Socially contagious urination in chimpanzees.

The decision to urinate involves a complex combination of both physiological and social considerations. However, the social dimensions of urination remain largely unexplored. More specifically, aligning urination in time (i.e. synchrony) and the triggering of urination by observing similar behavior in others (i.e. social contagion) are thought to occur in humans across different cultures (Figure S1A), and possibly also in non-human animals. However, neither has been scientifically quantified in any species. Contagious urination, like other forms of behavioral and emotional state matching, may have important implications in establishing and maintaining social cohesion, in addition to potential roles in preparation for collective departure (i.e. voiding before long-distance travel) and territorial scent-marking (i.e. coordination of chemosensory signals). Here, we report socially contagious urination in chimpanzees, one of our closest relatives, as measured through all-occurrence recording of 20 captive chimpanzees across >600 hours. Our results suggest that socially contagious urination may be an overlooked, and potentially widespread, facet of social behavior.