How does grooming serve as a social signal in birds and mammals?

In the study of animal behaviour, grooming—often referred to as preening in birds—serves as a vital social signal that helps maintain group cohesion. While grooming functions primarily as a cleaning behaviour to remove parasites or maintain physical health, mutual grooming (or allopreening in birds) has evolved into a display behaviour that cements social bonds between individuals within a group or colony.12

These social signals often evolve through a process called ritualization, where ordinary survival behaviours are elaborated into communicative acts. For instance, when animals experience conflicting motivations, such as fear and aggression, they may perform displacement behaviours like irrelevant preening. Over time, these movements can become ritualized into displays that signal the animal's internal state to others. In many species, such as primates, mutual grooming is a key mechanism for reducing tension and reinforcing hierarchical or cooperative relationships. By engaging in these shared activities, animals effectively communicate friendly intentions and strengthen the social fabric of their community.31