From All About Birds:
American White Pelicans cooperate when feeding. Sometimes, large groups gather in wetlands. They coordinate their swimming to drive schooling fish toward the shallows. The pelicans can then easily scoop up these corralled fish from the water.
This act of feeding created a whole frenzy eager to catch some of what the pelicans are eating including herons, egrets, cormorants, terns and gulls. These quiet, undisturbed swallow channels of the Mississippi provide good habitat for migrating birds.