How natural disasters bring monkeys — and maybe humans— together

December 14, 2021

Written by: Claudia Lopez-Lloreda

After more than half a day of 170 mile per hour winds thrashing Puerto Rico, there was next to nothing left on the small island of Cayo Santiago. Vegetation decreased by almost 60% and the island looked barren. Amazingly, the majority of the rhesus monkeys living on Cayo Santiago as part of a research institute survived the initial impact of the hurricane. However, with food and shade becoming scarcer by the day, social tensions would rise, and the researchers studying the monkeys asked: how would they treat each other in light of this natural disaster? Would they fight each other for scarce resources or band together to survive?

The research group, led by Penn’s own Michael Platt, has been tracking the relationships between monkeys in the small island of Cayo Santiago, or ‘Monkey Island’, for years. After Hurricane Maria hit, they analyzed how the monkeys interacted with each other and compared the social networks of the monkeys before and after the storm1. They wanted to understand how social relationships shifted in light of the natural disaster. To do so, they tracked the monkeys and recorded how close they physically were to each other as well as behaviors such as grooming, feeding, resting, and traveling. Specifically, grooming, in which the macaques clean each other, is a behavior indicative of a social relationship. Platt describes grooming as the macaque equivalent of grabbing a beer with a friend.

The results of the study were very surprising: monkeys became more social and expanded their social networks. Hurricane Maria and its aftermath drove monkeys to be friendlier to each other and to build new relationships and social ties, which they have sustained for three years now. Monkeys were more than 50% more likely to be found grooming after the hurricane than before, an indication that they were participating in more social interactions. Specifically, monkeys that were socially isolated before the hurricane increased their previously-lacking social ties. Many monkeys increased the total number of their social relationships, thus expanding their social networks, rather than intensifying the strength of their already established relationships.

The study’s findings are consistent with an idea called the social buffering hypothesis, which suggests that a social support system can help buffer, or protect, from harmful events. Research in primates including humans shows that strength of social relationships can provide protection to adversity throughout life, such as recovering from an illness or mental health disorders. In fact, the quantity and quality of social relationships can predict how long people live. Social support is actually just as predictive as smoking and drinking alcohol2. Social relationships also predict other aspects of health and wellbeing3. For example, social isolation, the lack of meaningful social interactions, has been associated with increased risk of cardiovascular disease4.

This study shows that rhesus macaques take advantage of this social strategy to adapt to an environmental disaster, possibly as a way to reduce their vulnerability during an unstable time. Understanding social interactions in monkeys after a hurricane may help us understand how humans respond to natural disasters. Although tensions increase during hard times like the current COVID-19 pandemic, the research of Cayo Santiago’s monkeys supports the idea that disasters can bring communities of mammals, including humans, together. In the face of increasing number of weather-related disasters due to climate change, it is crucial to understand these social dynamics because they can predict length and quality of life. These studies could highlight the importance of ensuring that people have access to a supportive social networks, particularly during adverse events.

It seems that the social buffering hypothesis holds true for the monkeys in Cayo Santiago. Now the remaining questions are how exactly these expanded social networks provide protection in light of an environmental disaster. And although the study looked only at monkeys, the findings could be used to help humans. After Hurricane Maria, 4,500 Puerto Ricans died according to official accounts (although the number is believed to be much higher) and Puerto Ricans lost power and water for months, which led to a surge in mental health disorders5. More research into how social networks impact the human response to environmental disasters could help mitigate the disastrous consequences that come after it.


Rhesus macaque mother grooming youngster in Cayo Santiago, Puerto Rico. From BDNf cynocephale via Flickr.


  1. Testard, C., Larson, S. M., Watowich, M. M., Kaplinsky, C. H., Bernau, A., Faulder, M., Marshall, H. H., Lehmann, J., Ruiz-Lambides, A., Higham, J. P., Montague, M. J., Snyder-Mackler, N., Platt, M. L., & Brent, L. J. N. (2021). Rhesus macaques build new social connections after a natural disaster. Current Biology, 31(11).
  2. Holt-Lunstad, J., Smith, T. B., & Layton, J. B. (2010). Social relationships and mortality risk: A meta-analytic review. PLoS Medicine, 7(7).
  3. Snyder-Mackler, N., Burger, J. R., Gaydosh, L., Belsky, D. W., Noppert, G. A., Campos, F. A., Bartolomucci, A., Yang, Y. C., Aiello, A. E., O’Rand, A., Harris, K. M., Shively, C. A., Alberts, S. C., & Tung, J. (2020). Social Determinants of health and survival in humans and other animals. Science, 368(6493).
  4. Valtorta, N. K., Kanaan, M., Gilbody, S., Ronzi, S., & Hanratty, B. (2016). Loneliness and social isolation as risk factors for coronary heart disease and stroke: Systematic review and meta-analysis of longitudinal observational studies. Heart, 102(13), 1009–1016.
  5. Kishore, N., Marqués, D., Mahmud, A., Kiang, M. V., Rodriguez, I., Fuller, A., Ebner, P., Sorensen, C., Racy, F., Lemery, J., Maas, L., Leaning, J., Irizarry, R. A., Balsari, S., & Buckee, C. O. (2018). Mortality in Puerto Rico after Hurricane Maria. New England Journal of Medicine, 379(2), 162–170.

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