  The migration of Twitter users to Mastodon following Elon Musk's acquisition
presents a unique opportunity to study collective behavior and gain insights
into the drivers of coordinated behavior in online media. We analyzed the
social network and the public conversations of about 75,000 migrated users and
observed that the temporal trace of their migrations is compatible with a
phenomenon of social influence, as described by a compartmental epidemic model
of information diffusion. Drawing from prior research on behavioral change, we
delved into the factors that account for variations across different Twitter
communities in the effectiveness of the spreading of the influence to migrate.
Communities in which the influence process unfolded more rapidly exhibit lower
density of social connections, higher levels of signaled commitment to
migrating, and more emphasis on shared identity and exchange of factual
knowledge in the community discussion. These factors account collectively for
57% of the variance in the observed data. Our results highlight the joint
importance of network structure, commitment, and psycho-linguistic aspects of
social interactions in describing grassroots collective action, and contribute
to deepen our understanding of the mechanisms driving processes of behavior
change of online groups.
