueling 14,000-mile sea voyage lasting 51 days to create a natural research facility to study the monkeys’ social and sexual behaviors. Although their early years on the island were challenging, with many monkeys succumbing to disease, enough survived to allow scientists to start tattooing them and conducting daily censuses by the 1950s. This meticulous record-keeping has continued with the current generation of monkeys, providing scientists with over six decades of invaluable biological and behavioral data.
Through their research, scientists discovered that these monkeys are remarkably adaptable, quickly adjusting to life on the island. They also observed their aggressive behavior, particularly during mating season and around food.
Lesley Stahl: Are these monkeys intelligent?
Noah Snyder-Mackler: Yes, they are socially intelligent.
Lesley Stahl: How closely do they resemble humans in terms of their behavior?
Noah Snyder-Mackler: They form strong social relationships with their friends and family members.
Lesley Stahl: They have best friends?
Noah Snyder-Mackler: Yes, they have close friends and even best friends.
Rhesus monkeys live in female-led societies, where mothers, daughters, aunts, and grandmothers form groups, while males leave once they reach maturity to join other troops for breeding.
Research assistants Daniel Phillips and Josue Negron, who have spent years on Cayo Santiago, possess extensive knowledge of troop tensions and allegiances. They arrive at the island every morning at 7 a.m. by boat, spending the next seven hours documenting aggression, grooming, vigilance, and feeding.
Lesley Stahl: Do you get to know individual monkeys? Can you differentiate between them?
Josue Negron: Yes, we need to recognize them instantly. We observe their interactions, grooming behaviors, and even attacks.
Lesley Stahl: How can you tell them apart? What characteristics do you rely on?
Daniel Phillips: You can distinguish them by how they walk, move, and even their facial features.
Lesley Stahl: In other words, their faces become as familiar to you as human faces?
Josue Negron: Yes.
Daniel Phillips: Absolutely.
Josue Negron: We can even recognize family members.
Daniel Phillips: Exactly.
Josue Negron: Your face is familiar, so you must be the offspring of this female.
Everything changed for the researchers and the monkeys when Hurricane Maria hit Puerto Rico in September 2017. The storm subjected the island to 155 mile-an-hour winds, resulting in widespread destruction, including the loss of power and communication systems. The team was unable to reach Monkey Island.
Angelina Ruiz-Lambides, the former scientific director of Cayo, sheltered in her home outside San Juan with her husband and two young children while being seven months pregnant at the time.
Lesley Stahl: You thought the monkeys were going to…
Angelina Ruiz-Lambides: We believed that the monkeys were going to…
Lesley Stahl: …die.
Angelina Ruiz-Lambides: …perish.
James Higham and Noah Snyder-Mackler were unable to obtain any information about their colleagues or the monkeys. Two days after the storm, the team came up with an idea.
Lesley Stahl: So, you chartered a helicopter?
James Higham: Yes, we did.
They hired a helicopter and asked the pilot to conduct a survey of Cayo Santiago. They provided the pilot with a list of questions.
James Higham: Could he spot any monkeys? Were they alive? What was the condition of the vegetation? Were there any pools of water where they could drink?
Angelina, joined by the pilot in the helicopter, captured footage of the destruction. She was devastated to witness the culmination of 80 years of work reduced to rubble.
Angelina Ruiz-Lambides: I witnessed the devastation, seeing the destruction of more than 80 years’ worth of effort.
The once-lush green oasis had turned brown, with two-thirds of the vegetation wiped out. The island’s forested landscape had transformed into barren branches. From the sky, Angelina couldn’t spot any monkeys.
Angelina Ruiz-Lambides: So, I boarded the helicopter again.
Lesley Stahl: Up in the air again.
Angelina Ruiz-Lambides: And that’s when I saw a social group fleeing from the helicopter. I exclaimed, “There are monkeys! Cayo is still alive!”
Angelina Ruiz-Lambides: I estimated that there were around 300 to 400 monkeys in that particular group.
Lesley Stahl: Out of 1,700.
Angelina Ruiz-Lambides: Yes.
However, when the staff returned to conduct a comprehensive census, they were astounded to discover that most of the monkeys had survived. Only around 50 were estimated to have perished.
Lesley Stahl: And you must have wondered, “How did they survive this? How?”
Angelina Ruiz-Lambides: How did they manage to survive?
The monkeys’ survival strategies during the storm remain a mystery. How did they weather the hurricane? Where did they find shelter from the ferocious winds? What did they eat?
Lesley Stahl: One of the major questions is, how did they nourish themselves without being fed?
James Higham: The hurricane severely depleted the island’s vegetation, but it also brought a significant amount of seaweed and algae. It’s possible that the monkeys turned to this vegetation as a food source.
Even after the hurricane, the monkeys had to adapt to a new and hostile environment. Their remarkable adaptability certainly played a role.
Six years later, they are still adjusting. Efforts to replant trees have been hindered by the monkeys’ curiosity, as they uproot any new trees before they can grow. Consequently, there is very little shade on the island.
Lesley Stahl: This area used to be densely forested, right?
Noah Snyder-Mackler: Yes, it used to offer lots of space and shade.
James Higham: Now the monkeys are forced to gather in a few shaded areas due to the changing distribution of shade.
James Higham and Noah Snyder-Mackler …
