  Avian flocks display a wide variety of flight behaviors, including steady
directed translation of center of mass, rapid change of overall morphology,
re-shuffling of positions of individuals within a persistent form, etc. These
behaviors may be viewed as flock-scale strategies, emerging from interactions
between individuals, accomplishing some collective adaptive purpose such as
finding a roost, or mitigating the danger from predator attacks. While we do
not conceive the flock as a single cognitive agent, the moment-to-moment
decisions of individuals, influenced by their neighbors, appear as if to
realize collective strategies that are cognizant of purpose. In this paper, we
identify the actions of the flock as allocation of energetic resources, and
thereby associate a cognitive cost to behavior. Our notion of cognitive cost
reflects the burden arising from rapid re-allocation of resource. Using a
recently developed natural geometric approach to kinetic energy allocation, we
map the flock behavior to a temporal signature on the standard (probability)
simplex. Given the signature of a flocking event, we calculate the cognitive
cost as a solution to an optimal control problem based on a game-theoretic
model. Alternatively, one can associate to a signature an entropic cost. These
two cost measures, when applied to data on starling flocks, show a consistent
spread in value across events, and we suggest the possibility that higher cost
may arise from predator attacks.
