Higher social tolerance is associated with more complex facial behavior in macaques

Area of Science:

• Primatology
• Ethology
• Animal Communication

Background:

• The social complexity hypothesis links social system complexity with communication complexity in animals.
• Macaque species exhibit varying degrees of social tolerance and complexity, making them ideal models for testing this hypothesis.

Purpose of the Study:

• To investigate the relationship between social complexity and communicative complexity in three macaque species.
• To determine if more socially tolerant macaques utilize more complex facial communication.

Main Methods:

• Observed and coded >3000 social interactions across aggressive, submissive, and affiliative contexts in 389 macaques.
• Utilized the Facial Action Coding System for macaques (MaqFACS) to analyze facial behaviors.
• Quantified communicative complexity using entropy, specificity, and prediction error measures.

Main Results:

• Crested macaques, known for higher social tolerance, displayed higher facial behavior entropy than Barbary and rhesus macaques.
• Rhesus macaques showed higher context specificity in facial behavior compared to Barbary and crested macaques.
• A random forest classifier predicted social context from facial behavior with the highest accuracy for rhesus macaques and the lowest for crested macaques, indicating greater facial communication complexity in the latter.

Conclusions:

• Findings support the social complexity hypothesis, suggesting a correlation between social tolerance and the diversity and complexity of facial communication in macaques.
• Facial behavior complexity varies across macaque species, influenced by their social structure and tolerance levels.