Active Collective Sway Synchrony in Pteropus Colonies

Collective synchronization in animal groups is associated with active communication and behavioral rules, as seen in fireflies, bird flocks, or fish schools. However, bats (Pteropus Colonies) roosting on trees provide a different case where synchrony seems to arise through passive mechanical coupling. Here, we investigate how groups of bats hanging from flexible branches sway collectively under wind excitation. The observation of dynamics combined with biomechanical modeling reveals that bats behave like pendulums coupled to the motion of the branch. When multiple bats share a substrate, their oscillations entrain through branch vibrations to produce active collective synchronization. The level of synchrony is modulated by branch stiffness, bat posture, and group size, with transitions from incoherent to collectively coherent states. This study uncovers a new form of substrate-mediated synchronization in living systems, providing both ecological insight and inspiration for mechanically coupled robotic swarms and living architecture.