This video from Kansas in the USA says about itself:
Half of All North American Shorebirds Use This Rest Stop
18 November 2016
Wildlife researchers have long tried to understand why birds fly in flocks and how different types of flocks work. A new study from the University of North Carolina at Chapel Hill explores the mechanics and benefits of the underlying flock structure used by four types of shorebirds. Understanding more about how these birds flock moves researchers a step closer to understanding why they flock: here.