Spatio-temporal organization during group formation in rats.

In the present study, the dynamic process of group formation in eight unfamiliar rats was followed in order to reveal how the group becomes oriented together in time and space, in light of the complexity that accompanies grouping. The focus was on who, where, and when joined together. We found that rats preferred to be in companionship over remaining alone, with all the rats gradually shifting to share the same location as a resting place. Group formation can be viewed as a tri-phasic process, with some rats gradually becoming more social than others, and thus playing a key role in group formation. Starting with seemingly independent traveling, the rats gradually converged to share the same location as a terminal (home base) for roundtrips in the arena. Because such a terminal is considered as the organizer of an individual's spatial behavior, the shared home-base location may be viewed as the organizer of spatial behavior of the entire group. Despite huddling together, the rats continued to travel alone or in duos throughout the 3 h of testing. We suggest that resting together and traveling alone or in duos enabled the maintenance of communal relationship while reducing the complexity involved in traveling in relatively large groups. Taken together, the present results demonstrate the dynamic process during which unfamiliar rats shift from independent to group spatial behavior.