Birds Establishing and Defending Territories

Whirling flocks of thousands of blackbirds descend at dusk upon a nighttime roost near Indianapolis. They have been foraging all day on the grain of local farms and have now come to roost in a shelter belt of trees. They land, then take off in a nervous leap, the whole roost exploding into excited calls and a rush of rapid wingbeats. The whir of the wings alone would drown out all other noises. Add to their calls and whistles, and the total force of sound seems too great for any one collection of birds. But when you consider the numbers -- in a winter roost of blackbirds more than a million birds may gather -- you can understand how it is possible for them to make so much noise.