At sunrise, an interested observer might see several thousand blackbirds leaving their roosting area, usually a low wetland area, in the space of five minutes, flying in a narrow band like a fast-moving stream. About a half-hour before sunset the same event can be seen in reverse, as blackbirds stream back to the roost.

Soon after adults stop caring for the young, blackbirds begin to flock together. Each night in summer, until they move farther south later in fall, huge congregations of common grackles, red-winged blackbirds and brown-headed cowbirds, all members of the blackbird family, will fly from their feeding grounds to their roosts, creating the largest and most commonly observed groups of land birds in North America.

Assemblies of red-wings reach a peak in about mid-October, and grackle flocks are at their peak a bit later. Slowly, as the season progresses, the enormous flights drift south into Iowa and beyond.