This report concerns the roosting behavior of the Red-winged blackbird and associated species ; and is based on observations made over a 14-year period mainly in the Southern United States....Th e greatest concentrations of Red-winged Blackbirds in the southern states occur in the Coastal Plain Province in or near major grain growing regions.....Roosts are formed during every month of the year. The largest roosts are usually found in winter; the smallest during the breeding season. Composition of roosts may vary from place to place and from season to season.....The general locality in which roosts are found is probably influenced by food supply. The precise location is determined by the character of the habitat. Wetland situations are preferred by Red-winged Blackbirds. Most of the roosts in the Coastal Plain Province are located in marshes and swamps. Rice fields are important in the southern rice producing area. Coniferous stands and bamboo are frequently used in the Piedmont Province.....Blackbirds move out of roosts each morning at about dawn or shortly after, and return in the evening usually before sunset. Some birds may travel 35 miles or more from the starting point in the course of a day?s feeding activity. On cloudy days blackbirds move into the roost earlier than on sunny days. At a Maryland roost subadult male Redwinged Blackbirds were the first to arrive at the roost. Females and then juveniles followed. Adult males were sporadic in their time of arrival. Stratification in a roost flight was observed where birds were flying downstream to a river marsh roost. Bobolinks flew at the greatest elevations; next in order of height were Starlings, Common Grackles, Brown-headed Cowbirds, and Red-winged Blackbirds. The exodus of a large roosting population is usually of shorter duration that the movement into the roost..... In virtually all roosts some segments of the population are segregated. Stratification by species and by sexes of some species has been noted in roosts. Blackbirds may roost on partly submerged vegetation in a marsh, on the ground in grassy fields, in branches of trees, or in various other sites. In deciduous thickets with high bird densities they may roost at elevations of 1 foot to 30 feet or more. In one Arkansas roost Red-winged Blackbirds were roosting along branches at an average of about three birds per foot.