  Collective dynamics of many interacting particles have been widely studied
because of a wealth of their behavioral patterns quite different from the
individual traits. A selective way of birds that reacts to their neighbors is
one of the main factors characterizing the collective behaviors. Individual
birds can react differently depending on their local environment during the
collective decision-making process, and these variable reactions can be a
source of complex spatiotemporal flocking dynamics. Here, we extend the
deterministic Cucker-Smale model by including the individual's reaction to
neighbors' acceleration where the reaction time depends on the local state of
polarity. Simulation results show that the adaptive reaction of individuals
induces the collective response of the flock. Birds are not frozen in a
complete synchronization but remain sensitive to perturbations coming from
environments. We confirm that the adaptivity of the reaction also generates
natural fluctuations of orientation and speed, both of which are indeed
scale-free as experimentally reported. This work may provide essential insight
in designing resilient systems of many active agents working in complex,
unpredictable environments.
