When disaster strikes, it often brings unexpected changes. For the rhesus macaques of Puerto Rico, Hurricane Maria was a turning point that made their community more cooperative and less aggressive. This shift not only altered their social dynamics but also improved their chances of survival year after year.
The History of Rhesus Macaques in Puerto Rico
How Rhesus Macaques Arrived on Cayo Santiago
Rhesus macaques are native to Asia, but in the 1930s, primatologist Clarence Carpenter introduced a colony of hundreds to Puerto Rico. His goal was to study their behavior more conveniently. The macaques were placed on Cayo Santiago, a small rocky island off Puerto Rico’s east coast. Since then, the colony has been a subject of ongoing research, providing valuable insights into their social structures and behaviors.
Social Hierarchies and Aggression Before the Hurricane
How Macaque Societies Function in Puerto Rico
Rhesus macaques typically live in large groups with multiple males and females. These groups are strictly hierarchical, with social status determining access to resources like food and shade. This hierarchy often led to aggressive behaviors as individuals vied for higher rankings.
“They are really hierarchical,” says Camille Testard, an ethologist at Harvard University.
Before Hurricane Maria, aggression and competition were central to the macaques’ interactions. But the storm changed everything.
Hurricane Maria’s Impact on Cayo Santiago
Destruction and Behavioral Changes
In 2017, Hurricane Maria devastated Puerto Rico, including Cayo Santiago. The storm knocked down most of the island’s trees, removing critical sources of shade. This environmental change forced the macaques to adapt their behaviors.
“They started associating with each other more and being nicer to each other,” Testard observed. “We are seeing a change from a very aggressive hierarchical society to a less aggressive hierarchical society.”
The Role of Shade in Social Tolerance
Why Shade Became Critical After the Hurricane
Shade became a vital resource after Hurricane Maria, as daytime temperatures on Cayo Santiago can exceed 100°F. Since rhesus macaques are unable to swim, they rely on shade to cool down.
“They are actually terrified of the water, so the only way they can lower their body temperature is by accessing shade,” Testard explains.
With fewer trees available, macaques had to cluster together to share the remaining shade. This physical proximity encouraged greater social tolerance, reducing aggression and fostering cooperation.
Long-Term Behavioral Changes in Puerto Rico
Cooperation Beyond Necessity in Puerto Rico
Interestingly, this shift toward cooperation extended beyond the immediate need for shade. The macaques became generally less aggressive and more tolerant, even at night or in cooler weather.
Testard notes that this consistent tolerance was a strong predictor of future access to shade on hot days. “Macaques that were nicer all the time were more likely not to be driven out of shady spots when they needed them,” she says.
How Cooperation Improved Survival
Decreasing Mortality Rates of Puerto Rico
The behavioral changes following Hurricane Maria had significant implications for survival. Before the storm, injuries from fights were a leading cause of death. After the hurricane, however, heat stress became the primary challenge.
Monkeys that tolerated 10 or more new social partners experienced a 43% decrease in mortality risk each year.
“The rules of the game have changed,” Testard explains. “Being less aggressive and more cooperative has become a survival advantage.”
Adapting to a Changing Environment in Puerto Rico
Long-Lasting Behavioral Shifts in Puerto Rico
The study, which tracked the macaques through 2022, found that these behavioral changes have persisted for years. The same levels of tolerance were observed last year, suggesting that the shift may have long-term effects on their social structure.
“This study highlights the importance of social relationships in the context of climate change,” says Testard.
What We Can Learn From Rhesus Macaques
Social Bonds in Times of Adversity
The changes observed in Cayo Santiago’s rhesus macaques demonstrate how environmental stress can reshape social behaviors. Their ability to adapt relationships to meet new challenges underscores the importance of cooperation in survival — a lesson that resonates far beyond the animal kingdom.
Conclusion
Hurricane Maria didn’t just alter the physical landscape of Cayo Santiago; it transformed the social dynamics of its rhesus macaque population. These monkeys, once defined by aggression and hierarchy, embraced tolerance and cooperation, improving their chances of survival in a changing environment.
Their story is a powerful reminder of how adversity can foster connection and adaptability, offering valuable insights for understanding social relationships in both animals and humans.
Sources:
- Camille Testard, Ethologist, Harvard University
- American Journal of Primatology: A 75-Year Pictofial History of the Cayo Santiago Rhesus Monkey Colony
