In the dense cloud forests of Ecuador, staying together is a matter of survival. A new scientific study has shed light on how primates maintain group cohesion through involuntary mechanisms. The research, led by Núria Hassina Hannaoui and Miquel Llorente from the Comparative Minds group (University of Girona), has demonstrated for the first time that scratching is highly contagious among wild Ecuadorian white-fronted capuchins.

The phenomenon of behavioral contagion—where one individual’s action triggers the same response in an observer—is a cornerstone of sociality. While contagious yawning is the most famous example, this study focuses on scratching, a less explored but crucial behavior for understanding how social information flows unconsciously within a group.

A mechanism for group synchronization. Conducting field research at the La Hesperia Natural Reserve, the team observed a group of 16 capuchins. Their results confirm that the likelihood of an individual scratching increases significantly after seeing a group mate do so. According to the authors, this "contagious scratching" acts as a social glue, helping individuals synchronize their states and transitions, such as moving, resting, or foraging together.

Independent of social bonds. One of the most striking findings of the study is that, unlike in some other primate species where empathy or friendship modulates contagion, this phenomenon in capuchins appears to be independent of social relationships. Neither hierarchical rank, age, nor the strength of social bonds (measured via the Composite Sociality Index) influenced the probability of contagion.

"These results suggest that contagious scratching is a low-level mechanism—an automatic response that is likely ancestral in the primate lineage," the researchers note.

The mystery of the missing yawns. Interestingly, the study did not record a single instance of yawning during the observation period. The scientists hypothesize that environmental conditions—such as the high humidity and stable temperatures of the cloud forest—might mitigate the need for yawning as a brain thermoregulation mechanism. This finding underscores the importance of studying animals in their natural habitats rather than only in captivity.

This work, a collaboration between the University of Girona, the University of Leipzig, the Max Planck Institute, and Fundación Tangaré, reinforces Comparative Minds as a leading group in the study of comparative cognition and animal behavior.

Reference: Hannaoui, N. H., Amici, F., Hoeneisen, A., & Llorente, M. (2026). Behavioral Contagion in Wild Ecuadorian White-Fronted Capuchins (Cebus aequatorialis). American Journal of Primatology. https://doi.org/10.1002/ajp.70122