A gregarious species, the red-winged blackbird nests in crowded groups, low among vertical shoots of marsh vegetation, shrubs, or trees. It is a polygamous species, the male mating with several females that nest inside its territory. In some populations, 90 percent of territorial males have more than one female nesting on their territories. However, the females may also mate with more than one partner, and as many as one-quarter of nestlings may turn out to have been sired by a different male (4) (5).
Prior to breeding, male red-winged blackbirds do everything they can to get noticed, sitting on high perches and belting out their “conk-la-ree” song all day long (5). Males may also chase after females with the shoulder feathers erected. Typically five or more females, sometimes up to 15, may crowd their nests into any one male’s territory. Females build the cup-shaped nests by winding stringy plant material around several close, upright stems and weaving them into a platform of coarse, wet vegetation. Between 2 and 4 eggs are laid, and are incubated by the female for 11 to 13 days. The male may help the female to feed the hatchlings while they are still in the nest, as well as for up to two weeks after they have fledged (4).
The red-winged blackbird gathers into roosts throughout the year. During the summer months it congregates around the wetlands where it breeds, but during the winter it may share roosts with other birds, in groups that range in number from a few individuals to several million (4). Each morning the roosts spread out, travelling as far as 50 miles to feed, then re-forming at night (5). The red-winged blackbird eats seeds in the winter, including corn and wheat, and mainly insects in the summer. It uses its robust bill to open the leaf bases of aquatic plants and reeds, or to lift sticks and stones to expose hidden insects. It also picks up seeds and other items from the ground and gleans insects from vegetation (4).