Chickadees, titmice and nuthatches flocking together benefit from a diversity bonus

Carolina chickadees are small, boisterous year-round residents of the southeastern United States. They are regularly found with much larger tufted titmice, white-breasted nuthatches and various woodpecker species.
In these mixed flocks, chickadees are almost always the subordinate individuals, outcompeted by their larger flockmates. Why, then, do chickadees regularly join these flocks? Might they have a symbiotic relationship with other species in these flocks?
Chickadees, titmice and nuthatches flocking together benefit from a diversity bonus – so do other animals, including humans