The old saying, “Birds of a feather flock together,” is particularly true among blackbirds in winter. Though many birds band together during winter, none are as notorious for their flocking behavior as blackbirds...red-winged blackbirds, European starlings, common grackles and brown-headed cowbirds.
This group of a feather often flock together in the many thousands, sometimes the millions. One winter roost in the Great Dismal Swamp on the Virginia-North Carolina border held an estimated 15 million birds. Flocks in the thousands often roost in urban and suburban areas, where their numbers and their noise make them unpopular among the people living nearby. Attempts by state and federal wildlife officials to discourage or destroy such flocks of wintering blackbirds have usually failed. One experiment, using a wetting agent sprayed on a huge flock of birds from an aircraft, left a much greater mess in the form of rotting carcasses.
Many wonder why birds in general and blackbirds in particular gather in flocks in winter. Though studies have been inconclusive, it is believed that there is safety in numbers. With many more eyes and ears to search for food and watch for predators, the chance of an individual bird surviving winter is increased. There are reports of hawks attacking flocks of flying birds time and again, but failing to capture even one when the prey closed ranks to form a mass that the hawk was unwilling or unable to penetrate without being injured.
-- George H. Harrison