Starling Dispersal From a Winter Roost

Abstract

Starling roosting behavior is considered in terms of resource acquisition. Our hypothesis is that dispersing starlings behave to maximize the efficiency and rate of energy gain. This hypothesis can explain of the winter starling roosting behavior. The value of strategies pursued by individuals within the system depends upon the size of the population utilizing a roost. As the roost population grows, more distant resources are utilized. At maximum roost populations individuals may disperse daily as much as 50 miles from the roost. During dispersal most individuals make in—transit stops to feed. These stops may provide information about the potentially more lucrative energy reserves nearer the roost, reducing the distance flown when they are favorable. Flocking actions probably make resource evaluation more efficient because the experience of the members of a group will provide more reliable information about the values of a resource field than an individual's personal experience. Linear dispersal directly away from roots is assumed to be maximally advantageous. This is because intraspecific competition declines with distance from the roost, and flight is costly of energy. On foggy, and overcast mornings dispersing starlings do not extend as far from the roost, and the flight is less accurately oriented. This suggest a relatively high adaptive value for accurate orientation mechanisms in this socio—economic system. Dispersing flocks are larger during overcast, supporting the hypothesis that group processes in orientation enhance orientation accuracy.